Window and Door Replacement: A Practical Guide

The four frame materials compared

Each material has a genuine case, and the right answer depends as much on the property as on the budget. Costs below are indicative South East figures for 2026, supplied and fitted for a standard casement window.

Window frame materials compared. Material | Cost per window | Lifespan | Maintenance | Best for. uPVC — £450 – £900 — 20 – 30 years — Minimal — Value and thermal performance; Aluminium — £800 – £1,600 — 40 – 50 years — Very low — Slim sightlines, large glazing; Timber (engineered softwood) — £900 – £1,600 — 40 – 60 years — Repaint every 5 – 8 years — Period and conservation properties; Timber (hardwood) — £1,200 – £2,200 — 60+ years — Repaint every 6 – 10 years — Listed and high-end work; Composite (timber core, alu clad) — £1,100 – £2,000 — 50+ years — Very low — Best of both, at a price Sizes, opening configurations, glazing spec and access all move these figures significantly.

Glazing: the part that determines comfort

The frame gets the attention, but the glazing unit does the work. A U-value measures heat loss, and lower is better. Building regulations currently require replacement windows in England to achieve a whole-window U-value of 1.4 W/m²K or better, or a Window Energy Rating of band B.

Good double glazing with a warm-edge spacer, argon fill and a low-emissivity coating achieves around 1.2 to 1.4. Triple glazing reaches 0.8 to 1.0 and costs roughly twenty to thirty per cent more, and it is genuinely worthwhile on north-facing elevations and in exposed locations, though on a leaky Victorian house the money is usually better spent on loft insulation and draught proofing first.

Low-e coating: the single biggest performance gain per pound · Argon fill: modest improvement, near-standard now · Warm-edge spacer bars: reduces condensation at the glass edge · Toughened or laminated glass: required near doors, floors and low sills · Obscure glazing: often a planning condition on flank windows · Acoustic laminated glass: worth specifying near a main road

Front doors and back doors

Composite doors dominate for good reason: a solid timber or foam core with a GRP skin gives good insulation, no maintenance and strong security for typically £1,200 to £2,200 installed. uPVC is cheaper at £700 to £1,400 and looks it on a period property. Timber doors are the right answer aesthetically on older houses and need repainting.

For rear elevations, French doors run around £1,500 to £3,000, sliding patio doors £2,500 to £6,000 and bifolds £3,000 to £8,000 depending on width and material. Bifolds give a fully open aperture; large sliders give more glass and less frame when closed, which most people prefer in winter, when the doors are shut for six months.

Security and certification

Look for PAS 24 certification on doors and ground-floor windows, and Secured by Design where insurers ask for it. On doors, the cylinder matters more than the door: a three-star TS007 cylinder or a Sold Secure Diamond cylinder resists snapping, which is the most common method of forced entry on uPVC and composite doors.

Multipoint locking should be standard. Hinge bolts, laminated glazing at ground level and a letterplate with a restrictor plate close the remaining common weaknesses.

FENSA, building control and the paperwork

Replacement windows and doors are notifiable work under building regulations. An installer registered with a competent person scheme such as FENSA or CERTASS self-certifies the work and you receive a certificate, usually within a few weeks.

If your installer is not registered, the work must be notified to building control separately and inspected. Missing certificates are a routine conveyancing problem, so check the registration before you sign, and chase the certificate if it does not arrive.

Conservation areas and period properties

In a conservation area, and always on a listed building, the frame material and the pattern of the glazing bars are frequently controlled. uPVC replacements for original timber sashes are commonly refused.

There are good alternatives. Slimline double glazing units of around 12 to 14mm now fit into refurbished timber sash boxes, and full sash refurbishment with draught sealing costs around £600 to £1,200 per window, retains the original joinery and often satisfies the planners where replacement would not.

Frequently asked questions

Do I need building regulations approval for new windows?

Yes. Either your installer is registered with FENSA or a similar competent person scheme and self-certifies, or the work must be notified to building control and inspected.

Is triple glazing worth it in the UK?

In an otherwise well-insulated house, on exposed or north-facing elevations, yes. In a draughty, poorly insulated property, loft insulation and draught proofing deliver more comfort per pound first.

How long do uPVC windows last?

Typically twenty to thirty years. Frames usually outlast the sealed units, which commonly fail at fifteen to twenty-five years and can often be replaced without changing the frame.

Can I replace windows in a conservation area?

Usually yes, but the material and appearance are likely to be controlled and permitted development rights may be removed. Check with the council before ordering, and consider sash refurbishment with slimline units.