There is a growing trend in which a layer of insulation is specified above the deck, whilst the rest is specified below the deck. While this may seem like a good idea, as it requires no ventilation plus keeps the build-up as thin as possible, this practice should not be encouraged.
In a warm roof, condensation is prevented by keeping the deck at a warm temperature, therefore there is no cold surface for the condensation to form on. In a cold roof, condensation is prevented as the ventilation taking away the moisture vapour before it can form as condensation.
In this type of roof, you remove both of these levels of protection – thinner insulation means the deck isn’t kept warm, and no ventilation space means the moisture is not removed before it forms as condensation.
If this practice is going to be attempted, a full condensation risk analysis must be conducted before the design is finalised. Even then, it is not advised to use this method as the workmanship standard will be assumed to be almost perfect – and if this is not the case, the condensation risk is greatly increased.
Tapered insulation as a flat roof solution
Tapered insulation is a great flat roof solution which allows falls to be created with specially shaped insulation, rather than requiring screed or timber firrings. Tapered insulation is compatible with many different roof types and in both new build and refurbishments. It is a flexible solution which allows for waste to be minimised through predesigned and factory-made processes. There are several advantages of using tapered insulation over alternative solution. It is up to 1.5% of the weight of screed, reducing the stress on the rest of the structure. It also eliminates the need for drying time which saves money by speeding up the overall construction time.
There are lots of important factors to consider when installing a flat roof. Whether it’s a new build or refurbishment, what waterproofing system you will use, what your budget is and much more. Whichever build up you choose, it’s vital to ensure that you adhere to building regulations and that the fall in your flat roof provides efficient drainage.