# Replacing Wall Insulation from the Outside



## jazzywhit (May 23, 2011)

Hi,

I was looking to replace the wooden shingles on our single family cape house that was built in 1952 with vinyl siding. This house has effectively no insulation in the walls, and the energy costs in the winter are very high.

Would it be possible to strip the outside, and put in insulation from the exterior of the house to minimize the dust from breaking up the drywall? Maybe a better question is: 'Would it be advisable' 

My idea would be to strip off the shingles and the exterior shell of the house, install insulation, clean up, put up new plywood, cover with tyvek, and then have the vinyl guys come and install the siding.

Any help would be appreciated!


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## MLMIB (Aug 12, 2010)

The company I just got a quote from for spray foam asked if I wanted to have it done from the inside or outside, so apparently it isn't all that uncommon to have it done from the outside. Are you looking to DIY?


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## jazzywhit (May 23, 2011)

*We had considered DIY*

We were thinking about doing it ourselves, to whatever degree makes sense. I was initially thinking that we could strip the outside of the house ourselves and have someone do the insulation for us since we are going to be redoing the siding anyways.

I had definitely considered using foam for insulation, considering how it can just be sprayed in, but as we were going to have access to the walls, I thought it might be cheaper to install batt.


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## MLMIB (Aug 12, 2010)

The big benefit to spray is that it won't sag, has a higher r value and, most importantly, will provide a solid air barrier.

I'd go foam, or at least flash and batt, but that's just me.

And you can DIY, shouldn't be all that bad.


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## Gary in WA (Mar 11, 2009)

Where are you located?

SPF and OSB don't mix, use plywood. Think of OSB as another vapor barrier. 

Gary


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## jazzywhit (May 23, 2011)

*Location*

I am located in the Boston area, and we are planning to have this done before the winter comes around again. Is there any way that you could expand on your acronyms? I am not familiar with them.


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## Gary in WA (Mar 11, 2009)

Boston is Zone 5: http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_11_sec001_par001.htm

Zone 5 requires R-20 or 13-5 (see Wood Frame Wall and footnote "h"); http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_11_sec002.htm

Need a Class 1 OR 2 vapor barrier against the drywall with fiberglass for your Zone; http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_6_sec001_par003.htm

AND: http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_6_sec001_par004.htm

Air seal by caulking the drywall/stud, plates joint, pp. 21,22: http://www.engr.psu.edu/phrc/training/understandingbarriers.pdf

Notice the air infiltration under the bottom plates with heat picture; http://www.arc.thermaldr.com/res_pg_3.htm

OSB: Oriented Strand Board (engineered wood, not to get wet as it takes way longer than plywood to dry)

SPF: Spray foam: ½# or 2# per cubic foot weight

Don’t mix: http://www.buildingscience.com/docu...nd-the-gap-eh/?searchterm=foam board in walls

I’d add rigid foam board outside the sheathing to raise the dew point temperature: http://www.greenbuildingadvisor.com/blogs/dept/musings/are-dew-point-calculations-really-necessary

Gary


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## HomeInsulation (May 25, 2011)

*Blown in Cellulose Insulation*

Hey Jazzywhit,

I applaud you on your courage to rip apart and rebuild an entire house from the outside to make it more energy efficient and comfortable. I've done a lot of crazy things in my day and have torn apart my house to insulate parts of it from the outside, but I wouldn't recommend doing it on an entire house.

Here's a link to a video of me tearing apart and insulating a wall from the outside.



In your situation, I would recommend blowing dense pack cellulose insulation into the walls. You'll need to hire an insulation contractor with powerful blowing machine (HD rental won't do). 

But if you tear off all the siding and prep the house...they'll be done in 1 day and it will be 1/4 the price of poured in place spray foam. Dense pack cellulose is forced into the wall cavity under pressure, usually 3.5 - 4.0 lbs./ft. This pressure locks it into place and it will not settle over time.

I agree with GBR in WA. You would get more of a bang for your buck if you add a layer of rigid foam board insulation over the exterior of the sheathing. Then air seal the framing and basement rim joists, etc.


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