Top tips to help you get the most out of your flat roof
BS 6229:2003 describes flat roofs as ‘those having a pitch not greater than 10 degrees’. As well as specifying the minimum pitch for flat roofs, the Standard recommends the minimum for designed and achieved falls for most flat roofs as 1:40 and 1:80 respectively (unless the materials used for the flat roof are designed for zero falls).
A roof which does not comply with these minimum industry Standards is likely to attract issues, including:
• Ponding water
• Moss
• Fungal and algae growth
• Increased maintenance costs
• Significantly higher risk of water entry in the event of damaged roof coverings
A roof that doesn’t follow the Standard can also negate any third-party insurance cover and/or a manufacturer’s guarantee. Clearly these are all things to be avoided, so as well as complying with the Standard here are a few top tips to ensure fuss-free flat roof installation and maintenance.
TIP 1: MAINTAIN MINIMUM UPSTAND HEIGHTS
Continuity of waterproof coverings should be maintained for a vertical height of 150mm above the finished roof level at all abutments, door openings and parapets.
Achieving this minimum upstand height is very important, but so is how the top of this upstand interfaces with flashings, cappings or the other building elements. The installation also needs to be sequenced properly, especially at door thresholds where there is a very small gap to seal between that and the upstand.
Also remember that the 150mm should be measured from roof finishes, NOT the waterproofing layer – so with green roofs or ballasted ones, the measurement should be taken from the green roof element or ballast, not the waterproofing itself!
TIP 2: ENSURE CORRECT COVERAGE RATE
When using a liquid applied system it’s essential to monitor consumption to make sure you achieve the correct coverage rate. You can do this by marking out the roof in grids to the size of the coverage rate of a tin of liquid. For example, 15 litres of FIX-R Liquid Waterproofing at 1.5ltrs m2 coverage will cover 10m2. A grid size of 10m2 will ensure you are monitoring consumption and creating an even thickness as you progress across the roof. This helps you avoid over or indeed under applying!
TIP 3: ASSUME A MINIMUM WASTAGE
When you estimate how much you need to cover your roof always factor in a minimum wastage of at least 10%. For example, if there’s a sudden downpour of rain or hail you may need to re-coat a liquid system if it’s still wet or cutting rolls of roofing felt and singleply may leave you with lengths of off-cuts you can’t use elsewhere. Allowing for a minimum wastage means you’re prepared for these eventualities.
It’s also a good idea to check the dimensions of the roof to confirm it’s the same size as stated on the roof plan, particularly with new builds. You might not have received that latest drawing from the main contractor or architect and the design may have changed or the drawing provided is a poor copy and is not to scale. Whatever the case, checking before you start can avoid any issues.
TIP 4: NIGHT JOINTS
Trapped moisture in new constructions can lead to damage and also constant call backs where there’s no actual water ingress! Night joints should be formed at the end of a day’s installation when all the insulation has been adequately covered to avoid trapping in any rain that falls overnight or the following day.
TIP 5: CHECK YOUR LAPS AS YOU GO
The installer laying the membrane is responsible for checking laps, fixing centres and monitoring adhesive consumption, etc. It’s not a job for the site inspection.
TIP 6: AND FINALLY…
Roofs need a bit of TLC, too. You can significantly extend the service life of a roofing system with some periodic maintenance. All flat roofs should have regular inspections both internally and externally every spring and autumn as a minimum, so make sure the end user knows their responsibility after the roofing is complete.
