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Old 04-23-2010, 12:34 PM   #1
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How to Insulate? Wall inside wall...


So you can see from the following pic, I have an outside wall that is Foundation and 2x6s.

http://i798.photobucket.com/albums/y...l/IMG_3165.jpg

I am building a 2x4 wall (PT plate already attached) just inside foundation wall - will also hide gas/hvac/plumbing that is inside from foundation/stud wall. My question is what to do about insulating?

Fiberglass (no batt) in 2x6 then with batt in 2x4? There will be about a 1" gap between foundation/stud wall and 2x4 wall...

Thanks for your opinions,
JB

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Old 04-23-2010, 03:11 PM   #2
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How to Insulate? Wall inside wall...


I've been delaying posting nearly the same question here for a couple of weeks. Its actually kinda scary, I've got the same scenario going on in my own basement that I'm about to start on.

I know someone's going to ask, so where are you located? Atlanta-area?

I got off the phone with Owen's Corning just a bit ago, and they confirmed my plan. If someone who knows better can shed some more light onto the situation, I think JB and I would both apprciate it.

I intend to build the 2x4 wall as stated and fill it with R-13 UNFACED fiberglass insulation. I will not be applying any rigid foam to anything. I have the same poured concrete walls, which are sprayed with damp proofing on the outside (black goup).

I think that using the UNFACED insulation is very important. You don't want to have 2 vapor barriers (the damp proofing and the kraft paper). The reason, I believe is that should moisture penetrate one of the barriers, it would become trapped in between, and eventually condense on the cold surface of the concrete wall leading to mold problems. Allowing the little bit of moisture that may find its way into the concrete wall to dry to the room inside is very important. Hopefully there it can be removed by your A/C, or even better a De-Humidifier.

I know that the building science articles all seem to point to putting a 1/2" layer of rigid foam behind the 2x4 wall, but I haven't been able to deduce if it is for additional R-value, or for further moisture control. The moisture answer doesn't seem likely to me, but I would love to hear some more "expert" opinions. As to R-value, if you are in fact in the Atlanta area, it is probably less of a concern. If your basement is like mine, it stays reasonable comfortable year 'round. Mine gets slightly chilly in winter, but cool all summer. It also seems that the foam would create a fire-blocking concern (see thekctermite's post) that would negate the gains from the extra R-value for the given effort. I would certainly understand it in a cooler climate, just not here.

Its probably also worth bringing up the subject of fire-blocking in the areas where your foundation wall steps down, and every 10' if you're leaving a 1" gap behind the wall. However, that's a topic for another post...

I know there are some 'folks on here much more knowledgeable than myself, and I would love to see some more definitive information regarding this topic.

Check out these references:
How to fireblock framing
http://www.buildingscience.com/docum...d/attachedFile

I'll be starting a thread in the "Project Showcase" shortly with pics of my progress on my basement.

Oh, BTW: JB, if you're in the Atlanta area, its weird...so am I, and we have the same initials...strange...

-J


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Old 04-24-2010, 08:53 AM   #3
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How to Insulate? Wall inside wall...


Hey biggidybankston,

You figured out my code :-)
I am in Atlanta and my initials are JB.

I too have the black goop "waterproofing."

I am finishing out one room in my basement (that requires me to put up two walls).
If you think about a townhouse (where the bottom floor is mostly a garage - more than half).
There is a little finished area to go up to the main level.
The one unfinished room is what I am finishing out. I am also tearing down the partition wall to make one large room - it is non loadbearing (it was built with those studs that are put together with pieces of studs.

The room is about 230 sq ft and tearing down the wall makes it about 350 sq ft.
I have wondered about fireblocking/draftstopping.
Can't I just use unfaced fiberglass at the stop of the ceiling?
Do I even need to worry about it?

So you think I should use unfaced in all of the basement - that I am finishing? I only have about 4 feet below grade on the walls I am finishing.

Thanks,
JB in Atanlta :-)
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Old 04-26-2010, 09:27 AM   #4
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How to Insulate? Wall inside wall...


Quote:
So you think I should use unfaced in all of the basement - that I am finishing? I only have about 4 feet below grade on the walls I am finishing.
Absolutely. You don't want two vapor barriers, because moisture that might find its way in between them would have no way out, leading to condensation, mold, and a host of bigger problems. And the wall above the concrete will also have its own vapor barrier, so how much is below grade is really irrelevant. Best bet is to let the concrete dry into the room. I plan on keeping a close eye on the humidity in my basement forever, so that I'll have some warning that perhaps something has gone wrong.

With regard to draft stopping, you should have no issues since your entire space is less than 1,000 sq ft. Fireblocking is a different issue. I'm not an expert on this subject (actually, I'm not even an amateur) so I would strongly suggest reading thekctermite's post I referenced in my first post, and also talking to your building inspector.

I would build your wall right up to the concrete and eliminate the gap. If you don't, you'll need to have a fireblock every 10' horizontally. Where the wall meets either the ceiling or a soffit (if you need one) you have to make sure that fire couldn't transition from vertical to horizontal movement. This becomes a bigger issue when the concrete wall steps down. I'll be posting pictures of how I do this on my basement thread when I get there. Hopefully someone will be able confirm that it is done right.

Personally, since this is a townhouse, I feel like you have an extra responsibility to get this right. If it isn't, not only do you put your unit, and your own family at risk, you do the same to you neighbors. You wouldn't like it if they did something sub-par, and it caused damage to your property or safety, right?

Hope this is helpful.

-J
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Old 04-29-2010, 09:20 PM   #5
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How to Insulate? Wall inside wall...


J-
Thanks for the info.
I am not in a townhouse - it is just the easiest wasy to describe my home. It is tall and narrow (like a townhouse).
I saw the pictures of your basement...Good luck with your job.

I am unsure the difference between draftstop and firestop.
Everyone has their own opinion.
Since I have already added top and bottom plates, i will have the gap.
I am also doing this to match a wall that was built with the house.

Thanks again, and good luck.

-JB
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