Hi,

I am building a new small 1570sqft house near Allentown, Pennsylvania and my architect and mostly me think its a great idea to put R10 2" exterior foam on the exterior walls to avoid thermal bridging and have a very efficient and comfortable home. I would need to box out the windows and have extension jambs on door and windows and it is more work then not having any foam on the exterior. I have talked to a few builders and they all think its a dumb idea and the house will be comfortable with r21 2x6 walls. I will be using 2x6 walls + 2"xps foam which is around wall r31. It will cost me around $4,000 more for the foam and extension jambs and will do the work myself. I will also need to add furring strips to attached the siding to. I also will need a HRV to have fresh air into the house as it will be a super tight house.

What are your thoughts? Do the 2" foam or skip it? I will also be using a 2 stage electric heat pump with variable speed air handler and keep it around 72f or 73 in the winter and 68 to 70f in the summer.

Thanks

I designed and assisted a homeowner build a 2x6 stud home in Columbia, SC back when electricity was expensive. Cedar weatherboard was installed over the Styrofoam. The Styrofoam outside the studs and the 6" fiberglass batts between the studs resulted in a very comfortable home with low energy bills. I would think that a home in your climate would benefit even more by insulating the studs. Another way to consider is to go with a package like NexGen Framing. I now try to avoid using wood because termites are so bad in the southeast.

Another option would be 2x4 wall with the foam so your doors and windows would fit as if it was a 2x6 wall. Tape the foam seams and your inspector should allow that as your wrb so no tyvek. EPS is much less expensive than XPS but also not as durable and will break more easily. Your air sealing details are more critical than throwing foam on the outside and hoping for a tight house so have a plan for that.

Or do what we do with 12” thick ICF walls having 2.5” of EPS on both sides...build your door and window bucks the full thickness of the wall and then use standard doors and windows for a 2x4 wall.

Posted By sailawayrb on 30 Jul 2018 01:45 PM
Or do what we do with 12” thick ICF walls having 2.5” of EPS on both sides...build your door and window bucks the full thickness of the wall and then use standard doors and windows for a 2x4 wall.

I agree! John

Nate, How are you planning to attach your furring strips to the foam so you can apply siding?

Posted By Roger R on 30 Jul 2018 05:49 PM
Nate, How are you planning to attach your furring strips to the foam so you can apply siding?

screws or nail furring strips. I will use furring strips over the foam and screw or nail into the studs  through the foam then attach the siding to the furring strips. This a good idea?

Why not just consider building your home with SIPs, it will be more cost effective and faster in getting your exterior shell up! I'd enjoy discussing your build with you. Bruce SIPS Resource & More A subsidiary of SIPS Resource, LLC [email protected] FL. Mobile 850-728-2685