Can the extension have aluminium if the house has uPVC?

Yes, and it is a common combination. Keeping the colour consistent, or replacing the most visible original windows in the same colour, is what stops it looking accidental.

Should the extension have bigger windows than the house?

Usually, yes — it is generally a modern space with different requirements. The important thing is that the increase looks intentional rather than arbitrary.

Design Inspiration

Should Extension Windows Match the Existing House?

Match or contrast deliberately; never half-match. The weakest extensions are the ones that nearly match the house and miss.

3 min read

Written by Windows in the Lakes · A trading name of Home Glazing Ltd · Last reviewed 21 September 2026

Short answer

In short: there are two good answers. Either the extension reads as a continuation of the house, using the same window family, proportions and colour, or it reads as a clearly modern addition with its own logic. A near-match — similar but not the same — is the one outcome to avoid.

Three strategies that work

Strategy	Best for	How to execute it
Continuation	Small side and rear extensions on ordinary houses	Same system, same colour, same proportions and divisions
Quiet contrast	Most contemporary rear extensions	Different composition, shared colour and hardware family
Clear contrast	Architect-led extensions to period property	A distinct modern language, usually with a physical link between old and new

The join is where it succeeds or fails

Make the change at a corner, a set-back or a change of material — not midway along a wall.
Carry one frame colour across both parts; it is the cheapest and strongest unifier available.
Align something: a head height, a cill line, a glazing line. One shared datum does most of the work.
Consider replacing the original windows in the same colour at the same time, even if the style differs.

Planning may already have decided

Where an extension has planning permission, the approved drawings will often specify window materials, colours and opening patterns. Changing them can require an amendment. Check the approved documents before specifying, particularly on a constrained property.

Sources and further reading

Regulatory and technical points in this guide should be checked against the current published guidance below, and against the specific circumstances of your property.

Planning Portal — Doors and windows

Guidance last reviewed 21 September 2026 by Windows in the Lakes

From a real Windows in the Lakes project

Near Keswick, North Lakes · Garden room extension · Two bifold runs, door and window set

A Garden Room Glazed on Three Sides

A rear extension on a terrace risks turning the original back rooms into a dark corridor, and a fully glazed box would have looked nothing like the Victorian brickwork it joins.

Brick piers and a tiled pitched roof keep the architecture in the same language as the house, while the spans between them are given over entirely to glazing. Rooflights carry daylight over the new roof and into the existing plan, and a single jet black finish across every frame, cill and handle ties the two builds together.

Read the project story

Next step

Considering aluminium windows for your own project?

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