# Insulating walls behind shower



## rbh123456789

Hey guys,

We recently ripped out our tile, drywall, vapor barrier and fiberglass insulation from our shower area in our washroom (photo attached).

I am doing the project slowly so i can ensure that i choose the correct products for the application.

I understand that rigid foam is superior to fiberglass in most situations. I would have preferred to have some spray-foam guys to do the work, but since its such a small project, the cost would be way too high.

Below is a link to some rigid foam I found at Home Depot. Since the inner-spacing between studs is 14.5", this product foam would be an easy installation.

http://www.homedepot.ca/product/plastispan-handipacs-48inch-x-145inch-x-15inch/940444#

My question is will 1.5" foam be thick enough for the exterior wall? Or should i double them up to make the thickness 3", or even triple? 

I plan on using concrete board instead of green-board (if that matters).
Also, i live around the Toronto area, so we get fairly cold winters.


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## Bonzai

Hello from BC.

If you're keen to go the stray foam route, there are a couple of options for smaller projects such as yours ... here is one of them:

http://www.tigerfoam.ca/

There are other companies doing the same thing.
If you've ever seen injection moulded ski boot liners being done then this is a similar concept ... the 2 components mix as you spray & turn in to a foam. When I looked in to this for a small attic job it was going to be around $400-500 all in. A lot more than fibreglass insulation, but to an extent you get what you pay for & too small for a contractor to be interested generally speaking unless they were doing the whole bathroom reno.

In terms of how much insulation is enough; you would need to check the Ontario code with your local building department ... there are major revisions to the Canadian building codes which have already been implemented in some provinces & will be implemented later this year or maybe early 2013 in others. Not sure where Ontario stands. There are 850 changes to the BC codes which are due to become effective this Fall and apparently much of this revolves around energy efficiency as well as fire safety.

Here is a useful table for the ratings for various types of insulation...
http://www.cmhc.ca/en/co/maho/enefcosa/enefcosa_002.cfm

Is your exterior wall 2x4 or 2x6 construction? (older homes are typically 2x4)


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## Donning

Spray foam is great but expensive for small projects. You can definitely can use a hybrid system of using rigid extruded instead of spray foam. You may want to cut it a little smaller and then use can foam to fill the crack on each side for a tighter seal. Is this an outside wall? if so before you foam, caulk all the cracks of the framing to draft seal the wall well. You do not necessarily have to fill the void completely and air gap makes a great thermal break. The most important will be the vapor barrier spend extra time and get it tight.


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## jklingel

Rigid foam is better than fg in several ways, since fg is the worst insulation available. No, 1.5" is not enough. You are going to have a time of it fitting rigid foam around those pipes, so you may want to look for Roxul batts; way better than fg, too. That said, if you have to buy a huge amount of Roxul and only use 10% of it, stick w/ the fg around the pipes and use rigid foam where you can; that's what is in the rest of the house, likely. XPS (usually blue or pink) has a better R/inch than EPS (white, bead board). Absolutely air seal like a maniac, and if you must use a vapor barrier, then use one; I think it is still a Canadian thing..... BTW: A layer of air in this situation is likely not a good idea. I believe you will get convective loops in it, cycling heat out. It is better to fill the voids with something more dense than fg, if possible.


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## rbh123456789

Bonzai said:


> If you're keen to go the stray foam route, there are a couple of options for smaller projects such as yours ... here is one of them:
> 
> http://www.tigerfoam.ca/


Thanks for the link. I actually found a guy near our area who said he has a minimum charge of $750. but he said that if he was doing a project in our area, he could do the work for $500.......which i still thought was high; but maybe not!



Bonzai said:


> Here is a useful table for the ratings for various types of insulation...
> http://www.cmhc.ca/en/co/maho/enefcosa/enefcosa_002.cfm
> 
> Is your exterior wall 2x4 or 2x6 construction? (older homes are typically 2x4)


That CMHC is a great site - lots of information, thanks.
Our exterior studs are 2x6, thats why i figured i would want at least 3" of insulation. Do you see a problem with layering the rigid foam to achieve the desired thickness?



Donnig said:


> Spray foam is great but expensive for small projects. You can definitely can use a hybrid system of using rigid extruded instead of spray foam. You may want to cut it a little smaller and then use can foam to fill the crack on each side for a tighter seal. Is this an outside wall? if so before you foam, caulk all the cracks of the framing to draft seal the wall well. You do not necessarily have to fill the void completely and air gap makes a great thermal break. The most important will be the vapor barrier spend extra time and get it tight.


The back wall in the photo is an exterior wall (you can see the chip-board behind the studs). Good thought about filling in the cracks. I know Home Depot has the 'Great Stuff' foam insulation in an aerosol can; i imagine i could use that.



jklingel said:


> Rigid foam is better than fg in several ways, since fg is the worst insulation available. No, 1.5" is not enough. You are going to have a time of it fitting rigid foam around those pipes, so you may want to look for Roxul batts; way better than fg, too. That said, if you have to buy a huge amount of Roxul and only use 10% of it, stick w/ the fg around the pipes and use rigid foam where you can; that's what is in the rest of the house, likely. XPS (usually blue or pink) has a better R/inch than EPS (white, bead board). Absolutely air seal like a maniac, and if you must use a vapor barrier, then use one; I think it is still a Canadian thing..... BTW: A layer of air in this situation is likely not a good idea. I believe you will get convective loops in it, cycling heat out. It is better to fill the voids with something more dense than fg, if possible.


Thanks for the tip. The pipes will pose a challenge, which is just another reason why the spray foam would be easier. Would the 1.5" thickness suffice for the non-exterior walls that are using 2x4s? (in the photo, they are on the left and right side)


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## Bonzai

Personally I would suggest batts of sound insulation on the interior walls so that, assuming there are bedrooms near by ... They don't get the "benefit" of someone making a late night deposit or having an early morning shower. You could use the spray foam from a can for small awkward areas ... And then rigid for everything else. And yes vapor barrier is an absolute essential here in Canada.


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## rbh123456789

Bonzai said:


> Personally I would suggest batts of sound insulation on the interior walls so that, assuming there are bedrooms near by ... They don't get the "benefit" of someone making a late night deposit or having an early morning shower. You could use the spray foam from a can for small awkward areas ... And then rigid for everything else. And yes vapor barrier is an absolute essential here in Canada.


Thanks for the information; much appreciated.

I've noticed that the maximum thickness of the rigid foam at Home Depot is only 3 inches. Would it be okay to use 2 layers? For example, 1 3" layer and 1 2" layer; leaving a 1/2" gap between my cement board and my rigid foam? (for my exterior facing wall with the 2x6's)


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## Bonzai

Yup you can layer up the foam insulation. Make sure to use the right adhesive as some will eat rigid foam insulation.


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## Gary in WA

So there is a gap under the siding? 

http://www.buildingscience.com/docu...nd-the-gap-eh/?searchterm=foam board in walls

http://www.buildingscience.com/documents/insights/bsi-058-parthenon/

Gary


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## rbh123456789

GBR in WA said:


> So there is a gap under the siding?
> 
> http://www.buildingscience.com/docu...nd-the-gap-eh/?searchterm=foam board in walls
> 
> http://www.buildingscience.com/documents/insights/bsi-058-parthenon/
> 
> Gary


Sorry if i wasn't clear. the potential gap would be in the following order:
House Brick->OSB->5" layered Rigid Foam->1/2" Air Gap->Moisture Barrier->Cement Board

The reason the gap would exist in that scenario is because my 2x6 studs are a true 5 1/2", so if i have 5 inches of foam, that would leave 1/2" of unused space.

If i read your links properly, i don't believe that should pose a problem. correct?


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## Gary in WA

Correct. OSB needs a gap at the siding when foam/board is in direct contact with it.You have that with the brick/wood sheathing air space. Wetting of the OSB on the South side with brick (Solar drive) can create problems. The foam inside the cavity may stop the moisture drive through the wet brick from wetting normal cavity insulation, but the OSB now has to dry outward only. It cannot be warmed to dry from the interior or diffuse through the thick foam at 5" = 0.28 perms PLUS the poly would not allow any moisture through. http://www.buildingscience.com/documents/reports/rr-0104-solar-driven-moisture-in-brick-veneer 

Foamboard outside with cavity insulation is the best choice as it is a thermal break on the studs and the cavity is treated as conditioned from the HVAC inside, the OSB is warmed by the foam thermal barrier- warm wood =dry wood= no mold. Putting the foamboard inside the cavity will keep the OSB colder, wet wood = mold. http://www.greenbuildingadvisor.com/blogs/dept/musings/how-risky-cold-osb-wall-sheathing

It may/not be fine, need to research this more... 

Gary


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