Overheating

Overheating

Window energy efficiency
The government has initiated a consultation concerning the introduction of a new Building Regulation for overheating in new dwellings in England. These changes are expected to have a significant impact on glass and glazing products in residential buildings.

Ending on 13th April 2021, the consultation sets out proposals for a new Approved Document [X]* covering the mitigation of overheating risk in new dwellings in England. This follows on from an earlier consultation on new dwellings, the Government's response to which has been published.

*the new Approved Document has yet to be assigned a letter

Applying only to new dwellings, the Approved Document would require dwellings to be designed and constructed in such a way as to limit unwanted solar gains in summer and provide an adequate means to remove excess heat from inside. Two methods of assessment are foreseen:

 

  • Simplified method, related to location, dwelling type, glazing and floor area
  • Detailed thermal analysis method, involving calculation of the risk of overheating

For the simplified method, England is split into two broad areas:
  • England, excluding Greater London (with a moderate risk of overheating), and
  • Greater London (with a significant risk of overheating)


Using the simplified method, residential buildings should meet the maximum glazing area and shading standards in the table below.

Group A buildings (with more than two fabric elements and openings on opposite facades)
Location Maximum glazing area
Shading
England (excluding
Greater London)
21% of floor area
None
Greater London
13% of floor area Shading on glazing between NE
and NW (via South)
Group B buildings (two or fewer fabric elements and openings on facades which are not opposite)
Location
Maximum glazing area
Shading
England (excluding
Greater London)
21% of floor area
None
Greater London
15% of floor area
Shading on glazing between NE
and NW (via South)

Where shading is required, glazing with a maximum g value of 0.40 and a high light transmittance of 0.70 can be used.

In terms of removing excess heat, the proposals set a minimum free area (geometric open area of a ventilator) dependent upon floor and glazing areas and whether the building is in group A or B.

To satisfy the above requirements, Pilkington provides a range of glass products that can provide solar control and / or thermal insulation, such as Pilkington Suncool™ 70/35 These include products that can meet the low g value glazing requirement of a maximum 0.40 as stated in the simplified method.

If using the dynamic thermal analysis method to predict overheating risk, the methodology set out in CIBSE TM59 'Design methodology for the assessment of overheating risk in homes' should be followed.

Documents related to the consultation on proposed requirements for mitigating the risk of overheating in new dwellings can be found here.

If you have any questions on Part L 2021 and what the implications might be for glass, please complete our online contact form, selecting 'Architect' or 'Trade' as the Enquiry Type and 'Part L 2021' as the Nature of Your Enquiry.