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When do I need building regulations approval for renovating a thermal element?

Thermal element - building regulations part L

It can be difficult to determine when the renovation of a thermal element triggers the need for a building regulation application. Here we look at why the Regulation was introduced and how you can calculate when you need to submit an application.

Background

Homes in the UK contribute 27% of the UK total carbon emissions, and given that 85% of homes will still be standing in 2050 the need to upgrade the existing housing stock has never been more evident.

The route the government has gone down is to put regulation in place that provides for the upgrading of a thermal element when work is being carried out on the building. The government’s target is to cut carbon emissions by 60% by the year 2050.

Regulations centred around conservation of fuel and power are covered in Section 5 of Approved Document L1B which relates to the renovation or replacement of a thermal element and in particular Regulation 23. It's important to understand that this Regulation is about upgrading the existing housing stock when a renovation of an individual element or a major renovation takes place.

Building regulation 23 - renovation or replacement of thermal elements

Regulation 23, which is the mandatory part in the building regulations, provides that where work is being carried out to an individual thermal element and the amount of the renovation is more than 50% of the elements surface area.

Such work must be carried out to meet the requirements of L1(a)(i). Similarly, where a major renovation is undertaken that also needs to meet the requirement of L1(a)(i).

Clearly, before we can proceed we need to understand what constitutes a renovation or a major renovation. Clause 5.6A outlines the meaning of major renovations and means: the renovation of a building where more than 25% of the surface are of the building envelope undergoes renovation where the whole of the building envelope (external walls, floor, roof, windows, doors, roof windows and rooflights) is taken into account.

A building envelope is defined as the physical separator between the conditioned and unconditioned environment of a building including the resistance to air, water, heat, light, and noise transfer.

Renovation on the other hand for the purposes of this regulation means:

Providing a new layer such as cladding or rendering to an external surface or dry-lining an internal surface which was not there before.

The replacement of an existing layer such as removing rendering or cladding on the walls, ground floor surfaces and roof tiling are all subject to requiring an upgrade in performance.
Mention is made in the Approved Document regarding replacing the water proof membrane on a flat roof which also constitutes a renovation, however, this requirement was removed by virtue of The Building (Amendment) Regulations 2011.

Where such work is undertaken then the performance of the thermal element needs to be improved. Table 3 gives a threshold U-value so any element which is worse than this threshold needs to be improved to the value given in the table (improved U-value) or better.

Table 3 - Upgrading retained thermal elements

The regulations provide that any work that is not technically and functionally feasible which cannot be achieved by simple payback within 15 years (guidance is given on how this is achieved) then the best standard that is technically and functionally feasible should be achieved.

It is worth considering the requirements for new thermal elements against the requirements for upgrading retained thermal elements, for instance new floors require a U-value of 0.22W/(m2.K), whereas, a lower value is acceptable when looking to the improved U-value requirements 0.25 W/(m2.K) and the same applies throughout the range of thermal elements.

Let us look at the 5% rule (Note 3 in Table 3).

This is covered in clause 5.12. What the regulations say is that if the thickness of insulation used might reduce the usable floor space or create difficulties with adjoining floor levels then a lessor provision than that given in Table 3 would be acceptable.

The worked examples below show how the percentages of a major and individual renovations are determined. Let us re-cap on the types of renovation and percentages as these can be confusing.

Major renovations consider all the surfaces between the conditioned and unconditioned environment to arrive at the percentage, whereas, when individual elements are being renovated it is only the surface of element between the conditioned and unconditioned space that is considered.

Worked example

Major renovation: Work is proposed to a semi-detached house 6m wide by 5m deep and 5m high (for simplicity we have kept to whole figures and ignored wall thickness). This gives a floor area of 30m2 and an elevation area of 85m2 ((6m + 6m + 5m) x 5m high). The roof area will depend on where the insulation is placed as this determines where the conditioned space is separated from the unconditioned environment. For this example we will assume it is at ceiling level so is the same as the floor area (30m2). If it was along the line of rafters then it would be slightly more.

If the total area of the building envelope is 145m2 (30m2 + 85m2 + 30m2) then 25% of this is 36.25m2 and any refurbishment over this figure would constitute a major refurbishment. 

Individual renovation: Consider that only the external end wall of the building is being renovated, this would have an area of 25m2 (5m x 5m), so if more than 12.5m2 (50%) of the area is removed or a new layer added then this would constitute a renovation and the regulations would apply. Similarly, if one wall of a room inside the building is renovated (looking at our building, say the end wall 2.5m deep and 2.5m high this would give an area of 6.25m2 so any surface removed or new layer over 3.125m2 would constitute an individual renovation.)

Using the dimensions given, we have a 30m2 floor area and an external perimeter of 16m. That means that 5% of the floor area would be 1.5m2 which over 16m equates to a dimension of 94mm of lost floor space. Therefore internal wall insulation of 100mm would exceed the 5% but a 65mm insulated plasterboard would not. Calculations would then be carried out to work out the simple payback within 15 years. This would be a comparison of the installation cost against the energy savings made by the proposed specification over the 15 years. Note that the installation cost is only for the additional insulation proposed and should not include the costs of plasterboard/plaster or the work to remove the original surface.

Appendix A in Approved Document L1B provides a list of cost effective U-value targets for a range of renovation works.   

This is covered in clause 5.12. What the regulations say is that if the thickness of insulation used might reduce the usable floor space or create difficulties with adjoining floor levels then a lessor provision than that given in Table 3 would be acceptable.

The worked examples below show how the percentages of a major and individual renovations are determined. Let us re-cap on the types of renovation and percentages as these can be confusing.

Major renovations consider all the surfaces between the conditioned and unconditioned environment to arrive at the percentage, whereas, when individual elements are being renovated it is only the surface of element between the conditioned and unconditioned space that is considered.

Worked example

Major Renovation: Work is proposed to a semi-detached house 6m wide by 5m deep and 5m high (for simplicity we have kept to whole figures and ignored wall thickness). This gives a floor area of 30m2 and an elevation area of 85m2 ((6m + 6m + 5m) x 5m high). The roof area will depend on where the insulation is placed as this determines where the conditioned space is separated from the unconditioned environment. For this example we will assume it is at ceiling level so is the same as the floor area (30m2). If it was along the line of rafters then it would be slightly more.

If the total area of the building envelope is 145m2 (30m2 + 85m2 + 30m2) then 25% of this is 36.25m2 and any refurbishment over this figure would constitute a major refurbishment. 

Individual Renovation: Consider that only the external end wall of the building is being renovated, this would have an area of 25m2 (5m x 5m), so if more than 12.5m2 (50%) of the area is removed or a new layer added then this would constitute a renovation and the regulations would apply. Similarly, if one wall of a room inside the building is renovated (looking at our building, say the end wall 2.5m deep and 2.5m high this would give an area of 6.25m2 so any surface removed or new layer over 3.125m2 would constitute an individual renovation.)

Using the dimensions given, we have a 30m2 floor area and an external perimeter of 16m. That means that 5% of the floor area would be 1.5m2 which over 16m equates to a dimension of 94mm of lost floor space. Therefore internal wall insulation of 100mm would exceed the 5% but a 65mm insulated plasterboard would not. Calculations would then be carried out to work out the simple payback within 15 years. This would be a comparison of the installation cost against the energy savings made by the proposed specification over the 15 years. Note that the installation cost is only for the additional insulation proposed and should not include the costs of plasterboard/plaster or the work to remove the original surface.

Appendix A in Approved Document L1B provides a list of cost effective U-value targets for a range of renovation works. 

Further information

Building regulations documents L1A, L2A, L1B and L2B England 

Building regulations documents L1A, L2A, L1B and L2B Wales

Upgrading historic buildings and the building regulations