Second in this ‘practical advice for roofing contractors and rooflight installers’ series, Jeremy Dunn, ‘Voice of the Industry’ and Technical Committee Member for The Rooflight Association, focuses on the single most common point of failure on rooflight installations – the upstand.
Above: Jeremy Dunn.
Typically, rooflights are fitted to an upstand. While some manufacturers do supply the rooflight with an integrated upstand, there are many instances where a builder’s upstand is required.
Construction of the upstand is usually the responsibility of the roofing contractor or general builder; this varies from project to project. It must be built to the correct dimensions, the correct pitch and with the correct fixings to prevent delays onsite, costly callbacks and to safeguard business reputation.
Allow for weathering
Does the upstand have the correct weatherproofing, for example? Often, this causes the biggest headache. The tradesperson responsible for building the upstand frequently doesn’t allow enough room for the weathering material which adds thickness, and so the upstand ends up being the wrong size.
When multi-layer membrane systems are used it is important to limit build-up of high points where the layers overlap at joins and on the corners. If not, this can cause significant problems particularly where the weathering is taken over the top of the upstand where rooflights require a flat surface to correctly transfer the loads into the upstand and provide air and watertightness.
The Rooflight Association is currently working with the NFRC to produce guidance to roofing contractors on the weathering of upstands for rooflights to help address this problem.
Image credit: Glazing Vision.
Airtightness and leaks
Air leakage is an issue if high points occur along the upstand, typically at the corners where the thick gauge material is folded and overlaps, while any fixings such as nails or screws may add localised bumps. This can impact the level of the upstand, creating an uneven surface with high and low points. Once placed on top, the rooflight will only connect with these high points, resulting in air gaps between the upstand and the frame.
While some installers may attempt to fill these gaps with sealant or mastic, this is an inadequate long-term solution. Over time, the sealant will expand and contract, and ultimately tear, making it impossible to maintain airtightness and weather-performance standards. Therefore, once again it’s important to limit significant build up at isolated points and ensure a straight and level upstand.
A poor upstand not only results in a costly delay during the rooflight installation, but, if left, it can compromise the building fabric and significantly impact rooflight performance.
Image credit: Brett Martin Daylight Systems.
Install in appropriate weather
My final piece of advice is to fit the rooflight in the right weather conditions. Normally, we would focus on cold and wet weather conditions – which can stop sealants from curing and adhering, but given the temperatures this summer, we must also consider extreme heat.
The most common mistake onsite is judging the air temperature rather than that of the surface sitting in direct sunlight. Often, the substrate, or the metal rooflight frame if left out in the sun prior to installation, will far exceed the maximum application temperature. Applying sealant to a hot surface will flash dry the product, ruining its ability to bond. There is also a danger of bubbling, rapid skinning and thermal movement. Best practice for hot weather installation is measuring the surface temperature before applying, work on the shaded side of the roof and apply the sealant early in the morning.