Written by Todd Fratzel.
TJI Floor Joist Framing
Engineered lumber continues to become more and more popular in today’s construction industry. TJI’s (engineered wood I joists) are my preferred framing members for floor systems. TJI’s offer many benefits compared to traditional dimensional lumber joists including: almost no twisting or warping, very little dimensional shrinkage, stiffness and strength.
Framing a floor with TJI’s is really no different than framing with dimensional lumber. The one big difference is the hardness of the material which makes nailing into it a bit more difficult. Engineered joists are also a little less stable (can’t walk on them) until the sub-floor is installed.
TJI’s are available in many different sizes ranging from 9-1/2″ to 16″ deep and flanges 1-3/4″ to 3-1/2″ wide. The wide range of sizes allow for framing many structures from residential houses to commercial buildings. Check out one of our other articles on How To Size TJI Floor Joists.
Engineered Lumber Beams
In addition to the TJI joists, we also use TimberStrand LSL Rim Boards and Parallam PSL Beams. The rim boards come in the same depths as the TJI joists. Parallam PSL Beams are the workhorse of beams for most buildings that we construct. Occasionally we’ll use the Microlams (LVL Beam) but PSL beams have great capacity and available sizes. Most lumber yards can help you size the beams to meet local and State building codes, otherwise you should consult with an engineer. You can read more about Engineered Lumber and why I think it’s a good investment.
Dropped Vs Flush Joist Framing
This particular floor system has two framing approaches. For the framing shown in the photo, the beams are framed “flush” meaning they are in the same plane as the joists. This type of “flush” framing allows for more head room below. At the other end of this house there is a beam that is framed “dropped” which means the beam is framed below the joists such that the joists rest on top of the beam.
In order to frame in a “flush” beam you’ll need appropriate hangers. As you can see in the photo hangers have been installed along the face of the carrying beam in order to carry the TJI joists. Anyone that’s ever nailed into a PSL beam will tell you it’s like trying to nail into rock.
That’s why I recommend you buy a Bostitch MCN-150 StrapShot Metal Connector Nailer. This pneumatic nail gun is specifically designed to allow you to shoot 1-1/2″ hanger nails directly into the pre-drilled hanger nail holes. This gun is an absolute necessity if you have any significant amount of hangers that need to be attached to PSL or Microlam beams. Metal Hanger Nail guns are specially designed to allow you to see the nail tip in the hole prior to shooting it in. This allows you to get each nail into the correct hole.
Installing Sub-Floor Over I-Joists
Once all the framing is in place we install 3/4″ Advantec sheathing on the deck. I highly recommend that you use a significant amount of PL Polyurethane Construction Adhesive between the Advantec and the TJI’s. Then make sure to either nail it down with ring shank nails or even better with screws. If you skimp on this step you’ll forever be haunted with floor squeaks. So don’t say I didn’t warn you, trust me, I’ve seen this happen far too many times.
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