Foam Board Insulation R Values
Foam Board Insulation Types
I’ve written several posts about how to insulation basement walls in which I promote the use of foam board insulation as the first line of defense against moisture and mold. Because of this I often get questions about which type of foam board insulation to use and what R values these products provide.
There are three basic foam board products on the market produced under several different manufacturer names. They include expanded polystyrene, extruded polystyrene, and polyisocyanurate unfaced or foil faced. DOW products has lots of information on their site about different foam board products here. I also recommend you read a recent article about Open Cell Vs Closed Cell Foam products to understand the differences between the two product types.
Expanded Polystyrene Foam
Expanded polystyrene foam (EPS) is the cheapest and least used foam board product on the market. This product typically has an R value of 3.6 to 4.0 per inch of thickness. Expanded polystyrene insulation is similar to the foam used for packing “peanuts” and it’s typically used for insulated concrete forms also knows as ICF’s. It is also sometimes used on commercial buildings for roof and wall panel insulation which is typically sandwiched between light gauge metal.
Cost = Cheapest of the foam insulation boards.
Extruded Polystyrene Foam
Extruded polystyrene foam (XPS) also known as blue board or pink board comes in many different thicknesses and edge profiles. This insulation board is probably one of the most widely used foam board insulation products in the residential construction industry. XPS has an R value of 4.5 to 5.0 per inch of thickness.
This is the product that I typically use to insulate basement walls. It’s reasonably priced, light weight and easy to use. This product is also used to insulate the outside of foundation walls and even under slabs.
Cost = This product is the middle of the road for these types of foam board insulation products.
Polyisocyanurate
Polyisocyanurate also known as polyiso is seen in all kinds of commercial building applications and more recently with residential building projects. Polyiso is typically used with a foil facing and it has an R value of 7.0 to 8.0 per inch of thickness. The reflective foil facing makes it an excellent insulation board when radiant heat is involved. The foil facing also makes it very easy to seal with good quality foil faced tapes.
Cost = Polyiso is the most expensive of the foam board insulation products however it’s the highest R value.
Related posts:
Subscribe Via RSS
Subscribe Via Email
[...] Foam board insulation products are quite popular with some aspects of today’s green construction. If you’re looking for some information on these products then check out: Foam Board Insulation Types and R Values. [...]
[...] Foam Board Insulation R Values [...]
Also Polyiso is the least moisture resistant. Not only is it subject to breakdown from extended exposure, it also loses significant insulation value when wet.
Use expanded or extruded in any potentially damp locations.
Mr. Wells is incorrect; the foil facing makes the Polyiso the MOST moisture-resistant of the products discussed.
All good info. Add to that the ability to purchase recycled/once-used rigid foam insulation boards of all types and sizes and you have a eco friendly solution.
Thanks,
Mike
[...] that stop moisture movement and prevent mold growth. Basements are the perfect location for foam type insulation products. Cellulose is also an option for basements but it’s not a product that I’ll cover here. [...]
[...] rigid foam board (read more about Foam Board Types and R Values) is an excellent alternative to spray foam. Foam board is cheaper to install and it can easily be [...]
I am going to build a new home on the Brad’Or Lake in Cape Breton Island Nova scotia. It will be a two story with a furnished walkout basement (built on a hill facing the water). The lower walls will be poured 8 inch reenforced concrete. On the inner side I intend to use one inch of rigid foamboard then 2″X 4″ 16 in OC framed wall. Fiberglass batton insulation and 1/2 inch gypsumboard. My question is, is this a good idea, what type of rigid board should I use? My understanding is that the polyiso foamboard does not hold up to any type of moisture but has a higher r factor per inch than the extruded but the extruded holds up better to moisture. If the polyiso is foil faced does that protect it against moisture and act as a vapor barrier. And in either case what is the best to use for a vapor barrier and where??
@ Robert Rein – Building a house that far north I would opt for a minimum of 2 inches of DOW extruded tongue and grove (other brands are fine as well), joints taped and sealed. Then go ahead and frame with 2×4 with R11 fiberglass insulation. No need for a vapor barrier if you install 2 inches of foam and seal all the joints really well. Best of luck!
@ Robert Rein:
I’m presently insulationg my basement with 2″ foil-faced polyisocyanurate glued directly to the blocks. Then I’ll screw resilient channel through the rigid, to the foundation wall using 3″ tapcons. Then drywall. 2″= R12, minimum.
Yes, the foil is moisture-resistant, but according to Dow, none of their rigid insulation is a barrier for water vapor.
John – It’s proven that closed cell foam is actually a good vapor barrier when it’s installed at a minimum thickness of 1.5 to 2 inches.
With not much room to build a 2×4 wall frame and insulate along the side of our basement stairs, we have opted for polyiso sheets with foil and plastic face. Now on the inside of the wall, which face (the plastic or the foil), goes against the block wall and do I still need a vapour barrier between it and the drywall?
@ Debbie – I would place the plastic side against the concrete. No need for vapor barrier if you seal all the joints well. For foil faced polyiso i suggest you get a good quality foil tape (used for duct work…..but NOT duct tape).
As long as you’re building new and have the luxury of doing it right the FIRST time, why not put the insulation, and the waterproofing on the OUTSIDE of the concrete?
You get the advantage of the thermal mass inside, to moderate temperature changes, and it doesn’t cost you any more.
Also, instead of conventional insulation, do superinsulation and cut your heating bill by 80%- you can save most of the cost of the insulation by installing a TINY (and much less expensive) heating system, and pay $300 a year to heat instead of $3000 (most of your heating would come from waste heat inside the building). A savings of $2400/year would pay for about $48,000 greater expense in construction.
@ PeterL – Insulating the outside is certainly one option. However, it’s not as simple as that. The big issue with insulating outside is the detail where the foundation comes above grade. Making the transition from below grade to above grade and transitioning to the interior insulation without a break it difficult to do properly. Furthermore, many people in the industry agree that exterior insulation still doesn’t’ address the severe moisture problem that exists throughout the life of concrete products.
Your point is well taken on spending up front to save in the long run. We’ve built several homes in the last two years that use less than 50% of the energy that previous homes use. Thanks for your input.
I am planning to insulate a large basement, over 200 ft of outside block wall. It is damp in basement but no water problems.There are mildew problems, especially in summer. We run two dehumidifiers constantly, which uses alot of electricity. The floor is concrete. I am wondering how much good it will do to put two inches of extruded or iso sheet on exterior walls, if I don’t cover floor with anything.
@ Charlie – You’d be amazed at the difference 2 inches of foam on the walls can make.
I’m going to use the XPS on basement walls, but i’m not sure what to do about the space above the concrete walls between the floor joists. Currently batt insulation is placed there. Do I need to do something special in this space? I don’t want to spend the time and money on the XPS only to have the moisture barrier benefits negated because I didn’t address this space. Thanks!
@ Mike – I recommend you replace the fiberglass with XPS. You can cut pieces to fit between the joists. Use spray can foam (Great Stuff or similar) to seal each piece in place.
todd….We are in need of any of your advice. We have a walkout basement, three framed walls,the other wall concrete. the framed walls have a paperfaced R 19.the basement is unfinished and has no drywall.The slab was poured over 2″ foamboard and plastic on top as a vapor barrier. In the winter, the framed walls have moisture and black mold behind the insulation. the dehumidifiers keep the basement @ 30% humidity. There is also a pellet stove which keeps the 1200 sq. basement @ 70 degrees. The exterior consists of vynil siding and Tvec. My husband dug the cellar hole,he stated, the ground is pervious, with no ground water. Any help or advice you could lend would be greatly appreciated. Thank you, Dawn Dicarlo
@ Frank – From the sounds of it the kraft faced insulation was not properly sealed and moisture has been trapped between the fiberglass and sheathing. If the basement will not be finished I recommend a poly vapor barrier, properly taped and sealed. At this point it sounds like you need to remove the damaged fiberglass, clean the mold, and start over.
[...] including fiberglass batt rolls, blow-in insulation (such as NuWool), spray foam insulation, rigid foam board insulation, and [...]
We live in the northern minnesota. The house I worked on has plaster walls, Kraft-faced R-ll insulation, shiplap exterior sheathing, and 3 layers of tar paper. We put 1 inch foil-faced polyiso insulation on the exterior of the house to get the most insulation for the price. With no poly vapor barrier, is this installation correct?
@ tnt – Sounds like a good detail. You do have kraft faced insulation on the warm side so it’s all good.
I live in Alaska and I am having a new build done this summer. The winters have gotten down to -70 in the past. I want the best insulation available. The slab will be radiant heated. I’ve seen previous posts about foam insulation on the outside of the concrete slab, how beneficial is it? What is the best possible insulation for the exterior wall? I’ve heard R-5 blue board on exterior of stick frame walls with vapor barrier and R-11 fiberglass on the inside. What would you do if it was your place and you were looking forward to that extreme of cold?
@ Brent – I’d look at two options.
1. Spray foam entire house inside stud wall cavities, I might even consider a 2×8 wall section for maximum insulation depth.
2. Spray applied dense pack cellulose in the wall and a layer (1″ to 2″) of blue board on the exterior of the house.
If I lived in Alaska I’d spend every dollar I could on insulation versus other nice to have things like nice countertops, etc.
As far as the slab goes you’ll want to install foam board insulation on the outside of your slab/walls, down at least 4 to 6 feet.
Greetings, I’d like to get your advice on insulating my basement. We live in MA in a middle townhouse with a walkout basement. One wall is completely below grade, two side walls are shared with neighbor’s basement and back wall is completely above grade studded with fg/vapor barrier/door/windows. Area is approx 800 square feet. The concrete walls are poured. I’d like to:
- glue 1″ XPS to all concrete walls, then stud
- NOT use bat insulation on shared walls, only front below grade wall/possibly back above grade wall (unfaced)
- lay 1″ XPS over slab, then carpet
Questions: Should I:
- Remove insulation/vapor barrier from above grade wall and use XPS
- Fill in studs on shared walls w/ bat unfaced insulation
- DryLoc walls before insulating. Is this necessary for the walls above grade/shared walls?
We plan to tie into HVAC for heat and air return and run dehumidifier when necessary. I did the moisture test with the taped foil on the walls, no moisture on either side.
Thank you, John
@ John –
1. I would leave the old grade wall insulation. However, check it and make sure there is no moisture or mold in it.
2. Just foam is fine on those walls..however…i recommend 1-1/2″ min. foam board.
3. DyLoc is just added protection…not sure how much it buys you in the grand scheme of things.
Can I use 2″ of foamboard (Polyiso) under my metal roof. foil facing up?
James – Sure can!
Hi. I building a new home in Ontario and will be installing hydronics in the basement floor. I will install 2″ of rigid foam insulation under the slab. Question is which rigid foam insulation is best “Pink or Blue”? I’ve noticed “pink” carries a premium price to the blue. Both have the same R value and the same compressive strength. Is there something I’m missing? Thanks D.
David – No difference….free markets driving price….nothing more.
I live in Geneva, Switzerland. Temperatures range between 25 and 35 in the winter. I am insolating my basement but the Swiss tend to over-engineer their walls so I want to provide some guidance to my wall-guy. I don’t have a lot of space and would like to forgo framing and batting. Is it possible to use 2″ Extruded Polystyrene, attach furring strips and then gypson board? By screwing the furring strips through the blue board into the cement, does that not let in the moisture that seems to be the trouble with basements?
Thank you in advance.
Christine
Christine – That method actually works quite well. You want to be sure you’re using galvanized or stainless steel screws and be sure the screw heads are sealed well afterwards before the gypsom board.
Todd, your article says polyiso is more expensive than XPS but is higher R-value per inch. Is polyiso also more expensive on a per R-value basis? OR is cost-per-R-value close enough that one or the other product may be less expensive per R-value in any given market?
I currently only specify polyiso when the insulation is exposed, as in an unfinished basement or closed crawlspace. The foil face satisfies code officials. Unfortunately, I never get to see the costs.
David – Good question, frankly I’ve never compared cost per inch. Next time I purchase some I’ll have to run those numbers. Good point!
I’m currently finishing out my basement. I’m going to use 1 1/2″ extruded polystyrene on the concrete walls and frame and drywall against them. What tape is recommended to seal the joints? I read somewhere about tyvek tape, but I’ve never seen that in my area. Also, I’m considering drywalling the ceilings, mainly due to costs of drop ceilings. Are drop ceilings a better idea to encourage air flow? Will a drywall ceiling create a basement that is too airtight?
Jacob – You can find Tyvek tape as most big box stores and lumber yards.
http://www2.dupont.com/Tyvek_Weatherization/en_US/products/residential/resi_seam_tape.html
You can also use this stuff, it’s similar, http://www.amazon.com/exec/obidos/ASIN/B002KM1APU/homeconstimpr-20
Drop ceiling are better just for future access. Drywall ceilings will perform just fine.
Todd, I did find a tape equivalent to the tyvek product, and I’m going to go w/ that. Thanks for the reply.
We have a two-thirds finished basement, and have stripped the finished side down to the studs. Currently there is no insulation nor vapor barriers. We would like to add some insulation to the finished side to help normalize the basement temperature to the rest of the house.
1. Does it make sense to insulate the finished side, if we are leaving the unfinished side alone?
2. Can we put foam board between the studs, since we don’t want to remove the studs and install the boards against the concrete walls?
2a. Would this configuration still require some type of vapor barrier?
We live in Ohio, if that helps, and have had no moisture problems in past.
Frank – Thanks for stopping by the site.
1. It certainly doesn’t hurt! You’ll probably find that the rooms above the finished/insulated area will feel more comfortable afterwards.
2. This isn’t the best option but it’s the best one if you don’t want to move the framing. Be sure to seal all the edges with spray foam from a can.
2a. If you install at least 1-1/2 inches of closed cell foam I think you’ll be ok without one.
Good luck.
[...] Foam Board Insulation [...]
Thanks for this forum and the great information! I will implement the basement wall according to your Oct 12th post. Love it!
But I have a foam board question for NON-basement walls.
Is there any advantage with using EPS insulation for “non Basement” framed wall?
Say 4 inches of solid EPS insulation stacked in a wall, then sealed with can foam (prior calking any sills and opening to prevent any air). I see no need for a vapor barrier Kraft paper. I haven’t priced it out – but since it’s “solid” though more work than then spray foam – if sealed well, it would achieve the same result – right?
As closed spray foam installers say – batt is really just a thick furnace filter, walls have convection, and even if the R values appear the same – Solid (spray) foam is warmer in use.
I’m building at 11,000 feet in Colorado. 2×6 construction and have the building weather tight but framing exposed inside.
(I should have done 2×4, saved money and did foam board layer on the outside to prevent “thermal bridging” from the wall studs)
But we are ready to start the cedar siding and the builder isn’t keen on adding layer(s) under the siding since the windows are in, tyvek is done, …) – he’s worried about moisture getting behind. So I’m pondering anything to beef up the walls
But I have very low moisture in Colorado. R21 is recommended for walls.
I likely will get the ceiling closed cell spray foamed but likely not spray foam the walls two story, plus a drive under garage is a lot of walls but not much roof.
Plus, spray foam is pricy and at the High Altitude the formulation gets even more costly (supposedly) since the microscopic air bubbles could pop.
I noticed one post above mentioned three layers of tar paper.
Could that be for R value – just for another cheap layer. Does it really help? My builder would be fine with tar paper layers.
Thanks in advance!
Joe – Using foam inside the cavities is a fine idea. However, I have a feeling it may end up costing as much as spray applied when you consider the labor to cut all the foam board, install it, seal it etc.
Not sure tar paper is going do to much of anything for you in this situation.
Hi Todd
Here is my dilemma…My finished basement got flooded…12 inches up…I cut up 12 inches of drywall & removed insulation w/vapor…I am going to go up to 4 ft because (Drywall is 4 x 8…would make it easier to replace…unless you think otherwise)… My mancave was damp to begin with which I believe is totally do to the foundation walls (totally in ground) not having any Foam xps board attached
I do not want to totally remove all drywall & studs…I will remove 4 ft of drywall from floor…This will probably be very difficult to fully tape foam boards together…but I will try my best…because I am sure XPS on the Foundation walls is better than none…Correct.
also insulation in between my studs R15 I can use a non vapor backing if I foam board my foundation walls correct?
And lastly I am installing new carpet…will the carpet pad be enough or should put down a thin foam board on the floor?
Any other ideas would be great
Thank you
Mark
Mark – First off let me say I wouldn’t go through all this trouble until you figure out why your basement flooded. If it happened once it’s likely to happen again. 12 inches of water is in my opinion a basement that shouldn’t be finished.
Having said that I also don’t think your approach will work very well. Unless you remove it all and create a good vapor barrier you’re doing to just push the wall moisture up higher and eventually into the remaining fiberglass.
Have you investigated the flooding situation?
Hi Todd
Yeah, my sump pump failed in the 2010 Greatest New England Flood of all time…Just my luck…I never had water before…
So the bottom line…I need to make sure I have a good vapor barrier…I plan on using foam board all the way up on my foundation walls some areas of basement I can make this happen easily…some other areas it will be tight but if I cut half my drywall out I may be able to reach it…How about putting foam board on my floor…or should I just use carpet pad & rug?
Thank you
Mark
Mark – The floor really depends on ceiling height, if you want to make it warmer, etc. You can read about insulating a floor here:
http://www.homeconstructionimprovement.com/how-to-insulate-a-concrete-floor/
Tood
We are going to reside with vinyl siding on an older home with 2×6 framing that has fiberglass bating insulation inside. To add insulation it seems our only option is the “blue board” installed under the siding? If so should it be house wrapped too? Thanks for any ideas. eric
Eric – The foam board should be installed first with all the joints taped. Then a house wrap should be installed over the foam prior to the new siding.
I live in Texas, the sun hits my converted garage and kitchen very hard, garage was insulated. I would like to know if I can put the polyisocyanurate over my outside wall which has stucco on it to reflect the sun rays and will it last?
Geo – I wouldn’t really recommend putting polyiso on the exterior and leaving it exposed. It really should be covered by a siding product.
I just found your site, and like the posts. I am removing my Alaskan house’s beveled cedar siding to install rigid foam insulation on the 2×4 wall’s exterior, prior to reinstalling the siding. My concern(s) are that I do not want to add furring strips for solid siding attachment, as I want to secure the siding directly through the rigid foam. I also am concerned about totally sealing off the foam, as I think it may be in my interests to allow water vapor to move from inside to out. I cannot vouch for the interior water vapor seal quality under the sheetrock. My home has been “breathing” for 40 years without mold in the walls,” so I’d better keep letting it do so.
What do you suggest as a maximum thickness for the foam, for use without furring strips? Should I really seal all foam sheet seams? I was even thinking of using house wrap on top of the foam just to provide the extra barrier for water moving into the wall. Also, what type of fasteners should I use for the foam and the siding? I admit to being new to this part of construction, and I’ve heard a different bit of advice from each person I ask.
Thank you in advance for your time.
Stan
Stan – You have lots of options and some of the options depend on the type of siding you’ll be installing. First of all I would strip the old siding, fix and damaged sheathing and then install a layer of housewrap. Next I would install a layer of rigid foam board (XPS would work fine). The thickness will depend mostly on how it affects trim details at doors and windows. Depending on the thickness you can use just nails to re-install the siding or you’ll need to use a foam product that accommodates strapping (like DOW Wallmate). However, a product like that will really only help with horizontal siding products.
Does this help?
I only mentioned once that I would reinstall the beveled cedar siding, so I do have a horizontal siding application. I’ll look at the strapping. The cedar siding was installed over celotex, which was directly attached to the studs. I’m putting OSB ontop to the celotex, except for one wall, which had the celotex removed. The XPS will be attached to the studs through the OSB. You recommend house wrap under the XPS. I was thinking over the XPS, but on second and third thought, your idea makes more sense.
Window and door trim will be dealt with by using 3/4 ply boxes inside the window RO’s, and custom furring trim on the few doors, for finish trim nailing I’m leaning towards 1″ XPS, while finding some type of fastener that will give me the stud penetration depth I would get without the foam. I can understand your inability to safely recommend details in “print” from far away.
Thanks for your time. I appreciate your thoughts on my problem.
Hi I’m looking to insulation my crawl space because my wood floors are cold in winter. What type should I use? I have a sump pump down there because sometimes have water.
Kyle – Without seeing the space it’s hard to recommend a system. Typically crawl spaces benefit nicely from foil faced polyiso foam board.
Todd,
I am reading the post’s and they are great! Here is my question. We have the foil backed insulation board on the bottom half of our walls in the basements. We have recently put in batting type insulation over the foil backed insulation board. We were recently told that we should remove the batting insulation as it will produce moisture between the two insulations. Is this true? What are your recomendations. (I hope this make sense)
Thank you in advance for your advice!
Dana – Thanks for the compliment.
The batts could be a problem depending on the details. First off how thick is the foam board? Are all the seams taped? If the foam goes from floor to ceiling and it’s properly sealed then it creates a great vapor barrier and it shouldn’t be a problem. Of course that depends on it’s thickness too.
Todd, we are just starting to build a new house in Michigan. I asked my builder to add 2″ of rigid foam boards to the exterior before adding brick and cement board siding and he panicked. (We have to have brick on the full front and partial sides/back.) He’s never done it before and he is concerned about several things:
1- how does it affect the foundation? He wonders if he’ll have to move the foundation wall out to accomodate another 2″ in addition to my planned 2×6 walls. (we have to have 2×6 on large side walls). of course, I need a brick ledge large enough to set brick on, so do we just move the foundation wall out or does it have to actually be thicker for my proposed 2X8 wall?
2- and he’s worried about the soffits and interfering with their depth/overhang.
3- I figured we could save money by eliminating the OSO sheathing but that worries him, too. He doesn’t know if it will pass code. Doesn’t know how to go about engineering it without sheathing.
4- He is worried if we do or don’t need a house wrap as I also suggested that we could eliminate that if we use the right foam.
5 – windows/ doors. He said he doesn’t know how to flash them with foam.
I have read your site and have investigated a little on my own but wonder if you can answer these basic questions and/or provide us with a few resources to find good solutions to build it right.
He asked me why I can’t ‘flash and fill’ inside my 2×6 wall cavity with spray foam and cellulose. From what I’ve read, and correct me if I’m wrong, here in Michigan with cold winters, I need enough spray foam to keep the dew point to the outside of the foam or risk condensation inside of my cellulose where it would get trapped. So, a little foam actually can do more harm than no foam. Exterior foam of 2″ will keep the dew point to the outside of the foam so the cellulose will stay drier and it will provide a thermal break and wind barrier over the whole wall, including the sill joists. Am I correct? Can I use both methods? ie: 1″ spray foam on interior and 1″ rigid foam on exterior? That may be more manageable for him…
Thanks, Laura
Laura – Thanks for stopping by this site. Your builder probably panicked as this is such a new concept to him. All of his concerns are valid, however, they area all manageable with proper details.
1. Typical foundation around here is 8″ minimum concrete wall. So you can actually install the pressure treated sill plate to the inside of the wall and frame above that with standard framing, 2×6, 1/2″ sheathing. Then you can install the 2″ of foam board which will bring the foam to the outside edge of the concrete wall. You could actually use a 2×8 sill, so the foam sits on the sill with a piece of flashing above the sill to keep water from migrating under the foam and back into the house. All of the joints in the foam should be sealed well.
2. By using step 1 above the face of soffit can still be in the original position.
3. I would not omit the sheathing.
4. If you tape it well the house wrap is probably over kill.
5. All this does to windows and doors is require 2″ deeper extension jambs which shouldn’t be a problem.
Installing exterior insulation is MUCH better than interior because it’s continuous. Spraying the cavities with and inch or so of foam could possibly work if you can get sufficient R value to prevent the dew point problem, but it’s hard to control. I think you’re on the right track.
Todd,
thanks for sharing your knowledge on this subject. I am a contractor preparing to renovate a 1965 house with homasote sheathing. Plan is to leave the homasote add 1 1/2 foam board, 1/2 osb or cdx and cement fiberboard clapboard siding. This will bring me to a 6 9/16 jam for the new windows. Dealing with the 2″ overhang on the foundation is under discussion. We want to avoid air and insect penetration. Proposed are metal flashing (sort of a reverse drip edge and covering the foundatiion with a manufactured stone product or using a a Weatherwatch ice/watershield and then applying an azek cornerboard as a water table. your thoughts?
Michele – Can you put an extension on the sill plate, then trim the bottom of the extension with a PVC trim board after caulking the joints? That would probably work pretty well.
yes we would need to do the extension as a nailer for the corner board idea as well. Any preference on Dow vs. Owens Corning vs Celotex?
Michele – Not really, the real issue is being sure it’s closed cell foam.
These are great comments. Here’s my situation. I have an old 1920′s home with a brick exterior and plaster interior. I am renovating it and just took down the plaster and lathe. Now all I have left is the back side of the brick with 1X3 furring strips nailed on the inside 16″ OC so I only have 3/4″ or so due to the furring strips. I plan to install sheetrock attached to the furring strips. It never had any insulation. What product do I use to get some kind of wall insulation ? Do I have to stud this out further somehow to get the thickness I need or be happy with some sort of foam insulation panel (Which type do you recommend) that gets me only a R-5 or so wall and will get this passed the building inspector and this is a permitted project. I don’t want to use spray insulation contractor and would like to do it myself. Any help would be great !!
Mark – Well it really does depend on where you live and what Energy Code if any is in effect. I’d start off by checking with your local building inspector to find out what the minimum (if any) required insulation value is. After that you can come up with a plan of attack. Most likely you’ll want to install a layer of foam board over the furring strips prior to installing the drywall.
todd I live in upstate ny I am putting a 2nd floor on my house 2×6 walls can I use foam board along with 6in faced fiberglass to get higher R value and is it better to install foam board on the interior or exterior or both and what kind of foam board do i use
Mike – Sounds like a big project. Couple of thoughts about your situation. First off are you looking to do all this work yourself or with contractors? For new construction (including an addition) I would consider having a contractor come in and fill the wall cavities with blown in dense pack cellulose insulation. I REALLY like this product for wood framed walls because it does an amazing job of air sealing and you can achieve a full R21.
If you’re looking to do all the work yourself then you’ve got a couple options. I guess I would lead towards applying the foam on the outside of the house. If you’re going to do that you need to pay special attention to all the details, depth of window and door jambs, etc. You should use a closed cell foam specially designed to be installed under siding. You’ll probably want to hold the framing back from the outside of the existing house by the thickness of the foam so that the siding all lines up.
Hello Todd. Your website is fantastic!! I read through all these posts and didn’t find my exact situation, so thought I’d post.
I live in Jacksonville, FL and due to age and water damage, I had to replace the bottom sill plate on my 1940′s garage apartment. To do this, I had to remove the shiplap tongue and groove siding. Doing this showed me that there was no insulation and I’d like to add it. Can foam board insulation be used instead of batts of fiberglass?
The lap siding was installed directly to the 2×4 studs with no sheathing. Can I use the foam board cut to fit between the studs for insulation and then re-install the lap siding directly to the studs? I could also use the spray foam (Great Stuff comes to mind) to seal the gaps between the foam and the studs. I would assume a layer of Tyvek house wrap should also be installed before the siding is replaced.
I am willing to remove and replace all the siding if I have to but if you have a better idea on how to insulate it without removing the siding, I’d love to hear it.
Thanks so much for any insight you can provide.
Kim – Foam board insulation can be used anywhere fiberglass can be used. I assume you’ve got access from the inside? Another solution would be installing foam directly over the old siding then installing new siding. This creates great insulation value but it does require some special details at doors and windows to address the added thickness. Good luck!
Thanks for the reply. We do not have access from the inside without tearing out sheetrock. And since we had to remove siding to repair the damaged sill (and also termite damage) I thought we would just insulate from the outside rather than tear out sheetrock on the inside. Sheetrock may be cheaper, but it is a lot quicker and easier to just remove all the siding rather than try to get behind tubs and kitchen counters and, and, and….. :) I don’t want to double up due to the issue you mentioned regarding doors/windows.
You didn’t comment on whether Tyvek would be needed over the insulation under the new siding. Is that required?
Thanks again!
~Kim
Kim – Your proposed method will work just fine, and yes you should use a house wrap. Best of luck.
can blue foam board insulation be used under a metal roof – I have an old cabin that has no insulation in the roof just metal roof on tongue and grove pine and need a new roof and thought this might be a way to gain some insulation
Brad – It sure can! Blue board works in almost any application. Good luck.
I started building a room in the basement. Part of the basement is above ground and was insulated with fiberglass. We moved back some of the insulation and found mold! In the process of removing and cleaning with vinegar.
So would thick xps work well with the areas that are above ground as well? Is this stuff a fire hazard if not covered with drywall? I was hoping to leave the above ground walls open in the unfinished area of the basement for easier insect and mold inspection.
Will a hepa vacuum filter work for cleaning up fiberglass particles after I’m done removing this garbage?
thanks! been asking everywhere but not getting a good response.
PS also bought a dehumidifier after finding mold.
Chris – Foam will work well there as well. Frankly foam board will be no more of a fire hazard than fiberglass. Most building inspectors would definitely require that you cover it, but lots of houses don’t. Good luck.
hI,
My contractor is installing what looks like polyiso panels 1.5 inch R10, behind new vinyl siding on 2nd floor exterior wall.
I asked about Tyvek wrap and he said not necessary, but can they really seal that well with tape
Wouldn’t it be better to put Tyvek over the foam insulation to protect the foam from water and stop airflow? He said Tyvek is expensive but I think I saw 1000 ft2 roll for $100, so maybe its labor intensive install.
Anyhow, not sure I like the idea of the siding acting as the only rain and wind membrane.
Any thoughts?
Jazz – First off the foam can be sealed very well with the right type of tape. There are many tapes on the market now that stick very well..just be sure it’s not duct tape! Secondly there are lots of folks out there that argue about Tyvek (or house wrap) over foam board insulation under siding. I will say that if you think it’s worth the cost then it’s certainly not going to hurt anything. I say make your decision based on sleeping well at night.
Thanks Todd,
1. So the Tyvek plus the tape sealed foam would not inhibit the wall’s ability to breathe.
2. Another quick question about siding selection. The contractor is offering Procanna siding for the color I want whioh seems to be OEM’ed from an Ontario siding manufacturer, thickness is .044 and 25 year fade resistance. They don’t have any detailed spec sheet touting any kind of advanced technology or features.
3. Are there big differences still in vinyl siding from different manufacturers?
Is .044 thick enough
If I could choose any brand/thickness of traditional double
panels, what are the top brands based on reputations and advanced features?
thanks
Jazz – Frankly you want to keep the water away from the framing. If you don’t tape those seems water will get in. Vinyl siding is only a facade and it’s far from a water barrier.
In my opinion there is a huge difference in siding products. We’ve tried dozens of them and my preference is Certainteed. In fact, my first preference is Certainteed’s Monogram line that has a 0.046″ panel thickness. That extra bit really makes a big difference in performance especially in climates with large temperature swings like here in the North East.
Hi Todd, I could also choose ABTCo timber creek premium plus .046 thickness rather than the OEM .044 which we chose only because the green was slightly more appealing but the more I research Procanna the more I have doubts I think it is contractor grade, no info available, they won’t tell me who makes their panels.
What do you think? IS ABTCO good?
thanks
Jazz – I’ve never heard of them but doesn’t mean the product is bad. At least it’s a thicker panel.
ABTCO is KP Building products, Home Depot carries it here.
http://www.kpproducts.com/kpbp/ca/p-norman-rockwell.htm
Jazz says:
July 11, 2010 at 10:53 pm
ABTCO is KP Building products, Home Depot carries it here.
http://www.kpproducts.com/kpbp/ca/p-norman-rockwell.htm
Do you know this manufacturer?
thanks again
Jazz – Haven’t seen them before but that doesn’t mean much. We purchase all of our building products from two large “contractor” supply companies and mostly deal with two or three large, well known siding manufactures.
I live in New Jersey and I’m currently finishing/renovating my basement and have several questions:
1. Any recommendations on how to insulate around (or behind) an existing electrical panel and wall mtd water heater? Do you actually try to get the insulation behind these items, or do you just get as tight as possible to them? Obviously, it’s a large task to get behind them.
2. When completed, my basement will have a “finished” area (that will serve as a kids play room & home gym)and an unfinished area (that will be a utility closet and tool area). The finished areas will be conditioned, and the unfinished areas will not be conditioned. In your opinion, can I get away with only insulating the “finished” portions, or would you recommend insulating all of the exterior walls? If I only did the finished portion, I was planning on insulating (w/vapor barrier)the interior dividing partitions between the finished and unfinished spaces.
3. One of my foundation walls is directly below a “family room” that is a “slab-on-grade” construction. I’d like to install a thinner insulation along this wall due to this wall will encroach on an already tight stairwell. Any thoughts on going with a 3/4 or smaller board for this section of wall? It is somewhat insulated from the outside since there is a slab on grade installed at the top of the wall.
4. For the detail at the top of the wall and into the joist cavities, do you run a horizontal piece of insulation between the top of the wall and bottom of the joist cavity so that it’s continuous, or do you just run the insulation to the top of the foundation wall, put the pieces in the joist cavity, and leave a gap?
5. With the foam board insulations, I was planning on installing 3/4″ furring strips on top of the insualtion board, and then fastening the sheetrock into the furring strips. Is there any problem with notching the insulation around electrical boxes, or would you recommend deeper strips (possibly even a full 2×4) so that the electrical boxes don’t cut into the insulation?
6. As far as adhering the insulation, do you just use construction adhesive to install the foam boards, and if so, how do you hold them tight to the foundation wall?
7. When you reference “Energy Code”, is there any website that shows the requirements for different areas?
Thanks for your time.
Pete -
1. In an existing situation most people would opt to insulate up to these type of utilities. Relocating or moving them would be a pretty costly task.
2. I would recommend insulating all of the exterior walls. Your home will be more comfortable all around and it’s easier to deal with vapor at that point.
3. In situations like this you’ve got to weight the pro’s and con’s. Using 3/4″ foam will most likely not provide a very good vapor barrier. However, that wall will likely not get very cold so if water vapor from the interior space hits the foam it may not condensate. I say do the best you can with what you’ve got.
4. You want things to be as continuous as possible. Typically we’ll run up to the top of the wall, then install a horizontal piece above that, then insulate the rim joist, then tape all the seams or seal with spray foam in a can.
5. I would just use 2×4′s or if code allows you may be able to use shallow boxes (if they will fit in the 1-1/4″ space you have. I’d try to avoid notching the foam.
6. We have recently been using DOW GREAT STUFF PRO http://building.dow.com/na/en/products/sealants/gspwallfloor.htm it works exceptionally well at adhering the foam to the wall quickly. Sometimes you do need to apply some temporary shoring but not often with this product.
7. Every state has different rules regarding energy codes. Here in NH where I live it’s governed by the Public Utilities Commission (PUC). I would call your local building officials and inquire about it.
Good luck.
Todd, What a neat website!! I’m building a home close to Houston Tx and have 2×4 walls, wrapped 100% with 1/2″ sheathing and then with 3/4″ R Max insulation boards (R-5). I’m also planning to install house wrap before putting on 3×10 log siding. While I plan to use bat insulatin in the wall cavities, is there anything else I can or should do to improve the insulation effectiveness?
I am also installing knotty pine T&G boards on the interior walls and was planning to use sheetrock as a backer on the inside to keep down any dust or airflow. Would it be better to use an insulation board and if so, what kind would you recommend?
I doing this myself, with the help of my lovely bride, and could use any help you might provide.
THANKS A LOT!!!
Earnie – Hot climates like TX are a different animal compared to here in the north. I would recommend checking out http://www.buildingscience.com they have great information on all types of insulation. You just need to be careful with where there vapor barriers are when it’s warm on the outside and cool inside (air conditioning).
I have an enclosed(aluminum) car hauler. There is about 2 inches between the roof and the bottom of the supports. I would like to insulate the roof with foam board and hold it up with some thin wood board/screws. Which would be the best kind of foam board to get and proper thickness ? Foil faced or not ? Which way should the foil face ?
Brian – is it curved? If it’s curved most of these products will be hard to curve unless you install it in several layers. Most of the foil faced products are covered with foil on both sides.
The roof is arced yes. I would say it is arced about 2ft with a length of 8.5ft. I am thinking about using 3/4″ polystyrene foam board that has foil on one side. That would leave about 1.5″ of clearance between the foam board and the metal roof.
Brian – That will probably work..might have to score the back side though.
Great site! I am planning to insulate the walls of my Illinois basement with the 2″ XPS. I’ve heard that it should be 1-3 inches off the floor to catch any condensation from behind the insulation boards. Is this true? In the past water has seeped in thru the joint (cove?) between wall and floor. Can this be sealed? How? Digging up the floor and installing drain tiles is not an option. Thanks for your advice.
Mary – Before insulating you really should address the water issues. Interior French Drains are a great way to intercept and remove water from basements. Typically that’s a job best left to professionals.
If and once you that then you can bring the insulation right down to the top of the drain, any water behind the foam will drop down into the drain. It’s VERY important that all the seams in the foam be sealed. We’ve got several articles on the site showing how to do that.
Good luck.
Hi Todd
Great website and very helpful…I have a slight variation in insulating my basement interior walls.
I was hoping you could provide some expert advise.
I had to frame out my basement walls 8″ away from the concrete walls on all sides since the house has alot of conduit and pipes. I have installed metal studs 16″ OC and the basement is moist not wet. A dehumidifier keeps the basement dry. This 8″ gap also allows me to run a fan behind the studs for good air cirulation.
Question: Can I install Extruded or polyisocyanuarate between the studs for my insulation needs then cover it up with 1/2″ sheetrock.
I’m concerned about the combustible nature of these products since the interior part of this product will be exposed (between concrete wall and metal studs)
Note: This unfinished basement without any insulation in the coldest season (NY) maintains an average temperature of 67 degrees, so I’m not that concerned
Thanks for the advise
Frank
Frank – I think I’d install a layer of foil faced polyiso OVER the metal studs then attach the drywall. I don’t have the specs handy but you could check online to see what the flame spread rating for foil faced is. I have a feeling it’s not bad at all. I wouldn’t put the foam between studs because you won’t have any thermal break.
Lots of good ideas!
I’m refurbishing a 1950′s finished basement in Seattle. It had 1/4″ plywood paneling over 3/4 furing strips on 24″ centers. I’ve removed the paneling, and was planning on gluing 3/4″ foam to the concrete between the furing strips, then another 3/4″ layer over it all. Then screw 1/2″ drywall over it all to the furing strips.
Does that sound like a reasonable plan? There’s no moisture problem, no mold found after removing the old paneling.
Brad – I’d rather see a full 1-1/2 inches of foam against the concrete. However, your system will probably work fine.
Todd,
Thanks for this informative site. The company I work for bought a large commercial building. There are many 68″x68″ openings for wall exhaust fans. My boss wants me to design some insulated covers that we can install in the winter (the previous occupants just stapled up blue tarps and they said it was still freezing inside). My boss was thinking about making steel boxes and using foam board inside. The outside temperature regularly gets into the teens and single digits during the winter. We will use a good diameter rubber tube seal between the boxes and the exterior walls. The boxes will be bolted down to compress the seal. The boxes will be stored indoors when not in use.
1. What R value of insulation do you think is right?
2. Since the boxes will be metal, does it matter what direction any liners may face?
3. Do you think open side of the box (foam side) should have a cover?
4. Would it help to have air gaps between the box’s exterior sides and the foam?
5. Do you see any problems with this idea?
Thanks for any advice you can offer (this is not really in my bailiwick).
Rich – Sounds like an interesting project. Here’s a few thoughts/questions.
- Will the box be installed on the outside or inside of the building?
- Do you know how much wall insulation the existing building has? Most commercial buildings have an R19 in the wall.
- Assuming the cover goes on the outside, I’m thinking you could install 3 inches of foil faced polyiso insulation in the “box”. I would only have steel on the outside and sides, leave the side facing the building with just exposed foil faced insulation.
- Remember that steel itself transmits cold very well, so the gasket will be key.
Make sense?
Todd,
Thanks for fast reply!
The boxes will be on the outside.
I don’t know about the insulation in existing walls, but I can probably find out. The outside walls are a decorative type masonry block.
Yes, metal tranmits cold very well, so that’s why I was wondering about having the foam actually touch the metal or not. I was thinking a little air gap would be good – ?
Hmmm, we may want to use a treated wood, or probably plastic, frame around the face of the box to mount the gasket. The insulation could extend into this volume. Does that sound good?
ps. My boss would love for these things to last a lifetime.
Rich – I think you’re on the right track. Making them slightly larger, having the foam extend slightly deeper than the box, and a gasket, should take care of it.
Thanks – I think I have a plan.
But … Thinking about it, there are four large rollup garage doors that I don’t think have much insulation. Three inches of polyiso may be a little overkill compared to three inches of blue/pink board. Well, I guess I’ll just price it out and see how the boss wants to go. Maybe we’ll see about insulating the garage doors too. In any case, this will be a lot better than blue tarps!
Rich – I suggested the foil faced as a bit of safety insurance. Foil faced insulation should have a much better flame spread number than just foam board.
Great site!
Simple question I can find nowhere on the net. I have a old dirt basement/crawlspace in my old farmhouse that is vented well. The house floor is also un-insulated so we get a lot of moisture in the house after very rainy spells. Time has come to insulate the underside of the floor and I wanted to go with spray closed cell foam for its vapor barrier and insulating qualities….Plus it will hide some ugly bits of framing, as this house was built out of what appears to be scrap wood from an earlier home.
To save money I was wondering if I could just tack 2″ foam board between each floor joist and spray the seams, joints and hard to get areas with the spray. The DIY spray foam kits run about $1.50 sf. for the foam, so this would be a huge savings if it will achieve the same effect. Is this ok to do and is a specific type of foam board more compatible with the spray foams?
Thanks
Joel L.
Franklin, NC
Jeol – Not a bad idea if you can’t afford a complete spray foam job. For this application I would recommend at least 2 inches of foam. Before installing the foam board though I would get some samples and test the spray foam on it to be sure there’s no reaction that would damage the foam board. Under a crawl space I would prefer to use foil faced polyiso myself. Good luck.
Tod,
I live in Madison, WI and I am converting a screened-in porch into a room. There is a concrete slab and the roof is held up by three 6×6 cedar posts. Because of the depths of the posts from the edge of the slab, I have framed the bottom section of the wall with 2x8s. That way the siding goes over the edge of the slab. Then, so that I can leave the posts (which are pretty and expensive) exposed, I have framed the top half of the wall (containing the windows) with 2x4s. The ceiling rafters will be furred out to 12.” And to allow for heating ducts, the floor is raised about 14′ on 2×8″ joists.
So what I’m looking for is the best and most cost effective way to insulate this monstrosity.
I was thinking of putting 6″ of foam board on the slab (the inspectors want r-30) and densepack cellulose in the ceiling. Does this make sense?
Then I was thinking of putting one inch ridged foam board over the outside of the slab and the lower 2×8 wall. Do I need house wrap for this? OVer or under the foam board?
But my big question is the walls. The upper 2×4 walls have lots of small cavities in the framing betweeen and above the window. Can you put dense pack cellulose in those? Or would spray foam be better?
What do you think?
thanks
cw – Thanks for visiting the site.
The 6 inches of foam board would work fine on the slab.
The 1 inch foam on the outside of the 2×8 is ok but you’ll need more R value (planning on more insulation in the wall cavity?).
House wrap is a good idea even with foam on the outside of the house. Over the foam.
Dense pack fiberglass or cellulose will work great in those wall.
Thanks for your help. The one inch on the outside is to insulate the studs, break the thermal transferance or whatever you call it. THere will be some kind of insullation inside the studs.
So they can blow dense pack cellulose into small cavities, say 1 1/2″ wide? Would that be better than spray in foam?
Thanks again for your help.
cw – dense pack can blow into voids that small. when the voids get down to like 1/2 inch then typically foam those while still dense packing the rest.
Hi,
Roof on Steel deck in Ottawa.
1- Is there a specific vapour barrier that goes under polyiso?
2- How to fix the polyiso on the vapour barrier? do we need to reach the deck?
3- I need one or two sheets of polyiso to get the 4 inches.
4- Can I install torch applied membrane on the insulation, is there any primer?
5- can isoply be tapered?
Thanks,
Mongi