U values: out of the classroom, onto the roof

U values: out of the classroom, onto the roof

St. Michael’s C of E School in Bristol lies nestled beside the historic church of St. Michael on the Mount. There has been continuous development of the area throughout the centuries since the church was founded in Norman times, and it is now part of the St. Michael’s Hill Conservation Area.

The school has seen some hard times, being badly damaged in the Blitz and faced with closure in 1999, but it is now a thriving school serving Bristol’s multicultural inner city population. So when the roof needed replacing there was an opportunity to add insulation at the same time, provided the plasterboard underneath was not disturbed.

TLX Gold, combining as it does a breather membrane with insulation and a reflective undersurface, can be draped over the rafters - so no need to raise the roof. An additional benefit of the low emissivity breathable surface is that the amount of heat being radiated into the attic void in summer is greatly reduced – especially useful with classrooms directly beneath and having only windows for ventilation. And in spite of being a high occupancy building, there is no risk of condensation from the water vapour produced because TLX Gold is fully breathable.

The Problem: How to provide insulation as part of a re-roof to be carried out and completed during the school holidays, and subject to the constraints of being in a conservation area.

The Solution: TLX Gold takes no more time to install than a conventional breather membrane, yet provides insulation at the same time with a U-value of 0.67 W/m2K. This was reduced to 0.32 W/m2K where it was possible to combine it with 50mm PIR board between the rafters.

TLX Gold is particularly useful in Conservation areas where it is not possible to raise the roof, and has the additional benefit of minimising solar gain in summer. So even though the pupils may not be tackling the U-value questions that are now part of GCSE science, they can appreciate feeling warmer in winter and cooler in summer. No more sweltering in June exams!