Attic Insulation

[*jtmerritt]

#49: Attic Insulation Author: jtmerritt, Posted: Tue Nov 25, 2003 2:36 pm
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Helping with a kitchen remodeling in a single floor ranch where the ceiling and the associated attic insulation over that ceiling was dropped and removed. Is it better to insulate that area over the ceiling with blown in insulation after the new drywall is hung or to staple batts between the rafters before the drywall ceiling is installed? This is assuming we can find batts or rolls for 24 inch rafters and that the R value for both will be the same.

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#52: Author: Wgoodrich, Posted: Tue Nov 25, 2003 6:48 pm
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I am picking up that you have removed the suspended ceiling and now plan to drywall the bottom of the joists as a ceiling. If this is true then most commonly blown in insulation is normally the product of choice.

To perform a blown in insulation project with exposed ceiling joists you first need to buy the styrofoam shutes that are stapled in place between the top of the outside walls and the roof decking in the low side of the roof lines. These shutes create a place for the soffitt and attic to breath without being blocked by the blown in insulation rolling against that low side of the attic area blocking off any air flow.

Then install your drywall. Then blow in insulation in the attic to a point about 6" above the ceiling joists.

You will get different recommendations from blown in fiberglass to celulous fiber insulation. My preference being an electrician having crawled in attics with blown fiberglass is to use cellulous fiber. Glass not fun to crawl in.

Good Luck

Wg

[Unregistered]

2 questions, I am adding add'l batts in my attic.
I am guessing they come w/a vapor barrier as both sides have a plastic sheet attached.
1. Do I apply the 2nd layer batt parallel to the old or criss-cross over the joists? And do I remove the one plastic layer so there are no 2 plastic layers touching?

2. It is hard to reach the ends of the joists as the angle of the roof comes to a point that I have to lay down and then use a broom stick to wedge the batts as close to edge (where the joists meet the rafters. I had extras pieces, can I wedge them into the 'corners' - where the joists meet the rafters? or will this cause a vapor/moisture problem.

Thanks in advance.

[Wgoodrich]

I am taking this new installation being installed in the attic over existing fiberglass insulation that has a vapor barrier on that existing fiberglass insulation.

If this is true no further vapor barriers should be installed. If you install a second layer of fiberglass insallation with a vapor barrier on top of an existing fiberglass insulation you have created a double vapor barrier that will trap moisture between the two vapor barriers doing more harm than good.

Absolutely do not close off the air space from your soffitt into your attic. This path is where the air enters you soffit to vent into the attic then out your attic vents to expel moisture in that attic. This venting is required and needed.

The intent is to create an insulation blanket separating the outside walls and ceiling from the outside and inside the unheated attic.

Block the air flow and you will have mold and rot in your attic. Bad thing.

If it were me I would buy the styrofoam shutes and slide them between the top plate and ceiling and the roof deck where that space enters from the soffitt into the attic. This air chase must be maintained for venting of attic and soffitt.

Once the styrofoam shutes are installed in each rafter space creating a 1" air shute for air flow to be maintained between the attic and the soffitt.

Then I would blow in celueluse fiber insulation on top of the old fiberglass existing insulation as thick as you feel you need. This seals any leakage of air the vapor backed fiberglass runs have by the blown in fiber settling into those cracks and leaves no further vapor blocking causing trapped moisture.

Just my opinion.

Wg

[Unregistered]

Wg - thanks.
Near as I can tell do not have Soffits to contend with. just seems that rafters meet the joists.

I am using the rolled Batt insulation as this is a DIY project.

What about adding (new) insulating to the rafters themselves. Which would mean I would have a sore neck by the end of the day.

There is not enough room in the attic to stand - only pretty much kneal(?) at the knees.

Thanks again,
Seth M.

[Wgoodrich]

Look outside under your roof. If you see bare rafters then you have no soffitt. If you see a flat board closing that area in and that flat board has vents in it then you have a vented soffitt.

Even if you have no soffitt you still have air flow from outside to inside attic in that low side of the roof. If you close that off you close off your air circulation in your attic.

If I were you I would check with your insulation supplier. Normally they will have a insulation blower that you can rent. One persion is in the attic aiming the hose and a second person man or woman opens bags and pours the celullose fiber insulation into the rented blower that then blows into the attic where you aim it. If you opt for the blown insulation or not you need those styrofoam shutes to maintain outside air filtering into that attic for venting.

If you must use fiberglass rolls then only use non paper or non plastic backed insulation rolls. Fiberglass only with no vapor barrier on this added insulation.

Good Luck

Wg

[Unregistered]

Wg-
Thanks