I recently had the opportunity to attend a conference on solid wall insulation in Edinburgh, sponsored by Changeworks and Historic Scotland, for the Strathbungo Society. I’m a building engineer (structural/building science) from North America, and I moved to the neighbourhood in 2010.
I’ve started a personal building blog called Sauce and have cross-posted this article. I’ll add more detailed notes and bits of research to Sauce over the next couple of weeks and either link to them or cross-post them to BungoBlog.
Most people who live in Strathbungo are probably aware that our exterior walls are yellow and red sandstone. These walls are load bearing (the roofs and floors are supported by them) and – unless they’ve been retrofitted – uninsulated except by lathe and plaster. They’re also quite thick. Some them may have more than one layer or method of construction – anyone who’s taken one apart could perhaps go into detail in the comments? Anyway…
Right now, improving the energy efficiency of buildings is a government priority. Less energy use means fewer greenhouse gas emissions. Of course, a more efficient house – one that holds onto heat rather than losing it – also saves us money on gas and electricity. So, there are all kinds of reasons to try to improve the thermal performance of our houses. However, like everything having to do with old buildings, there are significant expenses and even some risks involved. The risks with insulation are always related to moisture: mould, rot and deterioration of the building materials.
I’ll start with a summary of the main points I gathered from the conference, based on an e-mail I already sent to Strathbungo Society members.
- Although exterior wall insulation is technically the best solution for solid walls, it is obviously not appropriate for our buildings. Even the buildings in the neighborhood that aren’t listed historic properties are old and beautiful, and I doubt anyone would want to cover up the stone with exterior insulation, even if it were possible to get planning permission.
- There are very thin forms of interior wall insulation available, and they can be installed without ruining the interior detail in historic buildings. However, installing them on walls with moisture issues is not a good idea. I want to do a bit more research on this to clarify things, but basically, I’m thinking it’s a lot of expense, trouble and risk for minimal benefit.
- Conclusion: As a Strathbungoer, the best way to improve the thermal performance of your house is probably not by adding wall insulation.
Here’s the big news: A recent study explored actual vs. theoretical thermal resistance in stone walls. In reality, they tend to perform significantly better than the models currently in use by architects, engineers and the government suggest they should. We’re talking about a 50%+ difference in real vs. theoretical performance. In other words, our stone walls aren’t as bad as they say. I’m not surprised at all by this. Bryan’s and my flat is actually the second solid-walled property I’ve owned. Both have had lower than expected energy bills.
While it may not be worth it to try to insulate all along the exterior walls, I believe that it would be worth it to insulate anywhere the exterior wall is thinner than normal, notably at false windows/nooks. I’ve thought about doing this at our flat and have some plans drawn up for it. Basically, I’d strip out the shelves, put in board insulation, seal around it, and replace the shelves. There is a potential issue with moisture getting trapped between the stone wall and the insulation… Still thinking about that one.
I can’t emphasise enough that stopping drafts is absolutely vital to energy efficiency. Most heat escapes through air leakage, not diffusion through walls – this I know from studying building science in Canada.
BUT, if you do have a few quid on hand and want to improve the energy efficiency of your house, I saw one very impressive product: a window system that allows you to keep your original exterior windows, but adds a new, well sealed window between the exterior windows and the interior shutters. Now THAT would improve thermal performance. Does anyone already have these? What do you think of them?
I’ve embedded a video (from the conference) that shows how it works below.
In conclusion, I think it’s the picky detail work eliminating drafts and insulating thinner parts of the walls that’s going to make a big difference, not a big, expensive wall insulation project. Adding a double-glazed window between the original window and the shutter is also a promising idea.
More to come!
Hi Dee,
Thanks for all the research. It’s good to have someone on the case who has background knowledge.
I did work around the window openings in our house. I can confirm the air gaps behind the shutter pocket linings, and the front and back walls in our house sounded like hollow plaster, which I presumed to be lath and plaster. The video shows insulation being blown behind the shutter pocket linings – it did occur to me that it might be possible to do this for the entire front and back (ie external) walls – do you have any experience of this? It would presumably be easier than internal solid insulation panels. There is also a significant air gap around the front door in the old houses.
I slowly draught-proofed our windows, using staff beads and parting beads from Reddiseals. It does require some time and basic carpentry skills, but made a huge difference to warmth by excluding draughts. It’s going back a few years now, but I think it cost about £300 for enough materials to do all our windows. I can’t give accurate figures for energy cost saved, but the initial outlay was small.
Last, one simple idea, and one more complex. First, chimney balloons for unused chimneys cut down an enormous amount of updraft, and take seconds to put in place. They can be just as easily removed for occasional use of the chimney. Second, more complex. The ground floor of our house had suspended timber floors in all but the room that was, I assume, the original kitchen or laundry. Our water stopcock was accessed through the floorboards – whenever I did this, there was an enormous draught on windy days under here. We had carpet with underlay, but I always assumed there must be a good deal of heat loss downwards. Do you know if it’s possible to blow insulation into this space rather like a cavity wall? Under the timber there was just soil about 3-4 inches below, so it’s a worthwhile depth for insulation, without being excessive.
I hope this is food for thought, and once again thank you for a huge amount of work,
James
Hi James,
Oh, those are good suggestions and it’s nice to get the perspective of someone who has already done some of the work. As far as the post goes, I didn’t do much work at all. I just edited the post to clarify that the video is from the conference. 🙂
Dee
Hi Dee, having experienced yet another year of unbearable draughts, we took the time to locate where these were coming from. The draughts from the panels below the windows and behind the shutters in our front two rooms were quite extraordinary and so we have recently had all these panels removed, packed with insulation and then replaced. Already, the difference we have felt is incredible.
Allison.
It seems like just improving the window areas will make these buildings perform pretty well thermally. It makes sense. The stone walls may not have a high thermal resistance per inch compared to some other materials, but they are really thick. I don’t think that the high heating costs that a lot of us are dealing with are due to the thick parts of the stone walls so much as the places where the walls are thinner, near the windows.