i plan on using web floor trusses between the first and second stories of my house.i’m looking fo a way to eliminate thermal bridging without spending big$ on two part foam. can i leave two inches between the truss and exterior sheathing for ridgid foam?the walls and ceiling are getting blown cellulose. thanks.
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I doubt you could hold the trusses in 2". You need more bearing surface than that for the trusses to sit on.
Most people that I've seen just used pieces of R19 insulation stuffed into the cavities.
Ain't much an old country boy like me can't hack [John Denver]
Use cellulose in the trusses. It takes a little bit of cutting and extra stapling for the mesh but works fine.
how do you fasten the mesh so the cellulose doesn't blow away from the wall?? thanks for your time
Assuming the floor trusses are 16" deep, cut mesh 24" wide, feed mesh between the chords at the wall, staple the top to the subfloor slitting the mesh at the trusses so that it fits tightly. Staple the bottom of the mesh to the top plate, again slitting the mesh at the bottom chord so that it can be pulled tight. Staple the slits to the trusses.
That is essentially all there is to it. You may have to adjust to avoid truss plates and web members that are in the way but the mesh is flexible and you can overinsulate this area if it is easier.
Set the blower so there is not a lot of air going through the hose and you will lose as much insulation as you do in the walls, not much except when you switch holes.
what are you using to block the thermal bridging on the rest of the walls/house?
mooney wall 2x2's horizontal to 2x6
Will 1/2 R-board on the exterior work? I'm thinking there will be less heat transfer via the floor trusses Vs a solid 2x joist. Maybe if this is still in the planning stage look at a top hanging truss?
can you explain to me what a top hanging truss is? i haven't heard of those. yeah,we're still in the planning phase. thanks
I haven't seen them used in a while but they hang (literally) from the top chord of the truss. Down side is that you have to make up the height somewhere meaning taller walls. Where I saw them the most was on 1st floors set on 10ft poured walls (basement).
found a pic in the link. Look for pic with Circlenote 3 on the 2nd page. CircNote 18 could be an option for you as well
http://www.sbcindustry.com/images/publication_images/ttbfloor.pdf
and here http://www.trulinetruss.com/html/body_floor_truss.html where the correct (or at leat better then mine) terminology is Dropped Top Chord
Edited 4/14/2008 7:26 pm ET by john7g
where are you building? (This is a hint to fill out at least your loc in your profile. It helps people figure most appropriate responses since afterall this is the world wide web and techinques vary.)
Call your truss company. We frame our exterior walls with 2x6, and hold our trusses in 2 1/2". This is approved by the truss designer. We sheath the end of the trusses with 1/2"OSB, add 2" of XPS, and are done with it. I am in a cold climate, and our local building dept doesn't allow fiberglass against a rim joist. It really gets tricky, too, because any foam you use that is left exposed even between floor joists must be fire rated or protected by a thermal barrier. Thus the extra piece of OSB.
thanks for the reply.this sounds like what i had in mind.what about the wall above? does the foam you use need to be high density to bear some of the load?
No, the foam doesn't hold any load. 3" of the 2x6 wall above is landing on the floor below and that is sufficient bearing, unless you have some unusual loads on it...in that case call an engineer. This won't work if you are using 2x4's for ext. walls.