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Old 12-01-2008, 12:57 PM   #1
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Insulating Semi-Finished Attic... Need info


I am looking to insulate my attic... First some info:

-I live in upstate NY.
-The house is a cape and was built in 1949; the attic was not finished.
-Sometime after the center of the attic was finished into one big room, walls and ceiling were insulated with faced (R8, maybe) insulation.
-The two resulting spaces on either side were vented with one roof cap per side
-There is NO soffit venting
-There is NO ridge vent
-There are floor boards covering the joists which I will have to pull up
-During the winter I get ice dams

My first intention is to pop up the floor boards on each side and lay down faced R-19 bats (faced side down) between the joists and replace the floorboards (attic space is partially used for storage) and in the areas not used for storage, roll over un-faced R-19 over the boards (will still need to get to the other areas for future electrical work/possible storage)...

I also intend to staple up foam baffles at the existing soffit for future addition of soffit venting

Now, is my insulation selection and implementation sufficient? I would also over time like to:

-Replace the existing wall batts and what ceiling batts I can access with something thicker (Plus install foam baffles as there are none there right now and I'll need air flow to the ridge vent i want to install)
-Have a ridge vent installed

Any other recommendations, ideas, comments would be GREATLY appreciated! Thanks


Last edited by scrupul0us; 12-01-2008 at 01:01 PM.
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Old 12-01-2008, 09:05 PM   #2
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Insulating Semi-Finished Attic... Need info


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Old 12-01-2008, 11:25 PM   #3
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Insulating Semi-Finished Attic... Need info


R19 isnt enough for your area. You need for the unfinished portions over living space definitely R49 or close to it. The 2 sides you refer to i am assuming are on either side of the kneewalls of the big room. Here is a pdf that has good info on how to insulate around your attic room. Its for rooms over garages but the same principles apply. while you are resinsulating be sure to seal up any penetrations from below with caulk and sprayfoam and even foamboard when needed. http://www.dom.com/customer/efficien...er_garages.pdf
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Old 12-02-2008, 06:43 AM   #4
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Insulating Semi-Finished Attic... Need info


@Jaw: thanks for the info:

How can I possibly go R49? The joists are 2x6's so even with R19 in the bays (under the floor boards) there will be some compression.

I'm assuming I would have to do as I had originally intended:

Faced R19 in the joists under the boards but instead of R19 over that use un-faced R38 perpendicular on top of the boards?

I looked over the diagram and it didn't make much sense... If you go to page three "leave kneewall outside" on the ceiling space that separates the first floor from the second they don't run the insulation in the ceiling joists all the way out to the end of the space? and there's also no baffles for air flow to the peak (maybe this is just a really rough diagram or I'm missing something or it's different for a garage).
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Old 12-02-2008, 10:39 AM   #5
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Insulating Semi-Finished Attic... Need info


I live in Rochester, NY. I did my attic last year, its a 1960's ranch. There was only R 8 faced between the joists! The recommended R value for attic in this region is R 40 or higher. What we did was add in blow in to the top of the joists, use a wooden fabricated rake to smooth it off, then added R 19 unfaced, layed perpendicular to the joists. We also had very little venting at the soffits as they had stuffed the insulation right into the eave. I addded foam baffles to each rafter before laying the insulation. So the way I figured it we now have just under R 40 up there when all combined. What a difference it has made! No more ice build up and it is very cold up there in the winter as it should be becuase of proper venting.

If you want to use the 2 sides as storage I would think that you would then have to insulate the roof and not the floor, as like you said you will be compressing the heck out of the floor insulation and making it very inefficent.
As far as the room Id think that you could get rid of any insulation in the floor and insulate the roof for that area therefore allowing some heat from indoors in to that room, unless you plan on heating it seperate from the house itself.
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Old 12-02-2008, 10:51 AM   #6
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Insulating Semi-Finished Attic... Need info


yea i have insulation stuffed into my eaves as well...

I suppose I could insulate the roof itself BUT being that the two kneewall areas are vented to the outside (there is one roof vent per side) wouldn't that defeat the making the knee walls part of the enclosed envelope??

regardless of what I do, there is NOTHING there now, so even IF I just do R-19 in the joist space under the floor boards that's a considerable start, and If perp. layer R-38 over that in the areas I'm not using for storage, it can only further help

I guess my only question is will i have to worry about any vapor/condensation issues if I cover the floorboards with unfaced with faced R-19 underneath in the joists?
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Old 12-03-2008, 10:14 AM   #7
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Old 12-03-2008, 12:44 PM   #8
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Insulating Semi-Finished Attic... Need info


Since you really have very little space under the floor boards of the living space, one option that is expensive but effective would be the sprayed insulation that has to be done by a professional.
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Old 12-03-2008, 01:25 PM   #9
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Insulating Semi-Finished Attic... Need info


Quote:
Originally Posted by gma2rjc View Post
Since you really have very little space under the floor boards of the living space, one option that is expensive but effective would be the sprayed insulation that has to be done by a professional.
yea this definitely wont be an option monetarily and wouldn't make sense as they couldn't spray to the top 1/3 of the roof (remember theres a finished room occupying the entire length of the center of the attic)

Unless anyone can think of a reason not to I think I've decided upon:

1) Pull up boards, place R19 faced in the joists (face down) and replace boards

2) In the areas not used for storage, roll over with R38 unfaced perpendicular to the joists

3) Staple up foam baffles in the soffits that are currently stuffed with insulation and then replace that insulation

4) Replace chinsey 2" insulation on walls and ceiling points I can reach with at least R19

5) Place foam baffles above new R19 on ceiling points

6) On newly insulated walls place sheathing over studs and insulation (caulking as needed)

7) Come summer, install ridge vent and soffit venting accordingly to promote proper airflow to cool

8) Insulate backs of access doors with 2" rigid foam board and weather strip the frames

I measured up the area I'll be working in an I only have about 200 linear feet of joist cavity to fill which by my measure means I can get away with 3 bags of R19 batts (8x 93") from home creepo @ roughly 27$ or so a pop. R38 will be more spendy but figure about 125-130 for that, plus 27 baffles for the soffits @ roughly $1 a pop.

So to do both layers plus baffles will run around 300$ give or take but the energy savings and comfort alone will make it worth it.

Redoing the existing insulation on the room will have to be a side project but as it gets done the envelope will get tighter and tighter.

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