I'm a builder and this is the trouble with Part L of the Building Regulations

A picture of Andy Stevens
(Image credit: Andy Stevens)

Building regulations are important when working on a property — they’re there to make sure you build it to the most up-to-date standards and laws. If you fail to follow the latest regulations, the building inspector can ask you to take down work and ultimately refuse to sign it off with a completion certificate. 

For this reason, it’s important to be aware of any updates and amendments of regulations. One particular update that will affect self builders is the change to Building Regulations Part L that came into force on 15 June 2023. 

I’ll explain more about this below but rather than delve into the specifics of these changes to Part L, I’ll concentrate more on how it’s likely to affect self-builders and renovators. 

What are Part L Building Regulations?

The government has committed to delivering zero carbon homes by 2025 and the government website describes Part L as building regulations in England setting standards for the energy performance of new and existing buildings. Building Regulations Part L is split into several documents, which cover different areas: 

Approved Document Part L1A: Covers the requirements for new homes to be energy efficient, and individuals responsible for building work must ensure that the homes comply with the requirements provided within this document.

Approved Document Part L1B: Covers the requirements for renovations and extensions to existing homes to be energy efficient. It recognises that it is not always possible to meet new-build standards, but the regulations state that if a thermal element (roof, wall or floor) is being replaced or renovated then it must be done to Part L1A standard.

Approved Document L2A: Covers the required energy standards during construction of new commercial buildings, and Approved Document L2B covers existing buildings other than dwellings. 

black cladding and tiles on exterior of self build

The changes to Part L require new homes to have greater insulation and a new target primary energy rate. (Image credit: Emmaluelis Stasaitis c/o Edgley Design)

What are the changes to Part L?

In December 2021 the government announced that from June 2022 several new building regulation changes would affect those who are self building, renovating a house, adding an extension or taking on home improvements. Here’s a brief summary of the key changes to Part L:

1) Changes for new homes 

New homes will now be assessed under a new Standard Assessment Procedure (SAP) calculation called SAP10. This involves greater insulation requirements and a new target primary energy rate, expressed as kWhPE/(m² per year). Self builders will be encouraged to meet ‘notional’ dwelling targets for energy efficiency. These are measured in U values: if you can meet the reference targets for elements and systems including party walls, floors, doors and roofs then your home will result in a pass with building control. 

Another new requirement is for self builders to conduct an on-site audit to confirm that the design details in your plans have been constructed, and photographs must be taken as evidence. Moreover, due to concerns over thermal bridging causing heat loss and condensation, the new regulations advise that “opportunities should be considered to use products that help to reduce thermal bridges”.

2) Changes for existing homes

If you’re looking to introduce new or replacement thermal elements to your home, such as new windows and doors, then minimum new fabric efficiency standards will now apply. The government has introduced a ‘full fabric specification’ for setting the level of the Fabric Energy Efficiency Standard (FEES). This means a tightening of U values.

Extensions will also be required to have no more than 25% floor area as glazing (windows, roof windows, rooflights), alternatively homeowners must be able to demonstrate compliance with an area-weighted U value calculation or via SAP — which can offer more freedom of design. 

Improvements are also required in lighting efficiency but perhaps the biggest challenge is the new low-flow temperatures for heating systems. The maximum flow temperatures in a central heating system is now 55°C where it was previously over 75°C. 

How do these changes impact self builders?

So how do us builders keep up with these changes? How about all the other regulations, which are also being updated and amended? The honest answer is, it is virtually impossible if you are a sole trader or run a small company. We are not just on site, we are pricing jobs, replying to customer’s emails, ordering materials, in builder’s merchants etc etc, the list goes on. 

The best way, I believe, is to read the summaries on these regulations and then speak to the building inspector. To me this is vitally important as they are the ones that will sign off the work, they stipulate what they are looking for. 

The frustrating thing is, depending on where you are in the country and who the building inspector is, regulations – and the implementation of them – vary. That is why I think it is best to keep the same building inspector from job to job. This may not be possible if you move out of the area you work in and use a local authority building control. If you use a private building control company, you can generally keep the same building inspector so you know what they want from job to job. 

In my opinion, I find it ridiculous that we have these updates and amendments to Building Regs, but different building inspectors ask for different things. Sometimes I’ve even had Building Regs drawings signed off by the council and once work starts the building inspector from the same council asks for different things on the build!

How to avoid missing more regulation changes

dark grey self build cladding with large garden

Stay in touch with your building inspector throughout the building or renovating process. (Image credit: Graham Gaunt)

As everyone is aware, changes do happen on builds and this can be due to supply issues, client’s instructions etc. When this happens, the project manager (which could be the homeowner) needs to clarify everything with building control before they implement these. 

For example, you may have changed some windows or doors with their positioning, size etc. It is worth a quick call to the building inspector to run these new specs past them. If the U values aren’t low enough, then they’ll ask you to change them. 

The same with insulation; the cost has risen dramatically since Covid so you may shop around for a cheaper option. Different manufacturers may charge less for the ‘same’ product, e.g. 4-inch PIR board, but their U values will most likely be different. This is something I have got wrong in the past – I went for a cheaper option but the U values were poorer and it was an expensive mistake. 

The key thing with this is to check with the building inspector throughout the build, before you install things. 

What constitutes 'commencement'?

The requirement is that work must have started on site by 15 June 2023, and according to the government, commencement of work would usually be marked by work such as:

  • Excavation for strip or trench foundations or for pad footings
  • Digging out and preparation of ground for raft foundations
  • Vibrofloatation (stone columns) piling, boring for piles or pile driving
  • Drainage work specific to the building(s) concerned.

Whereas the following sorts of work would not be deemed as commencing work:

  • Removal of vegetation
  • Demolition of any previous buildings on the site
  • Removal of top soil
  • Removal or treatment of contaminated soil
  • Excavation of trial holes
  • Dynamic compaction
  • General site servicing works (e.g. roadways) 

The trouble with Part L

In summary, if you are carrying out a renovation/extension or building a new home, you have to be on top of the Building Regulations and any updates. If you are project managing your own build, this may involve a lot of work, but work with your builder and their team, work with the architect who specced the Building Regs drawings and, most importantly, work with your building control officer as they are ultimately the ones that have the say on whether your work is acceptable or needs to come down. As I keep saying in these articles, preparation is key. 


As Andy outlines above, preparation is key. Stay on top of changes to Building Regs by swotting up on areas that might impact your build like our guides to building regulations for extensions and garage conversions

Andy Stevens

Andy Stevens is a multiple award-winning builder who manages Surrey-based building company Eclipse Property Solutions; he specialises in new builds, extensions and loft conversions. 

While he is still on the tools, he is also widely involved in the construction industry. He presents a show on Fix Radio and hosts his own building podcast Build:It, as well as being a speaker at the Homebuilding & Renovating Shows. 


Andy has sat on the Board of the Federation of Master Builders (London region) and was previously Vice President. He also works with construction charities and is an advocate for mental health in the industry.

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