2x3 insulation outside wall

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Old 08-20-19, 08:15 PM
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2x3 insulation outside wall

We have an outside wall that we want to insulate. We need to put strapping on it since it's solid wood blocks. So as not to lose too much space, we thought 2x3s bit how can we achieve R12-14 ? Roxul is 3.5" so too thick.
 
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Old 08-21-19, 05:19 AM
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You will want 2x4 at minimum for batt insulation and if possible, spray foam for that small of space will get you more R for the space.
 
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Old 08-21-19, 06:25 AM
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Is it possible to achieve r13 in just 2.5"?
cellulose maybe, styrofoam?
 
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Old 08-21-19, 07:13 AM
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That would be in the r-5 per inch range and you would only get that with spray foam or detailed rigid foam cut to fit.

If you have a solid wood wall now you could skip the strapping idea and glue up a layer of rigid foam board and then glue and screw your drywall to that. The net result would be no thermal bridging loss so 2" of rigid at r-5 per inch would preform close to your target of r-14. Plus the continuous layer of foam board would reduce some of the air leakage.

Just a thought.

PS, what is that solid wood wall made of?

Bud
 
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Old 08-21-19, 07:51 AM
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Whatever they used to build with 100 years back. They look like dark 4x12"x10' blocks all laid on top of each other.
Will styrofoam cause any condensation trapping on the inside of this wood wall?
These old houses were built to breathe but they do get cold in winter due to no insulation.
 
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Old 08-21-19, 08:30 AM
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One of the advantages of using closed cell rigid insulation is it prevents the outside surface from becoming cold enough for condensation. Being in Canada you might need a thicker layer but even 2" will be better than fiber insulation.

Hard to get the insulation you want in that limited space.
Note, air seal as much as possible.

Bud
 
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Old 08-21-19, 08:53 AM
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Note, air seal as much as possible.
This is in my opinion the most important. The more air seal layers you have, the much, much better you are.
Run some tuck tape over each seam. Anywhere you use vapor barrier, tuck tape and PL Acoustic Sealant on all joists. Adds a lot of extra time to the job, but so worth it.
 
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