Part L changes for 2014: here’s how they might affect you

Part L Building Regulations have been updated for 2014. Here’s our primer to keep you up to speed with the changes.

An introduction: what is Part L?

Part L is the section of the Government’s Building Regulations concerning the conservation of fuel and power. All new and rebuilt buildings, whether dwellings or non-dwellings, must comply with the specifications in Part L. This includes targets for insulation values, heating efficiency, hot water storage, air tightness and carbon emissions. It also sets out the requirements for SAP calculations, which result in an Energy Performance Certificate for the building (a mandatory requirement).

Each time Part L is updated, the targets for CO2 emissions become tighter. This means that all of the individual calculations affecting the emissions total must be carefully calibrated, to contribute to the energy efficiency of the whole building.

When was Part L updated?

Consultations for revised CO2 targets took place in 2013. The revised document comes into force on 6th April 2014, and is for use in England. If plans have been submitted for new builds before 6th April 2014, and work begins on site before that date, the 2010 Part L applies instead.

What are the changes?

The main changes from previous Part L regulations, for dwellings, are as follows:

  • Carbon Reductions – now 6% for domestic buildings and 9% for non-domestic buildings.
  • CO2 reduction target is now aggregate across building type – this means that the dwellings with the most fabric, such as detached houses, will be asked to reduce emissions by more than those with less fabric, such as mid-floor flats.
  • FEES, a new target to meet – this stands for Fabric Energy Efficiency Standard, and measures the energy demand of the dwelling.
  • The effects of heat gains in summer are now limited – calculations include heat from pipes, not just solar gains.
  • There is a new Notional Building in SAP, and a recipe approach for compliance – the parameters to follow to achieve compliance are published within Part L Section 5: Model Designs. The Notional Dwelling specifications look like this:
Element or System Values
External Walls 0.18 W/m2K
Party Walls 0.0 W/m2K
Floor 0.13 W/m2K
Roof 0.13 W/m2K
Windows, roof windows, glazed rooflights & glazed doors 1.4 W/m2K

g-value 0.63

Opaque doors 1.0 W/m2K
Semi-glazed doors 1.2 W/m2K
Air-tightness 5.0 m3/hr/m2
Linear Thermal Transmittance 1. If the thermal bridging in the actual dwelling has been specified by using the default y-value of 0.15 W/m²K, the thermal bridging is defined by y = 0.05 W/m²K.

2. Otherwise the thermal bridging allowance is calculated using the lengths of junctions in the actual dwelling and the psi values in Table R2 in of SAP 2012

Ventilation type Natural (with extract fans)
Air conditioning None
Heating system Mains gas, boiler (SEDBUK 2009 89.5% efficient) and radiators
Low energy lighting 100%
Thermal Mass Parameter Medium (TMP=250)

For existing domestic dwellings, target U-values remain unchanged.

The main changes from previous Part L regulations, for non-dwellings, are as follows:

  • 9% aggregate CO2 reduction – buildings with more fabric asked to do more than buildings with less. For example, a small warehouse must reduce CO2 by 3%, whereas the target for a hotel is 12%, and that for a shallow plan office is 13%.
  • There is a wider range of Notional Buildings – Side Lit or unlit (heating only); Side Lit or unlit (includes cooling); Top Lit.
  • Air tightness values vary by Gross Internal Area.

 How can I learn more?

The revised Part L documents can be found here, and can be downloaded. You can find out more about our assessment services on our website.

We’ll be updating our website with new guidelines soon. Until then, you can call or email us with any questions, on 01454317940, or


Welcome to a new member of our team!

AnnaAt Darren Evans Assessments, we are thrilled to welcome Anna Da Col to our team of sustainability experts.

Anna is a skilled and experienced sustainability consultant with a strong interest in both the theory and practical implementation of sustainable design. She graduated with a degree in architecture, and then obtained an MSc in Energy Efficient Buildings. Most recently she worked as Environmental Performance Manager at Stride Treglown, where she led a sustainability team which delivered over 60 assessments and gained her BREEAM Accredited Professional qualification. She has also worked as a Sustainability Consultant with the University of Bristol, Blaenau Gwent Borough County Council, Provelio, Sweets and Willmott Dixon.

Anna brings to our customers fifteen years of environmental and sustainable design skills, particularly in the area of BREEAM assessments. She is detail-oriented, highly organised and translates extensive theoretical expertise into sound practical advice.

She says:

I am pleased to be part of the team at Darren Evans!

I really enjoy the relaxed atmosphere and the variety of work that our services provide. Being involved in different areas of the business is a real step forward for me and I look forward to the daily challenges. I hope to be a positive addition to the team.

Welcome, Anna!

What do our customers say about us?


We know our comprehensive service is reliable and cost-effective. But the best testimonials come from those we’ve worked with. Here are just a few quotes from our customers: whether architects, property developers or private property owners, they recommend our services without hesitation!

“I have worked with Darren Evans Assessments on many occasions, and would like to say the service provided every time is fantastic. Not only do they do an incredible job of interpreting my business needs, they allow me to prepare my quotes without fuss and issue the work to the highest standards. I wouldn’t work with anyone else!”

Julia Martin-Woodbridge, sustainability consultant.

“After having my planning application refused for not conforming to the Government’s green strategy, I had to resubmit my application with a design that incorporated on-site renewable and low carbon energy development. After discussions with solar panel suppliers I found they were unable to offer me what I need to comply with planning: they could not calculate the effectiveness of the energy saving measures that I would be using, as they just used averages and base figures.

Darren Evans Assessments helped perfect my design by increasing my thermal efficiency in a few key areas so I was able to reduce my solar panels from 12 down to 4, which saved a lot of money: about ten times what I paid for the consultancy work.

I found their service fast, efficient and very easy to deal with. I will be using Darren Evans on my next project.”

Edward Baker, architect.

“Darren Evans Assessment’s in-depth knowledge helped us make the right choices leading to cost savings for our clients. I found DEA to be very pro-active and helpful. Their team provided a prompt and professional service for my client in support of a challenging planning application for change of use from office to residential. Darren Evans ensured that SAP calculations and a strategy for onsite sustainable energy production were in place to meet strict local authority requirements. I am grateful for their help and highly recommend their team.”

Julian Lowther, architect.

“I rang on a Friday to make an appointment for a representative from Darren Evans Assessments to do an Energy Performance Certificate on our property and was given an appointment on the following Monday.  I was able to pay for it by credit card over the telephone and Darren Evans Assessments emailed our Estate Agent immediately to confirm payment, so they could begin to market the property straight away.  The representative who did the assessment was polite, cheerful and friendly and the Certificate was emailed not only to me but also my Estate Agent within two hours – fantastic considering the property was in Gloucester and their office is in Chipping Sodbury!  I would highly recommend their services.”

Emma Herycz, home owner.

“I have consistently used the services of Darren Evans Assessments over the past five years, due to competitive pricing, proactive approach and prompt service. I occasionally check their prices against services offered by other SAP assessors, but have had poor experience from other companies in the field who do not have the same approach or professionalism.”

Paul Davies, architect.

“The ever increasing demands put upon agents and design technicians to comply with rigorous planning policies and building regulations can be sometimes daunting. Maintaining the loop of communication between clients, planners, building control and an array of agencies is eye-watering! Meeting time-scales and budgets are an additional knee-jerking experience. Specialist companies have evolved to relieve the plight of would-be sufferers and thankfully Darren Evans Assessments is one of them.

I have been relieved from the burden of a huge segment of mandatory regulations by their professional, efficient and friendly service, in addition to which their prompt response to requests is no less than impressive. They have applied a helpful ear to my tones of ignorance, addressing issues by reply within minutes – not hours and not days!”

Derek Tomley, architect.

“I found the service of Darren Evans Assessments to be very efficient and professional and would not hesitate to recommend them.”

Pamela Roberts, home owner.

“Darren Evans Assessment’s in-depth knowledge helped us make the right choices leading to cost saving for our clients. I found them to be very pro-active and helpful.”

Alözie Nwankwö, architect.

“Darren Evans Assessments were very easy to liaise and work with. They were very quick and efficient when responding to queries and obtaining certificates. They were very knowledgeable and resourceful for any queries raised and advice given, and were very organised as a company. I would work with DEA again and would recommend them to others. They are friendly, easy to use, cost-efficient and come up with quick solutions. In particular, they made our lives simple by being very organised and providing a tracking update when required.”

Gita Tandon-Giles, design manager.

“‘Free’ or cheap SAP calculations are not always value-for-money. I think our recent collaboration has proven that your services will be very useful to us in the future to keep us on top of specifications and show us how best to meet the ever-changing requirements.”

Scott Edwards, sales and commercial manager.

We are pleased and proud to work with such a wide range of companies and customers. We’ll always strive to provide the very best service from beginning to end – hassle-free.

If you’d like to know more, please contact us on 01454 317940, or

Letters have been slightly edited for clarity.