Commercial RoofingThis large asbestos roof replacement in Newcastle upon Tyne, it consisted of 8no 15m slopes of bix 6 roof sheets, 5no internal valley gutters and a parapet wall approx 2m at the highest points, the total roof area was approx (8,400m2).
The building belong to a very well known national retailer, the asbestos cement roofing was around 40 years old and pretty much intact. though it did have the problems you would expect from a roof of this age such as irritating roof leaks at one area of the roof and then somehow leaking at different area the next time it rained.
The major problem with this roof arose when we had the flash downpour in the north east of England on June 28th 2012
( if your reading this and you're from the north east of England you will know what i mean) we had the biggest down pour in more than forty years and the whole of the north east of England was disrupted due to the drainage systems not being able to cope.
The warehouse was completely flooded causing tens of thousands of pounds of damage, the warehouse manager said " it was like a waterfall all the way down the centre of the valley gutters"
On inspection the asbestos roof sheeting itself wasn't too bad, the corrugated sheets were mostly intact although there were a few signs of problems such as loose ridge capping and cracked roofing sheets that had been filled with bitumen mastic etc. The biggest problem was the valley gutters they were only 150mm deep x 250mm wide, which was totally inadequate for the large roof slopes feeding into them and today's weather, they were originally designed for rain fall based on calculations from 40 years ago which may have been correct then - but certainly not for today's weather 2014, no matter if the roofing sheets were 100% sealed the rainfall that day and some days after that was too heavy and the 6inch deep gutters simply couldn't cope, the unfortunate thing is the roof is useless with gutters that cant take the rain fall so it either meant putting up with the old roof leaks and hoping for the best there were no more super storms, Obviously this was something the store owners couldn't take the risk with and decided the roof would have to be replaced
but this time to build in over size gutters, we explaind by using our built up insulated roofing system consisting of our 36/1000 liner and 36/1000 top sheet we could increase the depth of the gutter by the depth of spacer bar system far deeper than if they used a composite panel
The roof repacement was always going to be a bit tricky as the warehouse was a fully working distribution centre which serviced the clients retail stores throughout the country and could not stop during the roof works,
The original roof build up of cement / asbestos roofing sheets with plasterboard linings and mineral wool insulation, normally to strip out this type of roof system you would simply install safety nets to the underside of the roof and loosely lay debris netting on top of the nets, this would help to prevent any loose debri falling through the safety nets into the building, whilst this is usually sufficient for most strip and recover projects this was in no way good enough for Fenwick's , the management insisted on absolutely no debris or dust to enter the building what so ever during the demolition works.
We decided the only way we could achieve what the client wanted was to create an air tite membrane fitted to the underside of the
roof, this at the best of times this was always going to be difficult because of services such as the lighting and heater fittings
that hang just beneath the roof, but this particular roof also had a full blown water sprinkler system fitted which had to remain
in service throughout the works, this meant the air seal membrane had to be fitted above the sprinkler heads meaning a lot of
cutting and sealing around hundreds of pipes.
- The asbestos roofing sheets were generally in good condition considering there age and came off in more or less complete, that couldnt be said of the mineral wool and plaster boards linings which were falling apart as they were removed especially during windy weather
After talking the project through with David Nimmo an architect with Glasgow based WMP & partners, we eventually agreed on a 1.2gauge visqueen that would be screw fixed to the underside of the roof purlins and sealed at every joint , we fixed the visqueen with 5.1 tek screws which had 25mm dashcon washers, the visqueen membrane was also screw fixed to the hot rolled steel rafters, each bay was around 6.5 meters wide by 15 meters upslope so you can imagine there was a lot of cutting and sealing. Each time we completed fitting the visqueen to bay we then dropped back and set about sealing the numerous pipe and flue penetrations, this was done with an apoxlet based tape , this ensured a secure and air tite seal that would last throughout the duration of the works and would be simple to dismantle after the roofing works were completed, the underside of the whole roof area was sealed with the above method enabling the warehouse to operate as normal throughout their busiest time of the year - XMAS
The roof & guttering works were carried out in october - december during poor weather conditions 3 weeks ahead of program