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Old 02-12-2008, 04:22 AM   #1
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Insullation in Attic????????????


Hi I'm new to this forum and reqire some help regarding a few things.

1. If I put a floor in my attic and close off my insullation won't it rott? I heard the insullation has to breathe otherwise it will condense and rott the joists.

2. My joists are 2x6 16" OC, I reaserched the net and found that it's not strong enough to support a livable room. So I was going to sister them up with 2x8 to be safe. What type of wood should I use I live in Ontario Canada.... I know in order to sister I must take off all the insulation and cross-members, but I will put in a new one.

3. My roof is pyramid shaped and I have those knee walls, can I take them all off while I work, then put them back after (nailing them to the new floorboards)?

I will have more questions in the near future regarding my attic reno, so please if you could help me out with any of your tips I will greatly apprechiate it.

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Old 02-12-2008, 08:07 AM   #2
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Insullation in Attic????????????


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1. If I put a floor in my attic and close off my insullation won't it rott? I heard the insullation has to breathe otherwise it will condense and rott the joists.
First off, the insulation in your "ceiling joists" (that will ultimately become your new areas floor joists) should, really, already have a vapor barrier installed on the underside of the insulation. Check this to confirm.
Vapor barriers are always to face the living space/warm side.
If there is a vapor barrier present, especially in the attic areas where you will be building knee walls, then you are allset.

When you finish off your new living area, you must be planning to also insulate your rafter bays and knee walls, while providing some kind of heating source, as well.
When you do this, the insulation, located within the ceiling joists (that will be your floor joists) will be within the "Thermal Envelope" of your home. Thus, that insulation will no longer experience extreme temperature changes. These changes are what creates condensation and moisture.

Lastly, regarding your knee walls, you should plan on installing insulation in the rafter bays of these knee walls and also in the actual framework of the knee walls (with vapor barriers facing the new living area). If you have an access door that you plan on installing that goes to the attic knee wall area, this too should have insulation behind it.

NOTE: Be sure that you install proper "baffles" / "Rafter-Vents" in the rafter bays prior to installing your insulation. Also check to see what the required insulation is for your region. Realize too, that if you heat that new living space with an electrical source, the R-Value requirements are raised.

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2. My joists are 2x6 16" OC, I reaserched the net and found that it's not strong enough to support a livable room. So I was going to sister them up with 2x8 to be safe. What type of wood should I use I live in Ontario Canada.... I know in order to sister I must take off all the insulation and cross-members, but I will put in a new one.
I am in the U.S. - so I am not familiar with Canadian Code Spec. Requirements, or if there are any for this point.

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3. My roof is pyramid shaped and I have those knee walls, can I take them all off while I work, then put them back after (nailing them to the new floorboards)?
Yes....or you can simple install the floor boards up to them. If those knee walls are straight and plumb, and where you want them to be, my suggestion would just be to leave them where they are. You may, or may not want to add additional fasteners to secure them, and add additional framing to have studs 16" OC, if they are not set up that way already. In this case, there is no reason for you to "have to" install the floor sheathing "underneath" those knee walls.

Good Luck.

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Last edited by AtlanticWBConst.; 02-12-2008 at 08:10 AM.
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Old 02-12-2008, 02:56 PM   #3
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Insullation in Attic????????????


I need to cover my ENTIRE attic floor with floor boards because later I might be taking off my roof and making a 4 sided (barn) roof to create more head room. So my floor boards will come all the way to my roof rafters, and it won't be heated for at least saveral months maybe even a year. The knee walls are far from plumb they are very roughly installed.
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Old 02-12-2008, 03:30 PM   #4
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you can take down the knee walls.they are not structural.
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Old 02-12-2008, 03:31 PM   #5
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Insullation in Attic????????????


as long as your rafters run from sill plate to ridge.(one piece)
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Old 02-12-2008, 04:44 PM   #6
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Cool thanks man, but what about the insullation, If I cover the entire attic and there is a big Temperature difference between my attic and the room underneath, will it condense, and what can I do.
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Old 02-12-2008, 06:58 PM   #7
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Cool thanks man, but what about the insullation, If I cover the entire attic and there is a big Temperature difference between my attic and the room underneath, will it condense, and what can I do.
It will be fine...as long as you have a vapor barrier on the side facing your living area. Your walls should be built in a similar way.
Compare:

Your Walls:
WARM ENVIRONMENT > Sheetrock/vapor Barrier/insulation/plywood/Siding

Your Ceilings:
WARM ENVIRONMENT > Sheetrock/vapor barrier/insulation/plywood
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Old 02-12-2008, 08:36 PM   #8
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Insullation in Attic????????????


"My joists are 2x6 16" OC, I reaserched the net and found that it's not strong enough to support a livable room. So I was going to sister them up with 2x8 to be safe. What type of wood should I use I live in Ontario Canada.... I know in order to sister I must take off all the insulation and cross-members, but I will put in a new one. "


Hi, I'm from Canada too. Hi there Ontario!

There is a book called "Canadian wood-frame house construction" published by the CMHC which is a great start. In the appendix you'll find the allowed spans for different types of wood as well as nailing schedules and so on. Chapters has it.

Good luck with it.

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