William McDowell of Hambleside Danelaw explains how recent innovations in GRP rooflights can help specifiers contribute towards BREEAM and sustainability
It is impossible to be unaware of the drive to increase our sustainability in building design. However, many architects are unaware that by looking upwards they can shed light on a simple way to help increase a building’s sustainability.
A solution is rooflights manufactured from glass-reinforced plastic (GRP), whether designing a sustainable new build, fit-out or refurbishment project. GRP rooflights can make a positive contribution towards a building’s construction and operating energy efficiency, and its lifetime carbon footprint.
It is accepted that rooflights contribute towards BREEAM. They provide natural daylight, reducing the need for artificial light, and enhance occupant health and wellbeing. The contribution is seen as difficult to quantify – but is it? Rooflights that carry an Environmental Product Declaration (EPD) can make a tangible, proven contribution of 1.5 points towards BREEAM in the Materials (Mat 02) category. Now, for the first time, there are GRP rooflights that have attained an EPD (Environmental Product Declaration), from the Building Research Establishment.
The concept of rooflights being able to quantifiably contribute towards a BREEAM rated project in this way is a major innovation for the market. It provides massive potential for a change in the way we conceive, plan and construct the roofs of commercial and industrial buildings in the private and public sector. It builds on the historic platforms for rooflights within BREEAM. Now, GRP rooflights can ‘tick the boxes’ in all of the three most heavily weighted BREEAM categories – Materials, Energy, and Health & Wellbeing.
To address energy, both as part of BREEAM and beyond, the natural daylight transmitted through rooflights reduces the amount of supplementary, artificial lighting. A rooflight allows up to three times more daylight into a building than an equivalent-sized wall light or glazed penetration.
Historically, it has been accepted that a 10 per cent rooflight to roof area was the optimal ratio. The National Association of Rooflight Manufacturers (NARM) has commissioned independent research on the subject. The conclusion was that a 12 per cent rooflight area achieved Building Regulations Approved Document L requirements, and a rooflight area of 15-20 per cent is optimum. The cost of energy in financial and CO2 terms required to light a building using artificial light is accepted to be far greater than any potential heat loss through rooflights.
However, it costs four times more to heat a building than to light it. Modern rooflights increasingly tend to be composite, with an insulating core. Thus they actually enhance the building’s thermal performance. Indeed, depending on the specification, rooflights can achieve a U value as low as 0.9 W/m2K.
Increasing the thermal performance can adversely impact on the light transmission values, depending on the structure of the insulating core. Standard rooflights use structured multiwall polycarbonate for their insulating core, the internal horizontal layers of which reduce light transmission through reflectance. New, greener technologies are seeing the use of honeycomb cellulose acetate to form the insulating core. The honeycomb structure eliminates the multiple layers of multiwall polycarbonate, which delivers more light for the same insulation performance.
As an added weapon in the battle to reduce carbon emissions, cellulose acetate is a low embodied energy material, and is compostable at end of life. Technologies are being developed to reduce the carbon footprint of GRP too. Options now exist which use a mesh of continuous glass filaments to achieve greater strength than conventional GRP with 40 per cent lower embodied carbon.
Beyond Energy, the Health & Wellbeing category for BREEAM aims to “encourage best practice in visual performance and comfort by ensuring daylighting, artificial lighting and occupant controls are considered.”
Even without the need to address climate change, there is growing awareness of the need to take into account the health and wellbeing of a building’s occupants. Scientific studies have shown that the cost of not having a workplace wellness programme is greater than the cost of implementing one: a healthy workforce is a happier workforce, and a happier workforce is more productive. Similar studies have also shown people learn and heal more quickly in naturally-lit buildings.
Consideration needs to be given to the type of light. Being translucent, GRP provides a diffused, uniform light into the building, avoiding solar glare and shadowing. It minimises sudden transition between lit and unlit spaces, and actually disperses the light to a wider area. The improved uniformity of light increases the range of tasks that can be safely undertaken in the building, which potentially adds to the building’s value. Glass and polycarbonate, by contrast, give a direct light, often more appealing in locations such as enclosed shopping malls, but increasing solar glare and shadowing.
So sustainable design can be achieved using tools already known about. All that is needed is for them to be looked at in a different light.
William McDowell is national business development manager at Hambleside Danelaw