FENSA-registered glazing experts. Made-to-measure sealed units, shipped UK-wide, backed by a 10-year warranty.
Replacement window glass — sealed units made to your sizes
Misted between the panes? Cracked? Failing to keep the heat in? In most cases you don't need a whole new window — just a new sealed unit. Pane Relief manufactures replacement double-glazed, triple-glazed, low-E (A-rated), acoustic, toughened, laminated, obscure, and Georgian-bar sealed units to fit casement, sash, bay, tilt-and-turn, fixed-light, and conservation windows. Pick the window type below to see real prices and lead times — or use the configurator if your spec or size is non-standard.
Replacing your own window glass
Free UK mainland delivery on every order. 10-year manufacturer warranty on edge-seal integrity. FENSA-registered fitter recommendations in your postcode. Phone helpline (08:00-18:00 Mon-Fri) for sanity-checking your measurements before you order. Most stock-size units ship in 5-7 working days.
Configure my unitInstaller, builder, glazier
Net 30 trade accounts, tiered volume discount on 5+/20+/50+ unit orders, scheduled site delivery, priority dispatch for FENSA installers and developers. Every unit ships UKCA-marked with BS EN 1279 compliance; Declaration of Performance on request. Bespoke quotes via the trade portal.
Trade pricing & bulk ordersWhich window type are you replacing?
Six common window scenarios. Pick the closest match — each links to the relevant flagship product or filtered range.
Standard casement
UPVC, timber, or aluminium casements. Most common UK type — 24mm or 28mm rectangular sealed units.
Bay window
3-pane, 4-pane, or 5-pane bay configurations. Angled or square. We supply matching units across all lights.
Sash window
Vertical sliding sash. Slim 14mm Histoglass-equivalent for conservation areas. Listed-building friendly options.
Tilt & turn
Continental-style inward-opening. Often larger panes — toughened recommended on units over 1m².
Bedroom window
Acoustic and thermal options. Laminated acoustic interlayer cuts road and aircraft noise by up to 44 dB Rw.
Bathroom (obscure)
Privacy-rated obscure glass — Levels 1-5 (Pilkington Texture range). Toughened required for shower-screen height.
Measure twice, order once
For windows the measure is the same as for doors: measure the rebate, not the frame opening. We need the sealed-unit size, not the daylight opening.
The 5-step measure
- Open the window or carefully remove a glazing bead. Measure visible glass width at top, middle, and bottom — use the smallest number.
- Measure visible glass height at left, middle, and right — use the smallest number.
- Add 6mm to both dimensions (3mm clearance into each side of the rebate).
- Measure the overall sealed-unit thickness with vernier callipers (typical: 24mm, 28mm, or 36mm).
- Photograph the frame profile, the rebate depth, and any kitemark stamp on the existing glass. Send to our team for a free spec-match if you're unsure.
Pricing transparency
Prices shown on this collection are "From £X" — the smallest stock size at base specification (4mm-20mm-4mm argon-filled annealed). Custom sizes, toughened or laminated safety, low-E coatings (Planitherm, Optitherm), acoustic interlayers (PVB acoustic), obscure patterns, Georgian bars, or oversized panels are all priced live in the configurator.
Window glass — common questions answered
Q: My window is misted between the panes. Do I need a whole new window?
No — almost never. Misting between the panes means the edge-seal on the sealed unit has failed and moisture has migrated into the air gap. The frame, hinges, locks, and gaskets are usually fine. You just need a new sealed unit fitted into the existing frame. That's typically 60-80% cheaper than a full window replacement. If the frame itself is rotten, twisted, or has failed locks then yes — replace the whole window. Send a photo on the helpline for a free diagnosis.
Q: What's the difference between a sash window measure and a casement measure?
Both are measured at the rebate, but on sash windows the glass typically sits in putty (timber sashes) or a slim bead (modern UPVC sashes) rather than a deep gasketed rebate. The rule of thumb: ease back the putty fillet or pop a bead, measure visible glass plus 3mm of overlap each side. Listed sashes often require slim-profile units (14mm overall, Krypton-filled) to retain the timber muntin proportions — those are a separate stock line; ask via the helpline.
Q: Is low-E worth paying for?
Yes — for any window receiving long daylight hours. A low-E soft-coat unit (Planitherm Total+, Optitherm S3) drops the U-value from around 2.8 W/m²K (standard double-glazed) to 1.2-1.4 W/m²K. On a typical 3-bed UK semi that's a quantifiable drop in heating bills (typically £80-£140/year per window, depending on orientation). All our stock units use a low-E coating by default unless you opt out; the price difference is small and the payback is fast.
Q: U-value vs g-value — what do they mean and which matters more?
U-value (W/m²K) measures heat loss out — lower is better. g-value (also called solar factor) measures solar heat gain in — higher is better in winter but worse in summer. For most UK homes a unit with low U-value (~1.2) and mid g-value (~0.5) is the right balance. South-facing rooms that overheat in summer can benefit from a solar-control coating (lower g-value, around 0.3) — but those rooms are rare in the UK climate, so don't over-spec by default.
Q: A-rated vs C-rated — what's the difference?
BFRC (British Fenestration Rating Council) ratings A++ to E represent the net energy efficiency of a complete window assembly — frame plus glass. Sealed units alone don't get a BFRC rating; the assembly does. For a fair like-for-like, our stock low-E units typically push the existing frame from C-rated to A or A+ once retrofitted. If you're targeting a specific rating for a planning condition or new-build SAP submission, tell us the target — we'll spec the right glass build-up.
Q: I get condensation on the inside of the window. Is the glass failing?
Almost never — internal condensation is a humidity and ventilation problem, not a glass problem. It happens when warm moist indoor air contacts a cold internal glass surface. Fix: more trickle-vent airflow, run extractor fans during cooking and showering, dry laundry outside. Upgrading to a low-E unit raises the internal glass surface temperature and reduces (but doesn't eliminate) condensation. Misting between the panes (inside the sealed unit, where you can't wipe it off) is a different problem — that's a failed edge-seal and the unit needs replacing.
Q: I'm in a Conservation Area / listed building — what are my options?
Conservation and listed properties typically require slim-profile units (10mm-14mm overall thickness) to retain the original timber muntin proportions and external sightlines. We stock Krypton-filled slim units (Histoglass-equivalent) that hit U-values around 1.6 W/m²K — a meaningful upgrade on single glazing while satisfying most planning officers. Confirm with your local conservation officer first; we'll supply a spec-sheet for their approval before you order.
Q: Is safety glass required for window glass?
Sometimes. Approved Document N and BS 6262-4 mandate impact-resistant glazing (toughened BS EN 12150 or laminated BS EN 14449) in any pane that sits below 800mm from floor level, or near a door. Bathroom windows, low-cill bedroom windows, and floor-to-ceiling glazing all typically require safety glass. The configurator highlights critical-location panels automatically once you enter the dimensions and cill height.
Q: Acoustic glass — does it really work?
Yes, for the right frequencies. A standard double-glazed unit gets you to about 28-30 dB Rw acoustic insulation. A laminated acoustic unit (with PVB acoustic interlayer) jumps to 38-44 dB Rw — a noticeable, measurable improvement on busy roads, near flightpaths, or in railway corridors. If you're not sure whether acoustic glass is worth the upgrade for your situation, read the acoustic glass guide — it shows the dB drops by traffic type.
Q: What's the warranty and lead time?
10-year manufacturer warranty on edge-seal integrity (BS EN 1279-2 weathered durability), 5-year on coatings. Stock-size units: 5-7 working days. Custom rectangular non-stock: 7-10 working days. Shaped, arched, or oversized (any dimension >1500mm): 10-14 working days. Toughened or laminated specs add 2-3 working days. Mis-measurements remade at cost (materials only).
Related guides and specifications
Need help choosing the right window 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.