Aluminium Sash Windows: Vertical Sliders for Period Homes

Aluminium sash windows are vertical sliding windows, two sashes that slide up and down past each other in a single frame, made in slim thermally broken aluminium rather than timber. They give a Georgian, Victorian or Edwardian house the proportions it was built with, without the painting, swelling and rattling that come with original timber sashes. For a period home where the owner wants the right look and a modern spec, they are the closest thing to a like-for-like replacement.

What is an aluminium sash window?

A sash window is a box frame holding two sashes. In a traditional window both sashes slide, balanced by weights on cords or by spring balances, and they can be set to open at top and bottom together for ventilation. An aluminium sash window keeps the same movement and the same appearance, with slim aluminium sashes and spring or spiral balances hidden in the frame.

The elements that make a sash window read correctly are proportion and detail: tall sashes, a meeting rail at the middle, glazing bars dividing each sash into panes, and a horn detail at the bottom corners of the upper sash. A good aluminium sash reproduces all of these. A poor one is a wide-framed slider with a stuck-on bar.

Why replace timber sashes with aluminium?

Original timber sashes are worth repairing when they are sound. When they are not, the choice is new timber or aluminium. Aluminium sashes are slimmer for their strength, they do not swell or shrink with the weather, and the powder-coated finish never needs repainting. The frame has a thermal break, an insulating strip between the inner and outer aluminium, so it takes modern double or triple glazing without the frame itself becoming a cold bridge. Our aluminium windows and doors are made to measure in a wide RAL range.

How the two compare:

• Look: both can be made to the original proportions; aluminium has a slimmer, smoother frame.

• Maintenance: timber needs repainting every few years; powder-coated aluminium needs a wipe.

• Movement: timber swells and shrinks; aluminium stays true, so it does not stick or rattle.

• Heritage acceptance: timber is the safe choice on a listed house; aluminium is increasingly accepted in conservation areas where the detail matches.

Which period does a sash suit?

• Georgian: six-over-six or eight-over-eight, small panes with slim glazing bars and a very tall proportion.

• Victorian: larger panes as glass improved, typically two-over-two or one-over-one, with horns at the corners of the upper sash to strengthen the joint.

• Edwardian: often a multi-pane upper sash over a single-pane lower one.

An aluminium sash can be made to any of these patterns. The point is to match what the house had. If you are adding a period conservatory at the same time, our period hardwood conservatories are designed to the same proportions, and the glazing bar pattern can be carried from the windows into the conservatory so the two read as one building.

How do the glazing bars work?

On a sash, the bars decide whether the window passes for the original. A true divided light puts a separate small sealed unit in each pane: authentic, and the dearest. Applied bars are fixed to both faces of one large unit, with a spacer bar inside lined up behind them, so the bar reads as continuous from the pavement. Bars that sit only inside the cavity look flat and are best avoided on a period front. On a listed house or in a conservation area, ask the council which it will accept before ordering. Our guide to heritage aluminium windows covers the same choice for steel-look casements.

What glazing and hardware should a sash have?

Double glazing with a low-emissivity coating is the standard specification and meets the current energy requirement for a replacement window. Triple glazing is possible in a sash but adds weight, so the balances are specified for it. Laminated glass in the lower sash improves security and reduces noise, which matters on a street-facing elevation.

Hardware on a good aluminium sash is discreet: a fitch fastener at the meeting rail, sash lifts on the lower rail, and restrictors or travel limiters where a window is above ground floor. Multi-point locking is standard on our windows. Tilt-in sashes, which pivot inward for cleaning from inside, are available on some systems and are worth having on upper floors.

What about planning and Building Regulations?

In England, replacing windows on a house that is not listed usually does not need planning permission, but in a conservation area an Article 4 direction can bring materials and appearance under control, and a listed building needs listed building consent. A pre-application conversation with the conservation officer saves time.

Building Regulations apply to every replacement window: the energy standard, safety glass near doors and at low level, and escape openings where required. A FENSA or CERTASS-registered installer self-certifies this; otherwise building control inspects.

How much do aluminium sash windows cost?

A vertical slider is more complex than a casement, so it costs more per window, and bar style, triple glazing and tilt-in sashes each add to it. Our guide to aluminium windows cost explains what drives the price.

Aluminium sash windows questions, answered

Do aluminium sash windows look like timber?

From the street, a well-proportioned aluminium sash with applied bars and horns is very hard to tell from painted timber. Up close the frame is slimmer and the finish smoother.

Can both sashes open?

Yes. A double-hung aluminium sash opens top and bottom, which gives the same natural ventilation as the original: warm air out at the top, cool air in at the bottom.

Will they rattle?

No. Timber sashes rattle because the sash shrinks in its runners. Aluminium sashes run in gasketed channels with balances that hold them firmly at any height.

Can I keep the original box frame?

Sometimes. Where the box is sound, a new aluminium sash set can be fitted within it. Where the box has rotted, the whole window is replaced.

Talk to our design team

If you are weighing repair against replacement on a period house, we are happy to look at the windows with you and say which we would do.