solid wall insulation

With EPCs becoming ever more important for those with rental properties, we are taking a look at what exactly certain improvements can do to your EPC rating. It should help you understand which measures can make a big difference and which give only minimal value for your rating.

What is solid wall insulation?

Solid wall insulation is applied either internally or externally to the walls of a property in order to improve the thermal performance of the walls. It is typically used on properties with solid 9-inch brick walls, as opposed to cavity walls with a gap that can be insulated more easily.

This type of insulation is not cheap, often costing around £100 per square metre of wall, but it is extremely effective at bringing a property up to scratch thermally.

Improvement in the EPC rating with SWI

The improvement in your EPC rating will be directly proportional to the amount of exposed wall that is being insulated. So, if you have a mid-terraced house insulated front and back, the improvement is going to be much less than a detached house with all four sides insulated.

To give you an idea of the change you can expect, we’ll look at the example of a typical 100 year-old solid brick end-of-terrace house, with a current rating of F31. Adding thermal insulation to this property would bring the walls up to a U-value of 0.3, changing the property’s rating to D55. This was a huge improvement which ensured that the property now meets the new MEES standard for rentals. SWI would certainly make sense for this particular property.

How much does insulation thickness make a difference?

The first thing to point out here is that the insulation must bring the wall up to a U-value of 0.3 in order to meet building regulations. This is only really achievable on a 9-inch wall by adding 90mm of EPS, or 110mm of Rockwool. You can go above and beyond this level of insulation, but putting any less could mean you fall foul of building regulations.

Let’s take a look at a few scenarios based on thickness of insulation:

We took the same end of terraced mentioned in the scenario earlier and added some more insulation. As you may have worked out, by insulating with 100mm of insulation, the energy rating leapt by 24 points, which is a huge leap in efficiency. By adding an extra 50mm of insulation (taking the U-value to 0.22), the rating only increased by 1 extra point, to a D56. That is a lot of extra insulation for very little reward. Going up to 200mm insulation, (and a U-value of 0.16), the rating increases 1 more point to D57.

What does this mean for the benefit of SWI?

As we can see, solid wall insulation can be a great way to improve an EPC rating. In this our example, it went up two levels from F to D. In some detached properties, the rating increase could be even more stark, up to 3 level increase, whereas in properties with less exposed wall there will be a more modest improvement.

Get a survey and recommendations report

We should point out that every house is different, and we highly recommend getting a scenario analysis of your options via one of our recommendations reports before committing to a specific improvement. You may end up just falling short of the required rating!