6 August 2026
Do thicker walls mean better insulation? Comparing 8 Maltese wall types
Traditional limestone, a torba-infilled farmhouse wall, standard concrete block, and insulated block and limestone — compared using Malta's own Document F reference values.
There's a common assumption in Malta that a thick stone wall is automatically a well-insulated one — that mass alone keeps a home cool in summer and warm in winter. It's an understandable assumption, and it's wrong often enough to be worth correcting. If you haven't already, it's worth reading our guide to what a U-value is and how it's calculated first — everything below builds on it.
To test the assumption properly, we compared eight real Maltese wall constructions — solid limestone at two thicknesses, a traditional cavity wall, an old farmhouse wall, standard concrete block, and three insulated variants — using the same reference values Malta's building regulator uses: Technical Document F Part 1 (Building and Construction Authority, effective 1 July 2024). Its Appendix B publishes thermal conductivity values for local materials, including limestone, hollow concrete block, and even torba — crushed limestone chippings used as a traditional infill — which is exactly what we used to calculate every U-value below.
A quick note on the numbers
Every wall below uses soft Franka limestone throughout (so the comparison isolates thickness and construction, not stone type) and a standard 230mm hollow concrete block — rendered outside and plastered inside in every case. U-values are calculated using Document F's own layer-resistance method (R = d/λ, U = 1/R total, with its published surface resistances) and its own Appendix B material values. Document F's wall U-value limits are 1.22 W/m²K for new dwellings and 1.57 W/m²K for major renovations.
Limestone walls
Solid soft Franka limestone
197mm overall
A single 180mm leaf of soft Franka limestone, rendered outside and plastered inside. Thinner than most people picture a “stone wall,” but still solid stone, no cavity.
Solid soft Franka limestone
247mm overall
The same construction, 50mm thicker at 230mm — matching the width of a standard concrete block, for a like-for-like comparison later on.
Traditional cavity wall, air gap
367mm overall
Two 150mm limestone leaves with a 50mm unfilled air cavity between them — the classic “townhouse” wall build, no infill, no insulation.
Old farmhouse wall
917mm overall
Two thick 300mm limestone leaves around a 300mm torba (crushed limestone chippings) infill core — close to 90cm overall, the kind of wall you find in older farmhouses.
Solid Franka limestone + 50mm insulation
307mm overall
The same 230mm limestone leaf as above, with the same insulation upgrade used on the concrete block wall further down — an air gap, a 50mm insulation board, then plaster. Proof the fix isn't specific to concrete block: it's the insulation doing the work, on any substrate.
Modern concrete block walls
The standard build doesn't meet the standard
A rendered, unfilled 230mm HCB wall — no cavity insulation, no upgrade of any kind — is the most common wall construction going up in Malta right now. At 2.11 W/m²K it comes in well above Document F's 1.22 W/m²K limit for new dwellings. Building to what's common isn't the same as building to what's required.
Standard HCB — today’s typical build
247mm overall
A single 230mm hollow concrete block, rendered outside and plastered inside. No cavity, no insulation — this is the most common wall construction being built in Malta today, and on its own it doesn't meet Document F's requirement for new dwellings.
HCB + 25mm insulation
282mm overall
The same 230mm block, with a 25mm XPS insulation board and 10mm air gap added before the internal plaster — Document F Part 1’s own example for meeting the major-renovation limit.
HCB + 50mm insulation
307mm overall
The same block again, this time with a 50mm insulation board — Document F Part 1’s own example for meeting the new-build limit, with room to spare.
All eight, side by side
Sorted from best to worst performing. Notice where the thickest wall on the list — the farmhouse wall, at close to 90cm — actually lands.
Dashed lines mark Document F Part 1's wall U-value limits: 1.22 W/m²K for new dwellings, 1.57 W/m²K for major renovations. Values in W/m²K, lower is better.
View as a table
| wall type | U-value (W/m²K) | Status |
|---|---|---|
| HCB + 50mm insulation | 0.40 | Meets new-build limit |
| Limestone (230mm) + 50mm insulation | 0.42 | Meets new-build limit |
| HCB + 25mm insulation | 0.65 | Meets new-build limit |
| Old farmhouse wall (torba) | 0.90 | Meets new-build limit |
| Traditional cavity wall (air gap) | 1.56 | Above new-build limit |
| Standard HCB, no insulation | 2.11 | Above new-build limit |
| Solid limestone (230mm) | 2.51 | Above new-build limit |
| Solid limestone (180mm) | 2.83 | Above new-build limit |
What this actually shows
A few things stand out once the numbers are side by side. First, the standard concrete block wall being built across Malta right now — 230mm, rendered, no insulation — performs worse than a 90cm-thick farmhouse wall from a century ago. Nearly four times the thickness, and the old wall still wins, because torba, despite its reputation, has a genuinely useful thermal conductivity — it just takes an enormous amount of it to add up to real resistance.
Second, an unfilled air cavity and a torba-filled one perform almost identically once you compare a realistic thickness of each. Torba is just limestone, crushed into loose chippings — the air trapped between the fragments is what gives it a slightly lower conductivity than the same stone solid and dressed. It's not a different material, just a looser packing of the same one, and neither it nor a plain air gap is doing much real insulating work.
Third, and most importantly: adding a layer of real insulation to the exact same 230mm block — not a thicker wall, the same one — drops the U-value by up to 5×. A wall built to Document F's own new-build example ends up performing better than the farmhouse wall, at barely a third of the thickness. Thickness helps, a little, within the same material. What actually transforms a wall's performance is whether a proper insulation layer is present at all.
And it's not a concrete-block trick. Add the same insulation board to the 230mm solid limestone wall instead, and it lands at 0.42 W/m²K — practically identical to insulating the block. The leaf underneath barely matters once a real insulation layer is doing the work.
Walls are only half the envelope — see how seven real Maltese roof constructions compare using the same method.
Wondering what your own property's walls actually add up to? Request a free quote and we'll take it from there. We're also working on an interactive calculator so you can build up your own wall construction and see the U-value update live — keep an eye on this space.