General Insulation and U/Value for rooflights - NL500

General Notes:
When Part L regulations came into force there was much confusion over apparent contradictions in the document. The introduction of revised building regulations Part L (L1 and L2) in April caused concern in the construction industry. Not surprisingly, understanding was sketchy and this has not changed greatly to date. What both the specified and user are concerned with is whether the product they select complies with the new regulations. The good news is that virtually all current ranges of roof lights can be made to comply in one form or another. Actual compliance is a combination of factors ranging from the raw thermal performance of the product to the complexities of solar gain, the percentage
of the roof area, and so on.

As long as the roof light covers no more than 12 per cent of the roof area with clear glazing or up to 20 per cent if a special grade of solar control glazing is used, a triple skin system will generally fulfil everything that is required of it, it’s as simple as that. Of course with a high level of thermal performance, the roof light demands an equally high performance supporting system. the best supporting upstand for the roof light is one constructed with any of the above and can be insulated to suit the thermal specification required. As with many things, life isn't always that simple, the above approach will nine times out of ten, result in over specification. Coupled with this, triple skin (or better) roof light systems are dearer and if budgets are tight, a more cost effective solution may need to be found.

This can be done with careful evaluation:
There are many situations where a lower thermal specification product may be used to fully comply with the requirements. Typically, double skin or even in some situations, single skin will do the job very well without incurring extra expense. Carefully evaluating factors such as roof area, use of space beneath roof lights and total thermal performance of roof lights, doors and windows may help to specify roof lights in a more cost-effective way. However to be able to have the confidence to specify anything other than the most expensive option, requires someone to have a full and thorough knowledge of Part L and all of its intricacies.

This is why it is often the best bet to talk to a reputable manufacturer or your local building control officer depending on information you have available. A good example where this may be crucial is regarding upstands, a high spec upstand may be specified and used, as already explained, to satisfy the requirements, but what if the contractor wants to build his own kerb? A good rooflight manufacturer will be able to propose robust details for a builder’s kerb designed to closely match the thermal performance of the glazed element. Although Part L does not state a particular U/Value that has to be achieved, it does recommend the upstand is insulated.

To prevent condensation, similarly, if budget constraints dictate a lower specification, by inspecting information on the whole roof, windows and doors, an expert will be able to guide the specified on providing all of the required light and ventilation while still complying with Part L. Manufacturers will also be aware of hidden health and safety Executive issued new guidelines to cut the number of accidents on roofs.One of the main aims of the document HSG33 Health & safety in Roof Work is to eradicate fragile materials, including some older roof lights, shockingly, many fatalities and injuries are the result of people, often children, falling through roof lights, (Please see our impact test documentation NL507).

The guidelines stress that measures must be taken to eradicate the dangers and one of the strongest recommendations is that only non-fragile materials should be specified for roofs. The guidelines specify roof lights must be capable of withstanding a person or material falling on them. Our plain roof lights in particular, cannot be walked on or painted over. When selecting roof light products it is important to be aware of the following:

* Have the roof lights you specify been tested to the highest requirements of European pr EN1873 to provide information on the fragility status or tested to ACR(M)001:2000, the test for fragility of roofing assemblies?

* Does the manufacturer offer a guarantee against discoloration of glazing materials, loss of impact and light transmission, underwritten by the sheet material supplier?


Back to Technical Information