Building Regs U Values

2021 edition incorporating 2023 amendments – for use in England

These updates are designed to improve the energy efficiency of buildings and reduce their carbon footprint.

According to the updated Part L documents, the U values for new builds will be as follows:

Roofs: 0.11 W/m²K
Walls: 0.18 W/m²K
Floors: 0.13 W/m²K

For new elements in existing dwellings, the U values will be:

Roofs: 0.15 W/m²K
Walls: 0.18 W/m²K
Floors: 0.18 W/m²K

For existing elements in existing dwellings, the limiting U values will be:

Roofs: 0.16 W/m²K
Walls: 0.30 W/m²K
Floors: 0.25 W/m²K

It is important for builders and contractors to be aware of these updated U values and ensure that they are met in order to comply with building regulations. Improving the U values of a building can result in energy savings, improved comfort, and a lower carbon footprint.

Approved Document L, Conservation of fuel and power, Volume 1: Dwellings, 2021 edition incorporating 2023 amendments

Table 1.1 Summary of Notional Dwelling Specification for New Dwelling
Element or system	Reference value for target setting
Opening areas (windows, roof windows, rooflights and doors)	Same as for actual dwelling not exceeding a total area of openings of 25% of total floor area
External walls including semi-exposed walls	U = 0.18 W/(m²·K)
Party walls	U = 0
Floors	U = 0.13 W/(m²·K)
Roofs	U = 0.11 W/(m²·K)
Opaque door (less than 30% glazed area)	U = 1.0 W/(m²·K)
Semi-glazed door (30–60% glazed area)	U = 1.0 W/(m²·K)
Windows and glazed doors with greater than 60% glazed area	U = 1.2 W/(m²·K) Frame factor = 0.7
Roof windows	U = 1.2 W/(m²·K), when in vertical position
Rooflights	U = 1.7 W/(m²·K), when in horizontal position
Ventilation system	Natural ventilation with intermittent extract fans
Air permeability	5 m³/(h·m²) at 50 Pa
Main heating fuel (space and water)	Mains gas
Heating system	Boiler and radiators Central heating pump 2013 or later, in heated space Design flow temperature = 55 °C
Boiler	Efficiency, SEDBUK 2009 = 89.5%
Heating system controls	Boiler interlock, ErP Class V Either: - single storey dwelling in which the living area is greater than 70% of the total floor area: programmer and room thermostat - any other dwelling: time and temperature zone control, thermostatic radiator valves
Hot water system	Heated by boiler (regular or combi as above) Separate time control for space and water heating
Wastewater heat recovery (WWHR)	All showers connected to WWHR, including showers over baths Instantaneous WWHR with 36% recovery efficiency utilisation of 0.98
Hot water cylinder	If cylinder, declared loss factor = 0.85 × (0.2 + 0.051 √V²) kWh/day where V is the volume of the cylinder in litres
Lighting	Fixed lighting capacity (lm) = 185 × total floor area Efficacy of all fixed lighting = 80 lm/W
Air conditioning	None
Photovoltaic (PV) system	For houses: kWp = 40% of ground floor area, including unheated spaces / 6.5 For flats: kWp = 40% of dwelling floor area / (6.5 × number of storeys in block) System facing south-east or south-west

Table 4.2 Limiting U-values for New Fabric Elements in Existing Dwellings
Element type	Maximum U-value (W/(m²·K))
Roof	0.15
Wall	0.18
Floor	0.18
Swimming pool basin	0.25
Window	1.4 or Window Energy Rating Band B minimum
Rooflight	2.2
Doors with >60% of internal face glazed	1.4 or Doorset Energy Rating Band C minimum
Other doors	1.4 or Doorset Energy Rating Band B minimum

NOTES:

1. Area-weighted average values, except for windows, doors, roof windows and rooflights.

2. For dormer windows, ‘roof’ includes the roof parts of the windows and ‘wall’ includes the wall parts (cheeks).

3. If meeting such a standard would reduce the internal floor area of the room bounded by the wall by more than 5%, a lesser provision may be appropriate.

4. If meeting such a standard would create significant problems in relation to adjoining floor levels, a lesser provision may be appropriate.

5. The U-value of the floor of an extension may be calculated using the exposed perimeter and floor area of the whole enlarged dwelling.

6. The U-value of a swimming pool basin (walls and floor) calculated according to BS EN ISO 13370.

7. If other performance (e.g. wind load, safety, security or acoustic attenuation) requires thicker glass to be used, an equivalent window unit with standard thickness (6mm) glazing should be shown to meet the required standard.

8. Including roof windows and curtain walling.

9. For timber windows, a maximum U-value of 1.6 W/(m²·K) or Window Energy Rating Band C is permissible until 14 June 2023. From 15 June 2023 the full standard of 1.4 W/(m²·K) or Window Energy Rating Band B applies.

10. The methods for calculating Window Energy Rating and Doorset Energy Rating are set out in the Glass and Glazing Federation’s Glazing Manual Data Sheet 2.3, Guide to the Calculation of Energy Ratings for Windows, Roof Windows and Doors.

11. U-values for rooflights or rooflight-and-kerb assemblies should be based on the outer developed surface area, which is often greater than the area of the roof opening. Further guidance on U-values is given in the Building Research Establishment’s BR 443 and the National Association of Rooflight Manufacturers’ Technical Document NTD02.

12. The limiting value for rooflights also applies to kerbs that are supplied as part of a single rooflight-and-kerb assembly sourced from the same supplier and for which the supplier can provide a combined U-value for the unit. An upstand built on site should have a maximum U-value of 0.35 W/(m²·K).

13. For timber doors, a maximum U-value of 1.8 W/(m²·K) or Doorset Energy Rating Band E is permissible until 14 June 2023. From 15 June 2023 the full standard of 1.4 W/(m²·K) applies.

14. For internal fire doorsets, as defined in Appendix A of Approved Document B, Volume 1, a maximum U-value of 1.8 W/(m²·K) is permissible.

Table 4.3 Limiting U-values for Existing Elements in Existing Dwellings
Element	U-value(a) Threshold W/(m²·K)	U-value(b) Improved W/(m²·K)
Roof	0.35	0.16
Wall – cavity insulation	0.70	0.55
Wall – internal or external insulation	0.70	0.30
Floor	0.70	0.25

NOTES:

1. Area-weighted average values.

2. For dormer windows, ‘roof’ includes the roof parts of the windows and ‘wall’ includes the wall parts (cheeks).

3. If meeting such a standard would limit head room, a lesser standard may be appropriate. In such cases, both of the following should be achieved.
a. The depth of the insulation plus any required air gap should be at least to the depth of the rafters.
b. The insulant should be chosen to achieve the lowest practicable U-value.

4. If there are problems with the load-bearing capacity of the frame or height of the upstand, for a flat roof or roof with integral insulation, a lesser standard may be appropriate.

5. This applies only to a wall that is suitable for cavity insulation. Where this is not the case, it should be treated as ‘wall – internal or external insulation’.

6. If meeting such a standard would reduce the internal floor area of the room bounded by the wall by more than 5%, a lesser standard may be appropriate.

7. The U-value of the floor of an extension may be calculated using the exposed perimeter and floor area of the whole enlarged dwelling.

8. If meeting such a standard would create significant problems in relation to adjoining floor levels, a lesser standard may be appropriate.

Ref Link - The Building Regulations 2010 (2021 edition incorporating 2023 amendments – for use in England)

I. Introduction

Building regulations in the UK dictate standards for the construction and alteration of buildings in order to ensure the safety, health, and welfare of occupants. One important aspect of building regulations is the requirement for certain U values, which measure the heat loss through building elements such as walls, windows, and roofs. In this blog post, we will delve into what U values are, how they are calculated and regulated in the UK, and ways to improve U values in existing buildings. By understanding and optimising U values, builders and homeowners can improve the energy efficiency and comfort of their properties, ultimately saving money on heating and cooling costs and reducing their carbon footprint.

II. What are U values?

U values, also known as thermal transmittance or insulation values, measure the rate of heat loss through a building element. They are expressed in units of watts per square metre per degree Celsius (W/m²K) and represent the amount of heat that is transferred through a building element over a given area for a temperature difference of 1°C. In other words, the lower the U value, the better the insulation of the building element and the less heat is lost.

U values are an important consideration in building design and construction, as they can significantly impact the energy efficiency and comfort of a building. Poor insulation can result in high heating and cooling costs, drafts, and temperature fluctuations, whereas well-insulated buildings are more energy efficient and comfortable to live in.

U values can be calculated for various building elements, including walls, floors, roofs, windows, and doors. The U value of a building element is determined by its material, thickness, and any additional insulation or coatings applied to it. For example, a thick brick wall with insulation will have a lower U value than a thin wooden wall without insulation. It is important to ensure that all building elements meet the required U values as stipulated by building regulations.

III. Building Regulations in the UK

In the UK, building regulations set out standards for the construction and alteration of buildings to ensure their safety, health, and welfare. These standards apply to new builds, as well as renovations and extensions to existing buildings.

One aspect of building regulations that is relevant to U values is the requirement for energy efficiency. Building regulations in the UK require that new builds and renovations meet certain energy efficiency standards, including U values for various building elements. These standards are regularly updated to reflect advances in energy efficiency technology and techniques.

To ensure compliance with building regulations, builders and contractors must calculate the U values of all building elements and provide evidence of their compliance. This can be done using specialised software or by consulting tables of U values for common building materials.

Enforcement of building regulations is carried out by local authorities, which have the power to carry out inspections and issue fines for non-compliance. It is important for builders and contractors to ensure that their work meets the required U values to avoid any potential penalties.

In addition to ensuring compliance with building regulations, optimising U values can have long-term financial and environmental benefits. Energy efficient buildings are cheaper to heat and cool, which can save homeowners money on energy bills. They also have a lower carbon footprint, making them more sustainable and environmentally friendly.

IV. Improving U values in existing buildings

If you own an existing building that does not meet the current U value requirements, there are several techniques you can use to improve its energy efficiency and reduce heat loss. Some options for improving U values in existing buildings include:

Adding insulation: Insulation is one of the most effective ways to improve U values and reduce heat loss. It can be added to the walls, floors, and roof of a building to increase its insulation properties. There are various types of insulation available, including fiberglass, foam, and mineral wool, each with its own pros and cons.
Double glazing: Replacing single-paned windows with double-glazed windows can significantly improve the U value of windows. Double-glazed windows have two panes of glass separated by a layer of air or gas, which acts as insulation to reduce heat loss.
Upgrading doors: Replacing old doors with newer, more insulated models can also improve the U value of a building. Look for doors with a high R-value, which measures the resistance of a material to heat flow.
Draught-proofing: Simple measures like sealing gaps around windows and doors can significantly reduce drafts and heat loss. This can be done with weatherstripping, sealant, or draught excluders.

Before embarking on any improvements, it is important to conduct a cost-benefit analysis to determine the financial and environmental benefits of upgrading U values. While some improvements may have a high upfront cost, they may result in long-term savings on energy bills and a reduction in your carbon footprint.

V. Conclusion

In conclusion, U values are an important factor in building regulations for energy efficiency and comfort. They measure the heat loss through building elements and lower U values mean better insulation and less heat loss. Building regulations in the UK dictate U values for new builds and renovations, and builders and contractors must ensure compliance to avoid penalties. Improving U values in existing buildings can have long-term financial and environmental benefits, such as reduced energy bills and a lower carbon footprint. Techniques for improving U values include adding insulation, double glazing, upgrading doors, and draught-proofing. By understanding and optimising U values, builders and homeowners can create more energy efficient and comfortable buildings.