Non-standard construction: PRC, timber frame and system-built homes

Non-standard construction means a home is not built in the conventional way, usually brick or block walls with a slate or tiled roof. It includes post-war precast reinforced concrete (PRC) houses, steel-framed homes, no-fines concrete, some timber frame systems and other system-built designs. These homes can be good value, but they can be harder to mortgage and insure, and some have known defects, so you need the right survey and the right lender.

Key points

• Each lender has its own definition of non-standard construction and its own lending policy.
• Some PRC house types were designated defective under the Housing Defects Act 1984.
• Repaired PRC homes with a PRC Homes Ltd certificate are usually more mortgageable.
• Modern timber frame with a masonry outer leaf is generally treated as standard.
• A Level 3 Building Survey by a surveyor familiar with the construction is usually the best choice.

Why were non-standard homes built?

After the Second World War, the UK faced a severe housing shortage and a lack of skilled labour and traditional materials. Local authorities and government turned to factory-made and system-built homes that could be erected quickly. Hundreds of different systems were used, many of them by councils, and many of these homes were later sold to tenants under Right to Buy. They are now common in the resale market, particularly in former council estates.

What are the main types of non-standard construction?

Precast reinforced concrete (PRC)

PRC homes use concrete panels and columns cast in a factory and assembled on site. Common names include Airey, Cornish Unit, Orlit, Reema, Unity, Wates, Woolaway and Parkinson. In the 1980s, problems were found with the steel reinforcement corroding and the concrete cracking. Many PRC types were designated defective under the Housing Defects Act 1984.

Some PRC homes have been repaired by replacing the concrete structure with a brick outer wall or another approved method. A home repaired under an approved scheme and certified by PRC Homes Ltd is usually treated more favourably by lenders. Unrepaired designated homes are often difficult to mortgage.

In-situ concrete and no-fines

Wimpey No-Fines and similar systems used concrete poured on site into shutters. No-fines concrete is generally more accepted by lenders than PRC, but each lender's policy differs.

Steel-framed homes

Steel-framed systems such as BISF (British Iron and Steel Federation) houses used a steel frame with cladding. The main concern is corrosion of the steel frame, especially at the base of columns. Some lenders accept them with a satisfactory structural report.

Timber frame

Modern timber frame homes, with a timber structural frame inside a brick or block outer skin, are common and generally accepted as standard by most lenders. Older or less conventional timber frame systems, homes with timber cladding and some early post-war designs may be treated as non-standard. The main risks are moisture and decay in the frame, often caused by defective cavity barriers, damp proof courses or leaks.

Other construction types lenders may flag

• Mundic block homes in Cornwall and parts of Devon, where concrete made with mine waste aggregate can deteriorate. A mundic test is often required.
• Large panel systems, mainly in high-rise flats.
• Thatched roofs and flat roofs over a large part of the home.
• Cob, stone and other traditional methods in some areas, which are not defective but may need specialist knowledge.
• Modern methods of construction (MMC), such as volumetric modular and some panelised systems. Lenders often look for warranties and accreditation.

How do you know if a house is non-standard construction?

The estate agent should tell you, but it is not always clear from the listing. Clues include:

• The property is a former council house built from the late 1940s to the 1970s.
• External walls look like concrete panels, render or cladding rather than brick.
• The ground floor and upper floor have different finishes.
• Neighbouring homes look identical and unusual.

A lender's valuer will identify the construction type, and so will your surveyor. Ask the agent early so you can speak to a broker.

Getting a mortgage on a non-standard home

Lender policies vary. Some lenders will lend on many non-standard types, some on very few. You may face:

• A larger deposit requirement.
• A specialist structural engineer's report or certificate.
• Lower valuations than equivalent standard homes.
• Fewer lenders available, and potentially higher rates.

A broker with experience of non-standard construction is valuable here. Resale is also worth considering, because your future buyer will face the same restrictions.

Which survey is best for a non-standard home?

A Level 3 Building Survey is usually the best choice, because it gives a more detailed description of the construction, its known risks and condition. Choose a surveyor familiar with the system, and mention the construction type when booking. A Level 2 Home Survey may be enough for well-documented modern timber frame homes. If you are unsure, see Level 2 vs Level 3.

You may also need:

• A specialist structural engineer's report, particularly for PRC and steel frame homes.
• Copies of any repair certificates and building control sign-off.
• Evidence of warranties for newer MMC homes.

What do surveyors look for in non-standard homes?

• Concrete cracking, spalling and rust staining, which can indicate corroding reinforcement in PRC homes.
• Corrosion of steel frames, often at ground level or where damp is present.
• Damp, decay and condensation in timber frame homes.
• Cladding condition and fixings.
• Alterations such as extensions, which can be complicated on system-built homes.
• Asbestos-containing panels, which were used in some post-war systems. See our guide to asbestos in older homes.

Insurance for non-standard homes

Some mainstream insurers decline non-standard construction or charge more, so get buildings insurance quotes before you exchange. Specialist insurers and brokers often cover these homes, but you will need to describe the construction accurately. Getting it wrong could invalidate a claim, so use the construction type identified in your survey.

If you are buying a home of unusual construction, get a fixed-price survey booked with a local RICS or RPSA regulated surveyor. Tell us the construction type, and we will find a surveyor with the right experience.

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