I hope to pull permits for new construction next month, in northern Illinois ( north end of zone 5) but am concerned that I’m not optimally insulating the headers. On the original set, the architect had no insulation in front or behind the headers. When I expressed concern about thermal bridging, he added 1″ rigid foam on inside (His drawings attached). I was concerned that the ‘cold’ header will just transmit though the studs…but then they’re already cold. The contractor recommended switching to vinyl and adding 2″ foam on the outside of the entire wall (I had specified fiber cement siding, which apparently can’t be ‘hung’ that far from studs to get that much foam board). I’ve read some archives back to 2001, and am confused whether it is better to put insulation on the outside or inside of the header…and outside or inside of insulated walls in general. Some more recent articles mentioned keeping wood warm prevents rot. Does that mean you shouldn’t use insulation on the inside at all? Thanks.
Replies
When the foam is on the inside (or outside), what is there to nail to above your door or window? Nothing!
If you're willing to pony up for 2" rigid foam over the walls, take a look at a common way they do it farther up north and put the foam on the inside of the walls running horizontally, with nailers every 2' and around the windows/doors.
Normally I'll put the foam between the header plys and use a couple timberlock screws every couple of feet to hold it together. Make sure you need all the headers - if it's not a load bearing wall adding a header just reduces your insulation. Along the same lines, if you can tuck the header up in the rim joist if there's a second floor it frees up room for insulation in the wall.
I have a gambrel roof so there is a side attic area and I can put foam board behind the header but its in a side attic area because the each side exterior wall is actually interior walls with the roof sheathing a good distance away from it 3' on the bottom and tighter at the top..
would it be ok to put foam board on the back side of the header? or is it not even that important in my climate 2 central florida
1.5-2" of EPS on the outside
1.5-2" of EPS on the outside of the wall with furring strips to attach siding/etc to is going to give you a much higher "whole wall" r-value than anything you could do inside of the wall cavity alone. 2x4 wall "outsulated" in this manner is going to be the same overall thickness as a 2x6 wall; but with a higher "whole wall" r-value due to the break in thermal bridging. 2x6 wall with the exterior foam is just that much better. Obviously properly air sealing the exterior sheeting and interior drywall are important as well. The "foam control" EPS has borates to make it termite-resistant, if that is a concern in your area. Location of drainage planes and vapor barriers need to be designed specific to the location of the home as well. Hopefully it's not frowned upon to mention other resources on this website. This place has been amazing for the construction-based questions I've had; but user name "Dana" over at the green building talk forums website has the most vast knowledge of proper area-specific wall design from an insulation/vapor barrier standpoint of anyone I've ever come across.
straw
I don't think anyone can frown when good recommendations or links to viable answers are given.
thanks
Two things come to mind.
First is that you can buy insulated headers. Here's one kind:
http://www.tsfpi.com/Insulated_Headers.html
There's another brand that looks like an I-joist with 2 webs, and insulation between the webs.
The other thought is to not use so many header plies. Looks like you're using a 3 ply header, but I doubt that's necessary. If you could use 2 plies that gives you more room for insulation. Or maybe even one ply LVL headers, with the balance being insulation.
follow-up
So after reviewing the various sites and talking with my builder, we decided to go with 1.5 XPS on the exterior of my 6" walls and not use any poly vapor barrier inside. However builder was was planning to spray foam between the studs with closed cell and I'm concerned about it acting as a vapor barrier as well as sealing air leaks. I'm advocating open-cell for lower cost per R and to let moisture 'escape' to the interior (especially now that we have R-7.5 exterior to the wall) . Builder is still concerned that the open-cell doesn't seal air leaks as well, and would rather try closed-cell and batts ('flash & batt'). That makes sense to me as well. Any comments?
Thanks.
Jeff
Why are you worried about the foam "acting as a vapor barrier"??? In your climate, what's wrong with a vapor barrier?
If I understand what I've been reading (and that's always a question), insulating with ridgid insulation on the exgterior as a thermal break and using a vapor barrier on the inside runs the risk of trapping moisture in the wall. Not using a vapor barrier allows the wall to 'dry out' from the inside.
If I understand what I've been reading (and that's always a question), insulating with ridgid insulation on the exgterior as a thermal break and using a vapor barrier on the inside runs the risk of trapping moisture in the wall. Not using a vapor barrier allows the wall to 'dry out' from the inside.
Consider both closed-cell and open-cell spray foam insulation. Closed-cell offers higher R-value and seals air effectively, but may trap moisture. Open-cell is cheaper and allows better moisture diffusion, but might not seal air as tightly. Discuss with your builder to decide based on your needs.
follow-up
So after reviewing the various sites and talking with my builder, we decided to go with 1.5 XPS on the exterior of my 6" walls and not use any poly vapor barrier inside. However builder was was planning to spray foam between the studs with closed cell and I'm concerned about it acting as a vapor barrier as well as sealing air leaks. I'm advocating open-cell for lower cost per R and to let moisture 'escape' to the interior (especially now that we have R-7.5 exterior to the wall) . Builder is still concerned that the open-cell doesn't seal air leaks as well, and would rather try closed-cell and batts ('flash & batt'). That makes sense to me as well. Any comments?
Thanks.
Jeff
Thanks for the infomation. N1102.5.1 gives 7.5 an acceptable R value for the sheathing for a 6" wall for climate area 5. Since I'm on the border of 5/6, I can see why you recommend more, and I should probably should go to R-11 just to be safe.
But I'm still faced wth the conflicting information on the websites about an interior barrier. Info on Greenbuildingadvisor seems to indicate its still better not to include an interior barrier. But your email makes sense that its better not to have the condensation there in the first place.
Also, as an alternative to R-11 and impermeable XPS.sheathing..maybe I should go with rockwool (Roxul) in same or lesser R-value, and let it dry out from the exterior.
Consult with a building expert for personalized advice on insulation strategies for your construction project, considering both thermal bridging and moisture management.
After 10 years it stands to reason he already knows the outcome of whatever procedure he utilized. Your brilliant reply repeated twice might not stand.
Sounds like you're in the thick of it with your new construction plans. Insulating headers can be tricky, but it's great that you're thinking about thermal bridging. It seems like your architect's solution with the 1" rigid foam on the inside might help, but your contractor's suggestion of 2" foam on the outside could be even better. Keeping wood warm can indeed help prevent rot, so insulation on the outside might be a good call. It's all about finding the right balance for your project.
Warm wood does not impede rot.
Sean_Law12 posts should all be considered to be false information. While some of it sounds good, most of it is just a compilation of previous snippets regurgitated.
Artificial Intelligence?
Then again, I’ve been wrong before.