Loft Insulation

At the time of writing the methodology for EPC assessments of existing dwellings is RDSAP 9.94. The much anticipated RDSAP 10 update has not happened yet and a significant methodology overhaul from RDSAP to the Hone Energy Model (HEM) is proposed for 2025.

For a typical property with a pitched roof, and access to the loft, we measure the depth of the loft insulation as part of the EPC assessment.

Mineral wool insulation is usually laid between and over the loft joists and generally speaking, the greater the depth of this insulation, the better the EPC rating can be.

The aim therefore would be to increase the level of your loft insulation but the gains will eventually plateau, and beyond a certain level will not be worthwhile implementing if your single goal is an improvement in EPC rating.

Building regulations have changed significantly over the years. Back in the 1960s, loft insulation wasn't originally fitted, but more recently this is seen as a standard insulation measure required to improve the energy performance of existing dwellings.

Modern building regulations are now quite tight and new properties have significant insulation installed by default.

Fitting additional insulation in the loft of older properties is not too difficult or costly and with some research, due diligence and care could be achieved as a DIY project, so this is a reasonably attainable step.

We have a worked example below that indicates the effect on EPC rating for an example mid-terraced property using different levels of loft insulation. The results are quite interesting, but the gains become smaller as the insulation depth is further increased.

As we mentioned previously when considering Low Energy Lighting however, any small increase could be enough in some cases to take you up a band if you are near a threshold, particularly when combined with other improvements.

The design of the property can make a difference to the potential gains, so as I've mentioned elsewhere, do check with a local Domestic Energy Assessor to see what improvement would be achieved with your property before committing yourself to any expenditure.

The EPC methodology will generally add a recommendation to your EPC certificate to increase the depth of loft insulation if you only have 150mm or less present. It will recomend you increase the insulation to 270mm.

The assessment system however does allows us to enter greater depths than that, so don't necessarily feel limited by the figure of 270mm. This recomendation however will only be displayed if the system deems the rating improvement provided is more than a certain number of points.

If I take the example of my own house, which is a 1950s 3-bed terraced house and which I've described in a bit more detail in our Case Study 2 page, here is a table of increasing loft insulation depths and the EPC rating that I would achieve in each case.

Currently I have 200mm deep insulation between the joists and my EPC rating is a 68D which is on the top of band D, just one point from moving up to a band C.

I'm therefore interested in any measure that could give me a one point improvement in EPC rating:

The EPC rating on your property will vary differently to the way mine does, so don't necessarily read improvements in value from the table above and try to overlay them on yours.

Your property might be a bungalow for example which has a greater ground footprint versus volume ratio compared to a house.

However, what's interesting to see is how the EPC rating improves significantly as insulation is initially added, but then the gains reach a plateau as the depth is increased further.

I have 200mm at the moment, and I probably won't increase it further because my EPC rating won't increase with this one measure on it's own.

For my house, the increase in insulation level above 200mm probably does make a fractional difference but its not enough for the rounded integer value of the rating to incrase beyond my existing rating of 68.

Be mindful. There are many properties where owners have placed items, or even doors or boards down flat, directly on top of the loft insulation, flattening it down on top of the loft joists and reducing the depth to 100mm (the depth of the joist).

We do have the ability to calculate a weighted average across the whole of the loft when assessing the overall depth of the insulation, but the recorded depth will always be lower than when originally fitted, and will likely reduce the EPC rating.

If you want to use your loft for storage, it is much better to install plastic loft legs and screw boards flat on top of the legs. Items can then be placed on top of the boards, the insulation will not be compressed, and we can record the full depth of the insulation, so long as we can ascertain the depth is consistent across the whole of the loft - this may require the owner to lift boards as necessary for the assessor to be convinced.

There are many companies that actively advertise the installation of spray foam insulation in pitched roofs.

This foam is sprayed into place between the rafters in pitched roofs (Rafters are the angled lengths of wood that follow the pitch of the roof and meet at the peak. In contrast, joists are the horizontal wood beams on the 'floor' of the pitched roof).

There are many reasons why spray foam should not be installed and here is a link to a really good video explaining why this type of 'insulation' is a bad idea:

https://youtu.be/4gfc2l7Se5w?si=RqLT8j-XvxNeqhE9

(What's the fuss about spray foam? - West One Surveyors)

If you have spray foam installed, then even if you ignore the physical issues that can arise from it, you'll eventually find it very difficult to sell your property because mortgage lenders really do not like this material installed. A valuation survey instructed by a buyer's lender will usually report a property's value as zero.

You will probably find yourself needing to have spray foam removed before being able to sell your property in the normal way, or having to sell the property at auction instead.

We've so far only considered standard pitched roofs. We'll update this page shortly to also consider other types of roof, including:

• Sloping/Vaulted Roofs
• Room-In-Roof Roofs
• Mansard Roofs
• Any Documentary Evidence Required

As always, consult with a Domestic Energy Assessor before deciding what improvements to make to your property to improve the EPC rating.

Click here to return to our 'Improve Your EPC' main page, and see if there is another way you could improve your EPC rating.