No fines concrete construction is one of the most misunderstood and most problematic types of wall insulation when it comes to insulation. If your property was built between the 1940s and 1970s, particularly through a local authority housing programme, there is a meaningful chance it uses no fines concrete. Standard cavity wall insulation systems do not apply here, and applying the wrong treatment can cause serious and expensive problems. This guide explains what no fines concrete is, why it behaves differently from brick construction, and what your options actually are.
What Is No Fines Concrete?
No fines concrete is a construction method that uses coarse aggregate and cement but deliberately excludes the fine sand particles that give standard concrete its density. The result is a porous, open textured material full of interconnected voids. Walls built from no fines concrete are typically cast in a single leaf, around 230 to 250mm thick, with no cavity. The types of wall insulation here is different.
The method was popular in post war local authority housing programmes because it was fast to construct using shuttered formwork systems. Entire estates of identical properties were built using no fines concrete across Scotland, the north of England, and parts of Wales and the Midlands. Many of these properties are now in private ownership following the right to buy programme.
You can often identify no fines concrete from the outside by the distinctive dimpled, open textured render that covers the structural wall. Inside, the walls feel dense and cold to the touch but lack the smooth, regular surface of a plastered brick wall.
Why Standard Insulation Does Not Apply
No fines concrete walls present two specific challenges that make standard insulation approaches inappropriate or risky.
No Cavity
No fines concrete construction uses a single leaf wall with no cavity. Cavity wall insulation, the cheapest and most common form of wall insulation in the UK, simply does not apply. There is nothing to fill.
The Porosity Problem
Not all types of wall insulation are the same. The open, voided structure of no fines concrete means the wall absorbs and transmits moisture in a way that dense brick does not. Rain penetrates the outer face, travels through the voids in the concrete, and exits at the inner face. In an unmodified no fines concrete wall, this is managed by the original render coat on the outside, which is designed to be the primary weather barrier.
Any insulation system applied to a no fines concrete wall must either maintain this weather barrier function or replace it entirely. A system that compromises the weather barrier without providing an equivalent replacement will drive moisture inward.
This is the core reason why some insulation treatments that work well on brick properties fail badly on no fines concrete.
What Happens When the Wrong Types of Wall Insulation Are Used
The failure mode most commonly associated with poorly specified insulation on no fines concrete is internal damp following the injection of cavity wall insulation into properties that do not actually have a cavity, or that have a void in the render coat that gets filled without addressing the underlying structure.
Some no fines concrete properties were incorrectly assessed as cavity wall construction during large scale insulation programmes in the 1980s and 1990s. Insulation material was injected into the wall but, because the wall is solid porous concrete rather than a true cavity, the material bridged moisture pathways rather than filling a discrete void. Persistent internal damp followed in a proportion of these cases.
If your no fines concrete property had insulation injected and you subsequently experienced damp problems, this is the most likely explanation.
The Right Options for No Fines Concrete – Types of Wall Insulation
External Wall Insulation
EWI is generally the recommended solution for no fines concrete properties. Applied correctly, it provides a new weather barrier on the outside of the building, eliminates moisture ingress through the original porous structure, and delivers a substantial improvement in thermal performance.
The critical requirement is that the EWI system includes a continuous, weather resistant render or cladding finish that replaces the function of the original render coat. The system also needs to be breathable enough to allow any residual moisture in the concrete structure to escape outward during dry periods.
Woodfibre or mineral wool insulation boards are often preferred over EPS on no fines concrete because they are more vapour permeable, which supports the moisture management of the underlying wall. The finish coat should be a silicone or mineral render with good vapour permeability.
The substrate assessment is particularly important on no fines concrete. The pullout strength of mechanical fixings into porous concrete differs from that in dense brick, and the installer needs to test this before specifying the fixing pattern.
Internal Wall Insulation
Internal wall insulation is possible on no fines concrete but requires careful attention to vapour control. The insulation must include a vapour control layer on the warm side to prevent moisture from the room air condensing within the wall construction. Without this, interstitial condensation can occur at the cold, porous concrete surface behind the insulation.
Internal insulation on no fines concrete works best with a breathable insulation system, woodfibre or hemp, combined with a correctly positioned vapour control layer. Rigid closed cell insulation boards applied directly to the concrete face without adequate vapour control have a higher risk of moisture problems.
Internal insulation also reduces the internal floor area and requires repositioning skirting boards, radiators, electrical sockets, and window reveals, a significant disruption compared to EWI.
Solid Wall Insulation Through Government Schemes
No fines concrete properties are eligible for solid wall insulation funding through ECO4 and the Great British Insulation Scheme, provided the household meets the eligibility criteria. An installer who understands no fines concrete construction should be able to assess the property and confirm eligibility.
The key is finding an installer with specific experience in this construction type. Not all PAS 2030 certified installers have worked on no fines concrete, and the specification needs to come from someone who understands its particular moisture management requirements.
Finding Out If Your Property Is No Fines Concrete
If you are not certain whether your property uses no fines concrete construction, several checks help:
Build date and type. Properties built between 1945 and 1975 through local authority programmes in Scotland, the north of England, and Wales have a higher probability of no fines concrete construction.
External appearance. The original render on no fines concrete properties has a distinctive dimpled, coarse textured appearance that differs from sand and cement render on brick.
Local authority records. If the property was originally council owned, the local authority may have construction records. These are not always accessible to private owners but are worth requesting.
Professional survey. A building surveyor can identify no fines concrete from an inspection and confirm the wall construction type. This survey is worth commissioning before any insulation work to ensure the system is correctly specified.
Frequently Asked Questions About Types of Wall Insulation
Can I get free insulation for a no fines concrete house? Possibly. No fines concrete properties are eligible for solid wall insulation funding through ECO4 and GBIS if the household meets the eligibility criteria. Contact a TrustMark registered installer to run an eligibility check for all types of wall insulation.
Why did my no fines concrete house develop damp after insulation was installed? The most likely cause is that cavity wall insulation was injected into a wall that either had no true cavity or had the insulation material penetrate the porous structure in a way that bridged moisture pathways. If this has happened, a specialist survey is needed to diagnose the extent of the problem before deciding on remedial action and choosing between types of wall insulation.
Is EWI always the best option for no fines concrete? It is generally the preferred option because it addresses the weather barrier function of the original render and eliminates moisture ingress from outside. Internal insulation is technically possible but requires more careful specification and carries a higher risk if the vapour control is not correct.
Do I need planning permission for EWI on a no fines concrete house? The planning rules for EWI on no fines concrete houses are the same as for brick properties. Permitted development rights cover EWI for most houses in England, but conservation areas and listed buildings require specific consent. Check with your local planning authority if you are in a sensitive location for different types of wall insulation.
Information correct as of April 2026. Always commission a professional survey to confirm wall construction type before specifying any insulation system for a no fines concrete property.
Information and cost ranges correct as of April 2026. Always obtain a professional diagnosis before commissioning cavity wall insulation extraction.