FENSA-registered glazing experts. Made-to-measure sealed units, shipped UK-wide, backed by a 10-year warranty.
Window replacement glass — any window type, any glass spec
Any UK window style, any sealed-unit spec, made to your dimensions. Whether you've got a 1930s timber casement, a Victorian sash, a 1990s UPVC tilt-and-turn, a modern aluminium picture window, or a Georgian bay, the failure mode is usually the same: the sealed unit has misted, blown, or cracked, and you need a like-for-like (or better) replacement. Pane Relief manufactures sealed-unit window glass for every common UK window archetype — pick the window type below for stock sizes and spec notes, or jump to the configurator if you already have your dimensions.
Replacing your own window glass
Free UK mainland delivery, 10-year manufacturer warranty on edge-seal integrity (BS EN 1279-2), FENSA-registered fitter recommendations in your postcode. Phone helpline (08:00-18:00 Mon-Fri) for measurement sanity-checks before you order — especially worth doing for sash windows, where the parting bead complicates the rebate. Most stock-size sealed units ship in 5-7 working days.
Configure my unitInstaller, glazier, replacement-window specialist
Net 30 trade accounts, tiered volume discount on 5+/20+/50+ unit orders, scheduled site delivery, priority dispatch for FENSA installers. UKCA-marked, BS EN 1279-compliant units; Declaration of Performance on request. Bespoke supply agreements for replacement-window specialists running multi-property jobs.
Trade pricing & bulk ordersWhich window style are you replacing?
Six window archetypes cover almost every domestic and light-commercial UK window. Pick the closest match — the spec notes below each link to the right product or filter.
Casement
The UK default. Side-hung or top-hung, opens outward. Standard 24mm or 28mm units in rectangular openings — most common replacement scenario.
Sash
Vertical sliding (Victorian/Edwardian). Usually need slim-profile 14mm or 16mm units for original timber rebates. Conservation-area constraints common.
Bay / bow
Three- or five-pane bay window. Each pane is its own sealed unit — order individually or matched-set. Stress-cracks common on the corner panes.
Tilt-and-turn
Continental UPVC, tilts inward at the top or fully rotates inward. Usually 28mm units with reinforced edge-seals — heavier than casement units.
Oriel / projecting
Upper-floor projecting window (Edwardian, Tudor-style). Often shaped or arched. Photo-and-template service via the helpline — 10-14 day lead.
Picture / fixed-light
Large fixed pane, no opening. Frequently oversized (over 1.5m). Toughened mandatory in pieces over 1m² or where safety codes apply.
Measure twice, order once
Window measurement is more forgiving than door or conservatory measurement, but the same rule applies: measure the existing sealed unit, not the frame opening. Sash windows are the one tricky case — see step 4.
The 5-step measure (windows)
- From inside the room, measure the visible glass width at the top, middle, and bottom — use the smallest of the three.
- Measure the visible glass height at the left, middle, and right — use the smallest.
- Add 6mm to both dimensions — that's the sealed-unit size (3mm hidden in each side of the rebate).
- Sash windows only: remove one parting bead (the thin vertical strip) and check the rebate depth. Old sashes often only accept 14mm slim-profile units; measure the rebate width with a steel rule before ordering.
- Measure the existing sealed-unit thickness edge-on with vernier callipers — typically 14mm (slim), 24mm (standard), or 28mm (modern UPVC). Photograph the existing edge-seal for the helpline if unsure.
Pricing transparency
All prices on this collection are "From £X" — the smallest stock size at base specification (4mm-20mm-4mm argon-filled annealed). Custom sizes, low-E A-rated coatings, acoustic interlayers, toughened or laminated safety specs, slim-profile conservation units, Georgian bars, leaded effects, and oversized panels are priced live in the configurator.
See also our window glass spec range for technical comparison.
Window replacement glass — common questions answered
Q: My window's misted between the panes — does the whole window need replacing?
Almost certainly not. Misting between the panes is a failed edge-seal — moisture has penetrated the cavity and the desiccant inside the spacer bar has saturated. The frame, hinges, locks, and weather-seals are usually unaffected, so the fix is a like-for-like sealed unit. Glass-only replacement runs 60-80% cheaper than a full window swap and a competent glazier can change the unit in 30-45 minutes. If the frame itself has rotted (timber) or warped/cracked (UPVC), that's a different decision — send a photo to the helpline for a free read.
Q: I've got Victorian sash windows. Can you do slim-profile sealed units that fit the original rebate?
Yes — we supply slim-profile 14mm and 16mm sealed units designed specifically for retrofitting into traditional sash, casement, and conservation-grade timber windows where the original rebate was built for single glazing. Cavity gas is argon, U-values typically 1.4-1.6 W/m²K (versus 1.2 for a standard 28mm unit — the trade-off for fitting the original rebate). See our slim-profile units page for the full range.
Q: My bay window has one cracked pane — do I have to replace all three to match?
No. Sealed units age and weather extremely consistently — a new replacement in the same spec will visibly match the surviving 5- or 10-year-old units to within a fractional difference no one notices from the street. The exception is if you're upgrading the spec (basic argon → low-E A-rated, or annealed → toughened safety): in that case, mismatched coatings can show as a slight tint difference. Order all three at once if you're upgrading; one at a time if it's a like-for-like fix.
Q: Is safety glass legally required for window glass?
Only in specific locations. Approved Document N and BS 6262-4 mandate toughened (BS EN 12150) or laminated (BS EN 14449) for any pane below 800mm above floor level (within reach of children), or within 300mm of a door edge if below 1500mm. A regular first-floor bedroom window 1.2m off the floor doesn't legally require safety glass. The configurator highlights when the legal threshold applies based on the cill height you enter.
Q: What's the difference between A-rated, B-rated, and C-rated window glass?
The BFRC Window Energy Rating ladder. A-rated units (typically a low-E coating plus argon fill, U-value around 1.2 W/m²K) hit current Building Regs Part L for replacement glazing. A+ and A++ add improved low-E or krypton fill (U-values 1.0 and below) and are worth specifying if you're going the upgrade route. B and C rated units are older-spec — still functional but no longer compliant for new fit. Default sealed unit shipped from this collection is A-rated minimum unless you actively spec down.
Q: Do you supply obscure / patterned glass for bathroom and toilet windows?
Yes — full range of UK obscure patterns: Pilkington Cotswold (the most-requested), Stippolyte, Florielle, Charcoal Sticks, Mayflower, Minster, Contora, plus etched-finish satin. Privacy is rated 1-5 (Cotswold and Stippolyte are level 3-4; satin and charcoal sticks are level 5). All available in 4mm and 6mm thickness, in both standard and toughened. Configure as part of any sealed unit.
Q: I'm in a conservation area / listed building. Can you do glass that satisfies planning constraints?
Yes — this is a common request, and we supply both slim-profile 14mm sealed units (visually indistinguishable from single glazing at street view, sit in original timber rebates) and vacuum-insulated glass (VIG) for the strictest Grade I and II listed scenarios where any visible double-glazing line is rejected. Get the planning officer's written sign-off on the spec first — we'll then build to that exact spec. Lead times on conservation units are slightly longer (10-14 working days).
Q: Whole window vs just the glass — when does it make sense to replace the window?
Glass-only is right if the frame is sound and only the seal has failed. Replace the whole window if: the timber frame is rotted (you can push a screwdriver into it), the UPVC has cracked or warped, the hinges and locks have failed and parts are obsolete, you're upgrading from single to double in a rebate that won't accept slim-profile, or you're hitting Building Regs Part L on a major renovation. If you're not sure, photograph the frame and send it to the helpline — we'll tell you straight which scenario you're in.
Q: What's the lead time for window glass?
Stock-size double-glazed units: 5-7 working days. Custom-size rectangular non-stock: 7-10 working days. Slim-profile conservation units: 7-10 working days. Toughened or laminated specs: +2-3 working days. Triple-glazed: 10-14 working days. Shaped, arched, oriel, or radius-edged: 10-14 working days. Oversized (any dimension over 1500mm): 7-10 working days. Cross-link to the window glass collection for spec-specific filtering.
Related guides, collections, and specifications
Need help with your window replacement glass?
Call the helpline on 0117 330 3057 (08:00-18:00 Mon-Fri), or request a quote. Trade accounts unlock live tier pricing and Net 30 terms.