“The leakiest housing stock in Europe”. It is a refrain we have heard frequently in recent years. So what to do about it? 

One of the problems we have with retrofitting buildings is that we tend to opt for the easiest solution rather than the optimal solution. If we are living in our home, and assuming we are on a budget, we wouldn’t choose to move out during renovation works due to the added costs involved.  

So, if someone offers to fit cavity wall insulation into our walls, with a generous Government grant to boot, we’ll likely choose this over a different solution. Unfortunately, some poorly designed methods and materials used to retro-fit cavity wall insulation have resulted in problems with damp. 

What about internal wall insulation? Well that clearly involves some disruption. And you do lose a certain amount of internal room space. These two factors are enough to put off a lot of people. 

Let’s meet Mr Riley’s house 

Mr Riley lives in a 1930s semi-detached house in Bristol. Like most 1930s houses, his house has solid exterior walls. The standard U-Value for 228 mm thick brick walls with plaster is 2.11 W/(m²K).  

His living room benefits from an extension constructed in the 1960s. There are no plans of the extension, and the exterior walls are covered with render, which makes it difficult to determine the construction method. But judging by the thickness of the rear elevation wall, we can expect it to be 2x 102mm bricks with a 50mm cavity. The standard U-Value for this type of construction is 1.25 W/(m²K).  

Mr Riley was doing a refurbishment of his kitchen, which included opening up one internal wall to create an open plan dining-living room.  

“We were doing quite a bit of work, so we thought we’d take this opportunity to make the house a bit warmer. Our back room was previously quite chilly.” 

Mr Riley

Mr Riley chose to add internal insulation to the room. He used insulated plasterboard which comes with 50mm insulation already attached. There are a variety of thicknesses of insulated plasterboard available, ranging from 25mm through to almost 100mm. 

“The 50mm version offered excellent insulation properties without reducing the room size by too much. In fact, now that the work is done no one notices that the room has shrunk ever so slightly.” 

The U-Value for a 228mm solid brick wall with 50mm internal insulation is 0.3 W/(m²K), whilst the 1960s extension is slightly better at 0.28 W/(m²K). Not only has this dramatically improved the thermal properties of the wall, it has almost brought it up to the standards required of the 2022 Building Regulations in England, which is targeting 0.26 W/(m²K).   

If the 92.5mm Kingspan Kooltherm version used, the wall would be as low as 0.2 W/(m²K).

For reference, a Passive Haus external wall is targeting 0.1 W/(m²K).   

So what? 

Overall, adding internal insulation was a big job, but in the context of a kitchen refit and having a wall knocked down, not that big! If you were planning to redecorate a room, that would be the perfect time to have internal insulation added. The process is really quite easy, with the insulated plasterboard adhered to the wall, and then skimmed with plaster over the top. There will be a little bit of fiddling with the electric sockets and light switches, but again, not a big job. 

So, does Mr Riley think it was worth it? 

“Of course. Our back room is now the warmest in the house. We are actually considering what element of the fabric of the house we can upgrade next. We have the insulation bug!” 

Mr Riley