By william mcdowell, national business development manager- rooflights for hambleside danelaw
One of the most effective ways to improve a building’s sustainability when refurbishing is to look up, to the “hole in the roof”.
In many of our existing industrial buildings, the occupants may not even be fully aware that they have rooflights, because they are so old, dirty or discoloured. Yet a comparatively simple upgrade to ‘the hole in the roof’ can have a massive impact on the internal environment below, reducing lighting and heating costs and thus reducing carbon emissions.
Now too, for the first time, certain rooflights can make a tangible, proven contribution towards BREEAM accreditation, whether in new build, in-use or refurbishment schemes. BREEAM is proven to add up to 20% to sales and rental premiums. So there is a sound commercial argument, above and beyond the need to consider sustainability.
Addressing rooflights as part of a sustainable refurbishment is a change that will derive benefits for years to come: modern GRP rooflights can deliver a 30 year service life, in comparison to polycarbonate systems’ typically 15-20 years on average, according to the National Association of Rooflight Manufacturers (NARM NTD09).
Simply replacing the rooflight’s old, outer weather sheet (subject to the lining sheet being in good condition) will improve the amount of natural light allowed into a building.
The percentage of roof covering to rooflights can be addressed. Historically, the rule of thumb has been a 10% rooflight area being optimal, yet independent studies point to 15-20% rooflights as the optimum performance range. Notably though there will always be project-specific variables to consider. The National Association of Rooflight Manufacturers (NARM) commissioned research that indicates a rooflight area of 15-20% achieved savings in running costs of £5.92/m2/yr (at prices current when the report was compiled), and reduced emissions by 28.7kgCO2/m2/yr.
Replacing old rooflights with a modern, double skin system will enhance the building’s thermal performance, potentially reducing the supplementary heating requirement. A double skinned rooflight with an outer weather sheet, internal liner panel, and a transparent insulating core can attain a U value as low as 0.9W/m2K.
There is, however, a trade-off to be made. One needs to balance natural daylight with thermal performance. It costs roughly four times more to heat an industrial building than to light it.
Rooflights have generically always been accepted as contributing towards BREEAM, in Energy and Health & Wellbeing categories. Now, the contribution can be quantifiable, when used as part of a metal roof. A 1.5point contribution can be taken towards BREEAM under the Material Mat 02 category using rooflights that carry an Environmental Product Declaration (EPD)(*). Note that Energy, Health & Wellbeing and Materials are the three most heavily weighted BREEAM categories.
Beyond BREEAM, look into the sustainability of the rooflight itself. As a material, GRP does not emit any chemicals once installed, so is safe to use with grey water systems, and in green roof schemes. It is unaffected by contact with other materials, unlike some other products.
New technologies in the manufacturing processes mean that not all GRP rooflights are the same, with some versions using a stronger GRP substrate that is lighter in weight and has up to 40% less embodied carbon than traditional GRP rooflight sheeting. Insulating cores vary too: honeycomb cellulose acetate offers lower embodied energy than the traditional structured polycarbonate, and is biodegradable.
