Spain's CTE climate zones and which window you need

A window that easily passes in Málaga can fall short in Burgos. That's not a figure of speech: Spain's building code, the Código Técnico de la Edificación (CTE), divides the country into climate zones and, for each one, sets the maximum amount of heat a window may let escape. The colder the winter, the stricter the limit. And the zone doesn't depend on the province alone, but on altitude too: within the province of Granada there are villages in zone A and villages in zone E.

In this guide you'll find the climate zone of all 47 mainland provinces, with the capital and the altitude bands that change it, the maximum value the CTE sets for each zone and, most usefully, which combinations of profile and glazing meet it and which don't. Spoiler: almost everything comes down to the glass, not the profile.

What the letter and number of your climate zone mean

Each zone is written as a letter and a number, for example D3 in Madrid or B4 in Seville. The letter measures how harsh the winter is: it runs from α, found only in the Canary Islands, to E, the coldest. The number measures the summer, from 1 to 4, and the higher it is, the hotter.

When choosing a window, the letter matters most, because it sets the thermal transmittance limit. The number comes into play in a different decision, how to keep the sun out, and we'll get to that further down.

Climate zone of each province under the CTE

The table shows the zone of each provincial capital and how it changes with the altitude of the municipality, according to table a of Annex B of the DB-HE (2019 version, revised in 2022). If you don't live in the capital, look up your town's altitude and see which band it falls into: what counts is the altitude of the town centre.

The overall picture fits in one sentence: the Mediterranean coast and the low-lying south are in A and B, the Cantabrian coast, Galicia and Barcelona in C, and the whole central plateau, plus Madrid and the Ebro valley, in D or E. Of the 47 mainland capitals, 25 are in zone D or E. Watch out for intermediate altitudes: in the province of Toledo the boundary is at 500 m, so the capital, at 512 m, is already D3, while Talavera de la Reina, at 367 m, stays in C4.

How much heat a window may let through in each zone

The CTE calls it the thermal transmittance of the opening, UH, measured in W/m²K: the lower, the better it insulates. The limits in table 3.1.1.a-HE1 are: 2.7 in zone A, 2.3 in B, 2.1 in C and 1.8 in D and E (3.2 in α, Canary Islands only).

Two details almost nobody mentions. First, the value applies to the whole unit: frame, glass and, if there is one, the roller shutter box. Good glass with an uninsulated box can put you over the limit. Second, in a renovation the limit applies to the elements you replace. If you change your windows, the new ones must be below your zone's value; the rest of the façade doesn't oblige you to anything.

And if the house is old and the current windows are aluminium without a thermal break? They are typically somewhere between 4 and 6. Any of the low-E options you'll see below comes in at less than half of that.

Which profiles and glazing comply in each zone

We've estimated the transmittance of our windows with the simplified method of EN ISO 10077-1, using the Uf of each profile and the Ug of each glazing unit offered in the configurator. The reference is a single-sash window of 1230 × 1480 mm, the size used for CE marking. These are indicative figures, not a certificate.

The conclusion is plain to see. Low-E glass, an invisible metallic coating that reflects heat back inside, is what separates a compliant window from one that isn't. With it, every casement or tilt-and-turn profile we sell makes it into the coldest zone, even the budget 60 mm one. Without it, not even the best profile will save you outside the warmest stretch of coast. When configuring, look for the "i" at the end of the glazing code: 4-16-4i has a low-E coating; 4-16-4 doesn't.

Now the zone number. In zones 3 and 4, with tough summers, the problem is no longer just the cold getting out but the sun getting in. There a roller shutter or an awning helps more than any glass, and if you choose a shutter with a box, make it an insulated box, because it counts towards UH.

Which window to choose for your zone

Zones A and B, the Mediterranean coast and the low-lying south: a 70–72 mm profile with low-E double glazing is enough. Paying for triple glazing here rarely makes sense.

Zone C, from the Cantabrian coast to Barcelona: the same low-E double glazing complies with room to spare. Zones D and E, the plateau and the mountains: any profile with low-E glass meets the limit, but you'll feel the comfort with 40–44 mm triple glazing and argon, in VEKA 70, WDS 76 or VEKA 82, which also cuts condensation on frosty mornings.

In the configurator you choose the profile, glazing and sash type with your own measurements, and see the price straight away. If you're unsure which glass you need, ask us before confirming the order: every window is made to measure, so it pays to get it right first time.