Window Fitters Ltd provides professional uPVC window fitters for Document L compliant casement, tilt-and-turn, and sash window installation across London and Surrey. Our directly employed teams fit multi-chambered uPVC profiles achieving Uw values of 1.2 to 1.4 W/m²K, with integrated trickle vents, PAS 24 security, and a 10-year frame guarantee.
Why Choose uPVC Windows?
uPVC (unplasticised polyvinyl chloride) is the most widely fitted window frame material in UK homes. Modern multi-chambered uPVC profiles trap pockets of still air inside the frame. This slows heat transfer and makes uPVC one of the best-insulating frame materials available at a competitive price point.
Our uPVC window fitters install Document L compliant windows that meet or beat every current UK Building Regulation requirement. Whether you need a single replacement window or a full-house upgrade, our directly employed teams deliver precision fitting with written guarantees.
Thermal Performance: Sub-1.4 U-Values
Every uPVC window we install achieves whole-window U-values (Uw) between 1.2 and 1.4 W/m²K. This meets the Document L replacement maximum of 1.4 W/m²K and our typical installations sit comfortably below this threshold.
How We Achieve Sub-1.4 U-Values
The whole-window U-value (Uw) depends on three components working together:
| Component | Specification | Contribution to Uw |
|---|---|---|
| Frame (Uf) | Multi-chambered uPVC profile (5 to 7 chambers) | Uf = 1.1 to 1.3 W/m²K |
| Glass Centre (Ug) | Low-E coated, Argon-filled sealed unit (24mm or 28mm cavity) | Ug = 1.0 to 1.1 W/m²K |
| Spacer Bar (Ψ) | Warm-edge composite spacer (Superspacer or Thermobar) | Reduces edge heat loss by up to 65% vs aluminium spacers |
Standard aluminium spacer bars create a thermal bridge at the edge of the glass unit. We specify warm-edge composite spacers as standard because they reduce condensation at the glass edge and improve the overall Uw by 0.1 to 0.2 W/m²K.
Window Energy Ratings (WER) Explained
The Window Energy Rating scheme uses an A-rated to E band scale. The rating measures the overall energy balance of a window: how much heat it gains from sunlight versus how much it loses through conduction and air leakage.
- A-rated: Highest performance. Net energy gain in typical UK conditions. Triple-glazed or high-spec double-glazed units.
- A+ rated: Strong performance. Typical of our best double-glazed uPVC units with warm-edge spacers.
- A rated: Good performance. Standard specification for quality uPVC replacement windows.
- B rated: Minimum acceptable under Document L for replacement windows.
All uPVC windows we supply and fit are rated A or above. Most achieve A+ or A-rated ratings.
Trickle Vent Integration (Document F Compliance)
Document F of the UK Building Regulations requires background ventilation in habitable rooms when replacement windows are installed. Trickle vents are small openable slots fitted into the window frame head that allow controlled background airflow without opening the window.
Document F trickle vent requirements:
- Multi-storey dwellings (flats): 8,000 mm² equivalent area per habitable room
- Single-storey dwellings (bungalows): 10,000 mm² equivalent area per habitable room
- Wet rooms (bathrooms, kitchens): Additional 4,000 mm² equivalent area on top of habitable room requirements
Our uPVC window fitters calculate the required trickle vent equivalent area for each room and install the correct vent sise. If the original windows did not have trickle vents, Document F still requires them on the replacement windows unless the property has an alternative whole-house mechanical ventilation system.
Read our full guide on trickle vents explained for detailed specifications.
Sourcing Flexibility: Supply & Fit or Installation Only
- Supply and Fit: We take precise technical measurements, source top-grade A-rated frames from leading UK manufacturers at trade rates, deliver them to your property, and complete the installation.
- Installation Only: If you have already purchased your own frames and glazed units, our directly employed uPVC window fitters handle the labour. We ensure correct levelling, insulation packing, and weatherproof sealing. Read about our packages on our contracts page.
uPVC Casement Window Styles
- Side-Hung Casement: The standard UK window design. Hinged at the side, opening outward. Maximum airflow and clean sightlines.
- Top-Hung Casement: Hinged at the top, opening outward at the bottom. Provides ventilation while preventing rain ingress.
- Tilt & Turn: A European configuration that tilts inward at the top for secure draught-free ventilation, or swings fully open like a door for easy interior cleaning.
- Vertical Sliding Sash: Replicates traditional heritage window aesthetics using low-maintenance uPVC profiles with modern slide-and-tilt balances. See our sash windows page for details.
uPVC Profile Systems We Install
We work with a carefully selected range of leading UK and European uPVC profile systems. Our experienced surveyors recommend the best match for your property type, budget, and performance requirements.
- Deceuninck 2500: A robust, chamfered-edge profile system. Delivers 1.2 to 1.4 W/m²K (A-rated). Our most cost-effective option for whole-house replacement projects.
- Liniar Sculptured: A softer, rounded-edge aesthetic with superior thermal insulation at 1.2 W/m²K. Popular for modern flat conversions and refurbishments.
- Rehau T70C: Exceptional structural integrity and long-term durability. Delivers 1.2 to 1.4 W/m²K with a premium feel and high-grade rigidity.
- Profile 22 Optima: One of the most trusted PVC-U systems in the UK (Epwin Window Systems group). Achieves 1.2 W/m²K with clean modern aesthetics. Engineered to meet PAS 24 security from the ground up.
- Spectus: Part of the Epwin group. A strong performer for both casement and vertical sliding sash window applications. Widely used in social housing refurbishment programmes.
All systems are available in a wide range of foiled colour finishes. The most popular choice for modern properties is Anthracite Grey (RAL 7016), alongside Rosewood, Irish Oak, Chartwell Green, and Cream White.
Glass Unit Construction
The sealed glass unit is the heart of every double-glazed window. Our standard glass unit construction includes:
- Outer pane: 4mm float glass (clear or tinted)
- Cavity: 16mm to 20mm gas-filled gap (Argon as standard, Krypton for enhanced performance)
- Inner pane: 4mm Low-E coated glass (soft-coat Low-E reflects radiant heat back into the room)
- Spacer bar: Warm-edge composite spacer (reduces condensation and thermal bridging at the glass edge)
- Primary seal: Polyisobutylene (PIB) butyl sealant between the spacer bar and glass panes
- Secondary seal: Polysulphide or structural silicone sealant around the outer perimeter for structural bonding and moisture protection
The overall sealed unit thickness is typically 24mm (4/16/4) or 28mm (4/20/4). Thicker cavities with Argon gas fill deliver lower centre-pane U-values (Ug).
Security: PAS 24 & Document Q Compliance
All uPVC windows we fit include:
- Internal steel reinforcement ribs within the frame chambers
- Multi-point shootbolt locking mechanisms
- Key-locking handles with restricted opening positions for child safety
- Anti-lift hinge blocks and heavy-duty friction stays
- Toughened safety glass (BS EN 12150) in all critical zones below 800mm from floor level (Document K)
All ground-floor and easily accessible windows meet PAS 24 / Secured by Design standards as required by Document Q. Read more on our PAS 24 security windows page.
What Is Included in Every uPVC Installation
Our Supply and Fit service includes the following as standard:
- 10-Year Structural Frame Guarantee
- 5-Year Sealed Glass Unit Guarantee
- PAS 24 / Secured by Design multi-point locking
- Toughened safety glass in all Document K critical zones
- Trickle vents specified to Document F requirements
- Low-threshold options where Part M compliance is required
- Professional fitting by directly employed CSCS-carded glaziers
- Mechanical fixings, expanding foam insulation, and perimeter silicone sealing
- Removal and disposal of old frames
Read full guarantee terms on our guarantee page.
Estimated Lead Time
For standard uPVC Supply and Fit projects, our typical lead time from confirmed order to installation is 2 to 3 weeks. This includes manufacturing, quality checks, and scheduling your fitting date. Larger commercial or multi-unit projects may require extended timescales confirmed during the technical survey stage.
Frequently Asked Questions: uPVC Windows
How much do uPVC windows cost in London?
Costs vary depending on window sise, style (casement vs tilt-and-turn), profile system chosen (Deceuninck, Liniar, Rehau, or Profile 22), and glazing specification. Check our detailed cost guide for labour rates and turnkey prices, or contact us for a free estimate.
How long does a standard uPVC window installation take?
Replacing a single standard uPVC casement window takes roughly 2 to 3 hours, including clean-up and disposal of the old frame. A full house window upgrade (6 to 8 windows) is typically completed in 1 to 2 days.
Do replacement windows need trickle vents?
Yes. Document F of the UK Building Regulations requires trickle vents on replacement windows to provide background ventilation. The required equivalent area is 8,000 mm² for multi-storey dwellings and 10,000 mm² for single-storey dwellings per habitable room. Our uPVC window fitters calculate and install the correct specification for each room.
What colour finishes are available?
All our uPVC profile systems are available in a wide range of foiled colour finishes. The most popular choice for modern properties is Anthracite Grey (RAL 7016), alongside Rosewood, Irish Oak, Chartwell Green, and Cream White. Dual-colour options (different colours inside and outside) are also available.
How do I get started?
Request a free quote through our online quote form, call us on 020 3411 0589, or use our interactive Window & Door Survey Designer to upload your drawings and map out your openings before booking a site visit.
Author & Technical Reviewer: Marian Gheorghe
Head Installer & CEO, Window Fitters Ltd
Marian Gheorghe is the Active Director and Team Leader Installer at Window Fitters Ltd. With over 15 years of hands-on experience, he oversees technical safety and UK Building Regulations compliance for all residential and commercial glazing contracts.
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Window Fitters Ltd installs windows, doors, fire doors, and commercial glass facades across London and Surrey. Croydon head office, 40-mile service radius, 100% directly employed CSCS-carded fitters.
Our estimators respond within 24 business hours with a fixed-price quotation.
Verified Google & MyBuilder Reviews
"Stunning Sash Windows in Croydon"
"Marian and his team replaced our old Victorian sash windows. They were clean, fast, and the double glazing has completely blocked out the street noise. Highly recommended!"
"Excellent Bifold Doors in Bromley"
"Installed beautiful grey aluminium bifold doors for our new kitchen extension. Smooth gliding mechanism and great insulation. The best quote we got in Kent."
"Perfect Front Door Upgrade in Sutton"
"Very happy with our new composite door installation. Excellent lock security and high-quality GRP slab finish. Fast half-day fitting and no mess left behind."