Two small insulation jobs

We've make improvements to the efficiency of our home every year that we've lived here. Over time there are of course fewer large jobs left to do, but there's always something that can be improved. While installing solar panels or getting rid of the gas supply are more dramatic, the small jobs also reduce our energy usage and help to make the larger improvements more effective. The same small improvements will reduce energy usage in any home.

Over the last 12 months we've done two small jobs. Both of them were as a result of measuring indoor temperatures on outside walls or doors. The aim of these jobs was to improve the insulation of a small section of our outside wall and the rear door which leads from our kitchen directly into the garden.

Adding cavity wall insulation

We had cavity wall insulation installed in our home in 2008. It was one of the first things that we had done after moving into our new home because we knew from past experience in other homes that it was a very effective type of insulation. Unfortunately, the installers missed a bit: While they were concentrating on the large area of cavity wall at the end of our home, there was a roughly 2 m tall by 0.75 m wide piece of cavity wall on the other side of our living room next to our front door which they didn't treat at all. Measuring the temperature of the inner wall in winter revealed it to be easily the coldest spot in our living room. As a result some condensation occurred there and there was sometimes a little mildew to wipe away. I asked many companies to come and do this small job, but none of them were interested. They'd either just say no, or they would quote the same price as for a whole house,  which is not only ridiculous for a half hour job that they could have done at the end of a working day, but also not cost effective. So this had to be a DIY job and I finally got around to doing it in September 2022.

Obviously I don't have access to a professional machine which can inject insulation at high pressure so I would need the holes to be closer together. I decided to use expanding polyurethane insulation. To begin I drilled a couple of holes just a few cm apart to see if the foam was expanding sideways in the cavity and when this was confirmed I started drilling holes about 15 cm apart in a zip-zag pattern. It took about three hole cans of polyurethane foam to do the job. Much cheaper than the quotes I'd received. The holes were filled with mortar and there's now no sign at all that that was done to the wall.

The two holes near the centre were the first test holes. I then drilled holes in a zig-zag pattern up the wall and squirted in insulation until it was visible in the next hole along.

During winter 2022/2023 I could measure an obvious change. The interior wall was no longer cold, but actually slightly warmer than the opposite wall with the professionally applied insulation. We no longer have a condensation problem anywhere in our living room. So this is a definitely improvement. I can't say how much heating energy it saves as that's almost impossible to measure, but it will mean that we require at least a little less heating.

Insulating the back door

The wooden panel under the window in the back door from our kitchen to the garage is the coldest spot in the whole house. As a result it attracts a lot of condensation in the winter and has to be kept clean, and we also lose quite a lot of heat through it even though it's a relatively small area. The door was on the list of things that I intended to replace, but when I came to look for a more efficient replacement I couldn't find one. No-one seems to sell doors like this with insulation inside them. There are plenty of front doors with insulation, but the back door options all have glass right down to floor level, which is not an advantage for us with dogs which will respond to birds or (worse) cats in the back garden. So I decided instead to try to insulate the door that we already have. It's the least expensive and the least disruptive way of insulating our back door.

For this job I made wooden boxes of nearly the width and height of the wooden panel on the door, one to install inside and the other outside. The outer shell of each box is 3 mm thick marine grade plywood while I used 1 cm square wood to make the box form.

Boxes under construction. Marine ply, one cm square section wood and wood glue.

Each box is filled with two layers of aluminized bubble-wrap material. This is not the best insulating material, but I could fit two layers in each box, so there are four layers in total. I also wanted to use a material which would form a moisture barrier and which should reflect some heat.

Two layers of aluminized bubble-wrap type material fit inside each of the boxes. That's four layers in total either side of the existing wooden door. Opinions seem to vary widely about how good an insulating material this is, but four layers of it will of course work better than one. In this case it was selected because it's clean to work with and I'll be able to easily remove these panels from the door if they turn out to be a problem for some reason.

Each panel is nailed in place, with a layer of sealant between the box and the existing door.

Plenty of nails to make sure that the sealant really does seal. I don't want moisture getting inside.

After fitting the inner and outer panels they were both painted to match the door.

Before and after. The existing door was not in perfect shape, but most of the damage is now under the new panel so it should be more resistant to the weather than it was before. We will see.

So now I wait to see how well this works. In the summer when the door is in full sun I've been able to measure a 10 C difference in temperature on the inside of the door between the outer part of the door not covered by the new panels and the inner part of the door which is covered so it must already be helping to reduce the temperature of our home during the summer months. I'll make measurements during winter and add them here.

I wouldn't have done this to a new door, but our door was showing its age already so I'm hoping this will extend its useful life. While there is no rotten wood (there was some on the inside but I fixed that problem several years ago) there were gaps between the panels into which rain could penetrate. I'm hoping that the new outdoor panel will stop this from occurring, but of course if rain gets inside the panel that could create a problem. It's an experiment.

As with the cavity insulation job, I don't think it will ever be possible to measure exactly how much energy is saved by insulating this door, but it should mean that we need a little less heat next winter. As the next job is to change the way we heat our home, this will be important.

A previous blog post covered other small insulation jobs.