Guides · checked 29 October 2026
Limecrete floors
Insulated lime floors for old solid-wall houses: the layers, the values, and when they're the right call.
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Figures checked against each source on 29 October 2026. How we check
A limecrete floor is a ground-floor slab made with natural hydraulic lime instead of cement, laid on a bed of loose insulating aggregate such as foamed glass or expanded clay. It lets moisture move through the floor rather than trapping it at the foot of the walls.
Tŷ-Mawr's insulated limecrete floor uses at least 150 mm of foamed glass gravel under at least 100 mm of limecrete. Irish guidance says lime floors may suit old buildings with a delicate moisture balance, but not every old house.
The build-up
- Floor finish Breathable: GreenSpec advises against glazed tiles, cement adhesives and grout, and rubber underlay.
- Limecrete slab Natural hydraulic lime and aggregate, at least 100 mm (Tŷ-Mawr).
- Geotextile Breathable membrane.
- Foamed glass or expanded clay At least 150 mm of foamed glass gravel (Tŷ-Mawr). A capillary break as well as insulation.
- Geotextile
- Dug-out ground Excavated and levelled, after test pits by the walls.
Sources: Tŷ-Mawr, What is the Sublime floor (22 March 2024); GreenSpec, Limecrete floors for old buildings. Checked 29 October 2026.
The insulating aggregates
| Aggregate | Thermal conductivity |
|---|---|
| Foamed glass gravel (Tŷ-Mawr, Glapor) | 0.078 W/mK |
| Foamed glass (GreenSpec) | about 0.075–0.08 W/mK |
| Expanded clay (GreenSpec) | 0.1 W/mK |
Sources: Tŷ-Mawr, What is the Sublime floor (22 March 2024); GreenSpec, Limecrete floors for old buildings. Checked 29 October 2026.
GreenSpec puts foamed glass at about 20% more thermally efficient than expanded clay. The deeper the dig, the more insulation fits.
What the Irish guidance says
- Vapour-permeable floors using lime with hemp or expanded clay may be appropriate where a delicate moisture balance has to be kept.
- Where a radon barrier is needed, the case for these materials is less compelling.
- The Building Regulations imply new floors should be impermeable.
- Digging out a floor can undermine walls with very shallow foundations, or none, and vibration can cause damage. Take care where the water table is high or there's rising damp.
- A new sealed floor can trap moisture that used to evaporate through the floor and push it into the walls.
- In a protected structure, lifting or relaying a floor is likely to need planning permission. Decorative tiles, brick, wood block and stone flags shouldn't be covered.
Source: Department of the Environment, Heritage and Local Government, Energy Efficiency in Traditional Buildings (Advice Series) (2010). Checked 29 October 2026.
Radon
In High Radon Areas, a radon membrane has been required in new buildings since 1 July 1998, according to the EPA. GreenSpec says a membrane will very likely be needed for radon under a limecrete floor too. The EPA's county results show how much radon varies across Leinster: see each county page.
Sources: EPA, Radon advice for builders; GreenSpec, Limecrete floors for old buildings; EPA, Radon results by county (data to 31 December 2019). Checked 29 October 2026.
Underfloor heating
A limecrete floor can take underfloor heating. GreenSpec says the slab is usually left for about three weeks to cure before the pipes go on, and the pipes are then covered with a lime mortar screed. The Department's guidance notes that low, steady underfloor heating in a solid floor helps keep the bottom of the walls dry.
Sources: GreenSpec, Limecrete floors for old buildings; Department of the Environment, Heritage and Local Government, Energy Efficiency in Traditional Buildings (Advice Series) (2010). Checked 29 October 2026.
Old homes in Leinster
| County | Built before 1919 | Built before 1946 | All households |
|---|---|---|---|
| Carlow | 2,070 | 3,372 | 22,174 |
| Dublin | 42,120 | 79,150 | 518,490 |
| Kildare | 3,118 | 5,606 | 82,543 |
| Kilkenny | 4,162 | 6,287 | 36,685 |
| Laois | 2,838 | 4,323 | 31,112 |
| Longford | 1,403 | 2,224 | 16,206 |
| Louth | 3,511 | 6,764 | 49,332 |
| Meath | 3,928 | 6,839 | 72,549 |
| Offaly | 2,535 | 4,608 | 28,702 |
| Westmeath | 2,779 | 4,684 | 34,003 |
| Wexford | 5,725 | 8,936 | 59,081 |
| Wicklow | 5,183 | 8,488 | 54,059 |
Source: CSO Census 2022, table F2067. Checked 29 October 2026. Households in permanent housing units, Census 2022; Dublin is the four Dublin council areas together.
Questions people ask
What is a limecrete floor?
A floor slab made with natural hydraulic lime instead of cement, usually on a bed of foamed glass or expanded clay insulation, so moisture can move through it.
How thick is a limecrete floor?
Tŷ-Mawr's system: at least 150 mm of foamed glass gravel under at least 100 mm of limecrete, plus the floor finish.
Can you put underfloor heating in limecrete?
Yes. GreenSpec says the slab cures for about three weeks before the pipes go on, then a lime mortar screed covers them.
Does a limecrete floor need a radon barrier?
GreenSpec says a membrane will very likely be needed for radon. Irish guidance notes that where a radon barrier is needed, the case for a breathable floor is less compelling.
Can I tile a limecrete floor?
GreenSpec advises against glazed ceramic tiles, cement adhesives and grout, because they stop the floor breathing.
Sources (3)
Prices and facts on this page were checked against these published pages. We are not connected to these businesses.
- Tŷ-Mawr, What is the Sublime floor: lime.org.uk
- GreenSpec, Limecrete floors for old buildings: greenspec.co.uk
- Department of the Environment, Heritage and Local Government, Energy Efficiency in Traditional Buildings (Advice Series): buildingsofireland.ie
Get your floor priced
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