- TYPE: Triple Glazing
Patio / Bi-Fold Door Glass Unit
- BS EN 1279
- FENSA registered
- 10-year warranty
- Made in Bristol, UK
Enter your exact dimensions, glass type, gas fill, and accessories in our configurator for instant trade pricing.
Description
The triple-glazed unit engineered for full-height door apertures. A 36mm triple-glazed sealed unit (4mm toughened / 12mm argon / 4mm clear with low-E / 12mm argon / 4mm toughened) sized for the patio and bi-fold door market — 1500mm to 2700mm wide, 2100mm tall — with both outer faces toughened to BS EN 12150 so the unit meets Approved Document N "critical location" requirements for door glazing as a side benefit.
Patio and bi-fold doors are the most demanding application for sealed-unit glass in domestic construction. The apertures are huge (typically 2.1m tall, often 1.8-2.4m wide per leaf), the units must satisfy critical-location safety glazing, and thermal performance directly affects the EPC because doors of this size are often >20% of a room's external wall area. This flagship handles all three constraints in one stack.
Why triple glazed for patio doors specifically
Door glass faces a thermal punishment standard windows don't: every time the door opens, the entire glazed assembly is briefly exposed to outdoor conditions on both faces. That doesn't change the centre-pane U-value, but it does mean that any heat-loss penalty from sub-optimal glazing is paid much more often. For a south-facing patio door used 8-12 times daily, the difference between A-rated double (1.4 W/m²K) and standard triple (0.8 W/m²K) is meaningful over a heating season — typically 80-120 kWh/yr per door across a UK climate.
The second reason is comfort. Floor-to-ceiling glass at A-rated-double thermals produces a noticeably cold zone in front of the door on still winter nights — radiant cooling against the body. Triple glazing's inner-face surface temperature stays close to room temperature, and the cold-zone effect disappears.
Technical specification
| Overall thickness | 36mm |
|---|---|
| Build-up | 4mm toughened / 12mm argon / 4mm clear (Planitherm face 3) / 12mm argon / 4mm toughened |
| Cavities | 2 × 12mm argon-filled (BS EN 1279-3) |
| Outer + inner pane safety classification | BS EN 12150 + BS EN 12600 Class 1(C)1 (toughened) |
| U-value (centre-pane, low-E face 3) | 0.8 W/m²K |
| U-value (whole-door assembly, thermally-broken aluminium frame) | 1.4-1.6 W/m²K |
| g-value | 0.55 |
| Light transmittance | ~71% |
| Weight | ~30 kg/m² — a 2400 × 2100 unit is ~150 kg, requires lifting jig |
| Critical-location compliance | Approved Document N — door glazing requires Class 1(C)1 below 1500mm. This unit satisfies that across the full pane. |
| Standards | BS EN 1279, BS EN 12150, BS EN 12600, BS EN 673 (U-value), Approved Document N, Approved Document L |
Where this unit is the right call
- Bi-fold door replacement — original 4-pane and 6-pane bi-folds where the first-generation toughened double-glazed units have misted/blown. Heritage frames and tracks can usually be retained; only the unit is replaced.
- Patio (sliding) door reglazing — particularly aluminium and timber-aluminium composite systems where the 36mm rebate accepts triple. Older PVCu patio doors may need profile checks before specifying.
- Garden-room and orangery openings — full-height glazing onto landscaped gardens where comfort + thermal + safety all matter. Often pairs with the Triple Glazed Safety (Toughened + Laminated) flagship for overhead-adjacent panels.
- Bedroom Juliet-balcony French doors at first-floor level — fall-from-height risk plus thermal-comfort considerations make triple-glazed safety the right spec.
- Heat-pump retrofit projects with significant door glazing — the lower fabric heat loss directly improves ASHP coefficient-of-performance, particularly on shoulder-season cycling.
For French doors (single leaf, 600-900mm wide), see the French Door Glass Sealed Unit (Symmetric Pane) flagship — sized for door apertures rather than full-height patio openings. For composite door inserts (small toughened-laminated panels in solid composite doors), see the Composite Door Glass Insert flagship.
Stock sizes — patio/bi-fold-specific
Five oversize stock sizes are below, all 2100mm tall to match the UK patio-door standard:
- 1500 × 2100 mm — single bi-fold leaf, narrow opening
- 1800 × 2100 mm — small bi-fold leaf, common 2-leaf splits
- 2100 × 2100 mm — square split aperture, 2-leaf bi-fold middle leaf
- 2400 × 2100 mm — typical sliding patio door leaf (3-track)
- 2700 × 2100 mm — large bi-fold/slider, often the master leaf in 4-pane systems
Dispatch 14-21 working days from order (toughening + triple-glazed assembly + oversize handling). Custom sizes — including taller-than-2.1m, shaped tops (raked apex roof glazing), and asymmetric bi-fold leaf splits — are priced via the online glass configurator.
Delivery and handling: oversize units ship on bespoke timber A-frames via dedicated 2-person delivery service. Standard 5-7 day pallet networks cannot handle these units. A site survey for vehicle access (van width, gate clearance, pedestrian-route width) is included free with any order over 1.8m tall — contact the helpline before placing the order.
Frame compatibility — the critical specification step
Patio and bi-fold systems are highly system-specific. Major UK frame systems and their typical sealed-unit acceptance:
- Origin OB-72 / OW-80 aluminium bi-fold — accepts 28-36mm units, triple usually OK with bead change
- Smart Visofold / Visoglide — 28-32mm standard; some profiles take 36mm with deeper bead
- Schueco AWS / ASS series — designed for up to 50mm units, triple is straightforward
- Older PVCu bi-fold systems — typically 24-28mm only; triple usually means full-frame replacement
- Timber bi-fold (e.g. JS Joinery, Heritage) — depth-on-rebate varies; site survey recommended
Before ordering, send a frame profile photo and the existing unit edge thickness via our contact form for compatibility confirmation. The most common project blocker is the bead-rebate depth, not the sash size.
Certification and standards
Every unit ships with: UKCA mark, BS EN 1279 Declaration of Performance, BS EN 12150 toughening stamp permanently etched on both outer and inner panes, BS EN 12600 Class 1(C)1 impact certificate, and an oversize-handling declaration covering the lifting plan. Heat-soak-tested toughening (BS EN 14179) is available as an order option — strongly recommended for large-span (>3m²) door units where nickel-sulphide spontaneous breakage risk warrants the additional process step.
Frequently asked questions
Is triple glazing overkill for a door?
For new-build and heat-pump retrofit: no — the comfort and EPC win is real. For straight reglazing of an existing A-rated-double bi-fold where the frame is tired: the payback is long (20+ years). The honest call is that triple delivers most of its value when the rest of the building fabric is being upgraded to match — otherwise the heat loss simply shifts to elsewhere in the envelope.
Does the door still close properly with the heavier unit?
Depends on the system. Hinge load ratings are usually the limiting factor. A 2400 × 2100 triple unit at ~150 kg sits at or near the top of most bi-fold hinge specs — confirm the hinge model against the unit weight before ordering. For sliding patio systems, the running gear / track rollers are the equivalent constraint.
Will the unit fit my existing aluminium bi-fold frame?
Modern thermally-broken aluminium bi-fold profiles (Origin, Smart Architectural Aluminium, Schueco, Reynaers) typically accept 28-36mm units. Older non-thermally-broken aluminium and most PVCu bi-folds are designed for 24-28mm only. Send a frame profile photo to our contact form for confirmation — this is the most common project blocker.
Toughened both faces — is laminated middle worth specifying?
For most domestic patio/bi-fold doors, no. Floor-level glazing isn't classified as overhead under BS 5516, so the laminated fragment-retention requirement doesn't apply. For door panels above first-floor balcony level (fall-from-height risk), specify the Triple Glazed Safety (Toughened + Laminated) upgrade.
Acoustic performance on a busy road?
This unit's Rw is ~33-35 dB — modest, because the symmetric pane stack doesn't include acoustic-PVB damping. For door glazing facing busy roads, specify the asymmetric-acoustic variant in the configurator: 8.8mm acoustic-laminated outer + 4mm clear middle + 4mm toughened inner takes Rw to ~40 dB while preserving the Class 1(C)1 safety rating on the inner face.
What's the lead time?
14-21 working days for stock sizes (toughening + triple assembly + oversize handling). Custom (non-stock width or >2.1m tall) typically adds 5-7 working days. Heat-soak-tested toughening adds 3 working days. Shipping is by dedicated 2-person delivery on timber A-frame, not pallet network.
Warranty?
10 years on edge-seal integrity (BS EN 1279-2). 10 years on argon retention to ≥80% of initial fill. 5 years on the Planitherm coating. Toughened pane integrity is manufacturer-lifetime warranty against in-stock defect; spontaneous NiS-inclusion breakage is excluded unless heat-soak-testing is specified at order. Damage in transit is covered for 14 days from delivery — inspect on receipt and photograph before installer signs off.
Material
Glass Composition
Each sealed unit is constructed from float glass manufactured to BS EN 572 standards. Available in clear, low-iron, or tinted variants depending on your specification requirements.
Spacer Bars
We use warm-edge spacer bars as standard, which significantly reduce thermal bridging at the glass edge. Options include stainless steel, aluminium, or composite spacers in black, grey, or silver finishes.
Gas Fill
Standard units come with dry air fill. Argon gas fill is available as an upgrade, improving thermal performance by approximately 0.3 W/m²K. Krypton gas is available for maximum performance in slim-profile units.
Sealants
All units feature a dual-seal system: primary seal of polyisobutylene (PIB) for gas retention, and secondary seal of polysulphide or silicone for structural integrity. This dual-seal construction provides a minimum 20-year service life under normal conditions.
Care
First Six Months: Monthly Checks
Watching for Condensation
Condensation between panes indicates seal failure requiring complete unit replacement. Temporary external condensation is normal when outdoor temperature drops below dew point (typically below 5°C).
External condensation evaporates within 2-3 hours after sunrise. This is actually a good sign showing your glazing insulates effectively.
Testing Hardware Function
Window hardware should operate through 30 complete open/close cycles without resistance. Friction hinges maintain 90° opening position without sagging.
Increased resistance indicates debris accumulation in track channels. This requires cleaning to prevent hardware damage.
Every Three Months
Inspecting Seals
Perimeter seals should show no gaps, tears, or separation from the frame. Seal degradation appears as grey discolouration or hardening texture.
Replace seals at the first sign of deterioration. This prevents water ingress and maintains thermal performance.
Verifying Drainage
Weep hole covers should lift easily. Channels should drain within 30 seconds when you pour 50ml water into the frame cavity.
Blocked drainage requires clearing with a 5mm diameter nylon brush or compressed air at 30-40 PSI. Never use sharp metal objects that might damage drainage channels.
Lubricating Hardware
Friction stays, hinges, and locking mechanisms need lubrication. Apply 3-4 drops of 3-in-One oil per hinge point, or use PTFE-based dry lubricant.
Avoid WD-40 and petroleum-based lubricants. These attract dust and create gummy residue that degrades hardware function over time.
Twice a Year: Deep Clean
Cleaning Frames Properly
Wash frames with pH-neutral detergent (pH 6-8) diluted at 1:20 ratio with warm water (15-25°C). Use a soft cloth or sponge.
Never use abrasive cleaners containing pumice, silica, or alkaline compounds above pH 10. These etch uPVC surfaces and remove protective UV stabilisers that prevent yellowing.
Cleaning Glass Surfaces
Use microfibre cloths (300-400 GSM density) with 1:10 white vinegar solution. This removes mineral deposits without scratching Low-E coatings.
Overlap squeegee strokes by 20mm to prevent streaking. Avoid paper towels - their wood fibre content scratches soft Low-E coatings.
Conditioning Gaskets
EPDM and neoprene gaskets need silicone spray lubricant (silicone concentration 30-40%) to maintain flexibility. This simple step extends gasket life significantly.
Untreated gaskets harden within 5-7 years. Hardened gaskets lose compression properties and allow air infiltration that increases heating costs.
Annual Professional Check
Testing Thermal Performance
Thermal imaging identifies areas exceeding target U-value by more than 0.2 W/m²K. Double glazing should maintain 1.2-1.4 W/m²K. Triple glazing should maintain 0.8-1.0 W/m²K.
These values apply when glazing is properly installed and maintained according to manufacturer specifications.
Checking Seal Integrity
Inert gas concentration testing measures argon retention in sealed units. Argon concentration below 85% of original fill (starting at 90-95% fill) indicates seal breach.
This requires unit replacement within 12 months to prevent complete seal failure and internal condensation.
Adjusting Hardware
Euro-cylinder locks adjust at three points: height, width, and compression. Use a 4mm Allen key for adjustments.
Properly adjusted locks engage at 5-8mm penetration depth without forcing. Misadjustment causes lock mechanism failure within 3-4 years of installation.
Installation
Preparing for Installation
Understanding Frame Capacity
Your existing frames need proper assessment before new glazing installation. Triple glazing units weigh 28-32 kg/m², whilst double glazing weighs 18-20 kg/m². This weight difference matters significantly.
Timber frames older than 25 years require reinforcement. Steel or aluminium angle brackets install at 300mm intervals to support the additional weight. uPVC frames manufactured before 2002 lack internal reinforcement chambers and need complete replacement rather than retrofit.
Getting the Frame Square
Frame squareness directly affects glazing performance. Diagonal measurements must match within ±2mm for openings under 1200mm width. Larger openings allow ±3mm tolerance.
Out-of-square frames cause uneven seal compression. This irregularity reduces the expected 20-year lifespan down to just 8-12 years.
Setting Up Drainage
Proper drainage prevents water damage. Weep holes position at 600mm intervals along the bottom frame rail. Each hole measures 8mm diameter and angles 15° outward.
Blocked drainage allows water accumulation exceeding 200ml capacity. This leads to seal degradation within 18 months of installation.
Installation Process
Installing Glazing Beads Correctly
External glazing beads follow a specific sequence: bottom first, then sides, finally top. Internal beads reverse this order: top first, then sides, then bottom.
This sequence prevents glass unit sagging during installation. It maintains the critical 3mm minimum edge clearance around the entire perimeter.
Positioning Setting Blocks
Distance pieces position at quarter points along the bottom edge. Units under 1200mm width need two blocks. Units between 1200-2400mm require three blocks.
Setting blocks measure 25mm wide × 5mm thick. They use neoprene or EPDM rubber with Shore A hardness between 60-70.
Applying Sealants Properly
Low-modulus neutral-cure silicone applies at 6-8mm bead width with continuous coverage. Two-part polysulphide sealants cure at 3mm depth per 24 hours at 20°C ambient temperature.
Full cure takes 7-10 days. Avoid exposure to cleaning agents during this period.
Maintaining Edge Clearances
Glass edges maintain 3mm minimum clearance from frame on all sides. Inadequate clearance causes thermal stress cracking.
This cracking occurs when temperature differentials exceed 30°C between glass edges and centre pane.
Preventing Heat Loss
Insulating Frame Cavities
Frame cavities fill with polyurethane foam (0.024-0.028 W/mK thermal conductivity) or PIR board cut to exact dimensions. Gaps exceeding 2mm reduce frame U-value performance by 0.15-0.22 W/m²K.
Creating Expansion Gaps
Perimeter expansion gaps maintain 10-12mm width around the frame exterior. These fill with closed-cell polyethylene foam backer rod before external sealant application.
Temperature fluctuations cause uPVC frame expansion and contraction. Frames move 0.6mm per metre for every 10°C temperature change.
Warranty
Required Documentation
Maintain installation certificates, warranty documents, and maintenance logs in a safe place. Warranty claims require evidence of annual maintenance.
This maintenance must be performed by qualified installers or documented DIY maintenance following manufacturer specifications exactly.
Actions That Void Warranties
Warranty exclusions include several specific actions. Never drill frame members or apply paint and coatings to uPVC surfaces.
Don't install aftermarket restrictors without manufacturer approval. Avoid abrasive cleaners and never attempt to modify sealed units yourself.
Inspection Requirements
Manufacturers require access for inspection within 10 working days of warranty claim submission. Failed units must remain in place until inspection occurs.
Retain failed units until replacement authorisation is provided. This typically takes 14-21 days from the inspection date.
Shipping & Returns
- Free UK mainland shipping on orders over £300
- Made to order — lead time confirmed at order confirmation
- Non-mainland UK (Northern Ireland, Channel Islands, Isle of Man, Highlands & Islands): email orders@panerelief.co.uk for a delivery quote
- Returns: made-to-measure glass is manufactured to your exact specification and cannot be returned for change of mind (UK Consumer Contracts Regulations 2013 exemption for personalised goods). Units faulty on arrival are replaced free of charge — report within 48 hours of delivery.
Need a Custom Size?
Use our glass configurator to specify exact dimensions, gas fills, coatings, and more — with instant trade pricing.
Frequently Asked Questions
Everything you need to know about this product before ordering.
-
Our insulated glass units achieve U-values as low as 1.0 W/m²K with argon gas fill and low-emissivity coatings. The exact U-value depends on your chosen glass specification, spacer bar type, and gas fill. We can provide a detailed thermal calculation for your specific configuration on request.
-
Yes, we manufacture bespoke units to your exact specifications. Simply provide the width, height, and glass configuration you need. There is no minimum order quantity for custom sizes, and we can accommodate most non-standard shapes including arched, circular, and raked units.
-
Standard units ship within 2–3 weeks from order confirmation. Custom specifications such as toughened, laminated, or triple-glazed units may take 3–4 weeks depending on glass availability. We will confirm the exact lead time when we process your order.
-
We supply direct to trade — our units are designed for professional installation by qualified glaziers and window fitters. Each unit ships with fitting instructions and gasket recommendations. If you need installation support, we can recommend approved installers in your area.
How to Replace a Sealed Unit
Follow these steps for a professional sealed unit replacement. Always wear protective gloves and eyewear when handling glass.
Measure the Opening
Measure the width and height of the glass (not the frame) in at least three places. Take the smallest measurement and deduct 2mm for clearance. This gives you your order size.
Remove the Beading
Starting with the longest bead, insert a stiff putty knife or glazing chisel into the gap between bead and frame. Gently lever outward. For uPVC, the bead will unclip. For timber, carefully prise the pinned bead away.
Remove the Old Unit
Using suction cups, carefully lift the failed sealed unit out of the frame. Tilt the top edge toward you first, then lift clear. Have a second person assist with larger units.
Clean the Frame Rebate
Remove any old sealant, dirt, or glazing tape from the rebate using a scraper and white spirit. The rebate must be clean and dry for the new unit to sit properly and for sealant to adhere.
Position the Packers
Place setting blocks at the quarter and three-quarter points along the bottom of the frame. These support the weight of the glass and ensure even distribution. Use 5mm packers for standard units.
Insert the New Sealed Unit
Lower the new unit into the frame, resting it on the packers. Push the unit back into the rebate until it sits square. Check that the gap is even all around — adjust packers if needed.
Refit the Beading
Starting with the shortest bead, press each one firmly back into position. For uPVC, tap with a rubber mallet until it clicks home. For timber, pin back in place. Ensure all beads are flush with the frame.
Check & Finish
Use a spirit level to confirm the unit is sitting level. Check all four edges for even gaps. Clean the glass with a soft cloth. The new unit should operate smoothly within the window.
Not confident doing this yourself? We offer professional installation across Bristol and the South West.
Need Help? Contact UsTrade Support
How We Help Trade Customers
Bulk Trade Pricing
Volume discounts on all insulated glass units. The more you order, the more you save.
View trade pricingTechnical Support
Our glazing experts are on hand to help with specifications, Building Regs compliance, and installation advice.
Call 0117 330 3057Reliable Delivery
Nationwide delivery direct to site. Careful packaging ensures your units arrive in perfect condition.
Delivery informationReady to order?
Get Your Trade Quote Today
Fast specification-led pricing for insulated glass units. No middlemen, direct to your site.