The Ultimate Guide to Aluminium Windows

Aluminium's core advantage is strength relative to its cross-section. Because the material does not need to be as thick as timber or uPVC to support the same pane of glass, sightlines can be reduced substantially, which means more visible glass in the same opening. On a home with a good view — over a fell, a lake, or simply a well-landscaped garden — that difference is easy to see and hard to unsee once you have.

It is also dimensionally stable. Aluminium does not swell, shrink or warp with moisture the way timber can, and it does not soften in strong sun the way some uPVC profiles do over many years. For large sliding doors and tall windows, that stability matters more than it might on a small kitchen window.

• Slim sightlines — more glass, less frame, for the same opening size
• Long service life with minimal maintenance beyond occasional cleaning
• Powder-coated finish available in almost any RAL colour, inside and out
• Strong enough for large sliding doors, corner glazing and oversized fixed lights
• Recyclable material with a strong environmental case at end of life

A modern aluminium window is not a solid metal frame. It is two aluminium sections — an inner and an outer — separated by a thermal break, usually a polyamide bar, which stops heat conducting straight through the frame from outside to inside. Without a thermal break, aluminium would be a poor performer; with one, it competes with timber and uPVC on U-value.

The glass sits in the frame on setting blocks, sealed with gaskets, and is held by a bead that can be removed for reglazing without disturbing the frame itself. Corners are typically mechanically jointed and sealed, then the whole frame is powder coated after fabrication, which is why the finish covers welds and joints evenly.

Under Part L of the Building Regulations, replacement windows in an existing English dwelling need to achieve a whole-window U-value of 1.4 W/m²K or better, or a Window Energy Rating of Band B or above. A U-value measures how much heat escapes through the window: the lower the number, the better the insulation.

Typical modern aluminium, double glazed

1.2 - 1.4 W/m²K

Typical modern aluminium, triple glazed

0.9 - 1.1 W/m²K

Minimum required by Part L (existing homes)

1.4 W/m²K or better

Triple glazing cost premium over high-spec double

Roughly 10-20%

Three things drive the U-value of a finished window: the thermal break in the frame, the glass specification (double or triple, the coatings used, and the gas fill in the cavity), and the spacer bar that separates the panes. Warm-edge spacers, usually a composite rather than plain aluminium, reduce the cold bridge at the edge of the glass and are worth specifying as standard.

In an exposed Lake District location — a hillside, an open aspect, or anywhere that takes the weather straight off the fells — the case for triple glazing is stronger than it would be in a sheltered valley terrace. It is not compulsory, and double glazing to a good specification will meet regulations comfortably, but the comfort difference on the coldest nights is noticeable.

Powder coating is applied electrostatically and then baked on, producing a hard, even, UV-stable finish that does not need repainting. Anthracite grey (RAL 7016) remains the most popular colour nationally, followed by jet black (RAL 9005) and a scattering of heritage greens and blues, but almost any RAL colour is available, and dual-colour frames — a different shade inside and out — are common where a bold exterior would feel too heavy indoors.

• Anthracite grey (RAL 7016) — the default choice, works with stone, brick and render alike
• Jet black (RAL 9005) — sharper and more contemporary, strong against white render
• Heritage greens and off-whites — better suited to period and conservation settings
• Dual colour — a muted or white internal frame with a bolder external shade
• Textured and matt finishes — reduce glare and hide fingerprints on handles and frames

Hardware is worth as much attention as colour. Espagnolette locking with multiple shoot bolts is now standard on quality systems, and handle finishes — brushed steel, matt black, bronze — should be chosen to match doors and other ironmongery around the house rather than as an afterthought at survey stage.

Aluminium windows are available in the full range of opening styles, and the right choice depends on the room, the wall thickness and how the window will be used day to day, not just on appearance.

As a guide range, a supplied and installed aluminium casement window in the UK typically costs £1,400-£2,600 per window, depending on size, glazing specification, colour and access. A full replacement across a typical three or four bedroom house tends to fall between £20,000 and £70,000, while a partial replacement — a single elevation or a handful of windows — can start from around £8,000.

It is worth asking any quote to be broken down by these factors rather than presented as a single lump sum. That makes it far easier to compare two quotes that look different on the surface but are actually specifying similar glass and frames.

Replacement windows are controlled work under Part L of the Building Regulations. A FENSA or Certass registered installer can self-certify the work and issue a compliance certificate, which you will need if you ever sell the property. If you use an installer who is not registered with either scheme, you will need to arrange building control sign-off separately.

In a conservation area, or on a listed building, planning consent or listed building consent may be required before you replace windows at all, and aluminium is not always accepted on visible elevations of traditional properties. It is always worth a pre-application conversation with the local planning authority before ordering anything.

• Check listed status and conservation area status before specifying
• Confirm your installer is FENSA or Certass registered, or arrange building control separately
• Keep the compliance certificate safe — it is requested at the point of sale
• Safety glazing (Part K) is required in doors and low-level windows near floor level

1. 01Initial consultationDiscuss the brief, look at systems and colours, and get an indicative price range before committing to a survey.
2. 02SurveyA technical survey confirms exact sizes, structural openings, access and any issues that affect the quote.
3. 03Design and specificationFrame colour, glass, hardware and opening styles are confirmed and drawn up for sign-off.
4. 04ManufactureWindows are fabricated to order, typically taking four to eight weeks depending on the system and glass.
5. 05InstallationOld frames are removed and new ones fitted, sealed and made good, usually within one to three days for most homes.
6. 06HandoverYou receive guarantees, the FENSA or Certass certificate, and care instructions.

The frame system matters, but so does who fabricates and fits it. Ask which aluminium system is being used, whether the company fabricates in-house or buys in finished frames, and who will actually carry out the installation. Many companies design and sell, then bring in experienced installation teams they know and trust to fit — that is a normal and often sensible model, but it is worth knowing in advance rather than assuming.

“The system name on a brochure tells you less than the fabricator behind it. Ask to see finished installations, not just samples.”

• Ask which specific aluminium system is being quoted, not just the brand
• Check guarantees separately for the frame, the glass unit and the installation workmanship
• Ask to see a completed local installation if possible, particularly in similar conditions
• Get the U-value and Window Energy Rating in writing, not just verbally