Warm Tapered Insulation Design – falls and drainage
The publication of the updated BS 6229 in 2018 has been the cause of some significant controversy with regards to falls and drainage. As a code of practice BS 6229:2018 contains only recommendations and guidance, and has no legal standing, but the changes are causing confusion with regard to what is being requested, what is being designed and tendered, and what is being installed.
There are a wide variety of considerations with any tapered design; along with thermal performance, consideration should be given to achieving falls, elimination of condensation risks and ensuring proportional drainage is achieved to each outlet.
U-values: All U-values for tapered insulation systems should be calculated in accordance with BS 6946: 2017 Annex E. Thought should be given to the scheme arrangement over multiple dwellings or units under one continuous roof to confirm that individual dwellings and separate industrial units each achieve the U-value required by the client/architect.
Falls: Deck deflection – both positive and negative – can arise in all deck types, and the deck is the responsibility of the main contractor in new build and a consideration factor in refurbishment roofing. BS 6229:2018 recommends a design fall of 1:40 in the absence of a structural analysis but how many are designing to 1:80 and ignoring this requirement?
Drainage: All schemes should be designed either mitred to outlets or with falls in the gutter. Whilst falls in the gutter zones may appear the simple solution for contractor installation, pre-cut mitres can be provided with most insulants to aid ease of installation. A mitred scheme can reduce the number of different components required for a system as well as significantly reducing the maximum insulation thickness. Reduction in maximum thickness will mean reduced bonding area, reduced labour costs as well as other knock on effects such as reduced hard edge depths etc.
Outlets: Thought should be given to outlet locations to both minimise back falls (by locating outlets at points of maximum deflection) and to ensure water is distributed evenly to individual outlets. In the event that outlet locations are fixed, QI will work with you to design a tapered insulation scheme to mitigate both of these risks.
Each of the above should be briefed within your tapered insulation requirements.
QI design and supply tapered insulation schemes in all insulation types; PIR, cellular glass, mineral wool and VIP hybrid. Whether the key design criteria is non-combustibility, compressibility, acoustic, or thickness, QI have a range of solutions to tick any box with any waterproofing type and will work with you to provide the most commercially viable solution for your project.
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