The uPVC Windows Buying Guide

A plain-English guide to choosing made-to-measure uPVC windows in the UK — what to look for, what to avoid and how to stop overpaying.

Why uPVC?

uPVC (unplasticised polyvinyl chloride) became the dominant UK window material for good reason. It does not rot, does not need repainting, handles British weather without warping and, when combined with modern double or triple glazing, delivers thermal performance that timber frames simply cannot match without heavy ongoing maintenance.

A well-specified uPVC window has a typical service life of 25 to 35 years. The glazed unit inside it may need replacing sooner if the seal fails, but the frame itself is effectively fit-and-forget.

Start With the Profile System

The profile is the plastic frame — its shape, chamber count and steel reinforcement. Two uPVC windows that look identical from the street can be worlds apart once you cut them open. The profile determines thermal performance, rigidity, sound reduction and long-term dimensional stability.

In the UK, the profile systems you will encounter most often are:

• Rehau Total 70 — German-engineered, 5-chamber system, 70mm frame depth. Used throughout our range.
• Deceuninck 2500 — 6-chamber Belgian profile. Common in the trade.
• VEKA Matrix 70 — German, 5-chamber, similar class to Rehau.
• Liniar EnergyPlus — UK-made, multi-chamber.
• Eurocell Logik — UK-made, 70mm.

You should avoid generic unbranded profile unless the supplier can prove it meets BS EN 12608 for weather performance and BS 7950 for security. A brand name matters less for marketing than for traceability on the day a spare part is needed a decade later.

Chamber Count Is Not Everything

A "6-chamber" frame is not automatically warmer than a 5-chamber frame. What matters is the overall U-value of the complete window (frame plus glass plus spacer bar). Two different manufacturers can produce a 5-chamber frame with very different thermal performance depending on steel reinforcement design, gasket material and frame depth.

Understand the Energy Rating

uPVC windows are rated A++ down to E under the Window Energy Rating (WER) scheme. The rating bundles together heat loss, heat gain from sunlight, and air leakage into a single letter.

• A+ / A++ — The modern benchmark for new builds and decent replacement work. Low U-value, good solar gain.
• A — Meets current Building Regulations Part L for a replacement window in England and Wales.
• B or lower — Should not be fitted as a replacement in a habitable room. A legitimate supplier will not offer this.

The minimum legal U-value for a replacement window in England and Wales is 1.4 W/m²K (whole-window, per Approved Document L). Ask for the certificate if it is not shown on the quote.

Glass: Clear, Obscure or Toughened?

Every uPVC window you buy is double glazed as standard: two panes of glass with a sealed argon-filled cavity and a warm-edge spacer bar. Where specification matters is what type of glass goes into each pane.

• Clear glass — the default, used everywhere except where privacy or safety glazing is required.
• Obscure glass — textured or frosted for privacy. Required in bathrooms by preference, sometimes by Building Regulations in overlooked installations.
• Toughened glass — thermally treated to be around 4-5 times stronger than ordinary glass and to break into small cuboid fragments rather than dangerous shards. Required by Approved Document Part N of the Building Regulations in any pane that is within 800mm of floor level, or within 300mm of a door edge up to 1500mm from floor.

Our glass and glazing guide covers the full Part N requirements with diagrams.

Security Features That Actually Matter

There is a checklist of features that separate a serious domestic window from something designed to hit a price point:

• Multi-point locking — minimum three locking points per sash, ideally shoot-bolt and mushroom cam.
• Internal beading — the glass should be held in place from the inside so the glazing bead cannot be pried off from outside. All our windows are internally beaded.
• Fire escape hinges — allow the sash to swing wide enough in an emergency. Required in habitable rooms at first floor and above.
• PAS 24 or Secured by Design accreditation — tested against forced entry. If your insurer has asked for it, insist on it.

Trickle Vents Are Not Optional

Since June 2022 Approved Document Part F of the Building Regulations requires trickle vents to be fitted to replacement windows in habitable rooms. The rule is to maintain — or improve — background ventilation compared to what was there before.

In practice this means almost every replacement window you buy from a legitimate supplier will ship with a trickle vent already fitted into the top of the frame. Avoid suppliers who "disable" them or quietly leave them out: you will have difficulty signing off a Building Regulations compliance certificate later.

Measuring: Sight Size vs Brick Opening

The single most expensive mistake a DIY buyer makes is to measure the wrong thing. There are two measurements that matter:

• Sight size — the visible glass area, not the frame size. Do not order to this measurement.
• Brick-to-brick opening — the actual hole in the wall, measured from brickwork to brickwork, not frame to frame.

For a replacement window you order approximately 10mm smaller than the brick-to-brick opening in both width and height, to leave room for expansion foam and packing. Our measurement guide walks through this with pictures.

Made-to-measure windows are not returnable if you measure wrongly — they are manufactured to your exact figures. Measure twice, measure three times if it is the first time you have done it, and if in doubt ask a builder to double-check before you place the order.

Supply Only vs Supply & Fit

A supply-and-fit national company will typically charge two to three times the supply-only price for the same glass-and-frame specification. The difference is the in-person sales call, the fitter and the overhead of a showroom network.

If you have a trusted local joiner, if you are a builder running a refurbishment, or if you fit windows yourself, buying supply-only is the biggest single saving available on a window project. Our pricing is transparent supply-only across all 17 configurations.

Lead Times and Delivery

Made-to-measure uPVC windows are manufactured after you order — there is no "warehouse" of pre-made stock. A realistic lead time is 10 to 14 working days from payment to delivery, which is what we commit to. Anything substantially faster usually means someone has cut a corner on glass spec or on quality control.

Kerbside delivery to England and Wales is £69 flat, or free on orders over £1,450. Free collection is always available from our depot in West London (UB7 7HQ) for customers in the London area. Full zone detail on the delivery page.

Questions to Ask Any Supplier Before You Pay

1. What profile system is the window made from, and is it a named brand?
2. What is the whole-window U-value, and can I see the energy rating certificate?
3. Is the window internally beaded? (If the answer is "externally beaded", walk away.)
4. Are multi-point locks and fire escape hinges standard, or are they extras?
5. Does the window ship with a Building Regs Part F compliant trickle vent?
6. Is there a written 10-year guarantee on frame and glass?
7. What happens if I measure incorrectly — am I liable for the cost?
8. Is the price inclusive of delivery or does delivery land separately?

We answer all of these up front on every product page. No follow-up sales call, no pressure.