Last reviewed: June 2026
TL;DR- Standard construction means brick or stone walls with a pitched tiled or slated roof - anything else is typically considered non-standard.
- Non-standard construction types include prefabricated concrete (PRC), timber frame, steel frame, thatched roof, flat roof and modern methods of construction (MMC).
- Mainstream lenders often decline non-standard construction - specialist lenders assess on a case-by-case basis.
- Some non-standard construction types (particularly pre-1980 PRC homes) require a certificate of repair before most lenders will consider them.
What Is Non-Standard Construction?
Lenders define standard construction as a property built with brick or stone cavity or solid walls and a pitched roof covered with tiles or slates. Anything outside this definition is classified as non-standard. Common non-standard types in the UK include: prefabricated reinforced concrete (PRC) homes built after World War Two under government housing programmes; timber frame construction; steel frame construction; properties with flat roofs (even partially); thatched roofs; concrete panel construction; and modern methods of construction (MMC) including volumetric modular, cross-laminated timber (CLT) and structural insulated panels (SIPs).
Why Non-Standard Construction Affects Mortgage Availability
Lenders price mortgages against the risk of recovering their loan in a repossession scenario. Non-standard construction affects this risk in two ways: the property may be harder to sell (a smaller buyer market due to mortgage restrictions creates a self-reinforcing liquidity problem); and some non-standard construction types have specific maintenance or structural issues that affect long-term condition and value.
PRC homes - particularly those built using systems like Airey, Cornish Unit, Reema and Wimpey No-Fines - are the most restricted category. Many were built under post-war housing programmes and have been identified as structurally deficient under the Housing Defects Act 1984. Unmortgageable in their original condition, PRC homes can become mortgageable after undergoing a recognised repair scheme certified by the PRC Homes Ltd or equivalent body.
Timber Frame and Steel Frame
Timber frame construction is mainstream in Scotland and increasingly common across the UK. Most lenders accept modern timber frame construction, particularly where it is cavity-clad with brick or rendered externally and meets current Building Regulations. Older timber frame properties and those with specific system-built frames may face more restrictions. Steel frame construction is less common in residential properties and faces more variable lender acceptance - some mainstream lenders decline, others accept subject to survey.
Modern Methods of Construction
MMC covers a range of factory-manufactured building systems including volumetric modular (complete room pods assembled on site), panellised systems (pre-made wall and roof panels), CLT and SIPs. Lender acceptance of MMC has improved significantly in recent years, particularly for warranty-backed MMC systems. The NHBC, Premier Guarantee and other warranty providers have developed MMC-specific warranties that improve lender confidence. Some lenders have developed specific MMC mortgage criteria. Buyers of MMC homes should confirm lender acceptance before committing to a purchase.
Frequently Asked Questions
Can I get a mortgage on a PRC home?
Unmortgaged PRC homes in their original condition are typically unmortgageable from mainstream lenders. PRC homes that have been repaired under a recognised scheme (with a PRC certificate) are accepted by a range of specialist and some mainstream lenders. The certificate confirms the repair has been carried out to the required standard. Buyers should verify the repair certificate is valid and check lender acceptance before proceeding with a PRC home purchase.
Does a flat roof affect mortgage eligibility?
A property that is entirely flat-roofed faces significant mortgage restrictions from mainstream lenders. Properties where the flat roof covers only a small element (extension, garage) alongside a predominantly pitched roof are typically more straightforward. Flat roofs require more frequent maintenance and replacement than pitched roofs, which increases the lender's risk. Specialist lenders consider flat roof properties case by case.
How does a surveyor's report help with non-standard construction?
A full structural survey (RICS Level 3 Building Survey) identifies the construction type, condition and any specific issues. Lenders may request a specialist structural survey for non-standard properties before deciding whether to proceed. The survey provides the lender with comfort about the property's condition and longevity. For PRC and similar systems, the survey should comment on whether the repair has been carried out and its current condition.
Are thatched properties mortgageable?
Yes, thatched properties are mortgageable through specialist and some mainstream lenders, though lender choice is more restricted than for standard construction. Insurance is the primary challenge - specialist thatched building insurance is significantly more expensive than standard home insurance and not all insurers cover thatch. Lenders require evidence of adequate insurance before completion. The thatching material (water reed, long straw, combed wheat reed) and the condition of the thatch affect both insurability and value.
