Building Regulations and Planning Permissions
IQ Glass Solutions LTD, Sky House, Raans Road, Amersham, HP6 6FT
What do You Need to Know About Scottish Overheating Regulations in Glass Design?
Design mitigations for overheating in residential and commercial buildings in Scotland was previously dictated in Section 6. In 2023, changes were made to Sections 3 (environment), 6 (energy) and 7 (sustainability) and created Section 3.28 which specifically addresses overheating in new dwellings.
What is Section 3.28 of Scottish Building Regulations?
As the Welsh and English Approved Document O, Section 3.28 only applies to new dwellings and is designed to limit overheating in new dwellings in Scotland.
Overheating in buildings was highlighted as a key risk to health and productivity across the UK. This was due to various factors including increasing global temperatures and a general increase in local ’hot weather events’ or heat waves.
This increase in average temperatures is not restricted to the south of the UK and buildings in Scotland need to be designed to mitigate any negative impact on the built environment and occupants in designs.
The development of this part of Scottish Building Regulations looks to address all these risk factors in new building design, creating buildings that reduce the risk of overheating and have methods built into the design for removing excess heat.
Designing to Reduce Overheating in Scotland
The overheating regulation for new houses in Scotland allows the designer to use two ways to assess the risk of summer overheating;
- Simplified method.
- Dynamic thermal analysis.
Due to the type of projects that IQ undertake, most of the projects we work on will use the Dynamic Thermal Analysis modeling option for assessing the overheating risk. The dynamic thermal analysis options provide greater levels of design flexibility to designers and specifiers, allowing them to create buildings that are not ‘cookie cutter’ designs of buildings.
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Dynamic Thermal Analysis Modelling for Overheating in Scotland
The dynamic method of designing for overheating allows designers to consider the;
- building location
- construction type
- opening areas of the building
- orientation
- ventilation
Looking at all these aspects of the building together allows designers to create a truer picture of the performance of a building in relation to overheating.
This assessment is done in accordance with the TM59 methodology (Design methodology for assessing overheating risk in homes (2017)) using the ‘type 1’ occupancy which showcases that performance of the building for vulnerable occupants. The regulation sets out various parameters to be used in modelling the building which can be read in Section 3.28.
Typically, in order to design a building that will satisfy the requirements of the TM59 methodology a combination of solar protection methods need to be adopted.
These include;
- using a glass with a reduced g value
- the inclusion of external shading methods
However, the dynamic method provides greater flexibility in how these are included in a design. You can learn more about this in our article Glass Designs for Overheating.
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Simple Method of Assessing Overheating in Scotland
The simplified method of assessing for overheating stipulates that large areas of glazing can still be used within the design however, the risk of overheating with badly specified glazing design and location must be mitigated.
It is recognised that if large areas of glazing are not designed and specified thoughtfully then this could cause a risk of overheating. The simplified method is a simplified way of designing a building to ensure that these considerations have been made.
If the area of glazing (in relation to the floor area of the room) is greater than 20% then the below methods are suggested as a way to reduce the risk of overheating:
- Use external shading (louvres, external shutters etc).
- Use glass with a higher g value to reduce solar gain (in proportion to the increase in glazing area above 20%).
- Use ventilation to assist cooling.
When using the simplified method and requiring additional solar control coatings, it is recommended that the glass has a g value of 0.6 or less.
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Changing the G Value of Glazing for Overheating
Whether you are looking at using the dynamic or simplified method for assessing the overheating risk, it is likely that some form of solar control glass will need to be used on the building.
Solar control glass is a specialist glass with a coating within the unit that reduces the g value of the glass (this is the measurement of solar radiation that can come through the glass).
Modern solar control glass can be designed with a variety of colours and tints with the most popular option being ‘super neutral’ solar control which has no colouration or tint. With modern solar control coatings the light transmission of the glass can be maintained whilst you reduce the solar gain. This helps you to satisfy the requirement of Section 3.28 to maintain high levels of natural light into a home.
Contact the IQ team to find out more about what is possible from modern solar control coatings.
Solar Control Options for Glass Designs
When looking at your glass design there are various ways in which you can provide effective solar control to reduce the risk of overheating.
The simplest way is to use a solar control coating on the glass itself. This will stop a certain percentage of solar radiation from entering the building through the glass.
Next, you should look at shading the glass to reduce the amount of solar radiation that can enter through the glazing. There are various ways in which this can be done on a modern house build.
At IQ we work with a large range of glazing designs with the aim to keep them all minimal and modern. All these shading solutions are possible with even our most minimal of glazing systems including
Read more in our article Solar Control Options for Structural Glass
Solar Shading Designs for Glass
To learn more about the various solar shading options possible for your architectural glass design, read our articles below.
Ventilation for Overheating in New Dwellings in Scotland
Section 3 of Scottish Building Regulations lists ventilation as a key way to improve the internal environment of a building and to reduce overheating. They define this as ‘the process of changing air in an enclosed space’.
Essentially, you should be designing buildings so that a proportion of the air inside is regularly removed and replaced with external ‘fresh’ air. This helps with overheating designs by replacing warmer internal air with cooler external air.
The ways in which houses were typically ventilated are broken into two variations:
- Purpose provided ventilation = controlled
- Fortuitous infiltration = uncontrolled, through air leakage paths in a building.
Fortuitous infiltration ventilation is slowly becoming less prevalent as buildings become more airtight. This is needed for when creating more carbon neutral buildings however, this puts more pressure on purpose provided ventilation to provide fresh air movement through a house.
Section 3.28 suggests that if you can reduce the overall fortuitous infiltration rate to under 5 m3/h/m2 @ 50 Pa then continuous mechanical extract ventilation may be required.
Another aspect of the overheating regulation to consider is that air tightness tests are now recommended for each new house. If the results of this air tightness show that the building has a level of air tightness that is different to the design figure (be that lower or higher) the ventilation options might need to be reevaluated.
Options for Ventilation under Scottish Building Regulations
As above, buildings are getting more airtight and options for ventilation through fortuitous infiltration are reducing. This means that more emphasis is placed on introducing ventilation into buildings through purposed provided ventilation methods.
Natural Ventilation
Natural ventilation can be achieved in a building design by introducing ways in which fresh air can be brought into the building. This works on the understanding of air pressure differences between outside and inside, bringing fresh air into a building.
Opening a window, background ventilators and passive stack ventilators are all well used ways to introduce natural ventilation into a house design.
The design and shape of a building will also affect the effectiveness of natural ventilation methods. A house with multiple exposed walls can introduce opening windows and doors to draw air through a home. However, residential units with a single aspect might not get the benefit of this.
You must consider that natural ventilation has no filtering therefore the air you are bringing into the home will only ever be as good as the quality of the air outside.
Mechanical Ventilation
Mechanical ventilation is a more controlled option for ventilation and creates air movement generated by a powered fan. There are various options for mechanical ventilation within a new build house.
The recommendation in 3.28 of Scottish Building Regulations suggests that natural ventilation methods should be used in conjunction with mechanical ventilation methods.
Ventilation Rates for New Build Houses in Scotland
It is up to the architect or designer to determine the ventilation strategy for the new build house. This is recommended to be done at an early stage of the project design.
A balance must occur between the infiltration rate and the ventilation design. This is explored in more depth in clause 3.14.2.
Essentially, the higher the expected infiltration rates the less complex the ventilation methods for the building need to be. In any case, the expected infiltration rates must be calculated at an early stage of the project. Once the project is complete an air tightness test will be completed and the results compared to the expected rates.
If these values differ then additional works or consideration must be taken to the ventilation designs.
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Balancing Good Daylight Levels with Overheating
The regulation for overheating expressly stipulates that consideration must be given to the levels of daylight coming into a building.
All actions to mitigate overheating must be balanced against the requirement to have good levels of daylight entering a building. As well as making the internal spaces comfortable and pleasant to be in, these levels of natural light can also be used for additional heating of spaces in the winter through solar gain. The strategic use of natural light for solar gain heating can reduce a building’s dependency on other forms of heating.
A light transmission of over 70% is recommended to ensure the maximum amount of daylight can enter a space. Balancing this against the g value of the glazing for solar protection can be confusing, but the team at IQ can help conduct these calculations, so contact us for advice or guidance.
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Shading for Summer Sun Path
One way to balance natural light with protection against overheating is to use a shading system that has been designed for the ‘summer sun path’. Shading designed with this practice are designed to shade most effectively in the summer, with louvres or blades of a brise soleil system orientated to shade from direct sunlight when the sun is strongest.
For buildings in the northern hemisphere, it is typically understood that horizontal shading options are best for south facing glass elevations. These types of fixed shading designs shade the glass walls in high sun positions. Vertical shading designs are more effective on east and west facades for low angle sunlight.
You can learn more about designing shading systems for the summer sun path from Avino who offer a range of timber shading systems for glazing designs.
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Overheating in Conversions of Buildings
If a building is being ‘converted’ (as defined in Regulation 4) then it is expected that Section 3.28 will be followed “as far as reasonably practicable.
When buildings are converted, the performance of the building in relation to overheating cannot be worse than before the conversion.
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What is the Difference Between Scottish and English Regulations for Overheating?
The main difference between the regulations for overheating in Scotland when compared to England and Wales seems to be that the Scottish Regulations for Overheating have fewer dictated requirements for the design.
Whereas the English and Welsh Regulations for Overheating stipulate various required methods for shading and orientation, the Scotland Regulations for Overheating do not include that.
Instead, the Scotland Regulations for Overheating seem to be more flexible, allowing designers to create a design that suits the landscape and requirements of the build. Assessments and testing are still a core part of the overheating requirement; designing a building to a calculated performance and then testing the as built performance matches.
However overall, the ethos of all these regulations is the same; to create new build homes that are comfortable for even the most vulnerable of residents and are built to withstand the changing nature of our climate.
What Next?
If you are designing a new build house in Scotland contact the team at IQ Glass for expert advice and guidance regarding your glass specification. We can assist from early stages of a project with performance calculations to create specification requirements for the glazing and systems. We can also advise on shading solutions and how they would interface and interact with the glazing.
Contact the team today! We are available by phone or email to discuss your project.
Further Reading
Guide to Listed Building Classification and Regulations in Scotland
Controlling Solar Gain & Overheating in Highly Glazed Spaces
Glass Designs for Overheating: Approved Document O
Overheating in New Dwellings in Wales