pitched roof insulation

[harry palmer]

Hi all

we have an old victorian house and we are about to replace the gutters and insulate the roof. Is there a web site where I can see the different approaches? Do we have to ventilate from the soffits up to a ridge vent or is there an alternative? I really don't want to cut a slit in the roof right now, I would prefer a solution where we could spray something into the gaps in the rafters and just put up dry wall over it BUT I read somewhere that you have to have ventilation for moisture. This implies to me that when we get the gutters replaced and they throw away all the old crappy wood planks its hanging off, that we hang the gutters from aluminum with air slots in them. These slots vent air into the gap between the insulation and the roof. up to the ridge and out the ridge vent. I would prefer to A) not have the ventilation gap at all b) have the ventilation gap and have it go to a tube at the top that gets vented out of the sides of the house. Please help me out

[ransley]

Without air circulating up standard shingle roofing on the S side can go bad in 5-7 years from excessive heat in summer. Is it a heated attic, or is it open to air and the floor insulated.

[harry palmer]

the house is north south orientated and the attic will be heated as we are converting it into living space. The floor will be bare wood with living accomedation below. We do not intend to insulate the floor as it tops our bedrooms and we don't see the point.

[Astro]

Harry, I refer you to the following article:

The Building Science website has a wealth of information, based on actual research and scientific principles.

-Ted

[harry palmer]

thanks Ted

this seems to be exactly what I need to read and I will also contact them to see how to approach this. Thanks to all of you who replied and helped me out have a really great new year harry

[jamesgangnc]

Conventional approaches also include venting at the ends of the roof and having a small attic space at the top using collar ties. There are foam baffles that you can place against the roof where you will have insulation and wallboard directly on the inside. They provide a space for air flow from the soffits to the attic space. Lowes has them.

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[harry palmer]

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thanks James I am going to look at all the approaches.

[ransley]

I meant what is existing set up. An air space and R7" foam of a high R value near R60 would be best. Foams go from R5-R7.2". How much you use is most important, Codes are minimums, not optimal values. Im Zone

5, my local code is R35, here R 60 is considered optimal. But since I used Fiberglass and it Looses R value when real cold and it settles I used R 100 - 110 . To be optimal I bet R 60 is a good objective if you live in cold area, what are the beams, 2x6. 2x8, 2x10? shimming down should be connsidered for more foam. This is the most important area to insulate, do it right. is a place to research.

[harry palmer]

right now there is nothing but a 14' attic 25' wide and 60' long. 2' knee wall. not sure what the beam size is but will make sure I measure. Thanks for the advice and I agree R60 would be great BUT I will make the measurements to see what I can achieve in the space allowed. thanks for your great help it really has been useful

harry

[Voyager]

Yes, they do have some good stuff here and they have some questionable stuff, and I think this is an example of the latter. As someone has already mentioned, there are drawbacks to having a roof of this type. One is the heat issue for the roofing materials. With insulation right under the sheathing material, the heat from the sun has nowhere to go except into the shingles and then be radiated or convected to the air. Conduction through the sheathing will be minimal. Depending on your roofing materials, this may or may not be an issue.

I had to laugh at the "advantage" of the foam insulation providing an extra layer of leak protection. I agree that it likely will do that, but I see this as a major disadvantage, not an advantage. Sure, a leak will cause damage to interior drywall in a conventional design, but it also lets you know RIGHT NOW that you have a problem that needs attention. A roof with spray-on foam insulation could leak until the sheathing is rotted and structurally unsound and you might never know you had a problem ... until someone walks on the roof and falls into the attic. Trust me, that will cause more damage to interior materials than will a small water leak, not to mention the damage to the person who falls through you roof.

I am amazed that anyone would write that as being an advantage.

Matt

[tmurf.1]

check out Certain Teeds website

[jamesgangnc]

Yes, I agree. Let someone else find out what happens to those ideas in 20 years. Converntional constrution techniques allow for ample insulation and attic ventilation.

If you have 2x10 roof joists then that is deep enough. If they are less then build them out where you expect to put wallboard. Install baffles and create a small attic space above. Vent at the ends. Insulate and finish.