Insulating Roof

[mike_wood]

I am to the point of considering how to insulate my new shop. It is a 1.5 story structure and I am considering extending the insulated area to the upstairs storage space in order to mediate temps up there. I had a spray foam guy out today to give an estimate. When we discussed the roof insulation he said there was no need to put baffles for venting. I have always been told to vent insulated roofs to protect the shingles. His comment was that without baffles the shingle life may be reduced by 2-3 years but shingles usually don't last as long as claimed. My shingles are 30 yr Owens-Corning and they say to put the baffles.

Suggestions appreciated.

[FredP]

yes to baffles. it is my understanding that not only does the baffle allow the roof to breath but it also creates air flow to dry condensation on the nails that protrude through the sheathing. the nails condensate from changes in temperature and without the airflow to dry them they will remain wet causing the sheathing to rot. I may be wrong but I would err on the side of caution.

[MrAudio815]

I love this site,


Good info at every turn. I don't need this info now, but hey you never know when you'll need some info.


Thanks for the question and answer~!

[scsmith42]

You can go either way. The last roof that I spray foamed had the foam sprayed directly on the underside of the roof. The nice thing about this is that it keeps all condensation from forming on the lower side of the roof.

[gdoebs]

I know I've seen spray foam applied directly to the sheathing with no baffles. You could always call Owens-Corning and ask them about spray foam.

[crokett]

If you have spray foam you do not need venting, or at least you do not need the styrofoam channels. The venting keeps condensation from building up in the air trapped between the batts and the roof. With spray foam it is directly on the roof deck so there is no air between the insulation and the roof decking.

[mike_wood]

I understand about the moisture but my concern was about heat buildup since there was no way to dissipate it. Whatever happens it is too late now as it was done last Friday. It looks good and I can already tell the difference. Sunday was warm an normally the attic would get pretty hot as one sides faces SW. We worked up there all day and it did not get over 80. We'll see as I am putting in a mini-split HVAC on Tue.

Thanks for the comments.

[Mr. Bill]

Mike, I'm considering doing the same thing. Can you give me an idea of cost? Per sq foot of roof would work, I don't want to get nosey

[mike_wood]

It's pricey but worth it to me. Count on $1.25/ft2 for walls and $1.50/ft2 for the roof as it goes on thicker. I like how it fills all the voids.

Let me know if you have any more questions.

[mkepke]

Mike - what R-value at that cost per ft^2 ?

-Mark

[scsmith42]

The "R - value" scale does not accurately depict the efficiency of spray foam. For one thing, it creates a total vapor block so that you eliminate all drafts, etc. It is incredibly efficient.

Depending upon if it is open cell or closed cell foam, as well as the application depth, it can offer equivalent R-values up to R50.

[mike_wood]

Open cell foam is about 4/inch. But as indicated before that does not tell the whole story. Just looking at it I can see how much better it is than standard insulation.

Also when considering cost you get a 30% tax credit (credit, not deduction) from the feds and I think from NC too. I know NC passed some tax credits for energy savings (eg. geothemal heat pumps) but not sure of insulation. So if you put it in this year or next you get 30% off your taxes up to $1500. This is one of the reasons I did it.

[mkepke]

Originally Posted by scsmith42

The "R - value" scale does not accurately depict the efficiency of spray foam. For one thing, it creates a total vapor block so that you eliminate all drafts, etc. It is incredibly efficient.

Depending upon if it is open cell or closed cell foam, as well as the application depth, it can offer equivalent R-values up to R50.

?? This is like saying you can't compare the MPG of a Honda and a Lexus because the Lexus comes with extra cupholders.

R-value is a standardized measure of thermal resistance under specific conditions...and it's used by the foam manuf. to rate their products.

I think it's understood that spray foam has more advantages than simple R-4 per inch. Otherwise who would buy foam given the price ?

Mike - NC does not offer insulation credits that I have found, but your utility might give you something. Progress Energy (electric co) offers up to a $300 rebate if the work was performed by an approved contractor (no DIY allowed) - some other restrictions too (not sure a non-primary dwelling qualifies).

-Mark

[mike_wood]

I have already collected $600 from Progress for geothermal heat pumps. Considering the relative cost of geothermal heat pumps and insulation I don't think any rebate from Progress would be worth the stamp. But I will check. Thanks.

[scsmith42]

Originally Posted by mkepke

?? This is like saying you can't compare the MPG of a Honda and a Lexus because the Lexus comes with extra cupholders.

R-value is a standardized measure of thermal resistance under specific conditions...and it's used by the foam manuf. to rate their products.

I think it's understood that spray foam has more advantages than simple R-4 per inch. Otherwise who would buy foam given the price ?

Mike - NC does not offer insulation credits that I have found, but your utility might give you something. Progress Energy (electric co) offers up to a $300 rebate if the work was performed by an approved contractor (no DIY allowed) - some other restrictions too (not sure a non-primary dwelling qualifies).

-Mark

You mean that cupholders don't impact fuel mileage???? What about whitewall tires???

I should have been more descriptive in my comments about the benefits of spray foam, but I was rused at the time I typed it. That'll teach me...