Office in Leeds Case Study
Supporting EPC Improvement Through High-Performance Reglazing
Improved performance
Modern low-E units improve the centre-pane U-value from 2.8 to 1.27 W/m²K.
Better working environment
The replacement maintains a similar daylight level while reducing unwanted solar gain.
Reduced energy costs
Indicative combined annual saving is approximately £5,371 to £7,338 per year.
Case study overview
This downloadable case study summarises how Dortech Maintenance worked with TSK Group to support the energy-performance objectives of a confidential office building in Leeds through targeted replacement glazing.
The challenge: improving building performance
Concerns had been raised about the performance of the existing windows. In air-conditioned commercial buildings, glazing performance matters in both summer and winter: solar gain can increase cooling demand, while poor insulation can increase heat loss and heating demand.
Dortech visited site to assess the existing glazing and identify a practical replacement specification that would support TSK Group’s renovation requirements and the project’s energy-performance objectives for the office building in Leeds.
Existing and replacement glazing
| Performance measure | Existing glazing | Replacement glazing | Improvement |
|---|---|---|---|
| Light transmission | 0.39 / 39% | 0.38 / 38% | Similar daylight level |
| G-value | 0.47 / 47% | 0.35 / 35% | Reduced solar gain |
| Centre-pane U-value | 2.8 W/m²K | 1.27 W/m²K | Improved thermal insulation |
The replacement units comprise 6mm grey body-tinted glass / 12mm argon gas-filled cavity / 6mm clear low-E inner pane. The specification maintains a broadly similar daylight level while improving both solar-control and thermal performance.
Solar and thermal improvement
The reduction in g-value from 0.47 to 0.35 represents approximately 26% less solar energy transmission through the glass. For an air-conditioned building, that can reduce the burden on cooling systems during warmer periods.
The centre-pane U-value improved from 2.8 W/m²K to 1.27 W/m²K, giving a U-value improvement of 1.53 W/m²K. This helps reduce conductive heat loss through the glazing during colder periods and supports a better overall energy profile.
Indicative energy saving
| Saving category | Indicative annual saving |
|---|---|
| Heating-side saving | £4,213/year |
| Cooling-side saving | £1,158 to £3,125/year |
| Combined indicative saving | £5,371 to £7,338/year |
Supporting the pathway to EPC B
For commercial property owners, EPC performance has become increasingly important. Improving the building envelope is one practical way to support better energy performance, particularly where existing windows or glazed areas are underperforming.
At this office building in Leeds, the glazing upgrade helped address both summer and winter performance issues. In summer, the reduced g-value helps limit unwanted solar gain, while in winter, the improved U-value helps reduce heat loss and improve facade thermal performance.
Conclusion
This office building in Leeds demonstrates how targeted reglazing can help improve the performance of an existing commercial building without necessarily replacing the full window or facade system.
The replacement units maintained a similar level of visible light transmission while delivering a meaningful reduction in g-value and a significant improvement in centre-pane U-value.
Calculation assumptions
| Assumption | Value |
|---|---|
| Glazing area | 945m² |
| Existing glass light transmission | 0.39 / 39% |
| Replacement glass light transmission | 0.38 / 38% |
| Existing glass g-value | 0.47 / 47% |
| Replacement glass g-value | 0.35 / 35% |
| G-value reduction | 0.12 |
| Existing centre-pane U-value | 2.8 W/m²K |
| Replacement centre-pane U-value | 1.27 W/m²K |
| U-value improvement | 1.53 W/m²K |
| Heating degree days | 2,000 K-days/year |
| Assumed heating efficiency | 85% |
| Assumed gas rate | 5.16p/kWh |
| Assumed electricity rate | 22.19p/kWh |
Disclaimer: This case study is provided for general guidance. EPC references, performance data and indicative savings should not be treated as guaranteed performance, guaranteed EPC outcome or guaranteed financial return.