What should you do when fitting roof insulation to pass the new BREL report in the updated Part L 2021

The updated Part L 2021, that comes into force in June 2022, states that ‘gaps in insulation can have a significant impact on heat loss and thermal bypass and create a risk of condensation and mould’ So, when you fit roof insulation, the BREL report is looking for insulation to be installed ‘tight to the structure, without air gaps’ and it should ‘extend to the wall insulation’

The energy assessor and building control will see the BREL report and will look at the photographic evidence that insulation in the foundations/substructure and ground floor; external walls; roof and around openings has been installed correctly. If it is not and the insulation has already been covered up then it’s going to be a costly and frustrating exercise to strip the build back and rectify the errors.

In this blog we will just focus on roof insulation and we will start with insulating at ceiling level.

How do I insulate to ‘BREL standard’ at ceiling level?

When insulating at ceiling level with mineral fibre, getting a ‘BREL standard’ installation is relatively straightforward. As the insulation is flexible and, as long as you have cut it reasonably straight and to the right size, it can be pushed between the joists and it will fit snugly without any gaps. A secondary layer over the top to get to the required insulation thickness and U-value will be equally easy to fit, as the edges of the rolls if butted together correctly, will tend to mesh together and leave little opportunity for gaps to be left in place. 

It is unclear at the moment at what stages photographic evidence will be required, however, in the case of ceiling level insulation, using rolls of mineral fibre, it would make sense to photograph the first fit between the joists followed by one once the full depth of insulation has been achieved.

Part L says that at ceiling level that the ‘long term protection of the insulation layer should be considered: boarded areas should be provided above the insulation to give access for maintenance’. It would seem likely for evidence to be provided to show that any boarded areas are not compressing the insulation, as this will compromise its thermal performance.

How do I insulate to ‘BREL Standard’ at rafter level?

This is by no means as simple as at ceiling level, especially when using rigid insulation boards. They are, by their very nature, not flexible and using the traditional friction fitted method will require very careful measurements to account for any deviations in the rafters before cutting the boards to size. Once cut and pushed carefully into position, any gaps between insulation and rafters will need to be rectified either by re-fitting, or using a suitable gap filler.

How do I sort out any gaps in the insulation between rafters?

Part L gives advice on what to do about gaps between insulation boards:

Any unavoidable gaps between boards should be infilled using compressible tape (e.g. for boards within roof rafters) or low expansion foam (e.g. boards within wall cavities). 

However, this doesn’t say how to deal with gaps between insulation and the structure – in this case the wooden rafters. It will be interesting to see the view of Building Control on use of spray foam in these circumstances. 

How much spray foam will it take before the job is considered not to be able to demonstrate ‘thermal continuity and quality of insulation’? Building Control may view excessive spray foam as an indication of poorly fitted boards and require further inspection and potential stripping off of plasterboards.

This adds one more headache to the job of friction-fitting insulation, however, with the launch of Insulfix Track there is now a new way to ensure insulation between rafters is fitted in line with BREL requirements as it can:

•    Minimise gaps
•    Maximise air tightness 
•    Lock in the performance and demonstrate thermal continuity

This brand-new construction product has BBA Certification and has been tested by the  BECCI project at Wolverhampton University to show that it gives superior air tightness and thermal performance when compared to the traditional friction fitting method.

The BREL report was introduced to help to close the Performance Gap by showing that work complies with energy efficiency requirements. We believe that Insulfix Track is the best way to ensure you produce ‘BREL standard’ installations every time.

If that wasn’t enough ,it saves insulation board and reduces waste and, as highlighted in the BECCI report, has a payback time of just 3.7 years. Although sadly, given the rising prices of energy that payback time will be getting shorter all the time.

If you would like more information about Insulfix Track please contact us and we would be happy to have a chat.