Scottish Building Standards 2015 – Overview of Domestic Retrofits and Extensions

Scottish boy with the flag of Scotland

The Scottish government released the 2015 building standards earlier this week, ahead of their implementation (from October 2015). This allows industry plenty of time to get to grips with the requirements. This blog post considers the changes to domestic retrofit and extension requirements…

One of the key changes to the existing dwelling requirements is improved area weighted limiting fabric backstops for extensions and additional options for compensatory approaches where varying those values.

The key requirements for new extensions, material alterations /refurbishment and changes of use to domestic use are outlined in the following table, together with requirements for non exempt conservatories:

 Retrofit & Extensions

The values suggested above can typically be achieved without technical risk and so should be met wherever this is reasonably practicable.

Compensatory approaches may be used to vary from the above values, provided individual elements are no worse than the limiting ones.

For extensions, the performance of elements can be varied, providing that the overall heatloss from the extension is no greater than a notional one that did comply; thus an area of glazing greater than 25% of the floor area could, for example, be shown to still comply by the compensatory approach, if the other elements performance were improved to compensate.

A whole dwelling approach can also be adopted where the existing dwelling and it’s extension are modelled in SAP2012 to show that the Dwelling Emission rate of the extended property will be no higher than its Target Emission Rate. This approach would be a tricky thing to achieve for most existing dwellings (unless built to a fairly recent standard), but our existing bulding stock is very much in need of improvement overall, so while this approach may not prove popular overall, it is very much to be applauded for its inclusion.

The various retrofit sections also mention compensatory approaches for improving the overall U-value of other parts of the insulation envelope where for whatever reason, the targets laid out in column (b) cannot be achieved for one element.

The annexes make it clear that where refurbishing or converting a building into a dwelling, the area weighted U-value compensatory approach can also be used to compensate for a greater area of openings than the 25% of floor area allowance; however such a trade-off approach cannot be used where values are only being met as far as is reasonably practicable.

There is additional guidance in the Domestic Building Services Compliance Guide for Scotland and in Section 3: Environment for the provision of ventilation to buildings that should be considered when upgrading, extending or converting dwellings that I won’t go into here, but which should be considered alongside any other works undertaken.

Both domestic and non domestic standards, as well as the supporting documents are available at:

Overall, there’s a lot to like about the Scottish building standards energy advice – the standards are typically well thought out and explained, with examples in the annexes that make life simpler for the user (although some may find all the cross referring between clauses to be annoying at times).

The Scottish targets are also a lot more forward thinking than for the rest of the UK, which if met, will result in warmer, cheaper to run homes for the occupants.

See my other blog post about Scottish Domestic New Build Standards.


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Jon Ducker is a qualified energy assessor working for Kingspan Insulation Ltd. He has an extensive knowledge of energy efficiency, renewable energy systems and sustainability in buildings with an expert knowledge of the relevant sections of buildings regulations and standards and their interactions with SAP. He provides authoritative advice regarding energy assessments for a wide range of public and private sector clients.

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