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DIY Forum >> Building Questions >> Garage Flat Roof - Laying Flagstones
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Message started by Trevor.Howard on Aug 16th, 2017, 4:38pm

Title: Garage Flat Roof - Laying Flagstones
Post by Trevor.Howard on Aug 16th, 2017, 4:38pm

I have a double garage with a flat roof approx. 9 metres x 5 metres. The roof is covered with an EDPM membrane on top of 25mm thick plywood.
I want to lay indian sandstone flagstones to cover the flat roof area, with a view of making it into a rooftop garden area.
Question is can I lay the flagstones directly onto the EDPM membrane using a suitable cement/adhesive or should I first of all lay down a suitable underlay mesh mat (eg: Durabase C++) then lay the flagstones on top of that?
I look forward to your professional answers to this query.

Thanks,

Trevor

Title: Re: Garage Flat Roof - Laying Flagstones
Post by thescruff on Aug 16th, 2017, 5:29pm

Hi,
Not a Pro they should be along later to advise.

Any I have seen done has been laid on and fixed with Hot pitch.


Title: Re: Garage Flat Roof - Laying Flagstones
Post by woodsmith on Aug 17th, 2017, 8:30am

Firstly have you ascertained that the roof is able to take the weight of the flagstones and people etc? To take flagstones it must not flex at all and unless the roof was specifically designed to take this load I doubt it will be strong enough plus I expect this job would need building regulations approval from the local council before you could do anything.

As for laying flagstones on EDPM rubber, you really need to ask an EDPM roofing specialist but I would think at the minimum you would need to decouple the flagging completely from the EDPM? You could do this by laying pond underlay first, this is a thick polyester material and is extremely resistant to puncture and tearing. Then you may be able to lay the flags onto a thin bed of sharp sand but as I said you need to get specialist advice for this for both the EDPM and also to see if the roof is up to the job.

Thinking about it, this job is looking more and more impractical and expensive as you would also need compliant balustrading all round the roof, which you couldn't fix through the EDPM.

Another option to consider may be to deck the roof, this would be much lighter than flags and would make fitting a balustrade much easier.


Title: Re: Garage Flat Roof - Laying Flagstones
Post by CWatters on Aug 18th, 2017, 2:23pm

You will almost certainly need planning permission. It comes under creating a "raised platform". Anything like a raised deck, balcony or other platform over 30cm (1ft) above ground level needs Planning Permission.






Title: Re: Garage Flat Roof - Laying Flagstones
Post by Trevor.Howard on Aug 24th, 2017, 9:51am

Thanks for this information. We have already applied for planning permission and it has recently been approved. We are also planning to have a balustrade fitted around the perimeter parapet wall. This was also included as part of the planning approval.

Thanks again for your reply,

Trevor

Title: Re: Garage Flat Roof - Laying Flagstones
Post by londonman on Aug 28th, 2017, 5:37pm

I have a nasty feeling that Building Control like to be involved in something like this.

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