Home Improvement → Insulating an A-Frame house

I've looked this up online and haven't found much information.

This is a shot our weekend place located in Southern VT. This was taken last year...when we actually had snow. It's heated with a propane wall heater and when we're there, a wood stove. We have two electric baseboards in the lower level. We only leave one on when we're not there and that heats the utlity room where all the copper and well tank are located.

The house was built in the mid 60's; it's roughly 800-900 sq/ft. You can't see it from the front, but it has a finished lower level with a walkout to the back yard. The finished area downstairs is insulated with foam board and rolled insulation...which are behind tounge and grove boards as a wall.

The main level of the house has about 2" of rolled insulation in the walls/roof. This is covered by some snazzy 70's syled, cut to fit between the joists wood panneling.

The problem is....the walls are the roof...the roof is the wall. I'm concered that putting better insulaation in there will eventually cook off the current roof. Which I beleive is orginal...back when 30 year shingles were twice as thick as today's 30 year.

When we bought the place a few yeas back, the inspector suggested doing a "cold roof". Basically, a deck on top of the current deck with a gap for air flow.

I just wanted to see if anyone else had any thoughts or ideas.

Not exactly your situation, but I did the detail drawings to a roof similar to yours about a year ago where the owner didn't have any space for insulation. He had exposed tongue & groove ceilings so we designed it with 2-1/2" insulation above the decking, then 2x4 sleepers parallel with the slope of the roof so air could travel between it and lastly decking was added over the sleepers for his shingles.
This was adequate for south carolina ... not sure what it will take for your state

What do you mean "cook off the current roof?" You have insulation already in the A-frame along the roof? Isn't moisture accumulating? I assume you have no soffit or ridge vents, and no air gap behind the insulation for air to flow.

I don't have a clew as to how you would update your insulation. Our 10 year old home, with cathedral ceilings, has 2X12 framing in the roof. There are Styrofoam channels stapled to the bottom of the roof sheathing, to allow air flow from the soffit vents to the ridge vents. Beneath that is 12" fiberglass insulation and then the tongue and groove interior paneling.

I'm a fan of foam insulation. It is impervious to moisture and does not suffer reduced R-value due to wind driven air infiltration.

Isocyanurate has better r-value for a given thickness then Styrofoam but costs more.

Given this is a finished structure stripping the roof and adding exterior insulation is probably the best route. No matter how good the insulation is some heat will escape. Venting the roof deck will help reducing ice dams.

/tom

I'm concerned that adding more insulation to the inside, with the current setup, will just trap in heat during the warmer months; thus causing issues with the shingles.

"Hot Deck" insulation systems are becoming quite normal these days especially when using spray foam insulation. These type installations provide for no airflow below the roof deck making the entire interior conditioned space. Studies have shown no decreases in shingle life expectancy! Especially in a climate like where this cabin is located it certainly wouldn't be a problem and would make insulating much simpler.

Nice .......

This is the system I currently have. But I have wondered if I could reduce cooling load further by having that air space under the roof deck, where outside air would circulate underneath to dissipate whatever soaks through the deck. I also had heard of decking with an IR barrier (foil) but found it is not available here in the north.

In other words, with a hot deck, what additional measures to improve roof ventilation have a reasonable rate of return vs. doing nothing?

Interesting, our house is timber framed. Shell is stressed skin panels with 3.5" of Isocyanurate foam insulation (R-30).

The house faces due South we have always had ice dam problems in the North facing roof. When we re-shingled a couple of years ago added a ventilated roof deck on the North face. That has dramatically reduced ice buildup.

Even with high level of insulation melting snow will tend to freeze when it hits the cold drip edge at night.

If the OP decides to add rigid insulation to the roof deck he is going to need to add a deck over the insulation. Adding some strapping to raise the new deck off the insulation is cheap.

/tom

That's interesting...and good to know. So if I'm reading this (and some google results) correctly, I could, in theory, just add more insulation. Basically replace the old stuff with thicker, new stuff and be OK?

All of the studies I've read have been done with spray foam insulation but I don't see where the same thing wouldn't apply for any type of insulation.

Thanks. Sounds like this "may" be less involved than I thought.