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Old 04-15-2014, 01:42 AM   #1
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What thickness of XPS/Roxul?


I've read a bunch of posts about basement insulation but need some advice here. I apologize for the length of the post for such a simple question!

It started out as wanting to install a subpanel for some electrical expansion in our 80's split-level entry house outside of Vancouver, BC. I knew that at some point I would be re-doing the basement but it looks like I will be starting now:
  • Paper thin unsealed vapour barrier
  • Penetrations not sealed
  • Inadequate insulation installation
  • Lots of air movement behind the wall
  • Completely bizarre framing
  • No moisture barrier
  • I could go on and on!

Unfortunately I cannot do the whole basement at once so it will be section-by-section or room-by-room as time permits.

Info on the construction:
  • The foundation is 8" wide, stepped in a few places (one shown in a pic below)
  • 2x4 walls spaced at 16"
  • Old cedar siding on the house was removed. Covered house with Tyvek, all seams taped
  • Vinyl siding was attached to furring strips to create a vented space (I think the debate is still going on about this one)
  • Below grade consists of blue clay - lots of moisture

So, after ripping a section of wall down, and based on what I've read here, the plan is as follows:

Rim Joists Pockets
  • Caulk rim joist cavities
  • Install XPS with PL-300
  • Fill voids/edges with caulking or window/door foam
  • Cover XPS with R14 Roxul

Existing exterior wall
  • Caulk sill plate
  • Replace FB bats with R14 Roxul

Foundation
  • Install moisture barrier from just above grade down the foundation wall and under bottom plate - forms a "J" with vapour barrier
  • Cover foundation with XPS - PL-300 with pattern to reduce air flow. Covering front face and top of foundation wall taping up joints
  • Install 2x4 bottom plate, top plate, and studs on 16" centers
  • Add R14 Roxul on top of XPS - front face and top of foundation
  • Install outlets, new plumbing, venting etc with vapour barrier boxes/sealing where required
  • Install vapour barrier onto new framed wall - accoustic sealant on top/bottom plates
  • Fold up moisture barrier over bottom plate and tape to vapour barrier

Questions:

  1. Plan is good based on my location?
  2. What thickness of XPS and Roxul for rim joist pockets? The pocket is only 2-1/2" deep so after 1" XPS, there's only 1-1/2" left for Roxul
  3. I'm thinking of using 1" XPS to cover the foundation. With the R14 Roxul on top, is this sufficient?
  4. Is it worth using Blu Wood if using a moisture barrier?
Any advice is greatly appreciated!

Thanks,
Mike
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What thickness of XPS/Roxul?-2014-04-12-10.19.56.jpg   What thickness of XPS/Roxul?-2014-04-13-22.17.09.jpg   What thickness of XPS/Roxul?-2014-04-13-22.17.26.jpg   What thickness of XPS/Roxul?-2014-04-13-22.19.18.jpg   What thickness of XPS/Roxul?-2014-04-13-22.38.02.jpg  


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Old 04-15-2014, 07:07 AM   #2
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What thickness of XPS/Roxul?


1. Well thought out and scripted plan.
2. I would go with 2" XPS everywhere in including bands. You will want that thermal resistance and vapor control level. The area should be covered by drywall as part of your finishing plans so no worries there and you can cover with whatever batt insulation you see fit.
3. I would go 2" personally. Pretty cold up there.
4. Meh..? Not really sold on that stuff and if you build it right, you shouldn't have any moisture issues.

I know that IRC up in those parts requires a vapor retarder level of some significance but just make sure the exterior envelope is supremely well sealed before you start with the put back and make sure (as you mentioned you will) you take do ADA on the sheetrock (Airtight Drywall Approach).

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Old 04-16-2014, 12:17 AM   #3
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What thickness of XPS/Roxul?


1. Thanks. At least I have one person agreeing with my method and based on what I've read and see, it looks like the optimal way to do it
2. Yes, the area will be finished with drywall. I really don't want to leave unfinished wall exposed too long. I have enough of those already!
3. Depends on your definition of cold. We don't get below freezing very often but I'll see if I can squeeze another inch on the foundation wall - no problem for joist cavities.
4. That's what I thought. As long as wood isn't touching concrete then everything should be fine.

So after thinking about this two things came to mind:
1. Having the vapour barrier completely on the interior wall makes it a bit difficult to seal effectively since above the foundation wall, it will be ~6" from the exterior wall. With the subpanel and all the wiring, there will be lots of penetrations. What if a "middle plate" is installed so that the vapour barrier can run up along the batt insulation in front of the foundation, then back so it is against the batt insulation of the exterior wall? ie the void would be behind the drywall, not behind the drywall and vapour barrier. (does this make sense?) It seems this would be the same finished profile you would obtain from spray foam.

2. If this is done, then the moisture barrier and vapour barrier will create a closed cavity. I suppose then the moisture barrier shouldn't be used at all?

Last edited by mlowrie; 04-16-2014 at 12:31 AM.
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Old 04-16-2014, 09:34 AM   #4
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What thickness of XPS/Roxul?


Get the outside wall airtight and airtight the drywall.

After that, you shouldn't have any moisture issues and I am not a fan of plastic, interior, vapor barriers anyway.
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Old 04-16-2014, 04:03 PM   #5
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What thickness of XPS/Roxul?


IMHO, 2" is overkill for your location. On the rim joists, the 1"XPS is more than enough, same as Zone 4C;http://www.buildingscience.com/docum...r-requirements

On the poly, some reading for you; http://www.buildingscience.com/docum...Insulation.pdf

Fill the 6" gap between insulation/walls with cheaper Fg to limit convective looping/air movement there; https://docs.google.com/viewer?a=v&q...fHFsk1RrK9G2HQ

Using 3 coldest months averages of high/low for your location; http://www.weather.com/weather/wxcli...graph/CAXX1710

is 40*F-- temperatures of different thickness FB on cavity side (above grade/1' below grade) is; R-10 (2")XPS 9=(unfaced) with R-14 cavity - safe to basement air below 57%RH--- FB at 52*F.

R-5 XPS and R-14= FB at 47*F and 48%RH

R-2.5 XPS and R-14= FB at 44*F and 43%RH

Check your transition ducting to termination hood for dryer, appears you have a leak... canned foam any wiring holes through studs/plates to limit air movement in wood frame wall, cc pipe insulation on water supplies as they will be much colder once cavity-fill/new wall is added, fire-stop new wall area before install at ceiling to prevent joist cavities fire path and every 10' horizontally as in US codes; http://publicecodes.cyberregs.com/ic...002_par017.htm

Gary
PS. "no burst" washer hoses are cool...
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Old 04-17-2014, 05:21 PM   #6
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What thickness of XPS/Roxul?


Thanks for all the info Gary. That was some interesting reading and there seems to be a whole slough of stuff out there regarding this topic and it's hard to judge which is best for the area and design of the house.

So 1" XPS and R14 batt will be my method and I'll go through the calculations again myself to verify the numbers you got and ensure that condensation won't occur.

As for the "dead space", if it is on the warm side of the insulation and vapour barrier, are air currents still a factor? I don't really want to spend a whack more cash on filling in this void space just so the vapour barrier is in contact with the drywall. Not much different than creating a stepped wall, then deciding to eliminate the step later in the future.

As for my plumbing and vents, they are all getting replaced. New venting, new plumbing (PEX with manifold system), updated electrical, the whole works. I only want to do this once!

I'll check into the fire stop requirements here to make sure I don't miss anything.

Mike
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Old 04-17-2014, 06:17 PM   #7
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What thickness of XPS/Roxul?


Air currents aren't an issue if the space is tight, temp stable (i.e. convection), and drywalled tight.
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Old 04-18-2014, 12:25 AM   #8
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What thickness of XPS/Roxul?


You're welcome! The gap fill will stop any warm wall (interior one) temperatures mixing with the cold wall (exterior frame wall) temperatures through the studs (thermal bridges) slowly drawing your heat away, every time you warm the room. Standard 16"oc wall frame loses -9% to wood that is rated at R-1.25 per inch or R-4.4 at every stud and plate. Drops your wall rating from R-14 to R-9....

Radiation/conduction could also take place depending on the temps/frequency. Horizontal airspace has R-1 but with a cold upper wall (above grade) and a warm (interior) whole wall, IMO, insulate to control any tempering of the air space- your mild winters- you might not want to "cover all the bases" but at least you were informed; pp. 32-40; http://www.google.com/url?sa=t&rct=j...cKMAa3A8yDuYqg

Gary

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