NARM (National Association of Rooflight Manufacturers) Technical Committee
Over a 10 year period NARM (the National Association of Rooflight Manufacturers) has worked tirelessly to bring high quality, uniform and accurate technical information to the marketplace regarding rooflights/skylights and associated technology. Prior to that, there was a high degree of confusion regarding the role of rooflights/skylights – what they do and, what could be expected from them in terms of physical performance, ie, light transmissions, thermal values, “G” values and Non-Fragility status. Today, most of the UK’s leading rooflight manufacturers are members of NARM and all of them work to NARM guidelines when testing products and publishing data, thus allowing customers and specifiers to make meaningful comparisons product to product, make informed purchasing/specifying decisions and select the most appropriate product for the job.
Then along came the “Light Pipe”, “Sun Scope”, “Solar Pipe”, “Light Tube” and “Tubular Skylight/Rooflight” – all generic names for the same style of product but made by different manufacturers. Originally developed for use on tiled or slated pitched roofs, these products perform well in directing light into areas not accessible by traditional glazing. However, they are now being extensively used on “flat” roofs, that is with pitches up to 17 degrees.
I am unsure as to why in some current promotional materials, manufacturers appear to be segregating “tubular rooflights” from rooflights because, when all is said and done, these devices are simply just small rooflights, installed together with reflective tubes to direct light through roof structures. Having said that, the range of sizes seems to be on the march and currently units as big as 1.5 m diameter are now available.
Another concern relates to performance claims. Manufacturers of these products are using different ways of expressing performance and some appear to be vying to outdo each other with supporting information that cannot be used by the specifier to make comparisons and select the most appropriate product.
Latterly, I’ve even seen a current article in Roofzine by a tubular rooflight manufacturer claiming 98% light transmission for his product. Such a performance is impossible! The same article states that, “Research shows that over as little as a decade, a typical rooflight will lose up to 90% of its potential light transmission”. I would like to see the research that led to such an outrageous and hugely inaccurate claim. The same manufacturer also stated that their product is maintenance free. Impossible! If it’s mounted outside & on a roof, it will need cleaning to maintain its light transmission, just as any window or a rooflight does.
The fact is that rooflights and tubular rooflights, are fundamentally one and the same with only minor differences, and the physical principles involved will produce the same performance characteristics.
They both usually have at least one transparent polycarbonate outer skin and an inner skin of transparent material, again, typically polycarbonate. A clear double skin rooflight will have a light transmission of around 80% which will, due to weathering over say, a 10 year period, reduce by a few percentage points (provided the appropriate maintenance regime is followed – as with all products exposed to the elements). This minor and gradual reduction is due to the natural and predictable weathering characteristics of polycarbonate and, will be exactly the same for a tubular rooflight. BRE research has shown that a tubular rooflight with a 2.5m long light guide will have a light transmission of between 50 & 60% for an overcast sky.
Furthermore, light output from tubular rooflights is more often than not, measured and quoted using full direct sunlight rather than the standard British overcast sky which is the accepted normal practice for daylight measurements and calculations.
Then there is the subject of ‘non-fragility’. Roofs (including rooflights) that are specified today are generally required to be rated as ‘non-fragile’ and there is a specific, industry agreed test for measuring such performance called ACR[M] 001:2011. This test was developed by the industry working with HSE to provide a simple way to show compliance with this requirement.
In respect of non-fragility, specifiers should treat tubular rooflights as any other rooflight and ask their supplier what ACR non-fragility rating the product achieves.
As a general warning to anyone involved with the specification of larger tubular rooflights – CDM responsibilities may dictate that, if a roof is to be accessed for maintenance, unless the units are rated as ‘non-fragile’ they will almost certainly be required to be isolated with a barrier preventing access and reducing the risk of personnel falling against or through them. A CDM risk assessment will clearly demonstrate this.
Tubular rooflights play a valuable role in the rooflight market and are mostly well-made by reputable manufacturers. However, this relatively new sector of the market needs agreed performance and testing standards for their products to avoid confusion and misleading statements. NARM has a strong track record in providing support in this respect and we would be happy to help. For example, our recent work to agree definition of the Ud-value for out-of-plane rooflights has resolved the previously confusing picture in that sector of the market.
We at NARM offer an open invitation to all manufacturers of ‘Tubular Rooflights’ to join us in our efforts to unify the entire rooflight industry to simplify, focus and homogenise the information available to the specifier. Indeed, you are welcome to come along to our next meeting if you want to see us in action and perhaps discuss our differences but more importantly our similarities, before joining.