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How best do i convert a flat roof into a roof garden - i do need a new flat roof

My flat roof is leaking and it needs replacing but i do want to convert the area into a roof garden. I need steps coming down onto the roof from a higher floor and I would assume that these would need to be fixed to the roof/floor. So what type of flat roof should I go for and then should it be decked to make it harder wearing? help would be greatly appreciated

22 Answers from MyBuilder Roofers

Best Answer

You would definately need to get a structural designer to look at the roof if you are proposing to add a staircase and also some sort of roof deck. I would guess that the origional roof joists would not be able to take the extra weight in a safe manner. The staircase would have to be fixed to the existing roof deck/joist and then weathered with the membrane that you would use on the main area.

Regarding the roof covering you can use a high performance single ply pvc roofing membrane to weather your roof. This can then be overlayed with either a timber decking or a paving slab on supoorts/pebbled finish. The decked area would obviously NOT be fixed through the roof membrane and just sit loose on top of the roof. The weight of the deck will hold it down.You would have to use a fleece filter/protection layer between the finished membrane and whatever roof deck finish that you fancied. This protects the waterproofing membrane from becoming damaged and also acts as a filtration layer for all the dirt that would accumulate under your deck.

We are a registered contractor to supply such a membrane should you ever wish to go ahead with such an idea.


Answered 22nd Jul 2011

Fibreglass is the best option, leave the EPDM in the pond along with the installers!


Answered 29th Jul 2013

I think what you are proposing would come under planning and building regs.
You are going to need a S/E to design and calculate the stairs and probably beef up the roof timbers.
Probably start of with an architect who works with a S/E they will advise you, and also on the roof covering.
If you used a Firestone epdm roof, they also do the walk way pads and accessories that enable slabs to be laid.
If you need the gaurantee, you will have to use an approved fitter.


Answered 7th Jul 2011

Hi I have seen a few people saying the GRP fibreglass is the best way for you to go . I personally and talking from years of doing roof terraces and balconys etc .mastic Asphalt is the best option as it is hard wearing and wouldernt need decking unless that is what u want u can add promade tiles to Asphalt for decoration . Mastic Asphalt is a seem less application so can be adapted to any detail and can last up to 50-60 years .i hope this has helped you many thanks jack (oxley Asphalte roofing services)


Answered 5th Jan 2017

Yes I would agree fiberglass, we would reboard the whole roof and then fiberglass it. We could even do it in green for you, we would also check the joists to make sure it would be safe and strong enough to do


Answered 6th Sep 2013

the roof can be in high performance elastermeric ,3 layer felt system. finished in pavin slabs if the support is there if not ,terace tiles. stairs then can sit on top of these.


Answered 7th Jul 2011

Hello there are many ways to turn your roof in to a roof garden , on our previous jobs we strengthen roof and fibreglass, this is only product we specialise in , the you can lay decking , green roof, Astro turf , or choice of few ideas the stairs are then fitted down to suitable system , nothing is screwed or bolted to roof deck , hope this helps you out many thanks James


Answered 15th Dec 2015

Fibreglass is the best, it is durable and resistant coating that has a long-term guarantees. Before using fiberglass structures need to prepare accordingly. Please check joist or replace damaged. Make sure the roof will be flat. Sometimes you need to replace the board. Fibreglass is the best material for flat roofs. It is lightweight and resistant to temperature differences.


Answered 12th Jan 2017


Your choice of waterproofing would depend greatly upon the existing detailing. Abutments, drainage points and type of roof garden you are considering.

The existing structure would possibly need to be strengthened and this would be designed by a Structural Engineer. Another consideration would be the need for a permenant handrail if you are walking about on the roof. This would be required by Building Control Inspector.

We can assist with coordinating all this and providing free advice to produce a competitive quote.

Dave Middleton


Answered 15th Oct 2013

Without shadow of a doubt as the others have said: Fibre glass roof is the best solution but get some calcs and specifications done first.

Since fibreglass really hit the scene my blow torches have sat in the corner of the lock up and I never intend to have to torch on again!


Answered 8th Feb 2015

As many have quoted fibreglass grp would be you best option by far.
We have only ever used the brand cure it grp system but have been using it for applications like this for over 8 years.
In regards to the strucle strength you would possibly need a engineer to provide you with calculations hope this helps regards Buckland roofing


Answered 17th Apr 2016

Hi there, firstly I would agree with having a structural engineers report done prior to any work taking place and as for the roof covering I would highly recommend GRP fibreglass, this said I would also make sure that a higher quality of matting is used (600gsm) minimum especially if you are wanting to cover the roof with either turf or decking also making sure that if a decking is used not to penetrate the GRP. Once the fibreglass roof is installed it will give a high density seamless covering that if installed correctly will even allow for a fully functional living roof garden.
Hope this advice helps ! Craig @ C.A.V Roofing Fibreglass Flat Roof Specialists


Answered 3rd Aug 2016

I Am an asphalt spreader, and done it for 32 years. If installed correctly it is one of the best systems. Also qualify felt systems are as good. You will still need to look at the structural aspects, but I would stay away from single membrane and fibre glass systems. The reason is they are cold they don’t stick to structures as good. My company uses all these systems


Answered 24th Dec 2018

I would never use grp on a balcony you intend to communally use. You would regret getting grp after a few years when your ripping it up.


Answered 26th Sep 2019

Fibre glass would be the best possible option


Answered 21st Feb 2017

Fibre glass roof is definitely the way to go with this project as it is the toughest flat roof. With fibre glass there are many options such as using green topcoat to get the colour you want or you can then go further with adding a seedum roof on top of the fibre glass which then turns the roof into grass for you hence roof garden, or you can put floor tiles over the top or wood decking. These are just a few examples of what you can put on top of the fibre glass base it all really depends on your budget and what you want the final look of the roof to be.


Answered 23rd Feb 2017

I would recommend GRP fibreglass


Answered 20th Mar 2017

Asphalt and promanade tiles I would definitely recommend


Answered 21st Jun 2017

Fibreglass is the best option, leave the EPDM in the pond along with the installers! And I recommend never apply EPDM to your property!


Answered 7th Sep 2017

I'd go with the asphalt it's the only material to use when it comes to roof gardens and terraces, we also install GRP systems but I would recommend mastic asphalt over these systems. I hope you find this helpful.


Answered 8th Apr 2019

We would highly recommend Fibreglass


Answered 15th Aug 2022

3 layer felt system. Using other systems would mean less protection from objects falling onto surface creating possible leak areas.


Answered 1st Nov 2022

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