Thermal-break aluminium windows explained

Aluminium is a good conductor of heat. That is useful in a saucepan and unhelpful in a window frame. A thermal break is the fix: a bar of low-conductivity material set between the inner and outer aluminium shells of the profile, so the metal path from the warm room side to the hot or cold outside is interrupted. In the Schüco AWS 75 system literature the bars are polyamide. The principle is the same across manufacturers.

This matters in Malta for three separate reasons — the grant threshold, condensation on frames, and the direction of EU building rules — and they are worth keeping apart.

The numbers, and where they come from

There is no Maltese default window table that we could find. The clearest published set comes from the NSW Government planning portal in Australia, used for its BASIX thermal comfort method. It is foreign data, and we are saying so: Australian defaults, a mild-climate proxy rather than anything certified for Malta.

The jump from 4.8 to 3.6 is the thermal break doing its work. Nothing else changed in that row.

Why 3.7 is the number that matters here

The REWS RIDG 2023 scheme — roof insulation and double glazing, retrofitting only — requires the finished double-glazed unit to reach a U-value of 3.7 W/m²K or better. Schedule I of the guidelines puts the evidence burden on the retailer, who must supply a manufacturer's certificate of thermal conductivity, and on the installer, who certifies the gap. Products must appear on the REWS registered list, the glazing must be bought in Malta, and a five-year warranty is required. Part A goes in before you buy anything. Landlords are excluded; it is for your own primary residence, as owner or as a lessee of more than five years, and the work has to be fitted within six months. The grant pays 50% of eligible cost including VAT, capped at EUR 1,000 for double glazing, first come first served. GN 2031 of 2025 extended it to 31 December 2026.

Set the NSW defaults against that 3.7 and the shape of the problem is obvious. Plain aluminium with double glazing sits at about 4.8, or 4.5 with argon — above the limit. Thermally broken aluminium sits at about 3.6, or 3.5 with argon — below it. uPVC and timber are further below again.

Two honest caveats. First, those are whole-window values including the frame, whereas the RIDG wording attaches the 3.7 to the finished double-glazed unit; the sources do not reconcile the two metrics, so treat the table as a comparison of frame types rather than a compliance calculation. Second, the grant is decided by the certificate and the registered list, not by a default table from another country. We checked these grant figures before the Budget 2027 presentation on 26 October 2026, and a Budget can change them. Whether money remains in the pot at any given moment is not something we can verify.

Condensation on cold frames

The second reason is one people notice before they notice any bill. Technoform — which makes insulating bars and spacers, so read it as an industry source — sets it out directly: aluminium lets heat flow freely from the warm room side to the outside, so in cold weather the inner edge of the glass and the frame become much colder than the room. Condensation forms when that surface drops below the dew point. Low-conductivity components, whether an insulating bar in the frame or a warm-edge spacer at the glass edge, keep the inner surface warmer.

In Maltese flats with limited cross-ventilation and a lot of moisture from cooking and drying, a cold aluminium frame is a reliable place for water to appear in January. A thermal break raises the surface temperature. It does not control your indoor humidity.

What a manufacturer's brochure actually shows

To show the spread of frame values within one premium range, here is what the Schüco AWS 75 brochure published by Thermosash, a Schüco partner, states. This is a manufacturer's document, it is not a recommendation, and we have no data for how these figures translate to systems sold in Malta.

• AWS 75.SI+: frame U-value (Uf) from 0.92 W/m²K with special insulating bars, and 1.2 W/m²K at 117 mm face width, giving a whole-window Uw of 0.90 with a glass Ug of 0.6. Basic depth 75 mm.
• The range table: passive-house series Uf 0.71–0.8 at 90 mm depth; AWS 75 at 1.3–1.4; AWS 65 at 1.9–2.6; AWS 60 at 1.7–2.1.

Note how much of the range is simply profile depth. The same brochure lists RC3 burglar resistance to EN 1627, watertightness class 9A to EN 12208, air permeability class 4 to EN 12207 and wind load C5/B5 to EN 12210 — the classifications worth asking about for an exposed Gozo or coastal elevation, alongside the U-value.

Where the law sits

A 2017 Ecofys study for Glass for Europe recorded Malta's minimum requirement for replacement windows as Uw 4.0 W/m²K, with a g-value of 0.89, applying even to a single replaced window but only where glazing is at least 20% of the exposed wall area. For context, the same table gives Cyprus 2.9, Germany 1.3 and Austria 1.2. That figure came from the 2015 edition of Document F. We could not load the current 2023 Technical Guidance Document F to confirm what it now says, so treat 4.0 as historic and check the current requirement with the BCA or your perit rather than taking it from us.

The direction of travel is set by the revised Energy Performance of Buildings Directive, (EU) 2024/1275, in force since 28 May 2024 with a transposition deadline of 29 May 2026. For residential stock it targets a 16% cut in average primary energy use by 2030 and 20–22% by 2035, with at least 55% of the reduction coming from the worst-performing buildings, plus a zero-emission standard for new buildings, a common EPC template and renovation passports. How Malta transposes that is not something these sources settle.

Malta-specific practicalities

Replacing apertures is permitted development under DNO S.L. 552.08, Schedule I, Class 1(ii), unless the work materially alters the character of the building. In scheduled buildings and those of conservation value, restorable original timber apertures must be retained and restored — which can rule out an aluminium swap regardless of its U-value. In a block, condominium rules bind works to the common parts and the façade. Shell-form purchases mean the first set of apertures is usually yours to specify from scratch rather than a replacement, which puts the retrofit-only RIDG scheme out of reach for that work. And every Gozo delivery involves the ferry, which affects scheduling more than it affects price.

On cost, the published Maltese guide range for aluminium is EUR 200–450 per m² for non-thermal and EUR 350–700 per m² for thermal break. That gap is the premium you are weighing against a grant capped at EUR 1,000.

We survey and measure every job ourselves. From there it is delivered either by us as contractor, using CheckYourTraders-verified installers, or by a vetted partner who contracts directly with you. The U-value evidence for a grant application comes from the manufacturer's certificate and the REWS registered list, which is why specification is settled at the measure-up and not before.