Natural Insulation Guide for UK Homes: Cork, Lime, Hemp and Wood Fibre
- Daniel Turk
- 5 days ago
- 4 min read
“How can I make my home warmer and healthier without filling it with plastics and petrochemical foams?” More and more homeowners in the UK are asking the same question
The answer lies in a family of natural building materials that our grandparents would recognise – updated with modern testing and application methods.
In this guide, we’ll look at four of the most useful: cork, lime, hemp and wood fibre – what they are, how they behave, and where they make sense in a typical UK home.
Why Natural Materials?
Natural materials aren’t just about being “eco”. They change how a building feels:
They are often vapour‑permeable, helping walls breathe instead of trapping moisture.
Many are hygroscopic – they absorb and release moisture, smoothing out humidity swings.
They tend to have low embodied carbon and are easier to live with: fewer toxins, better indoor air quality.
You still need to think about U‑values and energy bills, but comfort, moisture and durability are just as important – especially in older solid‑wall homes.
Cork: Boards, Cork Plaster and Cork Spray
Cork comes from the bark of the cork oak tree. The tree isn’t cut down; the bark is harvested every few years, making cork a genuinely renewable material. It’s naturally rot‑resistant, mould‑resistant and fire‑resistant, which is why it’s so interesting for buildings.
Where cork is used
Cork Boards – for internal or external wall insulation, floors and roofs.
Cork Coatings – cork spray and cork plaster applied in thin layers on internal or external walls.
Cork boards have a thermal conductivity (lambda) around 0.037–0.040 W/m·K, similar to many mainstream insulations, but with the bonus of being breathable and natural.
Seamless Cork Coatings, like TIWI CorkPlaster and TIWI CorkSpray, sit between 0.04–0.07 W/m·K. At only 2–6mm thick, they’re not a replacement for say 100mm of insulation, but they:
Raise internal surface temperatures
Help reduce cold spots and condensation
Provide a flexible, crack‑resistant, breathable finish
Good sound insulation
Vapour‑open – allows moisture to move through the wall
Fire-resistance
That makes them ideal as a thermal corrector on solid walls, or as a protective, natural and pre-coloured façade coating.
Lime: Breathable Plasters and Mortars
Lime has been used in British buildings for centuries. Unlike modern cement, lime‑based plasters and mortars are:
Vapour‑open – they allow moisture to move through the wall
Slightly flexible, which helps reduce cracking on older structures
Naturally alkaline, which discourages mould growth
On its own, lime isn’t a strong insulator, but when combined with cork granules, hemp shiv or lightweight aggregates, it becomes an insulating lime plaster. These mixes don’t chase extreme lambda values; instead they focus on:
Warmer internal surfaces
Moisture buffering
Long‑term durability of solid brick and stone walls
Lime pairs beautifully with cork coatings – lime as the base, cork as the protective, thermal‑correcting finish.
Hemp: Batts and Hemp‑lime (hempcrete)
Hemp is a fast‑growing plant that locks up carbon as it grows. In construction you’ll mainly see:
Hemp batts – used between studs and rafters
Hemp‑lime (hempcrete) – a mix of hemp shiv and lime binder, cast into walls or used as an internal lining
Hemp‑based insulations typically sit around 0.038–0.045 W/m·K, with excellent moisture buffering and good acoustic performance. They’re ideal for:
Timber frame construction
Internal linings where you want a fully breathable build‑up
Deep retrofits where you can afford to add thickness
Hemp is rarely a thin surface layer; it’s a bulk insulation that works best when you can give it space.
Wood Fibre: Boards and Batts
Wood fibre insulation is made from wood chips and sawmill by‑products, pressed into boards or batts. It’s another material that fits perfectly with breathable, natural construction.
Typical lambda is around 0.037–0.045 W/m·K, but its real strength is:
High density and heat capacity – great for summer overheating control
Vapour‑permeability – lets walls dry out
Good sound insulation
Wood fibre boards are often used:
Internally on solid brick walls, finished with lime or clay plaster
Externally as part of an EWI system
In roofs and loft conversions
Again, this is a thicker layer solution, not a 2–3 mm skim for examples.
Putting it together: choosing the right natural material
There’s no single “best” natural material. The right choice depends on:
Space – how much thickness can you afford to lose?
Wall type – solid brick, stone, cavity, timber frame?
Moisture – is the wall currently damp, or at risk of condensation?
Goal – deep energy retrofit, or mainly comfort and mould control?
A sensible approach for many UK solid‑wall homes looks like:
Use wood fibre, hemp or cork boards where you can add real thickness and chase lower U‑values.
Use lime‑based plasters to keep the wall breathable and compatible with old masonry.
Use thin cork systems – cork plaster or cork spray – as a thermal corrector and protective finish, especially where space is tight or you’re targeting cold surfaces and condensation rather than a full insulation upgrade.
Final thoughts
Natural materials won’t always give you the absolute lowest U‑value on paper, but they can deliver something more valuable: warmer, drier, healthier homes that can breathe.
Cork, lime, hemp and wood fibre each bring something different to the table. When they’re combined intelligently, they create building envelopes that are comfortable to live in, kinder to the planet, and far more forgiving than hard, sealed‑up, plastic‑heavy constructions.
If you’re planning work on a solid‑wall UK home and want to explore how cork‑based plasters and sprays can sit alongside other natural materials, that’s exactly the space we specialise in.
