Insulated concrete slabs on a flat roof - or not?

[andyhunt]

I'm partly responsible for the maintenance of a small block of flats built in 2001. It has a flat roof, which consists of felt & asphalt on concrete, currently covered (as built) by large concrete slabs with insulation attached to their under sides. I believe this design is known as "warm roof".

Over the years, we've had many problems with plants rooting themselves in the gaps between the concrete slabs. Now we have a small leak in one area of the roof, but of course we can't see the roofing felt without removing the insulated concrete slabs.

We've been advised by a highly regarded local roofing contractor that having these insulated concrete slabs on top of the roof is an old fashioned design and a bad idea, because they keep the felt permanently wet, encouraging moss to grow and the felt to rot. He recommends permanently removing the insulated slabs, and repairing / coating the felt & asphalt then leaving it exposed.

I am seeking advice as to whether it's better to have insulated concrete slabs with permanently wet felt, or no slabs in which case the felt will be exposed to sunlight - I understand the felt can be coated to protect it from the latter.

Also, if the roof was designed with these insulated concrete slabs, will there be any harm in permanently removing them?

Thanks in advance for any assistance.

 

[Xenon]

You have an inverted roof, the isulation panel will probably be blue with an inch cement topping.

Probably Dow Corning TFX or similiar. Its still installed today, and is a very good system. Finding a leak is a pain though, as the slabs are interlocking. But, you can lift them up, repair the leak and re install the slabs. This is the cheapest option. If you remove them, you remove your insulation.

You may have a frame of paving slabs holding them down with a ballast perimeter. Your lucky its not fuly ballasted.

 

[andyhunt]

Xenon, you clearly know what you're talking about as you've described exactly what we have - there are concrete paving slabs holding down the edges of each section of insulating blocks.

If we were to replace the felt with GRP, would you still advise replacing the insulating blocks on top?

The building is in SW19. Would you be interested in quoting for the work?

 

[Xenon]

Do not, under any circumstances put GRP on it. The slabs can be lifted and the roof repaired. The slabs can then be re laid. We do cover SW19, and would be happy to have a look and advise.

 

[andyhunt]

Thanks Xenon - I've "friend requested" you so I can send you contact details.