PVC vs Aluminium Windows: Which Should You Choose for Your Extension?

You're pricing windows for your extension and the quotes are all over the place. PVC (uPVC) seems cheaper, but everyone says aluminium looks better. Your neighbour insists his aluminium windows were worth the premium. Your builder recommends PVC because "they're less hassle."

Here's what actually matters: cost, performance, aesthetics, and longevity. Not opinion—facts.

The Bottom Line: Cost Comparison

For a typical extension with 3 windows and bi-fold doors (about 15m² of glazing):

• PVC windows: £3,500-5,000 supplied and fitted
• Aluminium windows: £6,000-9,000 supplied and fitted

Aluminium costs 70-80% more upfront. Whether that premium is worth it depends on your priorities.

Head-to-Head Comparison

When PVC Makes Sense

Consider PVC windows if:

1. Budget Is Tight

The £2,500-4,000 saved on windows can go toward better finishes elsewhere—kitchen, flooring, or contingency fund.

2. Energy Efficiency Is Priority

Modern PVC windows with triple glazing achieve U-values of 0.8-1.0 W/m²K—better than most aluminium. If you're aiming for ultra-low energy bills, PVC wins on thermal performance.

3. You Want Zero Maintenance

PVC genuinely requires no maintenance. No painting, no treatment, no corrosion. Wipe with soapy water once a year and you're done.

4. Traditional Aesthetic Suits Your Home

Replacing windows on a Victorian terrace or traditional semi? PVC maintains the residential character better than industrial-looking aluminium.

5. Standard Window Sizes

For normal-sized windows (not huge panoramic openings), PVC performs perfectly well structurally.

When Aluminium Makes Sense

Consider aluminium windows if:

1. You Want Slim Frames and Maximum Glass

Aluminium frames can be 30-40% narrower than PVC, giving you significantly more glass area and better views. For contemporary extensions focused on bringing in light, this matters.

2. Large Openings (Bi-folds, Sliding Doors)

Aluminium's strength means you can have wider spans without mid-rails or reinforcement. A 4-metre bi-fold looks cleaner in aluminium.

3. Modern/Contemporary Design

If your extension has clean lines, flat roof, and a modern aesthetic, aluminium complements the design language. PVC can look out of place in ultra-modern builds.

4. Specific Colors Required

Want anthracite grey internally and white externally? Specific RAL color to match cladding? Aluminium can be powder-coated in any color with different finishes inside and out.

5. Long-Term Investment

Planning to stay in the house 20+ years? Aluminium's 30-40 year lifespan means you'll likely never replace them. PVC might need replacing once in that timeframe.

6. South-Facing or Heat-Exposed

PVC can warp or discolor in extreme heat exposure. Aluminium remains stable in all conditions.

The Thermal Performance Debate

10 years ago, aluminium had a reputation for being cold and causing condensation. This is outdated information.

Modern Aluminium: Thermally Broken

Quality aluminium windows now include thermal breaks—insulating barriers within the frame that prevent heat transfer. This brings U-values down to 1.4-1.6 W/m²K, comparable to good PVC.

For extensions with underfloor heating, the small difference in U-value (0.2-0.4 W/m²K) translates to about £50/year in heating costs. Not negligible, but not dramatic either.

Where Aluminium Struggles

If you're building to Passive House standards or aiming for EPC A++, PVC's superior insulation gives it an edge. For standard UK building regulations (1.6 W/m²K requirement), both materials easily comply.

Aesthetics: Subjective But Important

This is personal, but there are patterns:

PVC Looks Better When:

• White frames suit your property style
• You want traditional casement windows
• Neighboring properties have PVC (visual consistency)
• Frame thickness isn't a concern

Aluminium Looks Better When:

• You want slim, minimal frames
• Contemporary design is the goal
• You're maximizing glass for views/light
• You want bold or specific colors
• Your extension is distinctly modern vs your existing house

Visit show rooms. Look at real installations in similar properties. Photos don't do justice to frame proportions.

Durability and Longevity

PVC Lifespan: 20-25 Years

PVC windows last two decades with proper care. Issues that emerge:

• Gaskets and seals degrade (replaceable)
• White frames can yellow slightly in heavy sun exposure
• Hinges wear on heavy doors
• Frames can warp if low-quality or poorly installed

Quality matters enormously. Budget PVC fails in 10-15 years. Premium brands (Veka, Rehau) genuinely hit 25+ years.

Aluminium Lifespan: 30-40 Years

Aluminium framing outlasts PVC significantly:

• Powder coating resists fading for decades
• No warping or degradation in any weather
• Hinges and hardware still need maintenance/replacement
• Gaskets still degrade (same as PVC)

The frame itself basically lasts forever. The moving parts and seals are what require attention over time.

Security Considerations

Both materials achieve excellent security when properly specified:

• PVC: Reinforced internally with steel bars, multi-point locking, achieves Secured by Design standards
• Aluminium: Inherently stronger material, less reliant on reinforcement, harder to force open

For ground-floor windows and doors, specify anti-snap locks and laminated glass regardless of frame material.

Real Costs: A Detailed Example

Rear extension with 5m x 2.5m opening (bi-fold doors) plus two side windows:

PVC Estimate

• Bi-fold doors (5-panel): £3,200
• 2x casement windows: £900
• Installation & finishing: £650
• Total: £4,750

Aluminium Estimate

• Bi-fold doors (5-panel): £5,800
• 2x casement windows: £1,600
• Installation & finishing: £800
• Total: £8,200

Difference: £3,450

On a £120,000 extension, that's an extra 3% for aluminium. On a £80,000 extension, it's 4-5%. Significant but not project-breaking.

Track Every Cost Decision

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Hybrid Approach: Best of Both

You're not locked into one material for the whole project:

• Aluminium bi-folds + PVC windows: Get the premium look on main glazing, save on standard windows
• Aluminium extension + PVC main house: Keep existing PVC windows, use aluminium only on new extension
• Front PVC / Rear aluminium: Maintain street appearance with PVC, go modern at the back

This can save £1,500-2,500 vs all-aluminium while getting the aesthetic benefits where they matter most.

What About Timber?

Timber windows are a third option, offering:

• Pros: Beautiful natural material, excellent insulation, traditional character
• Cons: Requires regular maintenance (painting every 5-7 years), expensive (£8,000-12,000 for typical extension), can warp/rot if poorly maintained

Timber suits period properties or those prioritizing natural materials. For most new extensions, PVC or aluminium is more practical.

Making Your Decision

Choose PVC if:

• Budget is tight
• Energy efficiency is the priority
• You want zero maintenance
• Traditional aesthetic suits your property

Choose Aluminium if:

• Budget accommodates the premium
• You want slim frames and maximum glass
• Contemporary design is important
• Large openings require structural strength
• You're staying long-term (30+ year lifespan)

Both materials work. Your choice comes down to aesthetic preference, budget, and which trade-offs matter most to you.

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