Frame material affects cost, thermal performance, maintenance, look, lifespan and resale value. There's no single winner - the right answer depends on the house, the budget and the conservation rules where you live.
uPVC frames
By far the most common frame material in UK homes - around 85% of replacement windows fitted in the last decade have been uPVC. It's an extruded polymer (unplasticised polyvinyl chloride) reinforced internally with galvanised steel or aluminium box sections.
Strengths:
- Cheapest - typically £650-£950 fitted for a standard casement
- Zero maintenance - never needs painting or staining; a wash twice a year is enough
- Excellent thermal performance - the multi-chambered profile traps air and insulates well
- Good security - modern multi-point locking systems and internally beaded designs
- Wide range of colours and woodgrain finishes - anthracite grey, black, cream, oak effect, agate grey all common
Weaknesses:
- Frame profiles are visually chunkier than aluminium - more frame, less glass
- White uPVC can yellow over 15-20 years if not cleaned regularly
- Most conservation areas and listed buildings do not permit uPVC
- Modest resale value uplift compared to timber on period properties
Typical lifespan: 25-35 years before the gaskets, hinges and sealed units need significant work.
Aluminium frames
Powder-coated extruded aluminium with a thermal break (a strip of polyamide insulation) between the inner and outer profiles. Modern thermally-broken aluminium achieves U-values within touching distance of uPVC despite metal being a far better conductor.
Strengths:
- Slim sightlines - the frame can be 40-50% thinner than uPVC, letting in more light
- Very long lifespan - 40-50 years before the powder coat fades
- Strongest material - allows huge spans of glass (bi-fold doors, picture windows up to 3m)
- Sleek, contemporary look - the default for modern architecture and extensions
- Fully recyclable at end of life
Weaknesses:
- Most expensive - typically £1,100-£1,800 fitted, sometimes more for large sliders
- Powder coat scratches show silver underneath
- Slightly poorer U-value than the best uPVC despite the thermal break
- Condensation on the frame edge more common in poorly-ventilated rooms
Typical lifespan: 40-50 years. The frame outlasts almost everything else in the house.
Timber frames
The original window material and still the only option for many period properties, conservation areas and listed buildings. Modern timber windows use engineered laminated softwood (usually European redwood) or hardwood (oak, accoya) with factory-applied paint or stain.
Strengths:
- The only choice for many conservation areas and Grade II listed buildings
- Best thermal performance - timber is a naturally good insulator
- Authentic period look - sash windows, casements with putty lines, proper proportions
- Repairable indefinitely - rotted sections can be cut out and spliced rather than replacing the whole frame
- Adds value to period homes - replacing original sash windows with uPVC often reduces the price of a Victorian or Georgian property
Weaknesses:
- Highest maintenance - factory-finished paint lasts 8-10 years before recoating
- Premium cost - £900-£1,600 fitted for softwood, £1,400-£2,400 for hardwood
- Rot risk if maintenance lapses, particularly at cills and lower rails
- Longer lead times - 6-10 weeks vs 2-3 weeks for uPVC
Typical lifespan: 60+ years with proper maintenance; many original Victorian sash windows are still serviceable today.
Composite (timber-aluminium)
A hybrid: timber on the inside (for warmth, look, traditional joinery) with a clip-on aluminium weather skin on the outside (zero exterior maintenance). Common in Scandinavian and high-end UK builds. Combines most of the strengths of both but inherits the high price tag - usually £1,600-£2,800 fitted.
Side-by-side comparison (typical 600 x 900mm casement)
Cost ranges are 2026 Essex prices, supply and fit by a FENSA-registered installer:
- uPVC: £650-£950 | U-value 1.2 | Lifespan 25-35 years | Maintenance: wash only
- Aluminium: £1,100-£1,800 | U-value 1.4 | Lifespan 40-50 years | Maintenance: wash only
- Softwood timber: £900-£1,600 | U-value 1.1 | Lifespan 60+ years | Maintenance: repaint every 8-10 years
- Composite: £1,600-£2,800 | U-value 1.0 | Lifespan 60+ years | Maintenance: wash only
So which should you actually choose?
- Standard suburban semi or modern build: uPVC. Best value, totally fit for purpose, no real downside.
- Architect-designed extension or large openings: aluminium. Slim sightlines justify the cost.
- Victorian, Georgian, Edwardian or listed property: timber. Anything else hurts value and often isn't allowed.
- Premium new-build aiming for highest energy rating: composite or top-spec uPVC with triple glazing.
And if your existing frames are still solid - whichever material they are - repairing rather than replacing is almost always the smarter move.