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I have attic space above my house that I'd like to enclose and sheet rock. Is there any harm in installing insuation between the rafters, up against the sheeting of the roof? What about the roof vents? They'd be covered by the insulation. Would doing this cause my sheeting to rot?

Also, it's pretty hot up there in the summer. Would the insulation against the sheeting keep the heat out, or make it hotter? Thanks for any advise. Here's your chance to lead me astray and watch me screw up my house! :grin::grin::grin:
 

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I have attic space above my house that I'd like to enclose and sheet rock. Is there any harm in installing insuation between the rafters, up against the sheeting of the roof?

Yes, but it can be done. You may have to fur the bottom of the rafters to add space. Use rigid insulation instead of fiberglass. Not against the sheathing but the opposite.

What about the roof vents? They'd be covered by the insulation. Would doing this cause my sheeting to rot?

Possibly, but it's not the method of choice.

Also, it's pretty hot up there in the summer. Would the insulation against the sheeting keep the heat out, or make it hotter?

THE INSULATION DOESN"T GO AGAINST THE SHEATHING!
The hotter the sheathing gets the more it cooks the roofing.
This is one of the reason to fur the bottom of the rafters.
Hopefully there is space in the top room to create a attic. To do this, put in a cross piece about 7' above the floor, that will allow for a shalow attic above it.
The benefits of this are; allows you to add a gable vent at the end(s), allows for attic vents up high that are woking together rather than a vent in every third or fourth rafter chanel, allows for electricl runs and fixtures

By furring I mean to add at least 3/4" below the existing rafter; ie 2x6 rafter with a 1x3 nailed flat against the bottom of the rafter. This will give you plenty fo air flow even after you add 2" fo rigid insulation. The flat 1x3 gives you a ledge to lay the insulation on leaving an air gap (with positive ventilation, top and bottom) to help prevent the growth of the green and black stuff. The deeper the chanel the better. If you can attach more space by fastening to the side then do it. It also measns you can use more insulation.

Keep in mind the ventilation issue.
A family of 4 put's about 6 gallons of water into the air (in the house) eash week. Yea 6 gallons! That vapor rises and is released from attic through ventilation. With out the ventilation the moisture will collect to the cold side of warm surfaces and grow BAD STUFF.
I'm not a believer in some of the new construction practices that make a house so tight that it can't breath.


Thanks for any advise.
Here's your chance to lead me astray and watch me screw up my house!
:grin::grin::grin:
 

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Discussion Starter #3
Awesome! Thank you!
 

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If the rafters are fairly deep you can insulate between them and use a baffle to allow ventilation, as I recall a 2x12 rafter will allow the r30 insulation you will need, (check your building code or ask an inspector)

http://oikos.com/esb/34/raftermate.html

You will need to use a continuous ridge vent if you don't use collar ties to provide an 'attic' near the peak to carry air to roof vents or gable vents.


The insulation should be against the sheetrock, and between the heated and unheated space.
 

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If the rafters are fairly deep you can insulate between them and use a baffle to allow ventilation.

http://oikos.com/esb/34/raftermate.html

You will need to use a continuous ridge vent if you don't use collar ties to provide an 'attic' near the peak to carry air to roof vents or gable vents.


The insulation should be against the sheetrock, and between the heated and unheated space.
Bear in mind also if you do go to a continuous ridge vent, you will need to install soffit vents so as to allow airflow the entire length of the insulated rafters.
 

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Bear in mind also if you do go to a continuous ridge vent, you will need to install soffit vents so as to allow airflow the entire length of the insulated rafters.
Soffit vents work, but to vent each rafter bay properly 3" round vents should be installed in each bird block on both sides of the house ...If you don't provide enough air circulation your roof sheathing will rot ... I know from experience on this one ...
 

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Soffit vents work, but to vent each rafter bay properly 3" round vents should be installed in each bird block on both sides of the house ...If you don't provide enough air circulation your roof sheathing will rot ... I know from experience on this one ...
Agreed.
The bird blocking (if installed) definitely must be vented as must be the soffit (if installed).
The size vents depend on the local code and the size of the area vented with 3" round vents, as you indicated, being plenty adequate in most cases.
 

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I'm almost ready to do the same thing. I have 2x6 rafters, and have been using 4.5" rigid foam (R31) insulation. It is vitally important to allow air flow under the sheathing and above the insulation. This means ridge venting and soffit venting and making sure to not block air flow.

Good luck with your project!
 

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Geez its a long time since i read the codes, but as I recall for each 300 sq feet of roof you need 1 sq of vent. It doesn't hurt to surpass that.

There is a jillion ways to provide adequate venting. Bird blocks and roof vents being most common.

A vapor barrier is required by code between the sheetrock/heated space and the insulation. 4 mil or thicker poly works good there. Insulation often comes with foil or craft paper backing to do this. That will ******(I guess reetard is a naughty word) the moisture migration to the roof sheathing.
 

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less insulation and better venting will keep the space cooler and save your roof. a certin percentage of your home can have a lower r-value above the heated space. and still meet code. hire a lic contractor
 

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A vapor barrier is required by code between the sheetrock/heated space and the insulation. 4 mil or thicker poly works good there. Insulation often comes with foil or craft paper backing to do this. That will ******(I guess reetard is a naughty word) the moisture migration to the roof sheathing.
:bigshock: I don't think so, youv'e been watching to much TV

They do this in the north east because of the low humidity during the long cold winters.

Exception 2. Where the framed cavity or space is ventilated to allow moisture to escape.
 

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Thanks for the responsed, guys. Best one I heard was "Hire a licensed contractor". Momma agreed-----back to the Salmon!!!!!:laugh::laugh::laugh:
 

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Originally Posted by Chrome Bumper
A vapor barrier is required by code between the sheetrock/heated space and the insulation. 4 mil or thicker poly works good there. Insulation often comes with foil or craft paper backing to do this. That will ******(I guess reetard is a naughty word) the moisture migration to the roof sheathing.
:bigshock: I don't think so, youv'e been watching to much TV

They do this in the north east because of the low humidity during the long cold winters.

Exception 2. Where the framed cavity or space is ventilated to allow moisture to escape.
Well I do watch to much TV.

But all the house I have built required vapor barriers on the heated side of the insulation. And I have built a number of them.

If you buy insulation at the big box you will find two varieties of fiberglass insulation. Unfaced, which will require a separate vapor barrier, and faced which has treated craft paper or foil attached to act a a vapor barrier. Poly works better for moisture control and air infiltration than the facing on the bats.

Paint on the backsidfe if the sheetrock properly applied is allowed in some jurisdictions to serve as a vapor barrier.
 

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Thanks for the responsed, guys. Best one I heard was "Hire a licensed contractor". Momma agreed-----back to the Salmon!!!!!:laugh::laugh::laugh:
Insulation and sheetrock are both dirty nasty jobs. If momma doesn't want to do it for you you better hire someone soon.:wink:

Baltz is right, if you increase insulation in one place you can reduce it in other. Windows figure in too, they vary greatly in how much heat they let pass. The double pane insulated windows have an r value of 2 or 3. Versus r30 that goes in attics. Also insulation varies in R value per inch. High density FG, regular FG, rigid foam etc. I've noticed the insulation contractors get kinda chintzy if you don't call them on it.
 

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Well I do watch to much TV.

But all the house I have built required vapor barriers on the heated side of the insulation. And I have built a number of them.

If you buy insulation at the big box you will find two varieties of fiberglass insulation. Unfaced, which will require a separate vapor barrier, and faced which has treated craft paper or foil attached to act a a vapor barrier. Poly works better for moisture control and air infiltration than the facing on the bats.

Paint on the backsidfe if the sheetrock properly applied is allowed in some jurisdictions to serve as a vapor barrier.
I haven't bought the 2006 code book yet but the 2003 addition in section R322 / Exception 2, says different.

I'll defer to your tag line and let it go at that
Charter member of the BRI. (Bureau of Wrong Information.)
 

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I haven't bought the 2006 code book yet but the 2003 addition in section R322 / Exception 2, says different.

I'll defer to your tag line and let it go at that
Charter member of the BRI. (Bureau of Wrong Information.)
Thanks for the update, my books are dated. I think I'll continue with the visqueen against the ventilated voids just for the air infiltration control.
 

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We just got done building a house. My buddy at Vancouver Insulating helped me do additional insulation. A vapor barrier is required but they dont use visqueen cause it traps any moisture that gets in. They use a special primer on the drywall that meets code but breathes like Gore-tex.

Brad
 

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My concerns would be:
The rafters are probably designed to carry the roof weight only, adding drywall adds another 10lbs per square foot.
The joist are probably designed to carry the ceiling weight only, adding a floor adds another 20lbs per square foot.
The ventilation is very important also.
Being a retired building inspector I would suggest you approach your local inspector for advice. It may cause you more problems than it is worth.
 
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