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Old 08-21-2011, 01:37 PM   #1
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Cantilever containing plumbing, HVAC.


Hello,

I couldn't find a solid answer in a search. I have a 4' x 25' cantilever upon which sits my kitchen cupboards (and sink), a dishwasher, and in the other room an HVAC vent.

I want to insulate this space and it will be a lot of work to relocate the plumbing (running it up through a wall and under the space between the cupboard bottom and floor boards).

Should I insulate this with XPS to keep it a warm area? Meaning I would put a small piece of XPS against the rim joist in each cavity (caulked) and run another piece along under the joists (caulked), then cover this with screwed in ply and finish it off with capping and soffit or paint.

Inside I could put roxul batts and not block off the joist cavities over the sill plate.

Does this sound logical? can I get away with using 1" XPS for this?

Thanks

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Old 08-21-2011, 03:34 PM   #2
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Cantilever containing plumbing, HVAC.


You can do it either way, or use Tiger foam. http://tigerfoam.com/

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Old 08-21-2011, 07:29 PM   #3
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Cantilever containing plumbing, HVAC.


My only real concern here is condensation and ultimately mould due to thermal bridging at the rim joist - floor joist junction since this might be a cold spot in the winter. Am I being too uptight?

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Old 08-21-2011, 07:43 PM   #4
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How are you figuring that there will be condensation? Has there always been condensation in this space that you are sealing? I used R-13 kraft faced batts in my joist & rim bays, because I still wanted some air movement in my basement. The one thing that I did do, was due to we have old single pane windows down there, i used foil faced 1" styro-foam placed over the window, with the foil facing outward. That made a huge difference, due to the fact that my house is over 70 years old.

Whether you spray foam, or use 2" xps and caulk the seams to hold it in place, or use Rox-wool, or even just plain simple batt insulation, it does not make a difference how you do it, just that you get the job done. Remember, that with this, especially with Spray Foam, you are creating a vapor barrier to not allow convection of air from either side. As for the rest of the house, just making a difference in one spot, will not change how the rest of the house behaves, until you seal the rest of it up to help conserve energy. The buildingscience.com website has a lot of good info on what you are doing.
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Old 08-21-2011, 08:18 PM   #5
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Cantilever containing plumbing, HVAC.


^^Thanks. I'm just looking to fix the cold spot on the floor over this area and prevent pipe freeze during the winter. This cantilever is under the room where my thermostat is so it might affect the whole house in that the heat might be a little more even but that's not my goal here.

I was worried about condensation because the area is very cold and drafty (draughty?)now in the winter even when there is pink FG in the space...if I make it warmer, there might be cold spots that are cold enough to get wet.

Not a big deal though i guess
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Old 08-21-2011, 08:37 PM   #6
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Only way that you are going to get condensation is if you have a high humidity level in the home, or take showers without the bath fan on. What you are doing when you seal the rim & joist bays, is stopping air currents & the convection process. I have had no problems with my basement during the winter. Before I did the foam over the windows, and the r-13, it would be 76 to 78 in the summer down there, and in the winter around 54-56. It now stays around 68 in the Summer with the a/c on, and 62 during the winter. Only because my walls do stick up above the ground about 3 feet, but now it is tolerable. Before I did all of that, and when we moved in, there was a old "Octopus" furnace down there, that kept it nice and toasty during the winter, but after we got the more efficient furnace, it stays reasonable, that you can go down there and sit.

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