# Basement wall XPS insulation with furring strips



## MrAngles

I'm going to be finishing my basement, and I've pretty much decided for sure on doing a layer of 1.5" XPS rigid foam insulation with furring strips and attaching drywall to te furring strips, as it seems to be the best method for avoiding moisture damage.

What I'm not clear on is the idea of using tapcons to attach the furring strips through the XPS into the concrete. Doesn't that make a path for moisture to go right through the insulation into the wood?


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## mikegp

Yes, but it's not significant since it forms somewhat of a seal with itself. If it bothers you there are many options for sealing over the holes. You can put some silicone on the nails before driving them. Caulk, tape, etc. I went with XPS glued and taped to the wall and full 2x4 construction for my walls. This provides the best seal short of spray foam, but it robs you of space and is extra work. Are you planning to run electrical through the XPS?


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## MrAngles

I will need to run a couple outlets and some speaker wire, but I think I can do that by using 2x3 furring strips and low profile boxes. I want to use the furring strips to save space and money mostly (I have a lot less room than I'd like). It's a home theater and I'll be soundproofing it, which means in this case two layers of drywall decoupled from the studs using clips, and (at least the way I'm envisioning it) having furring strips attached to the exterior walls used as the studs and not having them actually meet the ceiling joists, I wouldn't need to use the clips or double drywall on those walls because there won't be any sound transfer through the studs to the joists above.


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## MrAngles

Two other questions, do I tape the seam prior to putting the furring strip on, and where do I screw into the furring strip, it seems like in all the pictures they are screwing right into the middle of the board, but won't that mean the screw is ending up in between the two sheets of insulation, rather than going through them to secure them to the wall?


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## mikegp

You're securing the strip. The strip is securing the foam.


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## mikegp

Most people tape before. If you're looking for a better seal, you'll want to overlap tape after. Going to use a lot of tape though.


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## Gary in WA

You'll need foamboard adhesive on the side touching concrete to stop any room air from condensing on the cold concrete. http://joneakes.com/jons-fixit-database/743 Caulk under the foamboard and sill sealer under the wood for an air/capillary/thermal break there. http://www.greenbuildingadvisor.com...ressure-treated-sill-plates-and-building-code Use the scraps on the rim joist, install with caulk/canned foam for an air seal there, also. http://www.buildingscience.com/docu...joist/files/bscinfo_408_critical_seal_rev.pdf

Gary


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## MrAngles

I appreciate the help guys.

This is the first I've heard of the sill sealer under the wood, do you cover that side of the wood with it then shove it on, then?

I'm planning on using 4x8 square edge sheets of Foamular or Styrofoam, will the the adhesive support the weight of the foam board while I do the prepping and drilling on the furring strips, or do I need some more hands? I'm assuming I should do 3" furring strips in the middle of each board as well on the seams so I end up having 24" oc "studs" for the drywall to attach to, should I attach the middle strip first to hold up the foam boards, then cover the seams after, or vice versa?

Also what about the fireblock? Do I just attach a 2x8 or whatever directly to the top of the foam board on the rim joist and the furring strips?


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## Ted White

MrAngles said:


> I will need to run a couple outlets and some speaker wire, but I think I can do that by using 2x3 furring strips and low profile boxes. I want to use the furring strips to save space and money mostly (I have a lot less room than I'd like). It's a home theater and I'll be soundproofing it, which means in this case two layers of drywall decoupled from the studs using clips, and (at least the way I'm envisioning it) having furring strips attached to the exterior walls used as the studs and not having them actually meet the ceiling joists, I wouldn't need to use the clips or double drywall on those walls because there won't be any sound transfer through the studs to the joists above.


You can install the clips to the furring channel, just select the right screw. Thinnest clip + channel combo is 1 1/8"


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## MrAngles

Ted White!

I was hoping that since the furring strips and the drywall attached to it won't be connected to anything but concrete that soundproofing on those walls would not be needed?


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## Ted White

Hi. Can the ceiling drywall be lowered a bit and extended all the way to the concrete or block? Then sealed to the block? Otherwise there will be a gap between the top of the foundation and the ceiling drywall. That gap will allow flanking sound up, up and away.


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## MrAngles

I don't think I want to down quite that far. Hopefully this not to scale crude drawing in paint will explain what I was planning.









So obviously the problem here is that sound will get through the one layer of drywall on the wall and travel up and around the decoupled double drywall and through the floorboards. I should add that I was planning on adding a couple layers of drywall between the floor joists as well, is there anything else that I can add that would seal up that area better without adding to the width of the wall?

How about a soffit? (Came up with the idea as I was doing the drawing) A double drywalled soffit with insulation inside could block it off couldn't it? I realize now that I have a water drain pipe right in that corner anyway, so I may have to do that either way.


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## Ted White

I really appreciate the way you're taking the time to think this through. The weak area at the top is onl part of the issue, as your diagram demonstrates. A soffit would shield that gap very effectively if that was our only weak point.

The real issue is the single layer of drywall itself. The entire wall is onlt shielded by a single layer of undamped drywall. Some frequencies will easily make it through one sheet of drywall and not be affected by that low-density foam. 

A second layer of drywall and damping compound would remedy this. Install the wall furring at 24" centers. If the furring could extend 1/2" past the foam, that would be really great, as this will allow that drywall to flex more freely. More flex = more damping.


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## MrAngles

Well I really appreciate you taking an interest and giving your input. To be honest, this being the fourth house I've lived in, and the first one with a basement and a actual spot for a dedicated theater room, I kind of feel like my whole life has been leading up to this point, so I'm taking it pretty seriously. That said, I also have a wife and kids, so every once in a while I get pulled back to reality and try to find ways to cut costs on it.

The plan is for the furring strips to be at 24" oc, and they will be directly on top of the foam, so there will be 1-1/2 inches between the drywall and the foam.

What if I cap the foam and furring strips with double (or more?) drywall behind the soffit, and seal the edges with acoustical sealant?








I'll have to look into the what possible moisture issues there might be with that, but being above grade I'm hoping there wouldn't be much of a problem?


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## Ted White

There's still a small gap. Can you completely connect the double drywall pieces that you have now? There's that little vertical piece on the furring.


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## MrAngles

Maybe moving the soffit out a bit like this?


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## Ted White

Bingo!


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## MrAngles

Awesome! Thanks a lot for the help.


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## Ted White

A pleasure! Good luck. :thumbsup:


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## MrAngles

Hey here's another question, for my interior walls, does it make sense to do a staggered stud wall WITH whisper clips and double drywall, or are staggered studs pointless after already decoupling the drywall? The mechanical room is going to be right next to the theater, and the furnace gets loud.


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## Ted White

Great question, and you've got it figured out. The wall can be decoupled by any of the following means, rated lowest to highest performance:

Resilient Channel (RC-1)
Staggered Studs
Single stud with Clip&Channel
Double Stud

Pick one, but not more than one.


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## MrAngles

Awesome, that makes sense. What do people normally do for mechanical rooms, drywall and insulation on the ceiling in there will be problematic due to wiring and pipes, but then I'd have a gap in drywall from the top plate of the wall to the floor above.

Should it be something like this?


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## Ted White

Well, one of the things we want to do when soundproofing is to limit the amount of vibration that enters the original structure. Once the vibration enters the old framing, it is conducted who-knows-where. That subfloor and all those joists would get hit with sound and conduct to some degree.

The upside is that the room next door would benefit from the treatment you proposed.


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## MrAngles

Yeah the room next door (theater room) is what I'm most concerned about. On the floor above the sound of the airflow through the ducts is louder than the sound of the furnace itself coming through the floor anyway, plus I won't be watching movies up there.


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## Ted White

10-4!


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## MrAngles

Back to the XPS intallation, what am I supposed to do around windows? It's easy enough to cut around the window and seal the seams with spray foam, but how do I frame the window in with wood and drywall while avoiding moisture issues?


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## Gary in WA

You will need a ceiling in that furnace room, possibly fire rated, check with your local AHJ. Ask about the fire-stopping, too; http://www.diychatroom.com/f98/how-fireblock-framing-37190/

Basement egress window or door: http://www.dmgov.org/Departments/CommunityDevelopment/PDF/Basement Egress Window Policy.pdf

Gary


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## MrAngles

Why do I need a ceiling in there if I'm not finishing the room? Here's the guidelines pdf for the city of Ankeny. I called the main inspector and he didn't mention it. All the wiring and plumbing to/from the main level of the house goes through there, so if I can avoid covering that stuff up with drywall it would be great.


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## Gary in WA

Usually, if finishing a certain percentage of the whole basement (50% around here), you are required to bring it all up to minimum safety Code for fire prevention. Drywall on the walls and ceiling are required in most spaces, etc.; "*CEILING HEIGHT.* The clear vertical distance from the finished floor to the finished ceiling." From your basement guide - *"TYPICAL CONSTRUCTION
 Drywall - walls: 3/8" limited to 16" oc studs, 1/2" or 5/8” limited to 24" oc studs; *ceilings:* 3/8” limited to 16” oc perpendicular to joists, 1/2" or 5/8” @ 16" oc either direction, 1/2" or 5/8” @ 24" oc perpendicular to joists" *Underline and color change is mine.
The whole purpose of drywall is to slow the flame-spread and smoke emitted from wood frame joists, studs, etc. from burning through quickly before the house collapses and give firemen time to extinguish it and occupants time to leave safely. Not covering exposed wood frame materials in a mechanical room with electric, gas, other- units there would be counter-productive and always check locally. Let us know the outcome....

Gary


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## MrAngles

I will do so, thank you very much.


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## Gary in WA

No problem, you are welcome! BTW- the *bold *above was not mine.... it was copied directly from your source, sounds like yelling to me...

Gary


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