Are you interested in learning the most important factors to consider when designing certain roof types – in particular, warm roofs, inverted roofs and cold roofs? Then this article is a must-read.
Warm Roof Considerations
1. Vapour Barrier
When designing warm roofs, you must first select the correct vapour control layer or vapour barrier, taking into account the use of the building. In the case of swimming pools or other areas of high humidity, a vapour barrier is always required.
2. Insulation Type
Secondly, also depending on the usage of the roof, selecting the right insulation type is key. You can, for instance, use non-combustible insulation or – when there are areas of very heavy weight due to the presence of plant or other heavy loads – opt for an inverted roof with XPS insulation, so that the weight will be distributed evenly across the XPS boards. Weight load is obviously not only an important design criterion with green roofs, but with blue roofs as well.
Maintenance has to be considered too – think of air conditioning units that may go onto the roof. But the selection of insulation material is not only critical in terms of load bearing capacity; it also determines what type of membrane will have to be used. If you are going to use a torch-on membrane, you need a torch board; whereas if you are adhering single-ply membrane, you need a glass faced board.
3. Upstands
Additional attention should be given to the location of any windows, higher-level roofs, doors coming out onto the roof and the height of the door thresholds. According to the British Standards, upstands have to be at least 150 millimetres above the finished roof level – a requirement that often gets overlooked. After all, if you install, for instance, a 150-millimetre upstand on an abutment and subsequently put a paving slab against it to create a walkway, the height of your upstand gets reduced and, subsequently, no longer complies with the British Standards. If you are designing a green roof, getting this right is critical. If the total green roof build-up is 100 millimetres, the upstand needs to be at least 250 millimetres to ensure it is 150 millimetres above the finished green roof.
Especially when it comes to insulated upstands, you have to keep the latest fire regulations in mind as well. After all, if an upstand is on the back of a façade, the insulation to the upstand must be non-combustible (this goes for both inverted warm roofs and warm roofs in general).
4. Drainage
You should also be aware of the drainage accessories – in particular the locations of any outlets and grates. These locations not only have to be determined prior to the design of the insulation, they also have to be carefully chosen to minimise the risk of leaf litter and debris gathering in certain roof areas. Similarly, when designing a single-ply roof with profiles, attention should be given to the location of the decorative profiles, so that they will not impede the flow of water. After all, the main concern is to avoid standing water on the roof surface (which would certainly end up gathering leaves and debris).
5. Condensation Risk Analysis
Lastly, when designing a warm roof, always make sure to carry out a condensation risk analysis. Such an analysis comes standard with the design in the case of a tapered roof system, but it must also be carried out in case of a flat roof. SOPREMA will take care of both condensation risk analysis and the necessary U-Value calculations for your project as part of our service.
Cold Roof Considerations
The upstand height requirements we discussed above obviously apply to cold roofs as well, but apart from that, this roof type comes with other considerations, too. First of all, if you have insulation on the underside of the substrate, cross-ventilation is key to avoid condensation. A condensation risk analysis should be carried out to ensure that the insulation beneath the substrate is not going to have a detrimental effect upon the substrate and lead to premature failure of the waterproofing system.
Naturally, it is essential to install a waterproofing system that is compatible with the substrate. With timber substrates, a cold-applied or self-adhesive product is in order. Liquid waterproofing can be applied to any cold roof system, with the deck or substrate type dictating exactly what product you should use.
Questions About Roof Types and Their Requirements
Wondering which waterproofing and insulation products would best suit the roof type you have in mind for your project? Please don’t hesitate to get in touch with our experts.