- TYPE: Double Glazing
Specialist Acoustic Laminated Double Glazed 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 cost-optimal acoustic flagship — Rw 40 dB in a 28mm double-glazed envelope. An asymmetric double-glazed unit with an 8.8mm acoustic-PVB laminated outer pane and a 4mm clear inner, separated by a 14mm argon-filled cavity, delivers acoustic performance previously only available from triple glazing — at roughly half the cost and weight.
For most urban-noise-mitigation projects, this is the right unit. It fits standard 28mm double-glazed rebates, weighs about 23 kg/m² (not the 38 kg/m² of acoustic triple), and achieves an Rw of 40 dB — a 10-12 dB improvement over a typical 1990s 4-12-4 double. The perceived loudness reduction is roughly halving — traffic that previously dominated a room moves into the background.
Asymmetric build — why it works
Symmetric double-glazed units (4-12-4, 4-20-4) have a coincidence-frequency dip where the two identical panes resonate together. Sound at that frequency punches through. Replacing one pane with a thicker laminated build shifts the coincidence frequency of that pane to a different band — so the two panes' dips no longer coincide.
The acoustic PVB interlayer in the 8.8mm laminate adds viscoelastic damping. Standard PVB (used in safety lamination) helps mildly. Acoustic-grade PVB (e.g., Trosifol SC, Saflex Q) is engineered with specific viscoelastic properties tuned to road and rail frequency bands — it absorbs 3-5 dB more than standard PVB across the critical 500-2500 Hz range.
Technical specification
| Overall thickness | ~28mm |
|---|---|
| Build-up | 8.8mm acoustic-laminated outer (4+4 with 0.76mm acoustic PVB) / 14mm argon cavity / 4mm clear inner with optional low-E |
| Outer-pane standard | BS EN 14449 (laminated) |
| Rw (Weighted Sound Reduction Index) | 40 dB to BS EN ISO 717-1 |
| Rw + Ctr (road-traffic spectrum) | 36-37 dB (typical) |
| U-value (centre-pane, with low-E inner face 3) | 1.2 W/m²K |
| U-value (without low-E) | 1.5 W/m²K |
| g-value | 0.58 |
| Light transmittance | ~78% |
| Weight | ~23 kg/m² (manageable load in standard frames) |
| Standards | BS EN 1279, BS EN ISO 717-1, BS EN 14449, BS EN 12600 (impact class 2(B)2 via laminated) |
Where this unit is the right call
- Urban frontage facing busy A-roads, ring roads, or town-centre traffic — typical existing Rw 28-30 dB, upgrading to 40 dB roughly halves perceived noise.
- Properties within 200m of a railway line — particularly Network Rail main lines, freight routes, and HS2/Crossrail corridors. Asymmetric stacks handle low-frequency rail noise better than symmetric.
- Flight-path properties outside the 60 dB LAeq,16h contour where Rw 40 typically delivers an acceptable internal noise level without needing the cost/weight of acoustic triple.
- Apartment buildings and HMOs where Approved Document E (sound insulation between dwellings) compliance crosses with external glazing performance.
- Boutique hotels and serviced apartments where guest noise expectations drive specification.
- Home offices and recording studios in urban areas where noise floors below ~35 dB are the target.
The full acoustic-glass guide, including the Rw vs Rw+Ctr distinction, frame-seal advice, and acoustic trickle-vent guidance, is on the acoustic glass topical page. For the highest-performance acoustic spec (44 dB Rw triple-glazed), see the Triple Glazed Acoustic flagship.
Stock sizes and pricing
Five UK-standard stock sizes are below. Dispatch 10-14 working days (acoustic-PVB lamination adds ~5 days to standard DG manufacturing). Custom sizes — including shaped, oversized, and bespoke pane-asymmetry builds (e.g., 8.8 + 6.4 for max-mass at boundaries) — are priced via the configurator.
Certification and standards
Every unit ships with: UKCA mark, BS EN 1279 DoP, Rw test certificate from a UKAS-accredited acoustic lab (BS EN ISO 10140 methodology), BS EN 14449 laminated-glass certificate on the outer pane, and BS EN 12600 impact classification (Class 2(B)2 via the laminated outer — meets most Approved Document N critical-location requirements as a side benefit). For noise-mitigation grant applications, we supply the Rw + Ctr + C figures as a complete documentation pack.
Frequently asked questions
How much quieter, in practice?
A 10-12 dB improvement is perceived as roughly halving loudness. If the room currently registers 50 dB(A) of background noise from outside (a typical urban room with 1990s DG facing a busy road), this upgrade typically drops that to 38-40 dB(A) — closer to a quiet residential street. The improvement is most noticeable for speech-intelligibility-band frequencies; low-frequency rumble drops less.
Does it block low-frequency noise (lorries, basses)?
Partially. Low frequencies (below 250 Hz) are hard to block with glass mass alone — they're better attenuated with secondary glazing or mass-loaded walls. This unit drops low-frequency noise about 6-8 dB, vs 12-15 dB at mid frequencies. For dominant low-frequency sources (heavy goods routes, freight rail), Rw+Ctr is the more honest figure (36-37 dB vs 40 dB Rw).
Can I get this as a triple-glazed unit?
Yes — the Triple Glazed Acoustic Unit (44 dB Rw) adds a third pane for a further 4 dB improvement, at additional cost and weight. For most projects, the double-glazed asymmetric flagship is the cost-optimal sweet spot.
Will my existing frame take this?
At 28mm overall, this fits the same rebates as a standard 28mm DG — modern PVCu, aluminium, and timber frames designed for double glazing. The 23 kg/m² weight is typically inside hinge ratings for windows up to 1500×1200. Confirm sash-balance ratings for very large units.
Acoustic PVB vs standard PVB — is the upgrade worth it?
Yes, for acoustic-priority projects. Acoustic-grade PVB adds 3-5 dB across the 500-2500 Hz speech-intelligibility band over standard PVB at roughly £10-15/m² premium. For a £200 unit, that's a 5-8% price increase for a 10-15% perceived noise reduction — typically the best £/dB in the configurator.
Side-benefit: does this also count as safety glass?
Yes. The laminated outer pane satisfies BS EN 12600 Class 2(B)2 — adequate for most critical locations under Approved Document N (door sidelights, low-level windows, bathroom glazing). For Class 1(C)1 (highest impact rating), specify toughened-plus-laminated in the configurator.
Warranty?
10 years on edge-seal integrity (BS EN 1279-2). 10 years on PVB delamination (BS EN 14449 standard). 10 years on argon retention to ≥80% of initial fill. Rw performance is warranted at the certified test value at installation date — frame-seal degradation over time is excluded from the glass warranty.
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.
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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.
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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.
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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.
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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.
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