Expert: Dave Johnson - 5/10/2009

Question
I am replacing the siding on my house and to make it more energy efficient i am adding one inch thick rigid foam and tyvek. Which should i install over the sheathing first the tyvek or foam? And please explain the reason why.

Answer
Hi Terry,
There is no need to use tyvek if you're using foam.
I would fit the foam as tightly as possible and tape the joints with duct tape (the tape they sell specifically for foam is too priceyAfter that there isn't a good reason for wrap.
To go a step further, you might want to consider using foil faced foam, I've found it actually adds enough to make it worthwhile.

Best of luck,

Davve