Residence 9 windows vs timber sash windows is a conversation and discussion that often comes up when looking for the best replacement windows for heritage properties. In terms of restrictions, a Grade II listed building is typically required to use Timber Sash. For unlisted homes in conservation areas, Residence 9 (R9) is often approved as a low-maintenance alternative. So, which are the best choices for heritage projects?
Grade II listed properties require listed building consent, and conservation officers generally prefer timber, but there are cases where R9 has been approved on Grade II properties, particularly when the original windows were already replaced unsympathetically at some point in the past.
| Residence 9 | Timber Sash | |
| Material | uPVC (9-chamber, 100mm profile) | Solid timber, typically hardwood |
| Authentic appearance | Excellent, flush sash, mechanical joints, decorative interior profile, indistinguishable from timber to most observers | Originally, the visual benchmark, though high-quality R9 installations are very close |
| Conservation areas | Regularly approved across the UK | Almost always approved |
| Grade II listed | Approval less common, but possible where original windows have already been replaced unsympathetically | Typically preferred by conservation officers |
| Thermal efficiency | 0.8 W/m²K (triple) or 1.2 W/m²K (double), meets PassivHaus standard | 1.2–1.6 W/m²K typical for double-glazed timber |
| Maintenance | None, no repainting, sanding, or treatment | Repainting every 5–8 years, plus periodic repair of rot or warping |
| Weather resistance | Excellent, won’t rot, warp, swell or fade | Vulnerable to moisture, particularly in exposed coastal or rural locations |
| Lifespan | 25+ years with effectively zero upkeep | 60+ years, but only if properly maintained throughout |
| Cost | Mid-range | Highest, typically 30–50% more than R9 |
| Best for | The vast majority of heritage projects: unlisted period homes, conservation areas, and properties where modern performance matters | Grade II listed properties and the most architecturally sensitive sites where original timber is being directly replaced |