PAS 2035
PAS 2035:2023 Retrofit Designer route (Annex A.3)
- where
- Annex A.3 sub-clause that applies (A.3.c)
- 1 if traditionally built with measures likely to affect heritage or fabric, else 0
- 1 if not b₈ and the work is on a high-rise or system-built dwelling or has 3 or more interacting fabric measures, else 0
- 1 if neither of the above and there are exactly 2 interacting fabric measures, else 0
- 1 if none of the above and there are 2 or more measures in total, else 0
- 1 if none of the above apply (a single measure), else 0
- Retrofit Coordinator review of the designer needed under A.3.6 (1 yes, 0 no)
Explain this equation
Works out which PAS 2035 Annex A.3 route applies for the Retrofit Designer's qualifications on a project. Use it when planning who can design a retrofit package.
This is a decision rule written as a sum. Each b is a yes/no switch, and exactly one of them is 1: the checks run from most to least demanding and the first that applies wins. Traditional buildings where measures could affect the fabric switch on b₈ (route A.3.8). Otherwise high-rise or system-built homes, or three or more interacting fabric measures, switch on b₇. Then two interacting fabric measures give b₅, two or more measures with no fabric interaction give b₉, and anything else (one measure) gives b₁. Multiplying each switch by its clause number and adding picks out the one clause.
R adds the two switches whose routes need the Retrofit Coordinator to review the designer's qualifications, A.3.5 and A.3.1, so it is 1 for those routes and 0 otherwise.
Sense check: external wall insulation plus new windows on an ordinary cavity-wall house is two interacting fabric measures, so b₅ = 1, c = 5 and R = 1.
Watch out: always check the current edition of PAS 2035 and any scheme requirements; this is a guide to the route, not a substitute for reading the standard.
Shows which Retrofit Designer qualification route in PAS 2035:2023 Annex A.3 applies to a project, from the number and type of measures.
Enter your values to see the result.
Good to know
In the equation, b8, b7, b5, b9 and b1 are 1 for the first route whose test is met, checked in that order (b8: traditional construction; b7: high-rise or system-built, or three or more interacting fabric measures; b5: two interacting fabric measures; b9: two or more measures; b1: a single measure), and 0 otherwise. PAS 2035:2023 removed the 2019 Risk Paths A, B and C. The level of design competence now depends on the measures: one measure, two interacting fabric measures, three or more interacting fabric measures (or any fabric/window work on high-rise or system-built homes), traditional construction, or other multi-measure projects. Interacting fabric measures meet at junctions, corners or edges (for example wall and roof, wall and floor, wall and windows).
Common mistake
Still classifying jobs as Path A, B or C. That procedure no longer exists in the 2023 edition.
Limits
Informational only. The Retrofit Coordinator decides the route and must read the full PAS 2035:2023 text and any scheme (TrustMark, funding) rules.
Sources
- BSI PAS 2035:2023 Retrofitting dwellings for improved energy efficiency — Specification and guidance (Annex A.3 Retrofit Designer qualifications; the 2019 risk path procedure was removed)
- Elmhurst Energy, PAS 2035:2023 changes (“The Risk Path procedure has been removed”)
- HM Government, Approved Document F Volume 1: Dwellings, 2021 edition (para 1.24 and Table 1.3 whole dwelling ventilation rates; Table 1.7 background ventilators; para 1.64 continuous extract; paras 1.45–1.46 airtightness; Section 3 existing dwellings)
Results are calculations from the published methods and figures shown, and depend on the data you enter. Follow BS EN ISO 6946, BS 5250, PAS 2035, Building Regulations Part L and manufacturers’ data. Whole-house retrofit needs a qualified retrofit assessor and coordinator.