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Framing a new wall over existing one to add insulation

Framing a new wall over existing one to add insulation

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  #1  
Old 08-31-10, 01:30 PM
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Framing a new wall over existing one to add insulation

Existing drywall was installed over furring strips, with no insulation. I want to re-frame over that with 2 x 4's, and add R-13 fiberglass under the 2nd layer of drywall. Anything wrong with this idea, or are there any better ways to go?
 
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  #2  
Old 08-31-10, 01:46 PM
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I'd be concerened about moisture - I think I'd remove the first wall and frame in the new wall in its place instead so you could put a moisture barrier up between the studs and the drywall
 
  #3  
Old 08-31-10, 02:13 PM
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Since there is currently no insulation in the existing wall, I would either add insulation to that one, or remove the drywall, add the new 2x4 wall and then insulate both of them.

The number you want to shoot for is between R-20 and R-30 or higher. R-13 fiberglass is better than nothing, but going to all of that effort, you might want more.

Bud
 
  #4  
Old 09-01-10, 06:01 AM
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Bud, I was thinking that the existing wall and small airspace might add to the R-13 value a little. I hear what you're saying about bumping it up, but R-13 would be a huge improvement for me over R-0.

Mitch, what is the concern about moisture, exactly? If I keep the moisture barrier against the new drywall, would I need to be concerned that moisture could settle between the two layers of drywall? If so, is there a reasonable solution? The exterior wall is brick, if that has any bearing on this issue.

I'd really like to avoid tearing out the old walls and starting from scratch, if I can get away with it.
 
  #5  
Old 09-01-10, 06:52 AM
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Including the brick exterior wall is a necessary detail. Brick need an air gap to allow for drying, so blowing in something like cellulose should be avoided. Here is a link with some discussion on brick walls: BSD-106: Understanding Vapor Barriers — Building Science Information

The issue with moisture deals with warm moist air leaking through your new wall and finding a cold surface with no ventilation where it can deposit some moisture and that moisture is trapped, ie a double vapor barrier. How much of a gap is behind the existing drywall and strapping?

I have seen and used rigid foam over existing drywall with no air gap so that you end up with new drywall, rigid foam, and old drywall all as one solid assembly. With it properly air sealed, including electrical boxes, there is no place for the moist air to contact a cold surface.

A couple of options for the insulation you choose, high density fiberglass is R-15 for 3.5" walls and mineral wool is a much denser material that will perform well.

Bud
 
  #6  
Old 09-01-10, 06:52 AM
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Yes, you want to avoid condensation on your drywall, thus the moisture barrier between it and the insulation

Without tearing out the existing drywall, you could end up with condensation forming on it, leading to a mold problem
 
  #7  
Old 09-01-10, 08:08 AM
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Bud - thanks for that great information! I'm reading up on that link you sent now.

The current wall construction is brick with only furring strips and drywall, so there's about 1/2" to 3/4" of air space in there. Do you think that the best approach would be to just glue up the rigid foam insulation and cover it with new drywall, or would you recommend a different approach? It sounds like Mitch thinks that the old drywall should come out. I don't want to risk mold issues, but your idea about the foam panels sounds pretty logical.
 
  #8  
Old 09-01-10, 08:48 AM
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I would think the foam idea is fine, I didn't like two layers of drywall separated by fiberglass
 
  #9  
Old 09-01-10, 09:31 AM
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Good news, Mitch - thanks! Sounds like that might just be the best approach. No demo, no framing, and a good R-per-inch value. As long as there is no mold concern, sounds like a winner.
 
  #10  
Old 09-01-10, 05:19 PM
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Hey, Bud - if you have any last-minute pointers, like how to fasten and seal the foam panels to the old and new drywall, I'd really appreciate it. Thanks for letting me pick your brain. I'm hoping to do this right the first time, and be done with it. IR reading of the interior wall today was 91 degrees!
 
  #11  
Old 09-01-10, 06:05 PM
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There are several different approaches. First, how much insulation do you want to add. I'll assume for the moment 2". That is easy to attach and electrical boxes can often be extended that far to simplify the wiring. Window trim will need to be pulled and jam extensions added.

You will have a choice of foil faced polyisocyanurate (PIC) aot pink or blue. The PIC is around R-6 or 7 per inch and the p/b is R-5 per inch.

1. If you use the PIC for the slight increase in R-value, you can tack it in place with 3" large head al roofing type nails. These just hold it in place so you can get the drywall up to hold everything. Sandwiched like this, the foil provides no additional advantage. Pink or blue could go up the same way. Foam or tape all seams to form a good air barrier.

2. The PIC can also be installed with strapping and then the drywall, where an air gap is left to create a radiant barrier. It is hard to place a number on the benefits of this approach. but I have read Dow's numbers allowing an additional R-2 for the foil. No confirmation of that anywhere, but there has to be some benefit. The disadvantage is it's another 3/4" to space out the electrical. The wires in each box may have to be pigtailed and you should check code to be sure that is acceptable.

Flooring, carpets, baseboard heat, floor vents, in-swing doors, all present little problems that complicate each job.

To hang the drywall you will need some long screws. If you use strapping the job becomes a bit easier. Glue can be used between all layers if you choose. Be sure to locate and mark all studs (strapping) so you can hit them later. Note any wiring paths as your spacing is tight and you have to avoid hitting any wires. Some stud finders will detect wiring as well.

The more I think about it the less I like the uncertainty of where everything attaches and avoiding those wires. Since the existing drywall is providing virtually no advantage, other than avoiding a mess, if you removed it you could check all wiring, protect as needed, and apply the foil faced with the benefit of the foil facing out or out and in as you choose (they are double sided). I'm not sure what you have for electrical boxes, but with the drywall removed you can upgrade properly.

Bud
 
  #12  
Old 09-02-10, 07:17 AM
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Thanks SO much for that post, Bud! I agree with you about ripping out the old drywall being the best solution, but I would seriously like to avoid having to re-frame the walls from scratch at this point, if it's not totally necessary. The foam panel solution does seem like a more expedient one. I'll stew on it today, and probably wind up flipping a coin.

For the foam panel approach, I figure I can use some Liquid Nails to secure and seal the foam to the drywall, along with nails. I'll either go with 2" or 3" of the foam board (a 2" and a 1" sandwiched between the drywall). I'll try and track down exactly where the outlet wires are run with my stud finder, too - great suggestion! One wall has a 36 x 54 window, and the other has a 60 x 54 window - no doors to work around. Three outlets to build out. I think I've seen extenders for that purpose - hopefully, they'll have the size I need.

Can't thank you enough for your help - I really appreciate the advice and guidance!
 
  #13  
Old 09-05-10, 07:32 AM
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Well, I decided to bite the bullet and do the job right, so I've begun ripping down the old drywall. Here is what I've got to work with - http://tempsite.shutterfly.com/28.

After trying to understand the detailed info in the links that Bud graciously shared, I'm left with two questions:
1. What's the best way to seal off the opening in the ceiling that goes straight into the attic? (Expanding foam, stuff loose insulation in there?) In the photo, you can see loose fill from the attic.
2. What's the best vapor barrier approach for this brick/block construction?

Thanks once again for your advice!
 
  #14  
Old 09-07-10, 08:27 AM
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Originally Posted by flukeslapper View Post
Well, I decided to bite the bullet and do the job right, so I've begun ripping down the old drywall. Here is what I've got to work with - http://tempsite.shutterfly.com/28.

After trying to understand the detailed info in the links that Bud graciously shared, I'm left with two questions:
1. What's the best way to seal off the opening in the ceiling that goes straight into the attic? (Expanding foam, stuff loose insulation in there?) In the photo, you can see loose fill from the attic.
2. What's the best vapor barrier approach for this brick/block construction?

Thanks once again for your advice!
Update: at the top, where the header should be, there are pieces of 2 x 4 nailed into a piece of lumbar on top of the bricks. These pieces jut out around 3/4" from the face of the brick. Do I need to remove every one of them (man, that would suck), or should I just move the new header further in? Lumber's ready, I just need the vapor barrier and header issues figured out, and I can get started.
 
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