Insulation help needed?
I am in the process of building a house and thought I had a good plan for insulating, but want to know if I can do better. My current method I planned on using will pass code, but i figured if I can increase R-value effectively, why not. Better to do it now. I live in zone 4a. We have hot summers and fairly cold winters.
1 story
2×6 construction
Vinyl siding
Tyvek house wrap
Osb sheathing
Fiberglass or denim batts in stud cavities for R-value of 21.
Drywall
Have a full basement, will be unfinished for awhile.
Attic will have like R 50 blown fiberglass
So here’s my dilemma, can I add some kind of rigid foam insulation to the house interior safely, without having to worry about moisture or vapor problems?
Ideally, it would go on the outside right, but I think I’m too late. The house is framed up, house wrap and windows are already installed. Without removing the windows and adding extensions to them, can rigid foam still be added to the outside, Over the house wrap?
Or is there a better solution altogether, maybe spray foam?
Thank you in advance for all replies and advice. I hope I’ve included enough details for a good assessment from everyone.
Nick
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Replies
Nick,
It's a little late for you to be asking this question.
There are a variety of ways that you can improve the R-value of your walls by making the walls thicker on the interior. Before you decide whether it's worth the effort to try one of these approaches, however, we need more information.
Is the electrical rough-in work already done? (In other words, has your electrician already installed your electrical boxes?) If so, changes are much more complicated than they would be if your electrician hasn't started.
One approach to improving the performance of your walls is to install sprayable caulk before your stud bays are insulated. For more information, see Air Sealing With Sprayable Caulk.
Martin, thank you for the reply.
No electrical work has been done yet. So, that should not pose extra problems. Hopefully that will give me a lot more options.
In the meantime I will research air sealing with spray caulk.
With your sheathing, housewrap, and windows installed, it's not necessarily too late to install exterior rigid foam or rigid mineral wool. You'll just have recessed windows. The detailing isn't really very complicated since you don't have to integrate the rigid insulation boards with your WRB layer. Exterior electrical boxes wouldn't have been a big deal anyway; you could just have added box extenders to make the ultimate opening flush with the boards or cladding. The bigger problem will be exterior hose bibs, exhaust vents, outside electrical panels and other such penetrations, which may be more difficult to lengthen or relocate if they terminate right at the current wall exterior. I had this problem when I covered my house in 2" of exterior foam during a retrofit; we ended up simply installing the foam around the exterior electrical panel since moving it was not going to be cost-effective.
Nick,
It's possible to install rigid foam on the interior of your walls. Here are some pointers:
1. This type of wall needs to be able to dry to the exterior. Since vinyl siding is very well ventilated, you should be OK.
2. The tricky areas are rim joists and partition intersections. If you remember to insulate and air seal these areas as well as the central areas of your exterior walls, your wall will perform better.
3. If you install only 1 or 2 inches of rigid foam, it's possible to install the drywall directly over the rigid foam, without any furring strips, using long screws through the foam into the studs. Most drywall contractors hate to do this, however, so have a discussion with your drywall contractor before finalizing your details.
4. If you decide to install horizontal furring strips, keep that detail in mind when choosing how deep to install your electrical boxes. Of course, you'll also have to have a conversation with your electrical contractor, who may not be thrilled with your plan.