FENSA-registered glazing experts. Made-to-measure sealed units, shipped UK-wide, backed by a 10-year warranty.
Triple-glazed door glass — thermal upgrade for front, patio, and French doors
Thermal upgrade for the room's weakest link. Doors are usually the worst-insulated part of an external wall — large glass area, more frame perimeter than a comparable window, and frequently the most exposed orientation. Triple-glazed door units (typically 36mm or 44mm) drop the door-glass U-value to 0.6-0.8 W/m²K — meaningfully better than even premium double-glazed door units (around 1.2) — and stop the cold-spot draughts at the door line that low-temperature heat-pump heating exposes. Pane Relief manufactures triple-glazed sealed units to fit front, back, French, patio, bi-fold, and composite-door inserts where the frame rebate and hinge rating support the additional weight. For the broader door-glass catalogue see /collections/door-glass-units.
Heat-pump install, eco-retrofit, comfort upgrade
Free UK mainland delivery, 10-year manufacturer warranty on edge-seal integrity (BS EN 1279-2), FENSA-registered installer recommendations in your postcode. Phone helpline (08:00-18:00 Mon-Fri) for spec, frame, and hinge sanity-checks — triple-glazed door units add significant weight and not every door will accept the upgrade without hinge replacement.
Configure my unitPassive House, eco-retrofit, new-build contractor
Net 30 trade accounts, tiered volume discount on 5+/20+/50+ unit orders, scheduled site delivery, priority dispatch. UKCA-marked, BS EN 1279 compliance, BFRC A+/A++ rating, full SAP/PHPP-ready U-value calculations on request. Bespoke supply agreements for Passive House, retrofit, and high-performance new-build contractors.
Trade pricing & bulk ordersWhich door is the triple-glazed unit for?
Five common scenarios for triple-glazed door units. Pick the closest match — note the weight and frame-rebate considerations below.
Front door
Half-glazed or fully-glazed front door. Toughened or laminated inner mandatory below 1500mm. Heaviest typical use case — confirm hinge rating.
French / patio doors
Tall, narrow units. Toughened mandatory. Triple-glazed pair adds 50-70kg per door — load-rate the hinges before specifying.
Sliding / bi-fold
Large oversized panels. Toughened mandatory by BS 6262. Triple-glazed bi-fold panels can exceed the manufacturer's weight rating — confirm first.
Composite door insert
Solidor, Endurance, Distinction, Rockdoor. Most composite-door inserts are sized for 24-28mm units — confirm rebate before ordering 44mm triple.
Other door glass
Back doors, conservatory doors, stable doors. See the full door-glass collection for the broader catalogue and stock-size options.
Measure twice, order once
Triple-glazed door units are heavy. Before measuring, check the existing door has the rebate depth and hinge rating to take a 36mm or 44mm unit.
The 5-step measure
- Measure the visible glass width at top, middle, and bottom — use the smallest.
- Measure the visible glass height at left, middle, and right — use the smallest.
- Add 6mm to both dimensions for the sealed-unit size.
- Measure the rebate depth. 36mm and 44mm units are physically deeper than the 24-28mm units most doors were built for. If your existing unit is 24mm, the door won't accept a triple upgrade without rebate modification or door replacement.
- Check hinge load-rating. Standard UPVC door hinges rate at 80-100kg per door. A 1m×2m triple-glazed unit weighs around 60-70kg, plus the door slab itself — frequently exceeds the rating. Replace with heavy-duty hinges or scale down to double-glazed.
Pricing transparency
Prices on this collection are "From £X" — the smallest 36mm argon-filled triple-glazed door unit at base spec. Krypton fill, A+/A++ coatings, safety glass (mandatory for door units), acoustic interlayers, and oversized panels are priced live in the configurator.
Cross-link: see the full door-glass collection for stock sizes, leaded patterns, Georgian bars, and composite-door inserts in double-glazed builds.
Triple-glazed door glass — common questions answered
Q: Is triple-glazing actually worth it on a door versus a window?
Often more worth it on a door than a window, because doors typically have a worse baseline. A typical front door has more frame perimeter relative to glass area than a window, plus a sweep gasket that leaks more air, plus the door is opened multiple times a day — so the thermal-bridge and infiltration losses are bigger. Triple-glazed door units drop the glass-area U-value from around 1.2 to 0.6-0.8 W/m²K, and the comfort difference at the door line (no cold downdraft) is genuinely noticeable. Heat-pump installs particularly benefit.
Q: Will my existing door frame accept a triple-glazed unit?
Only if it was built for one. Standard residential doors built before 2018 are nearly always rebated for 24mm or 28mm double-glazed units. A 36mm or 44mm triple-glazed unit won't physically fit. Modern doors built to Passive House or high-performance spec (and some post-2020 commercial doors) have 44mm rebates and can take triple straight in. Measure the existing unit thickness with vernier callipers before ordering — if it's already 36mm+, you're fine. If it's 24-28mm, you need a new door (or stay with the door-glass double-glazed range).
Q: Triple-glazed door units are heavy. How much heavier than double?
About 50-75% heavier per square metre. A typical 600×1500mm front-door insert: in 24mm double-glazed runs around 18kg; in 36mm triple it's 25-28kg; in 44mm krypton triple it's 30-32kg. For a single insert that's manageable. For a fully-glazed French door pair, you're looking at 60-100kg of glass total — frequently over the hinge load-rating of the existing door. Heavy-duty hinges (typically rated to 130-150kg per door) or restricted opening angles often become necessary.
Q: Is safety glass legally required for triple-glazed door units?
Yes — same rules as any door glass. Approved Document N and BS 6262-4 mandate toughened (BS EN 12150) or laminated (BS EN 14449) in any pane fitted in a door or sidelight below 1500mm, or within 300mm of a door edge. In a triple-glazed unit the spec applies to both outer and inner panes for full compliance — toughened-toughened or laminated-toughened are the typical builds. The configurator highlights the mandatory spec based on dimensions and cill height.
Q: Will a triple-glazed door look different from outside?
Marginally — the third pane reduces visible light transmittance slightly (around 70-72% vs 80% for double-glazed low-E), and the deeper sealed unit makes the edge spacer visibly thicker if you're up close. From the street the difference is negligible. The frame profile is the more obvious visual difference — a door rebated for 44mm units has a chunkier sash than one rebated for 24mm.
Q: What U-value should I expect?
Glass-area U-value for triple-glazed door units: 0.5 to 0.8 W/m²K depending on build. 36mm argon + two low-E coatings hits around 0.8; 44mm krypton + warm-edge spacer hits 0.5-0.6. Whole-door U-value (Ud) — which is what matters for SAP/EPC/PHPP — depends heavily on the door slab and frame, typically 0.8-1.4 even with a great triple-glazed insert because the frame is the limiting factor. Full Ud calculation supplied on request.
Q: Composite door (Solidor, Endurance, Rockdoor) — can I retrofit triple-glazed inserts?
Usually not — most composite-door manufacturers spec their slabs for 24-28mm inserts and the apertures are pre-cut to that thickness. A 36mm or 44mm triple won't fit without slab modification (not usually advisable — voids the manufacturer's warranty). The exception is the modern Passive-House-rated composite ranges (some Solidor and bespoke high-performance manufacturers), which offer triple-glazed insert apertures from new. Stick with double-glazed inserts (24mm or 28mm) for retrofits on standard composite doors — see the composite-door insert flagship.
Q: What's the lead time and warranty on triple-glazed door units?
Standard rectangular triple-glazed door units: 10-14 working days. Toughened or laminated safety spec (mandatory for most door units): typically built into the same cycle, no additional time. Bespoke composite-door insert shapes: 14-21 working days. Shaped, arched, or oversized: 14-21 working days. 10-year manufacturer warranty on edge-seal integrity (BS EN 1279-2 weathered durability), 5-year on low-E coatings. Free phone sanity-check on spec, rebate, and hinge rating before ordering: 0117 330 3057.
Related guides, collections, and specifications
Speccing a triple-glazed door upgrade?
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.