What is the correct thickness of insulation for my area? (Climate Zones)

Solutions & Applications · Decision-making tool

The correct thickness is not a case of ‘the thicker, the better’. It is determined by two factors multiplied together: the project’s climate zone and the material’s λ-value. Changing one alters the other.

Step 1 — The climate zone

According to KENAK, Greece is divided into four zones, from the warmest (A) to the coldest (D). The regulation specifies a maximum heat transfer coefficient (U_max) for walls in each zone — the lower the value, the more insulation is required.

Zone	Indicative areas	Umax wall	Indicative thickness*
A	Crete, the Aegean Islands, the Dodecanese, the southern Peloponnese	≤ 0.55 W/m²K	~5 cm
B	Attica, the Cyclades, the Ionian Islands, and a large part of the southern mainland	≤ 0.45 W/m²K	~6 cm
C	Central and Western Macedonia (lowlands), Thessaly, Epirus	≤ 0.40 W/m²K	~7 cm
D	Western Macedonia, Florina, Grevena, mountainous areas	≤ 0.35 W/m²K	~8 cm

*Indicative thickness for insulation with λ ≈ 0.035 W/mK. The exact thickness is determined by the energy assessment in accordance with TOTE 20701-1.

Step 2 — The material: why the ‘l’ determines the thickness

Two materials with different thermal conductivity coefficients give the same U-value at different thicknesses: the lower the λ, the thinner the slab.

Material	λ (W/mK)	Its unique selling point
Stone wool	≈ 0.036	Non-combustible A1, breathable, sound insulation — mandatory where the design requires fire safety
White EPS	≈ 0.036	Cost-effective and lightweight — maximum thickness per euro
Graphite-filled EPS	≈ 0.031	The same U-value with ~10–15 per cent less thickness — where space is limited
XPS	≈ 0.034	Waterproofing — base course, plinth, areas with damp

The l column shows that the four values fall within the same range. The choice is therefore not based on thermal performance — it is based on fire safety, vapour permeability, moisture resistance or available thickness. The thermal performance is determined by the thickness.

Four practical observations

1. The table is for illustrative purposes only. The final thickness is determined by the energy assessment, taking into account the composition of the existing wall — a double-skin wall with a cavity starts from a different basis than a concrete wall.
2. New buildings have stricter requirements than major refurbishments. The same zone does not necessarily mean the same thickness.
3. Commercial thicknesses are available in the following increments: 50 / 60 / 70 / 80 / 100 mm. We always round up: the cost difference of one centimetre is small, but failure in inspection is not.
4. The base layer is always XPS, regardless of the climate zone. In this case, the criterion is not thermal but moisture-related.

From thickness to system

Thickness is half the decision. The other half is which system will provide it — and the criteria are different:

If the crucial factor is…	System
Cost per square metre and maximum thickness	Ceretherm POPULAR — EPS
Classification A2 or ventilation in an old building	CERETHERM WOOL CLASSIC — stone wool
Seismic reinforcement, impacts, ground contact	SST with XPS
Architectural elevation of exposed concrete	CERETHERM VISAGE CONCRETE

The Four Insulation Materials

System Materials & Basic Details

System Selection