Buying a Non-Standard Construction House: What the Survey Needs to Check and Why Lenders Say No

Reviewed and signed off by Lyman Marshall Surveyors, Director, Chartered Surveyor and RICS Registered Valuer at Lyman Marshall Chartered Surveyors. Published 13 October 2026 · Updated 13 October 2026

Some house types in this country are officially defective. Not “a bit tired”, not “in need of work” — formally designated as defective by government, in law. That designation is why a mortgage offer on an otherwise pleasant three-bedroom semi can collapse in a fortnight.

Non-standard construction is one of the few areas where a survey does more than tell you about the building. It tells you whether the sale can happen at all. Here is what a surveyor is actually looking for, and why lenders behave the way they do.

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What “non-standard construction” actually means

Standard construction, in lending terms, is narrow: masonry walls of brick or stone, with a roof of tile or slate. Anything outside that is non-standard. That covers a great deal more housing than most buyers expect.

• Precast reinforced concrete (PRC) — panel systems such as Airey, Cornish Unit, Woolaway, Orlit and Dorran
• Poured or no-fines concrete, including Wimpey No-Fines
• Steel-framed houses, including the BISF type
• Timber-framed homes, both post-war and modern
• Cob, clay lump and other earth-built walls, which are far from rare in Lincolnshire villages
• Thatched roofs, flat roofs over the majority of the footprint, and single-skin walls
• Large-panel system blocks and some 1960s and 1970s local authority housing

Two homes can look almost identical from the pavement and sit in completely different lending categories. Render hides a great deal. A surveyor who has walked a lot of estates will read the roof line, the window reveals, the panel joints and the eaves detail rather than the front elevation.

The law that still shapes lending decisions

The reason certain concrete house types are treated so cautiously is not lender folklore. It is statute. Under Part XVI of the Housing Act 1985, the Secretary of State may designate a class of buildings as defective where they appear to be defective by reason of their design or construction, and where the value of the dwellings has been substantially reduced as a result of that becoming generally known.

That is a strikingly blunt piece of drafting. It ties the legal status of the house to two things at once: a physical defect, and a collapse in market confidence. Both still follow the affected house types today, decades after the assistance schemes attached to the legislation closed.

The underlying problem in PRC housing is corrosion. Steel reinforcement inside the concrete panels rusts, and rusting steel expands, cracking the concrete around it from the inside out. By the time it is visible on the surface, it has usually been progressing for years.

What the survey needs to check

A competent inspection of a non-standard home answers a different set of questions from a conventional one. Identification comes first — everything else follows from it.

1. What is it, precisely?

Not “it’s concrete” but which system, because the known failure modes differ between them. This dictates what the surveyor examines and what the lender will ask for.

2. Has it been repaired, and to what standard?

Many PRC homes have been structurally repaired under a recognised scheme, with the original panels replaced or reinforced. A repaired house is a very different proposition from an unrepaired one, and the paperwork matters as much as the brickwork.

3. Is there evidence of the type-specific defect?

Cracking following the line of a panel joint, rust staining, spalling concrete at column bases, movement at the junction between panels and roof. In steel-framed housing, corrosion at the frame feet where it meets the ground floor slab.

4. What has been done to it since?

Over-cladding, render, insulation and extensions can conceal the structure entirely. They can also introduce moisture problems that accelerate the original defect. A surveyor will want to know what is behind the finish, and will say plainly where they cannot see.

5. Is the rest of the house sound?

The construction type absorbs the attention, but these are still houses. Roofs, drainage, damp, windows and services all still need reporting on.

Why lenders say no — and what changes their mind

A lender is not primarily worried about whether the house will fall down. It is worried about whether it could sell the property if it ever had to repossess it. A house type with a restricted buyer pool is weak security, and that alone is enough for a decline.

For designated PRC types, the thing that usually unlocks lending is documented structural repair under a recognised scheme, evidenced by a certificate of structural adequacy from an approved engineer. The Building Research Establishment operates a scheme covering repairs to precast reinforced concrete homes, and lenders look for that kind of recognised route rather than an undocumented private repair.

Without that evidence, options narrow to specialist lenders, larger deposits, or a cash purchase. With it, many mainstream lenders will treat the property far more conventionally.

Timber frame and steel frame sit differently again. Both are widely accepted in principle, but lenders frequently ask for a specific comment from the surveyor confirming the frame’s condition and how the external skin is performing.

Which survey do you need?

For any home outside standard construction, the more detailed inspection is the sensible choice. A RICS Level 3 Building Survey examines the fabric of the building in depth and reports on the causes of defects rather than simply recording that they exist — which is exactly what you need when the construction type is itself the question.

The difference in scope between the two survey levels matters more here than on a conventional house. If you are weighing them up, our guide to choosing between a Level 2 and a Level 3 survey sets out where the line falls. The same logic applies to older and unusual buildings generally, as our note on surveying listed buildings explains.

It is also worth being clear about what your lender’s own valuation does and does not do. It is a valuation for the lender’s purposes, not an inspection for yours — a distinction we cover in more detail in our piece on whether mortgage lenders require a survey.

If you are already under offer

Finding out mid-transaction is uncomfortable but far from fatal. In order:

• Establish the construction type properly before doing anything else. Ask the agent for the deeds, any repair certificates, and the address history.
• Commission a detailed survey from a surveyor who has inspected that system before, and tell them what the lender has said.
• Give the report and any certification to your broker, so the case can be placed with a lender that accepts the type.
• Where repair is needed, get costs before renegotiating — a figure supported by a report is far more persuasive than an estimate.

The buyers who lose money on these purchases are usually the ones who discovered the issue late and made a decision quickly. The ones who do well take an extra fortnight and buy the information first.