With the price of gas and electricity rocketing, we are all looking for ways to reduce our energy bills. But what can you do once you’ve insulated the roof and sorted out those draughty windows? In more modern homes, you can add some cavity wall insulation. Not only will it reduce your bills, you may also need it if you want to install any kind of heat pump. More importantly, it could soon be essential for rental properties - from 2025, they will need to achieve a minimum EPC rating of C or it will be illegal to rent them out. The problem is, for the majority of properties built before the 1920s, the walls will be solid and there is no cavity to fill. Fortunately, there are a couple of alternatives.
One option is to use external wall insulation (EWI). This is essentially an insulating jacket on the outside of the house. The good thing about it is that it causes very little disruption to your domestic arrangements, as all the work happens on the exterior of the house. It is a very simple process - insulating material is fixed to the outer walls and you can then choose your covering finish, the most common of which is either render or timber boarding. There are some drawbacks - due to the extra layers, the outside dimensions of your house will change and that means you may have to adjust things. Window and door openings will be reduced and gutters and downpipes may need to be repositioned. The other main drawback is that it is not ideal for brick houses, period ones in particular, as the original finish will be covered over.
If you are thinking of having some EWI fitted, there is some debate as to whether or not it requires planning permission.
The safest thing to do is to check with your local planning authority first, especially if you live in a conservation area or your house is a listed building. The costs will vary greatly depending on the size and complexity of the job. As a rough guide, according to Checkatrade, it is around £100/sqm or £7,000 for a typical mid-terrace house and £20,000+ for a detached house. And don’t expect instant returns. Your heating bills will come down, but it is estimated that you may have to wait up to twenty years before you recover your costs.
The second option is to add some internal solid wall insulation. In this instance, insulating material is fixed to the surface of internal walls and then covered by a plaster finish. This is a much more invasive process and is likely to cause disruption in almost every room in the house and so is probably best done during a major renovation. Like EWI, it will alter the dimensions of your house, reducing room sizes by between 60mm and 100mm per external wall, which, for small rooms, can be a serious problem. Also, like EWI, it may require you to reposition things, such as light switches, sockets, and radiators. Another disadvantage is that it can cause condensation problems within the walls themselves. This is normally cured by using special plasterboard with a damp-proof membrane but if you subsequently fix any pictures or shelves to it, you will probably hammer a nail straight through the membrane.
The cost of internal solid wall insulation is half the price of EWI at approximately £50/sqm and will take up to ten years to pay off. It is, though, the only real option for period brick houses.
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