Steel and the Practical Impact of Changes to Part L1A & Part F

The impending changes to Part L1A and Part F of the Building Regulations for new dwellings will increase energy efficiency requirements for new homes. Trevor Richards, Operations Director of offsite experts Cogent, discusses the potential implications for lightweight structural solutions.

The impending Future Homes Standard requires that newbuild homes be future-proofed with low carbon heating and world-leading levels of energy efficiency. But have you started to consider the practical effect of the imminent changes to Part L1A and Part F on your product design or system solution? 

The ‘Fabric First’ approach of the current Part L1A can now be considered a given, and the proposed change in metrics to SAP, with the introduction of the Design Primary Energy Rate (DPER) and Target Primary Energy Rate (TPER) – create a new set of challenges to achieving compliance. 

These changes are more than simply improved U-Values, reduced thermal bridging, reduced air-permeability – all challenges that offsite technology can clearly overcome. In fact, many have seen these changes as a way to promote a competitive advantage for offsite technology. The superior build quality and the consistency of the delivered ‘as-built performance’ achieved through factory manufactured solutions is the mantra for the offsite sector and this will continue to be a key part of the ‘conversion rationale’ for those promoting offsite technologies as a fundamentally better way to build. However, the proposed changes to Part L1A and Part F considers the home’s energy package, and the first indications from the available ‘beta’ SAP software, which Cogent has been trialling on a range of offsite system developments since the end of 2019, indicate those lightweight structural offsite technologies that have an integral lack of thermal mass, would appear to be presented a greater challenge.

The proposed changes are giving further clarity on the issues of security (ground floor dwellings) and noise (all dwellings), and the interpretation of how ‘open’ a window can be, and when ‘opening’ a window is allowable more clearly defined. For over-heating and cooling, which is already an issue for the current Part L1A particularly in bungalows and ground floor flats, this will present a potential problem where the structure does not provide sufficient thermal mass. 

Within SAP calculations, thermal mass aids the heating and cooling performance. Thermal mass is determined for SAP by the first 100mm of a structure from the internal face (i.e. from inside to outside) or when an insulation is met - whichever occurs first. 

At Cogent, we are currently working on a series of low-rise and high-rise structural offsite manufactured technologies for the residential sector and futureproofing is a fundamental part of any good design process. Working with the currently available ‘beta’ SAP software from Elmhurst Energy to model the effect of the two options proposed for the changes to Part L1A and Part F, it is evident that there is an underlying issue for low-rise solutions in particular from the proposed changes. In short, for certain systems and applications there is a lack of thermal mass in a number of the mature offsite technology system designs. 

What does this mean? For most it could well mean that more thermal mass needs to be added to the structure to make it future SAP compliant. However, more mass is likely to mean more material, more labour, more weight, and in the case of external walls, ‘thicker’ elements, meaning either a greater external footprint, or a loss of internal floor area. Alternatively, it could mean the requirement to introduce and enhanced MVHR system into the home. Or it could mean both. 

Alternatively, it could mean a product redesign and re-validation under the new performance requirements. The Future Homes Standard might act as a stimulus to evolve the product design along a new route to establish new solutions – effectively ‘taking the product back to formula’, or considering new material choices, such as phase change materials. 

This might sound like a radical suggestion, but in an ever increasingly competitive environment where offsite manufactured technologies already work with the handicap of a greater upfront capital cost (in most instances), will the market afford you the solution of additional layers of material content to your product, that is not necessarily providing value!? Only time will tell and no doubt ‘necessity will remain the mother of invention’ so we will see some fantastic next-generation offsite technologies emerge to rise to the challenge. 

The changes to Part L1A and Part F are not finalised, and nor is the SAP software, but if you have not yet started to consider the practical effect of the imminent changes to Part L1A and Part F on your product design/system solution, then the advice is you should start now! This is a complex challenge and one that will need to be addressed head on.


Cogent Consulting

Cogent Consulting is a leading multi-disciplinary consultancy specialising in the field of offsite construction and manufacturing - offering independent advice on successfully exploiting innovative construction processes. Through our unparalleled range of skills, we can help you to manage practical issues of developing and deploying offsite construction systems and processes to dramatically improve project delivery performance. If you would like to find out how the offsite experts at Cogent Consulting can assist with the proposed Building Regulation changes to Part L1A and Part F then visit: www.cogent-consulting.co.uk or call 01743 290010 

 

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