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.
Check which edition of TM59 your modeller is using
Clause 3.28.3 pins its reference to CIBSE TM59 (2017), and that's the edition to model against.
CIBSE published a rewritten TM59 in July 2026 under a new title, "Overheating risk in dwellings: a design stage methodology", and renumbered it throughout. Clause 3.28.3 sends a modeller to TM59 sections 3.1, 3.3, 3.7 and 4.4. In the 2026 edition those numbers no longer hold the same content, and there's no section 4 at all.
There's nothing wrong with the handbook. It came into force on 6 April 2026, three months before the rewrite, and it pins the citation to the 2017 edition by year, so anyone working from that edition is on solid ground. The risk sits with anyone who picks up the current edition and follows the clause's section numbers instead. It's worth a line in your modeller's brief.
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.
Standard 3.28 covers new build. The bigger problem is the homes already standing.
Standard 3.28 applies to new dwellings and to conversions. That leaves out most of the housing stock, and the national picture is where that gap gets addressed.
In August 2026 the House of Commons Library published a research briefing, Is the UK prepared for heatwaves? It records that "air conditioning and passive cooling measures (such as increasing shading, ventilation and insulation) are less common in homes in the UK than in homes in warmer countries," and that as a result people here are more likely to experience prolonged exposure to heat.
On what to do about it, the briefing reports that the Climate Change Committee recommended both active cooling and "low-cost passive-cooling measures (such as installing shutters or shading)." The Committee welcomed the building regulations requiring new homes to consider overheating, but noted that existing homes will make up most of the housing stock by 2050, "emphasising the importance of retrofit."
The Committee's 2026 Well-Adapted UK report went further, identifying cooling and protection from heat as among the highest adaptation priorities, and calling for vulnerable settings such as hospitals, schools and prisons to be made more resilient through a mix of active cooling, passive measures and retrofit "such as the installation of shutters."
There is no comprehensive national heat resilience strategy at present, though the briefing notes calls for a national cooling plan. For a specifier, the practical read is that the direction of travel on existing buildings points the same way Standard 3.28 already points on new ones: shade the glass before you cool the room.
Source: House of Commons Library, Is the UK prepared for heatwaves?, research briefing CBP-10956, 14 August 2026. Contains Parliamentary information licensed under the Open Parliament Licence v3.0. The briefing is guidance on the national policy position and is not a building regulation; Standard 3.28 and the Technical Handbooks remain the compliance route in Scotland.
Solar gain reduction by shading type
These figures are quoted from Annex 7.A of the Non-domestic Technical Handbook (April 2026), "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
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 can provide the manufacturer technical data your thermal modeller needs for a CIBSE TM59 assessment, and we come into practices to talk through the regulation and the external shading options. For homeowners, our plain-English guide to external versus internal shading covers the same principle with indicative costs.
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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 April 2026 Technical Handbook, applicable to work subject to a building warrant submitted on or after 6 April 2026. The wording of Standard 3.28 is unchanged from the January 2025 edition.
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.
Which edition of CIBSE TM59 applies?
The 2017 edition. Clause 3.28.3 cites CIBSE TM59 (2017) by year, so that is the edition to model against. CIBSE published a rewritten TM59 in July 2026 with a new title and different section numbering, and the handbook's section references don't carry across to it. It's worth confirming which edition your thermal modeller is working from.
Does Standard 3.28 apply to existing homes?
No. It applies to new dwellings, residential units within non-domestic buildings, and conversions in so far as is reasonably practicable. Existing homes fall outside it. The national policy position is where that gap is addressed: a House of Commons Library research briefing of August 2026 records the Climate Change Committee recommending low-cost passive-cooling measures such as installing shutters or shading, and notes that because existing homes will make up most of the housing stock by 2050, retrofit matters. That is policy direction rather than a regulation, and nothing in it changes what a building warrant requires.
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 take the values straight into the CIBSE TM59 assessment. Ask us for it using the request form on this page, and the earlier the better.
Sources
- Scottish Building Standards, Domestic Technical Handbook (April 2026 edition, applicable from 6 April 2026), Standard 3.28 Overheating Risk, clauses 3.28.1 to 3.28.5. The wording of Standard 3.28 is unchanged from the January 2025 edition.
- Scottish Building Standards, Non-domestic Technical Handbook (April 2026 edition, applicable from 6 April 2026), Standard 3.28 and Annex 7.A "Example options of measures for the control of solar gain."
- CIBSE TM59, "Design methodology for the assessment of overheating risk in homes" (2017), the edition cited by clause 3.28.3. A rewritten TM59 was published by CIBSE in July 2026 under a different title and with different section numbering.
- 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'll help you specify compliant external shading, provide the technical data your thermal modeller needs, and come into your practice to talk the regulation through.