# Insulating Existing 3:12 Roof



## Plaisted (Feb 18, 2014)

Hello-
I just picked up a neglected house up here in the Pacific Northwest through an Estate Sale. I plan on renovating and living there with my 2 kids, at least for the next 2-4 years. 
I'm looking for ideas on how to add insulation to the existing roof deck. The house is a 1950's rambler with exposed car-decking over beams. I want to retain that look. Guessing it is around a 3:12 pitch.
I got a quote from a local roofer to do a tear off and add rigid insulation then TPO membrane for over $20,000! This is for a 1,000 SF house, so, with overhangs, maybe 1,500 SF of roof area.
I am looking for suggestions, Thanks


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## LeeFowler (Nov 3, 2012)

That is no doubt flat but TPO on that roof? Is it leaking currently?


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## Plaisted (Feb 18, 2014)

No evidence of leaking. I am going to be bumping out the front about 8' for a new master bath, so will need to deal with the roof and thought I'd add insulation as well. I could go with a shingle or metal in lieu of TPO. I use TPO quite a bit on commercial buildings (the bulk of my work) and have had good results.


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## Calidecks (Nov 19, 2011)

I just did a 1400 sq. ft. Home my roofer charged me 5600 for TPO. Why can't you use comp? 3/12 is ok for comp. I think that's plenty of fall. Of course I'm in a place where it rarely rains.


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## Calidecks (Nov 19, 2011)

We also used dens deck which is a fire retardant. Don't know if it has an R-value


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## Plaisted (Feb 18, 2014)

Yes, I could and may use comp. The only issue there is that if I add insulation, I believe it needs to be vented. I seem to recall a project in the past that we had problems with the comp shingle getting too hot because they were installed on a solid insulated panel, causing premature failure and voiding warranty. Memory is a bit fuzzy on this though.


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## SLSTech (Sep 13, 2008)

2 layers of foam - offset seams is the way to go (as I recall you need 3" plus in your area to eliminate dew point concerns) For more http://bit.ly/HotRoof
most shingle issues happen because people use the wrong type of foam &/or install shingles incorrectly
this method is used in Atlanta, Phoenix, etc... so shingle temps is not a legit concern, but if worried add some batons on top of foam and vent away
As for making it look good Building Science had a good piece on that


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