Guide
Non-traditional houses and external wall insulation
Most non-traditional houses — concrete, steel-framed or system-built homes from the 1940s to 1970s — have no fillable cavity, so external wall insulation is the usual way to insulate them. EWI improves comfort and appearance, but it isn't a structural repair: some PRC house types need a certified repair before many lenders will offer a mortgage.
Common types
- Wimpey no-fines — poured concrete walls
- Airey, Cornish Unit, Orlit, Reema — precast reinforced concrete (PRC)
- BISF — steel frame with sheet cladding on the upper floor
- Easiform, Laing and others — in-situ concrete systems
What the survey checks
The construction type, concrete condition (spalling, cracking, exposed reinforcement), steel condition where visible, and how the walls meet the roof and neighbouring houses. Fixings are designed for the substrate.
Mortgages and PRC houses
Some PRC types were designated defective, and lenders often want a certified structural repair. External insulation and render doesn't replace that repair. If mortgageability matters, talk to your lender before booking work.
Questions
Can you insulate half of a semi?
Yes, with a neat closing detail at the boundary.
Are non-traditional houses harder to insulate?
They need more preparation and fixing design, which is reflected in the price.
Do I need a structural survey?
For PRC types and where defects are visible, a structural engineer's view is wise.