Options and options for Insulating an A-frame

[kenrevo]

I have an A-frame we want to turn into a year round house/ cabin. The main areas that need improvement are the windows and the insulation in the roof; on a hot day it can get to 90F inside. The windows are floor to ceiling single pane glass on both end walls; the plan is to reframe the end walls to fit the new energy efficient windows.

Currently the roof only has R13 fiberglass insulation under it where there are 2x4 walls in between the large beam rafters (48" OC). Inside the 2x4 walls is finished space and don't have space space to put 16" thick walls to meet current code. A couple contractors said to frame out a cavity on the exterior of the current roof to fill with insulation; this sound great but the quotes are between $35k and $50k. We are concerned about the ROI on spending that much.

We're looking for other suggestions or thoughts on the best course of action.

 

[Russell King]

Look at closed cell spray foam. You may also want to build a second wall with the 2x4 offset from the current ones and increase the wall thickness a few inches if you can stand to lose floor space. Offsetting the studs provides a good thermal break.

 

[Scm]

remove old roofing, add a rim board to the outer perimeter of the roof, 2x8-10 or 12". Then infill with (2" x X layers) foam board and cap with 5/8" (3/4" better) using long screws to hit the original rafters. add new roof and done.

 

[Henro]

Might be helpful if you give a little more background information.

Since you already talked to a contractor, is it safe to assume you’re not going to do the work with your own hands?

My guess is it makes a big difference in approach if you’re doing it yourself or if you’re paying people to do the work.

We personally built our house with our own hands from the ground up (mostly my hands; wife had two girls to take care of plus me, of course ). But I sure couldn’t do that again now!

 

[Hoserman]

All the above will work just fine. But be aware of a fire that might get to the roof. I had a friend I worked with that put a roof over a roof without fire stops and he lost his house. Good luck on your project.

 

[North Idaho Wolfman]

Look at Rockwool comfort board to install on the exterior under roofing.
Look at Rockwool or Thermafiber for between studs on the interior.
It is more then fiberglass, but it does not compare, Mineral wool is hands down much better!

 

[kenrevo]

Thanks for the feedback. We haven't decided if we are going to do the work ourselves or have someone do it. I don't mind taking on a large project but the roof is large and steep (each side is ~35ft x~30ft at 23/12 pitch). I talked to a couple contractors to get ideas.

It sounds like the structure on the exterior of the existing roof deck is only option if we want to retain the interior space. We'll need to compare the different insulation options and the investigate the code; one contractor say our area is R60 for attic/ cathedral ceilings.

 

[Scm]

R60

That's 8.5" of closed cell spray foam
12" of foam board or
15" of comfortboard insulation.
Sounds right for MA. When their goal is to make housing less affordable.