Thermal Regulations

Part L of the Building Regulations (Conservation of Fuel and Power) has recently been updated. The aim is to improve the thermal efficiency of new dwellings by around 20% on previous Part L (2002) requirements. The superior thermal properties of Airtec products offer simple, cost-effective solutions to help achieve thermal efficiency in buildings as outlined in Part L (2006). The Airtec range offers the best thermal properties for this class of product currently available in the UK and therefore gives the builder the opportunity of meeting U-Value targets with the minimum of cost and effort.
 
 

PART L OF THE BUILDING REGULATIONS

The energy consumption used to heat buildings accounts for a significantly large proportion of all carbon dioxide produced annually – current estimates are between 40% and 50%. Clearly therefore, there is a real need to reduce the amount of energy used to heat a building. The best way to do this is to improve the thermal insulation of the fabric of the building. Part L of the Building Regulations (Conservation of Fuel and Power) requires that buildings achieve sufficient thermal efficiency as a means to reduce the need for extra heating and therefore counter the growth in greenhouse gas emissions.
 
As such, construction elements such as external walls, roofs and floors are set maximum U-Values so that the entire building achieves the required level of thermal efficiency. Thermally efficient building materials can offer the best solutions to achieve required U-Values.
 

WHAT ARE THE REQUIRED U-VALUES NOW? WHAT IS A SAP RATING?

Part L 1A(2006) for New Dwellings has moved away from simple prescribed U-Values for the various components of the building into the performance of the building as a whole. This involves an in-depth set of methods and calculations to determine the CO2 Dwelling Emission Rate (DER) based on the actual fabric of the building in question. Factors such as windows, doors, boiler type, fuel, heating controls and lighting are taken into consideration in addition to the actual structural and insulation components.
 
The DER is then compared to the Target Emission Rate (TER); the TER being set by Building Regulations and is the maximum permissible emissions per dwelling per annum expressed in kg of CO2.   
If the DER is less than the TER, then the property complies.
 
SAP (Standard Assessment Procedure) is a calculation method whereby the DER and TER for the dwelling is produced and a SAP Rating given. This is used to give advice and guidance on how best to maximise efficiency. SAP 2005 is the latest version and is in line with Part L 2006 requirements.
 
To help the building achieve a lower DER, a set of guideline U-Values have been formulated for each component of the building. By meeting these U-Values, the chance of complying is greatly increased. These figures are shown opposite.
 

A NOTE ON AIR TIGHTNESS

The air permeability of a dwelling greatly affects the SAP rating; the lower the air permeability is the better.
SAP 2005 uses a default air permeability figure applied in the calculation. By conducting an actual pressure test on a dwelling for air leakage, the builder may improve the SAP rating of the construction by lowering the air permeability figure in the calculation.
 
Building Element
Part L 2006
 
Max allowed
U-Values
SAP 2005
 
Guideline
U-Values
Wall
0.35
0.30
Roof
0.25
0.16
Floor
0.25
0.22
Openings
2.20
1.80
 
 
 
 
 
 
 
 
 
 
Notes:
  • The above table refers to new dwellings only.
  • Extensions in existing dwellings must achieve 0.30 W/mēK to comply with Part L. Therefore, a U-Value of 0.35 will not comply.
  • It should be noted that the actual target U-Values in the new Part L 1A 2006 remain unchanged from Part L (2002) and if the builder achieves these, he will comply with Building Regulations for that particular component of the building. However, the likelihood will be that SAP 2005 will not be achieved and it is strongly recommended that a target of 0.30 or better is aimed for.
  • A further reduction in the guideline U-Value for walls to 0.27 W/mēK or less is likely to occur within the next few years.

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