GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Re-roof Question

JHRockwell | Posted in Energy Efficiency and Durability on

This Zone 5, coastal roof is leaking and going to be replaced via a low-interest, deferred HUD loan. (See photos). I had dreams of a Deep Energy Retrofit, but even with generous incentives from the electric utility, the expense is too great for the loan recipient, and a VERY incremental approach is required.

The attic is finished, has 4′ kneewalls, access to the triangular storage space behind, sloping ceilings and about 6′ of flat ceiling. There is one old, single-glazed double-hung window at each gable end (conveniently arch-topped). There is no insulation in the 2×6 rafters at 2′ o.c. There are 2 skylights on the south side. There is a disused chimney on the north side which will be demolished to beneath the roof line to provide continuity of insulation/water control layer, etc.

After the shingles are stripped and the sheathing is evaluated/repaired/secured, I’d like to add polyisocyanurate to the existing roof sheathing, and dense pack the rafter bays with cellulose. I realize this is a Pandora’s box of lead paint, historic details, and “where do you stop” junctions. Eventually this lovely old house will be re-sided (probably with vinyl, it pains me to reveal); the overhangs at eaves and rake will doubtless get modified, but it can’t be done in this phase.

I’d love to hear suggestions about how to deal with this situation, specifically intersections at eave/wall and rake profile; what is an appropriate amount of polyiso; and any other thoughts you all have…


GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. JHRockwell | | #1

    Photos are attached in this "answer".

  2. wjrobinson | | #2

    John, A home near me had ridgid foam added to walls only not the roof at a cost of $60,000 using recycled foam. It can be done. It's an expensive project done through a contractor.

    Commercial roof companies have used foam, also others say check Craig's list.

  3. GBA Editor
    Martin Holladay | | #3

    The short answer is that most building codes require R-20 of foam (3 inches of polyiso) above your roof sheathing in your climate. For more information, see How to Build an Insulated Cathedral Ceiling and Creating a Conditioned Attic.

    In the triangular knee-wall areas, you'll need to install some rigid foam or spray foam to connect the thermal barrier on your roof to the thermal barrier on the your walls. Make that transition as airtight as possible. That means getting down to the tight, hard-to-work-in area and bringing insulation up to the roof sheathing.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |