Insulated headers
I am in the Chicago area (CZ 5) and we are using a modified version of IECC 2012. Our exterior wall is a masonry veneer wall and we are using 2×6 wall studs for framing, allowing R-21 insulation in the stud cavities. Structurally, the wall could be built with 2×4 studs but it was decided that going with 2×6 and R-21 would be more cost effective than using 2x4s with 2″ of rigid on the outside.
Some of the headers in this wall only need a double Microllam (3-1/2″), and the rest of the space can be filled with 2″ rigid insulation. Where is the best place to put this insulation? I’ve seen some details that show the rigid sandwiched between the two 1-3/4″ Microllams. This would support both sides of the 2×6 wall above and prevent twisting. But I think the double Microllam has more structural integrity when the two are nailed together, then putting the rigid on one side or the other. SInce the floor joists only need 3-1/2″ of bearing, I don’t think twisting is a concern. So is it better to put the rigid on the interior side or exterior side of the wall. My inclination is to put the Microllams to the outside, to provide additional support at that side, since that is where the windows/doors in the opening have their nailing flange.
Does this make sense, or are there other considerations I should be factoring in?
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
That's what I would do. You will also need a furring strip on the inside of the header, at the bottom, to fasten the drywall.
I'm just a DIYer but I did a few replacement headers recently. I put the foam board in the center and used RSS lag screws from both sides. The screws from both sides suck the headers together.
You'd have to show some video or science for me to believe that the two spaced headers would separate somehow. It's common to see 2x6s, 2x12s etc in older homes assembled this way with blocking. A nailer on both sides is helpful, yes?
I do think this is a question for your engineer however as you will be changing the depth of the bearing end of the truss or joist if you place the foam to the interior. (ie the trusses/joists will bear on 3.5" instead of 5.25").
There is a discussion here that might help:
http://forums.jlconline.com/forums/showthread.php?15564-Headers-2X6-walls