National Windows Dispatch installs FENSA-certified double-glazed windows that reduce heat loss, eliminate draughts, and cut noise pollution. We survey existing frames (measure openings, check structural condition), specify energy-rated glass (A-rated U 1.2, argon-filled 16mm cavity, low-E coating), manufacture uPVC/timber/aluminum frames to exact dimensions—then remove old windows, fit new units with DPC membrane weatherproofing, seal with expanding foam + silicone, and register with FENSA for Building Regulations compliance.
Survey week 1. Quote approved. Windows manufactured week 2-3 (custom sizes). Old windows removed day 1. New frames fitted + glazed day 2. Sealed + finished day 3. FENSA certificate week 4.
FENSA certification required for replacement windows (self-certification scheme—installer registers work with Building Control, homeowner receives compliance certificate). Typical whole-house replacement (8 windows, 3-bed semi) costs £4,000-5,500. A-rated windows (U 1.2 or better) mandatory from 2026 in England. Glass: 4mm outer pane, 16mm argon cavity, 4mm inner low-E pane. Warm-edge spacer (reduces cold bridging at glass edge). Frame: uPVC (cheapest, £350-500/window), timber (traditional, £600-900), aluminum (slim sightlines, £800-1,200). Savings: replacing single-glazed (U 5.0) with A-rated (U 1.2) saves 75% heat loss through windows = £180/year typical semi.
📞 0333 600 0994Energy rating A-G scale (like appliances). A-rated = U-value 1.2 or better. Achieved with: 4mm low-E glass (tin oxide coating reflects heat back inside), 16mm argon cavity (argon gas is denser than air, reduces convection), warm-edge spacer (insulated bar between panes, stops cold bridging). Cost: £400-550/window (1.2m × 1.2m typical casement). Upgrade from old double-glazing (C-rated, U 1.8): saves £80/year on heating (whole house). Upgrade from single-glazing (U 5.0): saves £180/year. Payback on £4,500 whole-house replacement: 6 years vs single-glazed, 12 years vs old double-glazing. FENSA certificate proves energy rating (needed for property sale EPC).
FENSA (Fenestration Self-Assessment Scheme) allows approved installers to self-certify window replacements for Building Regulations compliance. Alternative: apply to Building Control (£300-500 fee, slower). FENSA installers register every job, homeowner receives certificate 4-6 weeks later. Certificate required for: property sales (solicitors request it), insurance claims (some insurers require for replacement windows), warranties (10-year guarantee only valid with FENSA cert). FENSA inspectors randomly audit 2% of jobs (surprise visit within 3 months—check installation quality, U-value compliance, weatherproofing). Failed audit = re-work at installer's cost. We're FENSA registered (#12345), 15 years, zero failed audits.
U-value measures heat loss: watts per m² per degree temperature difference. Lower = better insulation. Part L (Building Regs) requires U 1.4 or better for replacement windows (A-rated U 1.2 exceeds this). Whole-window U-value includes frame + glass + spacer. Example: 4-16-4 argon low-E glass (U 1.1 center-pane), uPVC frame (U 1.3), warm-edge spacer (Psi 0.04) = whole-window U 1.19 (A-rated). Old double-glazing (air-filled, no low-E): U 2.8 (C-rated). Single-glazing: U 5.0+ (G-rated—fails Part L, must upgrade if replacing). We calculate exact U-values for every quote (considers frame material, glass spec, window size—larger windows have better U-values because glass proportion increases, frame edge effects reduce).
uPVC: £350-500/window. Maintenance-free, good insulation (U 1.2 achievable), 25-year lifespan, available in white/woodgrain/colors. Drawbacks: can't be repainted (color fades over 15 years), less traditional appearance. Timber: £600-900/window. Traditional looks, can be painted any color, sustainable (FSC-certified). Drawbacks: needs repainting every 5-7 years (£80-120/window), can rot if not maintained. Aluminum: £800-1,200/window. Slim frames (more glass area, better views), strongest (spans large openings without mullions), powder-coated any color, 40-year lifespan. Drawbacks: cold bridge (aluminum conducts heat), needs thermal break (insulated spacer inside frame adds £100-150). We recommend: uPVC for most (best value + performance), timber for listed buildings/conservation areas, aluminum for large glazing (bifolds, curtain walls).
Standard double-glazing reduces noise 28-32dB. Acoustic glazing achieves 40-48dB reduction (near-silent indoors even with busy road outside). How: asymmetric glass thickness (6mm outer + 4mm inner stops resonance—sound wave can't travel through different-thickness panes at same frequency), wider cavity (20mm instead of 16mm—more air gap absorbs sound), laminated inner pane (acoustic interlayer dampens vibration). Cost: +£80-120/window vs standard. When worth it: main roads (traffic noise), flight paths, city centers, noisy neighbors. Example: 70dB traffic noise outside → 32dB inside with standard glazing (still audible), 22dB with acoustic (barely noticeable, like whisper). Building Regs don't require acoustic glazing but Planning may in conservation areas (to allow road-facing windows where previously restricted).
Victorian/Georgian sash windows (pre-1920s) often listed or in conservation areas—Planning permission may prohibit replacement. Options: (1) Restore existing sashes (repair timber, replace cords, install draught-proofing, fit secondary glazing inside)—costs £600-900/window, maintains original appearance, U-value improves to 2.8 (not great but acceptable for heritage properties). (2) Replace with replica timber sash windows (double-glazed, matches original design)—costs £1,200-1,800/window, requires Planning approval (conservation officer assesses), achieves U 1.4. (3) Install secondary glazing (internal acrylic panel 100mm behind original window)—costs £300-450/window, no Planning needed (internal change), achieves U 2.0 combined with single-glazed primary window. We assess property during survey, advise on Planning requirements, recommend most appropriate solution (not all properties can have replacement windows).