Spray Foam Over Attic Floor
![](https://secure.gravatar.com/avatar/cab94eba88213999df64a4279af49e7c?s=52&d=https%3A%2F%2Fimages.greenbuildingadvisor.com%2Fapp%2Favatars%2F200x200%2Fc.png&r=g)
Climate Zone 6A – A friend with a tight budget is getting new roof sheathing and shingles due to hail damage. The home is 60+ years old, drafty, with minimal attic insulation. They have attic trusses, so there is a kneewall-to-cathedral-to-small overhead attic condition.
8-12″ of continuous exterior insulation (they would only do EPS) is likely out of their budget.
Would it be disastrously ill-advised for them to just do 4″ of HFO closed-cell spray foam the backside of their ceiling/walls during the short time that all their roof decking is removed?
I understand its not an idea R-value…but seems like it would be a substantial improvement for vapor, air leakage and R-value for what they have and not risk long term mold/moisture issues like just packing batts in would.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
![](https://www.greenbuildingadvisor.com/app/themes/greenbuildingadvisor/dist/img/modules/detail-library/thumb1.png)
![](https://www.greenbuildingadvisor.com/app/themes/greenbuildingadvisor/dist/img/modules/detail-library/thumb2.png)
Replies
Anyone out there able to offer thoughts on this? Attached are two photos with the possible application plane of 4-5" of closed cell HFO spray foam.