What can I use to insulate the outside of my extension?
The extension was built over 40 years ago onto a stone built Edwardian house, the extension includes my kitchen, bathroom and utility room and has always been the coldest areas, I believe the extension was built using breeze block then covered with rough casting or harling, which is now starting to crack and fall off, I would appreciate any advice you can give me and who would I contact to complete such a task ? Thank you
The best way to insulate an older home is from the outside if you are able to. When choosing which insulation to use for energy efficiency upgrades like this you need to be careful about the products and thickness you choose so you don’t inadvertently trap moisture in walls. This page explains the issues and solutions in detail
How to insulate the exterior walls of a home from the outside
To help in your specific case, there area few things to know that could help us help you more-
Where you are located? Tell us the closest city or the climate zone you live in.
What is the current make up of the walls? Meaning – 2x4, 2x6, how much insulation if any, and if there is a vapor barrier.
The short story on choosing which insulation is best is that rigid foam insulation will act as a vapor barrier, which can trap moisture, but if it is thick enough it stops being a problem due to what is called the 2/3rds rule of insulation. You would always want at least 2/3rds of your insulation outside of the vapor barrier, that is why the thickness of the existing insulation as well as the thickness of the insulation you want to add matters. Unless you choose a breathable rigid insulation panel like mineral wool, which is sort of a failsafe material choice since moisture moves right through it without harming it, so your wall can continue to dry as needed. If you can install it thick enough, these foam panels have an interior rail for fastening them which avoids thermal bridging.
Thank you very much for your advice, I like the sound of the breathable mineral wool insulation, the nearest city to my home is Stirling in Scotland. As for what the current make up of the walls? Meaning – 2x4, 2x6, how much insulation if any, and if there is a vapor barrier, I don't know the answers sorry. Can you recommend a company near me who could do this work? Thank you.
Hi Roberta, given that you aren't sure about the current wall I think mineral wool is the right choice for you. Looking at the climate there I can see that your low temperatures are not that extreme, so I would add at least what building code requires for wall performance of new homes, and more would be better as thermal requirements in building codes denote a minimum amount, not the optium amount. Also important for preventing heat loss is to make it airtight, so if you are removing the siding you might want to put on a weather barrier to seal it if there is not one already. As for builders to do the work fo you, we are based out of Canada so I have no resources to offer you over there sorry!