Building Regulations & Glazing
Complete guide to Approved Documents Part L (thermal), Part K/N (safety), Part B (fire), Part O (overheating) and Part E (acoustic) as they apply to glazing specification.
Part L — Thermal Performance (2021)
Part L sets maximum U-values for glazing to minimise heat loss:
| Application | Max U-Value (New Build) | Max U-Value (Replacement) | CSU Standard (28mm) |
|---|---|---|---|
| Windows | 1.4 W/m²K | 1.4 W/m²K | 0.9 W/m²K ✓ Exceeds 36% |
| Roof windows | 1.4 W/m²K | 1.4 W/m²K | 1.0 W/m²K ✓ Exceeds 29% |
| Rooflights | 1.7 W/m²K | 1.7 W/m²K | 1.0 W/m²K ✓ Exceeds 41% |
| Doors (>60% glazed) | 1.4 W/m²K | 1.4 W/m²K | 0.9 W/m²K ✓ Exceeds 36% |
| Curtain walling | 1.6 W/m²K | — | 1.0 W/m²K ✓ |
Part K/N — Safety Glass Locations
Toughened or laminated glass required in these critical locations:
- Doors & side panels: Within door leaf or 300mm of door edge, floor to 1500mm
- Low-level: Lowest edge below 800mm from FFL
- Bathrooms: All glazing in rooms with bath/shower, floor to 1500mm
- Full-height panels: Floor-to-ceiling
- Adjacent to stairs: Staircase enclosures
Critical locations shown on a typical elevation:
Part B — Fire Safety
Fire-rated glass required in compartment walls, fire doors, escape routes. Must achieve required E/EW/EI rating (30-120 minutes) and be installed in tested approved framing. See our Fire-Rated Glass page for full details.
Part O — Overheating (2022)
New residential buildings must demonstrate overheating risk is managed. Solar control glass (g-value ≤0.40) is a primary compliance tool for south/west-facing glazing. Recommend: Suncool 66/33 (g=0.33) or Suncool 50/25 (g=0.25).
Part E — Sound Insulation
Minimum airborne sound insulation between dwellings. Acoustic glass (Optiphon, Stadip Silence) with asymmetric configurations achieves 36-50+ dB Rw. See our Acoustic Glass page.
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