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Insulation of the Underside of the Roof

Posted by plumeriavine_2010 (My Page) on
Fri, Feb 19, 10 at 11:23

Well, did you do it? Is it worth it? How did you do it?


Follow-Up Postings:

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RE: Insulation of the Underside of the Roof

I'm a little unclear as to what you are asking. I think you are asking have "we" insulated the attic, and the answer is yes. First a vapor barrier and then a pile of insulation, in my case fiberglass batts but there are other products. My attic is up to a R-30 level but I'm adding more this spring


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RE: Insulation of the Underside of the Roof

What I am wondering about is insulation that is not on the attic floor but, instead, on the ceiling of the attic on the underside of the roof.

We have 8 inches of insulation on the floor of the attic and some batting which is, oddly enough, distributed unevenly, but we are considering the pros and cons of spending time and money to attach insulation to the ceiling of the attic. My insulation man struggled to calculate if we are at R 30 because the insulation is so variable from place to place. He did not think we should add any more to the floor and we are now wondering about the wisdom and effectiveness of insulating the roof.


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RE: Insulation of the Underside of the Roof

I'm sympathetic to your plight, but it is most unhelpful when neither your post nor your 'MyPage' profile bothers to even mention what part of the planet (climate zone) your home is sited on. i.e. Are you trying to keep heat in or out? If in a hot climate and trying to keep heat out, ventilating the attic space might be more effective (and cheaper) than insulating the underside of the sheathing.

Beyond that vital data, we'd need to know the style and construction of your house, and the existing roofing materials. No doubt your sheathing is some kind of wood. Attaching insulation directly to the sheathing might create condensation issues that compromises not just the wood sheathing, but the structural rafters as well! I suspect this is why it is seldom done.

Check with a LOT of contractors, engineers if possible, and your state/county building dept... somewhere there is a wise person who knows the real world pitfalls vs. benefits of this scheme.

Beyond that, I'd still get a handle on why your existing insulation is uneven, and the feasibility of getting it "evened out". Is your so-called "insulation man" the one who's pushing the insulate-the-underside-of-the-sheathing scheme? Be very wary, and again, check many sources.

The "nail man" only pushes nails, but sometimes you need glue, lol.

And PLEASE follow-up on this thread, even if you do nothing. It's the only way the forum can deliver its lessons. ;')


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RE: Insulation of the Underside of the Roof

It should be fine to add insulation to the rafter bays if you also provide eave and ridge venting so the insulation can dry if it gets wet.

If you are in a very hot sunny climate a radiant barrier on the interior face of the rafter insulation might also be effective as long as there is at least a 3/4" air space in front of it.


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RE: Insulation of the Underside of the Roof

sorry to not include relevant details - - we have two houses, but I'll emphasize the main house in this post:

one story ranch house built in the 1940's. there are two large attic fans (possibly too large) - one on either end of the house. We have a very long ridge line, so roofers dissuade me from doing a ridge vent on the main house. We get about 20-25 inches of rain on average, maybe 10 days over 100 degrees each year, one or two days of freezing nights, that's it.

The south facing side of the house is too hot in summer and too cold in winter. THe current ducting favors the north facing side of the house.

We want to use the air and heat less.

Current roofing material is Hardi-Slate. We plan to change it to asphalt (maybe) in the next 1-2 years.

Any advice?


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RE: Insulation of the Underside of the Roof

This old house indicated you want your attic to be the same temp as the outside air, if that is the case dont bother.


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RE: Insulation of the Underside of the Roof

Our attic seems to be much hotter.


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RE: Insulation of the Underside of the Roof

You need more vents in the roof and more insulation on the floor of the attic. Blow in that shredded stuff to even out the insulation layer and fill any gaps. Above the insulation you want to try to match the outside temperature with enough venting.


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