Beam Pocket insulation/Prevention of Moisture
Ar1976
| Posted in Energy Efficiency and Durability on
Looking to have 2x W12x26 spanning across the first floor in my future build, they will sit in beam pockets like the one pictured, and in exterior walls holding up the second floor framing. What is the best way to prevent moisture in a case like this? Also a way to have less thermal bridging? Looking for some ideas on this. Close to Canada, cold climate. The exterior of the building will have no provisions for foam insulation, 2×6 walls I plan to insulate with HD batts. Thanks!
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Replies
AR1976,
Find out how much bearing depth the beams require. That may dictate the options.
At an absolute minimum it’ll have to be the full 5.5” depth. Trying to think of how I can somehow set the beam just to the drywall inside and support via the interior with a column of some sort.
The most important thing, by far, is to provide insulation between the beam and the exterior. Even R-5 makes a big difference, but ideally you'd have the beam entirely within the conditioned space.
If you use a PSL post (parallel strand lumber, i.e. Parallam) the limiting factor is often not the bearing area but the height of the post. Below you mention the steel beam spans 26' and carries 20' of flooring width. Is 20' the full building width or is it 40' wide? Even at 40' wide, the load on the end of the beam is only 13,000 lbs or so, which is large but not huge. The length of the beam span makes a big difference on the required beam size.
And if you figure the wood has a crush strength of 2000 psi, the beam only has to have about seven square inches of bearing for 13,000 lbs. I'd be thinking of ways to have it end 2" or so short of the sheathing and packing the pocket with foam.
Another way to gain more bearing without extra depth is to have more studs under the beam. You can weld a bearing plate to the bottom of the beam which can be used to spread the load out to these extra studs. You can then put say an 1" or so rigid into the pocket to insulate.
I think overall, the steel post is the simplest idea. A short 3.5" steel column can hold a surprising amount of load. This would leave you 2" gap you can fill with rigid. Make sure to put the rigid in before the column and the beam as you won't be able to insulate it afterwards.
P.S. Steel beams are not cheap, and if pocketed into the floor they get in the way of services. I would try to clear span first and see where you end up. Taller joists especially with floor trusses are not a lot of extra money.
Have you gone through the exercise of sizing engineered lumber to replace the beam? That may end up being easier.
Yes, The beam is spanning 26’ with 20’ width of floor to support. Steel I believe is the only way to go unless I get some giant LVL setup but that cuts a lot of headspace.
I'm going to guess the building is 26x40 since you said there were two beams? I-joists could span 26.
If you use a steel column to support the end of the beam, that should free up enough depth to add at least an inch, maybe two, of rigid foam into the exterior side/end of the beam pocket. That's probably your only real option here aside from covering the entire exterior of the wall with rigid foam, or making a bump out on the exterior to add some rigid foam only over the beam pocket. It's pretty common to support steel beams with steel tube (usually round, but you can also get square tube), and your engineer should have no problem drawing up a detail for that for you. Steel can handle much higher loads per unit area than wood can in compression like this.
Bill
Good idea. Maybe I’ll try something like that then. I imagine it’ll sit directly on the ICF rather than the sill plate as well. Exterior of the building will have a rain screen setup so I could add about 3/4” of foam there too.
You can use a steel plate as a "foot" on the column to help distribute the load. Steel is better than wood when you need a more compact structural element like this. The big downside is steel really needs to be prefabricated off site, since it's difficult to work with in the field. Be sure to measure EXACTLY when putting your drawing together for the fabricator.
BTW, be sure to order any steel with primer pre-applied.
Bill
Thank you bill. I appreciate the insight
Before installation, seal the steel beams with a high-quality rust-inhibiting paint or coating. This will protect them from moisture that may accumulate over time. Try also reaching out to hoodsly customer service https://www.pissedconsumer.com/company/hoodsly/customer-service.html to see if they might be able to help. They’re usually quite responsive and may offer some practical solutions or alternatives to resolve the issue quickly