1 Helpful?

Do not insulate exterior walls of old homes

I was recently talking to a potential customer that lived in a home built in the 1930s and wanted to make his home more efficient. I of course explained that we would start in the attic - air seal and insulate, go the crawl air seal and insulate and then take a look at his duct work. After all of that would move to the exterior walls where a dense packed cellulose product would be best for his home. He had mentioned that he had always heard not to insulate his walls - would cause too many problems and too long of a payback. Referred me to this article:


Curious to hear people's thoughts and comments.

Asked by Danny Kelly
Posted Feb 9, 2011 2:45 PM ET


12 Answers

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Bob Yapp, in the article, may have had some problems with exterior wall insulation in the past, but his conclusions and solutions don't make any sense.

Retrofit cellulose has been done successfully and economically for many years.

Answered by Kevin Dickson, MSME
Posted Feb 9, 2011 2:57 PM ET

Answered by John Brooks
Posted Feb 9, 2011 2:59 PM ET


Well, if that's true, don't tell the homeowners in the U.K.


Answered by Mike Collignon
Posted Feb 9, 2011 3:54 PM ET


Many painters have told me that houses retrofitted with insulation have more problems with paint peeling.

Answered by william goodwin
Posted Feb 9, 2011 4:36 PM ET

Answered by John Brooks
Posted Feb 9, 2011 5:07 PM ET


This article was written in 2009??? I would have thought it was written in the 70s.

I don't know this Bob Yapp character, but he obviously isn't up to date on his building science.

Advising people to insulate the rim joist area with kraft-faced fiberglass insulation? Advising people not to retrofit walls with exterior insulated sheathings?

Yeah Danny, don't pay attention to this article or anything that Bob Yapp writes.

Answered by Brett Moyer
Posted Feb 9, 2011 5:28 PM ET


Thanks for the quick replies (and links) and pretty much the same thoughts I had - was curious if everyone was going to agree with me or not - not sure where this guy was coming from. I had read all the BSC articles and did understand that there are some sideaffects with insulating but thought the dense packing would resolve most of them compared to a loose blown in product. The biggest thing that I could not find much information on is the payback period. If the top and bottom are in fact selaed and insulated is the expense for the walls worth it. Further comfusing the reasining is the fact that the windows are almost 100 years old and he is in love with them and does not want to touch them. So will insulating a wall while the windows remain do any good at all? I was thinking back to Allison Bailes blog with lumpy attic insulation - what if you do manage to get the exterior walls to an R-13 or so but have R-1 windows everywhere (not sure what the U-factor of 1928 clear glass is but I'm guessing between .75 and 1) is the payback going to be there? I guess even an R-8 is better than zero.

Answered by Danny Kelly
Posted Feb 9, 2011 6:20 PM ET


When Yapp reported his inspection of "thousands" of old homes, 80% of which had the problem, he did not break them down by the type of insulation that had been used. Were they dense packed cellulose, or something else, and was the installation of that material well done? My folks have had their old home blown twice, but I still found sections loosely filled with crumpled newsprint from the 1930s.

He also did not mention whether the old homes had been detailed on the exterior against bulk water infiltration.

Nonetheless, I have been wondering about this question. Let's take a 2x6 wall and customers whose budget simply prohibits exterior foam sheathing..... in other words, we're locked into the existing clapboard cladding. Air seal the attic, and insulate the attic. All other things being equal, interior relative humidity will go up. That moisture will head for the walls.

If the walls remain leaky and uninsulated, then sure BTUS and $$ are wasted, but winter condensation hopefully will dry in spring/summer before doing much damage. If the walls are leaky but insulated, my layman common sense suggests the drying part of that equation will be compromised. It was for this reason Yapp mentioned low permeable paints and caulking penetrations. Then we have the installation methods such as dense packing.

So... it is indeed an interesting question, whether insulating then brings on a series of addtional issues requiring mitigation strategies, and increased cost.

Danny, the client is in love with the windows.... is that feeling greater about the interior look or the exterior look? Would they entertain better storms (maybe interior ones)?

Answered by Steve El
Posted Feb 9, 2011 6:47 PM ET


The energy savings are definitely there, at least in a cold climate. However, your exterior paint may not last quite as long after you have insulated the walls.

In Vermont, the weatherization agencies have been installing dense-packed cellulose in the walls of older homes for decades, because this measure almost always rises to the top of the cost-effectiveness list -- always way ahead of replacement windows, which offer far too long a payback for weatherization agencies to consider doing windows.

Answered by Martin Holladay
Posted Feb 10, 2011 5:54 AM ET


I believe Joe said in one of his BSC papers that the cure was to put shims under the bottom edge of the wood siding. This would allow the cladding to dry on t he back side.

The other thing said in BSC puplications is to take care of the water leaks.

If these simple things werent implemented than I dont think you can lay the blame on the insulation.

Answered by Robert Hronek
Posted Feb 10, 2011 10:57 AM ET


To andwer a few questions:
House is brick so peeling exterior paint should not be a concern.
I did bring up interior storms. He may use them in a few problem areas like bathroom and bedroom but does not want to use them everywhere.
Thanks for all the thoughts.

Answered by Danny Kelly
Posted Feb 10, 2011 5:11 PM ET


He's right about slowing and vapor with PVA primers, and with the Kraft paper faced insulation, both are Class II vapor barriers. @Martin, you thought I was alarmist.......the siding failures have more to do with caulking the bottom of the siding than it does with insulating, this guys is just trying to piss off Martin. If it weren't for the heartwood lath behind that plaster, and the plaster being alkaline , those old house would ALL be moldy, since that would be the cold side of the warm side. There is no way that the hydrophilic material can't diffuse a little vapor, leaks are a different issue. He brings up a good point though, how tight is too tight? No one is perfect, and no one can build perfectly airtight. The closer we get, with inorganic materials, the more trouble we find ourselves in. Those old carpenters didn't know the ph of the plaster or that heartwood WILL NOT support mold, they were just carrying on a tradition, one that is all but lost.

Answered by Matthew Amann
Posted Feb 11, 2011 2:49 AM ET
Edited Feb 11, 2011 11:55 AM ET.

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