Overheating in new domestic buildings

Overheating in new domestic buildings

Window energy efficiency
Effective from 1st February 2023 (deferred from 1st December 2022), the Scottish Government has introduced changes to Sections 3 (environment), 6 (energy) and 7 (sustainability) of the Building Standards Technical Handbooks for domestic and non-domestic buildings.

For new dwellings, a new Section 3.28 introduces a new mandatory standard to assess and mitigate the summertime overheating risk.

Applying only to new residential buildings, the new standard requires dwellings to be designed and constructed in such a way as to limit solar gains through glazing and provide ventilation to assist in effective cooling. Two methods of assessment are provided:
  • Simple method, specifying measures to mitigate risk of summer overheating
  • Detailed thermal analysis modelling, involving calculation of the risk of overheating
Using the simple method, for new residential buildings with a glazed area greater than 20% of the room floor area, shading (e.g. louvres, external shutters, etc.) should be provided. Alternatively, the glazing g value should be revised to reduce solar gain in proportion to the increase in glazed area above 20%. The latter should be based on heat gain no greater than an unshaded opening, 20% of the room floor area and a g value of 0.60.  If the glazed area is doubled, then the g value should be halved.

Changes to the glass specification to reduce the g value should, where practicable, maintain a high light transmittance to minimise the adverse impact on daylighting. A light transmittance of 0.70 or higher is recommended..

By implication, glazed areas of 20% or lower would not require shading or glazing with lower g value than 0.60 when using the simple method.

To satisfy the above requirements, Pilkington offers a range of glass that can provide solar control and / or thermal insulation. This includes products that can achieve g values of 0.60 or lower, as stated in the simple method.

If using dynamic thermal analysis modelling to predict overheating risk, the methodology set out in CIBSE TM59 'Design methodology for the assessment of overheating risk in homes' should be followed.  This approach may be useful for conversions, more complex dwellings and those where significant areas of glazing are proposed.  

More details can be found in the new Technical Handbooks which can be found here.

If you have any questions on changes and what the implications might be for glass, please complete our online contact form, selecting 'Architect' or 'Trade' as the Nature of Enquiry and 'Other' as the Enquiry Type.
Please state 'Technical Handbook Section 6' in the Question / Comment box when completing the form.

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