5 things roofing contractors need to know about the changes to Part L

2 June 2020 Building Innovation
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By the end of the year, updates are expected to be published to Part L of the Building Regulations in England and Wales. These changes are designed to raise the energy performance of properties and form part of the Government’s wider strategic commitment to achieving net-zero carbon emissions by 2050 (2045 in Scotland). In this blog, we’ll take a look at these changes and what they will mean when installing a roof.

What is Part L?

Part L sets the energy performance targets that all buildings in England and Wales have to meet. As control of the Building Regulations is devolved, the requirements are different in the two countries. Both countries also provide their own technical guidance handbooks – called Approved Document L – which explain how to keep your construction compliant with the regulations.
 

Which properties will be affected by the changes to Part L due this year?

The first properties to be impacted will be new homes. Both England and Wales ran consultations into changes to the Part L requirements for these properties which closed in the Spring. Work is underway to publish the final requirements before the end of the year (along with revised versions of Approved Document L1A). Further consultations are expected later in the year looking at the requirements for all other properties.
 

What are the key changes proposed in the Part L consultations?

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Each of the consultations proposed two improved options over existing carbon emission targets. In England, these were for further reductions of either 20% or 31% on existing Part L targets. The document states that the 31% option is its preferred solution. Wales set tougher targets of a 37% or 56% reduction although its consultation highlights the first option as its preference.
 
A new principal performance metric – Primary Energy – has also been added. This looks to calculate how much energy is used both running the property, and in getting its fuel source ready for use (i.e. refining and transporting oil).
 
Looking a little further ahead, the energy performance requirements for all new homes are expected to tighten again by the middle of the decade. In England, for example, homes are expected to need to have 75-80% less emissions than under current requirements. This means it is important to ensure roofs are well insulated.
 

What thermal performance (U-value) will roofs need to achieve under the new Part L?

The consultations set out clear worst case U-values which roofs on all new homes will need to meet.

These are 0.13 W/m2K in Wales and 0.16 W/m2K in England. It is highly recommended, however, that installers look to go above and beyond these minimum requirements. Roofs can act as a key source of heat loss on a property, and by insulating them correctly from the outset, it is possible to achieve significant energy and cost savings year-on-year. This is even more important with performance targets for existing homes also set to tighten over the coming years. By getting the envelope right from the start, you can allow customers to avoid costly insulation refurbishment work further down the line and ensure you are properly prepared for the future changes.

We would suggest adopting a U-value of 0.11 W/m2K which is the value proposed in the notional dwelling for both Welsh consultation options. By using Polyisocyanurate (PIR) insulation, which has a low thermal conductivity and is therefore a more effective insulant than hybrid alternatives which use materials such as mineral fibre, it is possible to keep the construction slim whilst hitting this target.
 
Building Innovation can work with you to develop a fully calculated tapered or flat roof scheme which meets both your requirements, and those of the Building Regulations/Standards.
 

Is there anything else to be aware of when installing insulation?

Aside from the thermal performance of each element, the consultations also tackled detailing when installing insulation. They recommended removing the Approved Construction Details (ACDs), the detailed drawings of junctions which can be used at present to estimate heat loss values for these areas.
 
Part of the reason for this is that poor detailing has been identified as a key contributing factor in the so called ‘performance gap’ between the estimated energy performance of a building and its actual performance. Rather than relying on standard set of details, therefore, the new requirements aim to encourage contractors to generate their own drawing for junctions to raise standards.
 
Building Innovation can support you at every stage from initial consultation to site delivery and can help to develop details to ensure the construction is well insulated and fully compliant with the new requirements.
 
If you have a flat or tapered roof project on the horizon and you need some advice, get in touch with our expert team. Thermal performance that’s calculated, not estimated.

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