For architects and specifiers
Scottish overheating regulations:
satisfying Standard 3.28 with external shading
Since February 2023, new homes in Scotland must be designed to reduce the risk of summer overheating. Where a room has a lot of glazing on a sun-facing elevation, external shading is a named route to compliance, and the guidance is clear that it should be considered first. This is a specifier's summary of what the regulation requires and how to satisfy it.
What Standard 3.28 requires
Standard 3.28 Overheating Risk was introduced on 1 February 2023. The mandatory standard is that "every building must be designed and constructed in such a way that the risk to the health of the occupants from overheating is reduced." It applies to new dwellings and to residential units within non-domestic buildings.
Compliance can be shown by one of two methods:
- The simple method (clause 3.28.2). Assess every elevation oriented between east (90 degrees), through south, to west (270 degrees). If the area of glazing is greater than 20% of the floor area of the room it serves, the guidance says to "provide shading such as louvres or external shutters, or revise the glazing g-value to reduce solar gain in proportion to the increase in glazing area above 20%."
- Dynamic Thermal Analysis (clause 3.28.3). Model the overheating risk in accordance with CIBSE TM59 (2017). This route suits larger glazed areas and more complex dwellings.
The 20% figure is a screening trigger, not a maximum. Larger glazing areas can still comply through the modelling route. The standard's intent is simply that increased glazing on sun-facing elevations is accompanied by mitigating measures.
Why external shading leads the hierarchy
Two points in the guidance matter for specification. First, for the modelling route, the Domestic Technical Handbook states plainly that "internal blinds should not be used in the building design to assess compliance." Internal shading is recognised as useful for occupants, but it does not count towards demonstrating that the standard is met.
Second, the Non-domestic Technical Handbook's Annex 7.A is explicit about the order of preference: "external shading devices are the most effective as they deflect solar radiation before it enters the building," and "external shading devices should be considered in the first instance." Internal devices may be used only where external shading cannot form part of the external fabric, for reasons such as planning restrictions.
The standard also sets a passive-first hierarchy: passive mitigation should be prioritised, and active measures such as air conditioning considered only where all reasonable passive measures have first been applied.
Solar gain reduction by shading type
These figures are quoted from Annex 7.A of the Non-domestic Technical Handbook (January 2025), "example options of measures for the control of solar gain."
| External shading device | Solar gain reduction | Notes |
|---|---|---|
| Horizontal overhangs and window reveals | up to 75% | Best suited to south-facing openings. |
| Horizontal louvres with a horizontal overhang | up to 90 to 95% | Used on south facades. |
| Shutters (sliding or rotating) | recognised, not separately quantified | South, east and west facades. Lockable shutters allow secure night-time cooling. |
| Vertical fins with a horizontal overhang | up to 85 to 90% | Best suited to east and west facades. |
| Awnings or roller shades | up to 60 to 75% | South, east and west facades. |
Shutters are recognised across south, east and west facades. Awnings and roller shades are named with quantified effectiveness. Extendable and retractable products such as awnings and canopies are not treated as fixed solar shading attachments under Regulation 8.
How our external shading maps to the standard
We supply and install external shading that sits within the categories the regulation names. We are happy to work brand-agnostically to your specification; where it helps, here is how our range maps to the guidance.
Luxaflex external screens (tensioned ZIP screens)
Vertical external shading suited to south, east and west elevations, including large glazed areas, bi-fold doors and glazed extensions. Recognised external shading within the simple method, and adjustable for winter solar gain.
Luxaflex awnings
Retractable folding-arm awnings correspond to the Annex 7.A "awnings or roller shades" category, quoted at up to 60 to 75% solar gain reduction, and are outside the Regulation 8 fixed-attachment provisions.
External shutters
Sliding or rotating external shutters are recognised on south, east and west facades, and allow secure night-time cooling. Combined with a horizontal overhang, louvred external shading is quoted at up to 90 to 95%.
Specify online with our sunscreen selector
Our sunscreen selector helps you compare external screen fabrics by openness factor and solar performance for a given elevation, so you can shortlist a compliant specification before you get in touch.
Open the sunscreen selectorSpecification support and CPD
The Scottish Shutter Company has shaded Scottish homes since 1987. Our Technical Director, David D'Ambrosio, is a Past President of the British Blind and Shutter Association (BBSA), the trade body for the sector, and can advise on specifying external shading to satisfy Standard 3.28.
We offer practice CPD sessions on the regulation and the external shading options, and we can provide the manufacturer technical data your thermal modeller needs for a CIBSE TM59 assessment. For homeowners, our plain-English guide to external versus internal shading covers the same principle with indicative costs.
Common questions
When did Standard 3.28 come into force?
Standard 3.28 Overheating Risk was introduced on 1 February 2023 under the Building (Scotland) Amendment Regulations 2022. The current edition is the January 2025 Technical Handbook, applicable to work subject to a building warrant submitted on or after 1 January 2025.
Which buildings does it apply to?
New dwellings, and residential units within non-domestic buildings such as student accommodation, care homes, sheltered housing and residential institutions. It also applies to conversions in so far as is reasonably practicable.
Can I still design large areas of glazing?
Yes. The 20% figure is the simple method screening trigger, not a maximum. Larger glazing areas can still demonstrate compliance through Dynamic Thermal Analysis modelling in accordance with CIBSE TM59 (2017). The point of the standard is that increased glazing on risk facades should be accompanied by mitigating measures.
Do the products have to be motorised or permanent?
No. The regulation recognises adjustable devices, including sliding and rotating shutters, awnings and roller shades. Adjustability is recognised but not mandated.
What evidence do you provide for a TM59 model?
We can supply the manufacturer technical data (g-value and solar performance) for the specified external shading products so your thermal modeller can drop the values into the CIBSE TM59 assessment. Talk to us early and we will provide the datasheets.
Sources
- Scottish Building Standards, Domestic Technical Handbook (January 2025), Standard 3.28 Overheating Risk, clauses 3.28.1 to 3.28.5.
- Scottish Building Standards, Non-domestic Technical Handbook (January 2025), Standard 3.28 and Annex 7.A "Example options of measures for the control of solar gain."
- Building (Scotland) Amendment Regulations 2022 (Standard 3.28 introduced 1 February 2023). Published by the Scottish Government, gov.scot. Always confirm the current requirement for a specific project with your building standards verifier.
This page is a plain-English summary for specifiers and is not a substitute for the Technical Handbooks or project-specific building standards advice.
Last reviewed: by David Browne, Project Director
Specifying external shading for a Scottish project?
Talk to us early. We will help you specify compliant external shading, provide the technical data your thermal modeller needs, and can run a CPD session for your practice.