# 2" foam or Foil Back?



## hellothere123 (Aug 16, 2008)

I have 2 options:
1) 3/8" Foil Back Styrofoam (R5) overtop of existing x90 - without removing x90 for $1700.00
2) Remove x90, housewrap, 2" styrofoam insulation (R10) for $4200.00

I live in Canada


I'm not sure aboout option 1...if you put the r5 overtop of the x90, I think there would be a ton of air gaps as it is lap siding...but how much do you really gain with the r10 and vinyl siding vs r5 + the r value you'd have from your existing x90?

Your thoughts?:wink:


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## AGWhitehouse (Jul 1, 2011)

2"@R-10 is XPS and at that thickness is considered a class II vapor retarder. The foil facing is likely considered a class I vapor retarder. Best to make sure you're not creating a double vapor barrier system and create the "Sick building syndrome". The walls need to breath...


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## Windows on Wash (Aug 30, 2011)

AGWhitehouse said:


> 2"@R-10 is XPS and at that thickness is considered a class II vapor retarder. The foil facing is likely considered a class I vapor retarder. Best to make sure you're not creating a double vapor barrier system and create the "Sick building syndrome". The walls need to breath...


+1

Foil facing is going to make it Class I in about 99% of the cases.

Be careful of that moisture trap.


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## hellothere123 (Aug 16, 2008)

I'm sorry...I don't know what you are trying to say...dumb it down for me a bunch!


Thanks!


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## hellothere123 (Aug 16, 2008)

anything further? :huh:


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## Gary in WA (Mar 11, 2009)

Please ask the identical question in *one* forum, not multiple areas, thank you.

Gary


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## Gary in WA (Mar 11, 2009)

1. How thick are the walls?

2. Is there poly vapor barrier inside? Hence the concern of a faced foamboard outside and poly inside. Unfaced XPS foamboard (2") exterior and poly inside will work if the inside air leaks are stopped. 

3. Where in Canada are you located (to find your insulation requirements)?

Gary


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## hellothere123 (Aug 16, 2008)

GBR in WA said:


> 1. How thick are the walls?
> 
> 2. Is there poly vapor barrier inside? Hence the concern of a faced foamboard outside and poly inside. Unfaced XPS foamboard (2") exterior and poly inside will work if the inside air leaks are stopped.
> 
> ...


Sorry :wink:

2x4 walls
vapor barrier is installed on inside
Saskatchewan

I think it should be alright...everyone around here does that..some even go with a R12 insulation on the outside

I'm not totally sold on the benefits vs cost of doing this...

Funny thing is some people will put the 2" foam insulation ontheir house but won't replace the windows until they have the money...I think windows are the biggest loser in terms of losing heat / cold for your house..I dunno


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## Gary in WA (Mar 11, 2009)

Compare the square footage of walls to windows. If older R-9 f.g. batts with air movement, you need the added insulation for your climate. 2" f.b. is fine without facing as I said earlier. No vapor problems: http://docs.google.com/viewer?a=v&q...iZ9vwo&sig=AHIEtbRlhNBCWID8xGZ54EyM707m0gPdXQ

Cruise around here: http://oee.nrcan.gc.ca/publications/residential/8584

Drain your cladding; http://www.buildingscience.com/docu...iles/bsi-028_energy_flow_across_enclosure.pdf

Gary


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## hellothere123 (Aug 16, 2008)

Thanks..I'll read up :thumbup:


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## Chemist1961 (Dec 13, 2008)

*do it right*

I sided a house in Regina in 1976 with X90. Why not strip down in the spring and do it right. For the money you will spend you can probably pay a couple of kids $100 each and dig in. For the improved level surface it will likely pay you back in a proper seal and fight off those COLD winters!!!!At least if you strip it you can use up to date material and inspect the whole structure, seal your windows, etc.


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