Maybe people who replace their windows are not so deluded.

Building science expert John Straube had something to say about a previous post.

Shannon Kyles shows how to restore an old window

In my earlier post, The deluded world of window replacement, I complained about how everyone is obsessed with replacing windows and wrapping buildings in foam to save energy and reduce carbon emissions while ignoring simpler and cheaper methods such as air sealing and attic insulation.

John Straube was not impressed. He’s a principal at RDH Building Science and literally wrote the book on the subject, being author or co-author of over 100 published technical papers, author of the book High Performance Enclosures and co-author, with Eric Burnett, of Building Science for Building Enclosures. He wrote a long comment about the original post and I think it is worth discussing:

“While you have a lot of good and factual points, you (and Orr whom you quote) are applying far too broad a brush. The reason many, if not most, people in the UK and old houses in Canada replace windows has nothing to do with energy savings: they do it because the comfort levels are terrible (the UK still has tons of single glazing) and/or the windows are at the end of durability cycle. As stated by another, no one said you have to replace the windows with vinyl, nor even that you need to use sealed IGUs (which will fail="wear out" in about 40 years). Just be prepared to pay a lot more. But improving the R-value to 4 or more is a huge benefit to comfort. And the draughts people feel are often cold air falling off of poorly insulated glazing, not air leaks, so you can’t fix the comfort complaints by weatherstripping.”

Now I should have been clearer about where I was coming from. I did not mention in the post that I am a Past President of the Architectural Conservancy of Ontario (ACO), an organization dedicated to preserving our architectural heritage, or that I spent years in the trenches fighting the vinyl window industry. I also might have talked a bit more about Shannon Kyle’s work at Mohawk College, which found virtually no difference in air infiltration between a restored window with a storm window added versus a new double-glazed window. But this is expensive and storms or inserts are necessary for comfort.

“Yes, you are totally correct the storm windows are a partial solution, one that deserves a lot more attention, but many people dont want the hastle of removing them, giving up operability, condensation between panes etc. I think you need to understand what drives people to make the decisions, and not assume it is ignorance: in my experience, even when the facts you describe are explained, homeowners still look for affordable ways to get comfortable low maintenance windows. The life-cycle energy sales pitch is not that important and often false.”

Here I must admit that John is correct. When I was talking to people about why they replaced their windows, it was more often about maintenance than it was about energy savings; they were tired of painting and putting up storms and did not share our views about “heritage.”

How you can tell from driving by a site that someone adding 1.5" of foam to their house has not already done all the airsealing they can and filled the attic with insulation is beyond me. Actually, it is not: you can't tell you can only assume. Insulating walls when you are recladding (again, done for durability and style, not energy) is not a waste of money it is incredibly smart money, as this is the lowest cost time to upgrade for the next 50 years. Even if air sealing has not been attempted, I can do that from the interior at a later date, and I can always insulate the attic. When I decide to install new siding, this is the only sensible time to add the insulation. Exterior insulation definitely DOES make a difference, to comfort, to energy use, and even improves durability.

I assume that air sealing has not been done because I have been told by experts in the UK that nobody talks much about them or does blower tests, and they are not on many of the lists of recommendations. They are terrified of moisture buildup and mould, and many windows have “trickle vents” to leak deliberately. They haven’t read Allison Bailes’ new book "A house needs to breathe... or does it?"

In the end, I have to acknowledge that John is right; exterior insulation “definitely DOES make a difference, to comfort, to energy use, and even improves durability.” It is not the only way to get there, and it does destroy the character and historicity of the building. But the alternatives can cost a lot more money.

John does not list carbon emissions in his list. I have tried to make the case that heatpumpification combined with a lighter retrofit that did not involve exterior insulation could reduce carbon emissions and might lower overall carbon emissions because new windows and the foams used for exterior insulation can have a lot of embodied carbon. Engineer Toby Cambray discussed this and suggested that we need to think “about whether it is time to adjust our tactics in the great game of decarbonisation. This does not mean that it’s a good idea to put a heat pump in a building with poor fabric efficiency. Although there are cases where other constraints mean we have little choice; ultimately we need to both (mostly) InsulateBritain and (mostly) Heatpumpify Britain."

But as John Straube notes, comfort is important. Mould is a huge issue. There are times when I should put away my heritage preservation hat, and this may be one of them.

Another commenter noted:

“You're quite a cheerleader for Amsterdam, I believe, Lloyd. Quite right too. But that is a historic city in which large plate-glass windows are to be seen everywhere, even in houses which are hundreds of years old. I believe they are double-glazed. It's maybe not a historically accurate look, but it's a good look, in the same way that a wind turbine in a lovely setting can be a good look: because you know it's sustainable and because it's a sign that someone cares.”

I am going to Amsterdam next week and will be sure to keep an eye out for this.