If your mortgage valuer has flagged the property as non-standard construction, or you've identified it yourself from the title register or a survey, the path to a mortgage is navigable — but it requires specialist knowledge and the right professionals from the outset. This is not a situation where a standard high street mortgage application will sail through unchallenged.
What Counts as Non-Standard Construction?
Lenders define "standard construction" as brick or stone external walls with a slate or tile pitched roof. Anything outside that is non-standard. The most commonly encountered types in UK residential stock:
Pre-Fabricated and System-Built Concrete
- Airey: Steel-reinforced concrete posts with pre-cast concrete panel infill. Common post-war, particularly in East Midlands, Yorkshire, and former mining communities.
- BISF (British Iron and Steel Federation): Steel frame structure with concrete or sheet metal cladding panels.
- Wimpey No-Fines: Poured in-situ concrete without fine aggregate — appears similar to brick from outside but is solid concrete construction throughout.
- Cornish Units (Types 1 and 2): Pre-cast concrete panel construction common in Cornwall and the South West.
- Laing Easiform: Poured in-situ concrete, similar to Wimpey No-Fines.
- Reema Hollow Panel: Pre-cast concrete panels with hollow cores.
- Woolaway: Storey-height pre-cast concrete panels; asbestos content is common in original construction.
Other Non-Standard Types
- Timber frame (modern, documented): Generally accepted by lenders when properly documented with NHBC certification or equivalent. Older, undocumented pre-1945 timber frame is more problematic.
- Thatched roof: Specialist insurance required; limited lender appetite.
- Flat roof (entire roof or significant proportion): Most mainstream lenders decline flat-roofed properties.
- Steel frame (CLASP, HORSA): Predominantly found in converted schools and public buildings; difficult to mortgage.
- Concrete frame: Various post-war commercial conversion types.
Why Lenders Flag Non-Standard Properties
Three core risk factors drive lender caution:
Valuation difficulty: Without comparable sales evidence from similar properties (scarce for non-standard types), valuers cannot be confident of open market value. Valuers will either down-value relative to local comparables or decline to value at all.
Resale constraint: Fewer buyers can obtain mortgages on non-standard properties, permanently reducing the buyer pool in any future sale or repossession. This directly affects the quality of the lender's security.
Repair cost unpredictability: Carbonated concrete, corroded steel reinforcement, failed panel connections, or deteriorated wall ties create repair costs that can dwarf the property's market value.
The Defective Premises Act 1984 and Designated Types
The Housing Defects Act 1984 (consolidated into Part XVI of the Housing Act 1985) designated specific post-war construction types as "defective" on account of inherent structural problems. Designated types include Airey, Boot, Boswell, Cornish Units (Types 1 and 2), Dorran, Dyke, Gregory, Hamish Cross, Laing Easiform (certain configurations), Myton, Newland, Orlit, Parkinson Frame, Reema Hollow Panel, Schindler, Tarran, Unity, Wates, and Woolaway.
What designation means for buyers today: Local authorities once administered grant schemes to fund approved repair of designated properties. Those schemes are largely exhausted. What designation means in practice is that the construction type appears flagged on housing stock records, may be identified in a local authority search, and will trigger immediate enhanced scrutiny from any lender's valuer.
Designation does not automatically make a property unmortgageable — but it requires a specific response, not a general-purpose mortgage application.
Lender-by-Lender Positions
| Construction Type | Nationwide | Halifax | Santander |
|---|---|---|---|
| Airey (unrepaired, no PRC Certificate) | Generally declined | Generally declined | Generally declined |
| Airey (current PRC Certificate) | Case by case | Acceptable subject to valuation | Case by case |
| BISF (unrepaired) | Generally declined | Generally declined | Generally declined |
| Wimpey No-Fines | Case by case — valuer dependent | May accept with structural engineer's report | Case by case |
| Timber frame (modern, NHBC/BOPAS documented) | Generally acceptable | Generally acceptable | Generally acceptable |
| Timber frame (pre-1945, undocumented) | Generally declined | Declined | Generally declined |
| Thatched roof | May accept with specialist insurance confirmed | Case by case | Case by case |
| Entire flat roof | Declined | Declined | Declined |
| Cornish Unit (unrepaired) | Generally declined | Generally declined | Generally declined |
| Cornish Unit (current PRC Certificate) | Acceptable | Acceptable | Acceptable |
Lender positions shift. Always confirm with the specific lender or a whole-of-market broker before committing to survey costs on a non-standard property.
PRC Certificates: What They Are and What They Cost
The PRC (Pre-cast Reinforced Concrete) Certificate scheme was established by the BRE to certify that concrete properties have been repaired to an approved engineering standard. Where a property holds a valid PRC Certificate, mainstream lenders including Halifax, Nationwide, and Santander will generally lend subject to valuation.
The scheme covers: Airey, Boot, Cornish Units (Types 1 and 2), Dorran, Dyke, Gregory, Laing Easiform, Newland, Orlit, Reema Hollow Panel, Schindler, Tarran, Unity, Wates, and Woolaway.
What the Approved Repair Involves
- Demolition of external concrete panels or removal of external skin
- Construction of new external cavity or solid masonry skin over the structural frame
- Structural repairs to concrete frame and connections where required
- New thermal insulation to current or agreed standard
- Re-plastering and internal reinstatement where required
- Engineer's inspection and certification throughout
PRC Certificate Cost Guide (mid-2026)
| Property Type | Estimated Repair Cost | Certificate Validity |
|---|---|---|
| Airey 3-bed semi-detached | £18,000–£28,000 | Runs with the land |
| Cornish Unit 2-bed terraced | £12,000–£20,000 | Runs with the land |
| Wates 3-bed semi-detached | £15,000–£25,000 | Runs with the land |
| Reema / Boot 3-bed semi | £12,000–£22,000 | Runs with the land |
| Woolaway bungalow | £14,000–£24,000 | Runs with the land |
The certificate is issued by an approved PRC Engineer, registered with PRC Homes Ltd, and is attached to the title — it is disclosed in conveyancing and transfers with ownership.
A critical caveat: the certificate must cover the full approved repair scheme. If a previous owner applied pebble-dash over concrete, unapproved render, or a partial repair without obtaining a certificate, the property remains unmortgageable on most lenders' criteria regardless of its appearance.
Specialist Lenders
Where mainstream lenders decline, these specialists may offer terms:
- Skipton Building Society: Will lend on some non-standard types including certain concrete construction with structural reports
- Leeds Building Society: Active in the non-standard market, including Airey with PRC Certificate and timber frame
- Ecology Building Society: Specialist focus on unusual and sustainable construction; not a volume residential lender
- Pepper Money: Non-standard and adverse credit specialist residential mortgages
- Precise Mortgages: Will consider some non-standard types case by case
- West One: Bridging and specialist residential including non-standard construction
Specialist lenders typically charge higher rates (0.5–2% above mainstream equivalent), require a larger deposit (25–40% LTV is common), and may impose conditions around structural insurance and inspection.
Survey Requirements
A mortgage valuation is wholly insufficient for non-standard construction. As a minimum you need an RICS Level 3 Building Survey (Full Structural Survey). For most concrete, steel-frame, and designated types, you additionally need a Chartered Structural Engineer's report.
The structural engineer's report should:
- Confirm the exact construction type and any documented modifications
- Assess current structural condition of frame, panels, connections, and foundations
- Test for carbonation of concrete and corrosion of steel reinforcement where accessible
- Identify required remediation works with cost estimates
- State whether the property is suitable for the PRC approved repair scheme (where applicable)
Use an engineer registered with the Institution of Structural Engineers (IStructE) or a RICS-accredited Chartered Structural Engineer — not a standard residential building surveyor, who will lack the specialist knowledge required to assess reinforced concrete or steel-frame construction.
Cost Implications Table
| Construction Type | Estimated Remediation or Repair | Mortgageability After Works |
|---|---|---|
| Airey (no PRC Certificate) | £18,000–£28,000 for PRC repair + certificate | Mainstream lenders, case by case |
| Cornish Unit (no certificate) | £12,000–£20,000 for PRC repair + certificate | Mainstream lenders |
| BISF (deteriorated cladding) | £15,000–£35,000 for re-cladding | Specialist lender required |
| Wimpey No-Fines (sound condition) | Re-render £3,000–£8,000 | Lender dependent |
| Flat roof (full replacement) | £8,000–£18,000 for pitched conversion | Mainstream lenders after conversion |
| Thatched roof (full re-thatch) | £15,000–£35,000 depending on size | Specialist lender + specialist insurer |
| Woolaway (no PRC Certificate) | £14,000–£24,000 for PRC repair + certificate | Mainstream lenders |
When to Walk Away
Non-standard construction is not automatically a deal-breaker. Airey houses with PRC Certificates in good condition sell regularly and can be financed at competitive rates. The key is working through the investigation in the right order: identify the construction type → confirm lender position → commission specialist survey → decide.
Walk away if:
- The property is a designated defective type with no PRC Certificate and is structurally too deteriorated for the approved repair scheme
- No mainstream or specialist mortgage lender will lend in any circumstances (rare but applies to certain HORSA and converted prefab types)
- You are buying as a short-term investment — the buyer pool for non-standard construction is permanently smaller and average time to sell is measurably longer
- The structural engineer's report identifies defects whose remediation cost exceeds or approaches the property's market value
- The seller or agent cannot confirm the construction type and no documentary evidence is available — you cannot assess risk without knowing what you are buying
Proceed with caution if:
- A current PRC Certificate is held and has been confirmed by the issuing engineer
- A structural engineer has confirmed the building is in sound condition with no active deterioration
- You have a mortgage agreement in principle from a specialist lender who has been given full details of the construction type before issuing the offer
Related Guides
- Structural Engineer Report UK — when to commission a structural assessment, what it costs (£300–£2,500+), and how to read defect categories
- Home Buyers Survey vs Full Structural Survey UK — why a Level 3 survey is the starting point for any non-standard property
- Mortgage on a Property with Issues UK — how construction type and other property conditions affect lending decisions
- Cladding and EWS1 Forms: What Buyers and Leaseholders Need to Know — external wall system risk for flat buyers, overlapping with some non-standard cladding types
- Damp Proof Injection: Does It Actually Work? — damp diagnosis in older construction, including solid concrete and rubble-fill walls where injection is unreliable
- Asbestos in the Home UK: Testing, Removal and Costs — asbestos risk in Woolaway, BISF, and other pre-1980 system-built properties
- Buying a Fixer-Upper Checklist UK — how to build non-standard construction remediation costs into a purchase offer