New Flat Walk on Roof Terrace - Best Hardwearing load bearing waterproof floor finish???

27 Oct 2006
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United Kingdom
I'd like to extend my flat with a new single storey extension.

A section of the roof is a shared party structure with the upstairs flat / neighbour (who are tenants).

The neighbours will want to use part of the roof as a walk on terrace with tables and chairs, plants etc, which is fine.

I just need to design it in with a structural engineer to take the load, and choose the most hard wearing low maintenance finish to the roof, that is tenant proof!

So options I'm considering on a concrete deck as a base with insulation on top are:

1) GRP walk on grippy membrane
2) Paving on small pedestals
3) bitumen / polyurethane type single ply membrane (hot applied)
4) cold liquid applied membrane

If the roof terrace belonged solely to me, I would do paving slabs on pedestals, as it's the nicest looking solution.

However, as the roof terrace will be used by the neighbours, who do not have a good track record with maintenance - what is the best solution?

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Are you aware of the ownership/ responsibility issues with your proposed arrangement?

Do you have the room for the required thickness of roof, or are you prepared to have lower ceiling level?

You can't have a roof covering as a wearing surface. The only one that comes to mind is asphalt. Otherwise you'll need a suitable additional layer for walking on.
Hiya woody,

Yes - the freeholder is involved in my proposals.(y) they're not really bothered as I'm providing a bigger nicer terrace than existing.

I just about have the required thickness for the roof to this small area of the extension, with a ceiling height of 2m inside.
It will be tight. :unsure:
If not - I will have to lower the floor by about a step - depending on drainage outlet levels in the manhole outside - which I don't know yet.

I contacted Sika who recommended:
- Sika Rapid liquid applied membrane for a cold roof option.
- Sika Shield cold applied felt with paving on 20mm pedestals for a warm roof option.

Obviously cold roof option frowned upon by BR, but if it's a small tight area it's an option.

I need to check if Sika have waterproofing suitable for a warm roof, that is hard wearing and can be heavily trafficked and take variable loadings!

The Sika Rep ofcourse warned against using EPDM or GRP as they said most cases they called out to rectify defects in these types of roof. :sneaky:
The neighbours will want to use part of the roof as a walk on terrace with tables and chairs, plants etc, which is fine.
Have you got or applied for Planning Permission?

Are you aware of the strict regulations regards balustrading and hand-rails etc?
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Hey Noseall

Good point....not applied for planning permission yet but I am aware of privacy issues.

However, as I'm proposing to replace an existing big landing and garden stairs - with a new extension and stairs - it could it be argued it will still be just a landing for garden access only.

I wanted to design the floor, so it's robust, as the tenants keep putting stuff on it as storage.

The existing landing and metal balustrade would be replaced with new extension with a 215 x 1500mm high parapet walls to act as guarding.

I will argue privacy is not an issue since it is still just a landing that serves as an access route to the occupants garden.

Unfortunately I know that a 1700mm privacy screen has been required by the LA as a Planning Condition before, to this type of situation - I just need to figure out how to get around it .

Any ideas??
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I spoke to Sika who advised best surface for highly trafficked roof terraces are:
1) Cold applied felting with pavers on pedestals on top ( warm roof build up)
2) liquid applied membrane ( cold roof build up)

I just need to check if there is a 3rd Option, with a bitumen / asphalt / liquid applied floor finish, suited to variable loads and high traffic on a warm roof build up.

The Sika Rep really was against EPDM or GRP as a roof finish, as apparently they've been called out to replace these type of roofs before.
The Sika Rep really was against EPDM or GRP
A Sika rep is going to be against anything that is not Sika!

Sika may offer a 10/15/20 year warranty, but can the terms be implemented (use/maintenance/inspection) to obtain the warranty?

The lease implications are very important, as it could put onerous restrictions or responsibilities into the lease, and that in turn could put future buyers off or insurance premiums up.
Who will be responsibly for the roof surface or the walking surface. Likewise the perimeter guarding and the fixings - and the wall fixed to? Who pays for future service charge costs - again these could be onerous or off putting.

I'd be more inclined to do the design and cost feasibility first before the detail of roof covering.
Hi Woody,

In the lease the 'structure' (e.g. existing garden concrete landing and stairs) is the freeholders responsibility to manage the repairs.
They charge repairs to leaseholders/tenants in the 'service charge'.

However, in this instance, I made it clear that I would be paying for all the new works, including replacement landing and stairs.

So the freeholders surveyor (who is the Council) doesn't have a problem with this, as the existing is so degraded, in poor condition and unsafe.
He already visited the flat, to assess the condition of the landing and my proposals.....also commented that there seems to be asb. under the landing slab! :sneaky:

So my aim was to choose robust materials to the landing area and try to replace like with like or better, as I definitely don't want to increase the maintenance with regards to that landing / balustrade / stairs.

However, talking to Sika, they seem to think that a cold applied felt membrane with concrete slabs on pedestals is the most robust solution.
It would replace a landing concrete/asb. slab with bitumen on top - at least 70 years old.

With regards to the existing metal balustrades, I was planning to replace them with 1500mm high double brick walls, to provide more privacy, and quite robust.

As far as I know, the freeholder only requires any new building work to be signed off by the Building Control department / Approved Inspector - if I don't use a CPS registered contractor.

The freeholder organises building insurance for the structure, but I am assuming anything signed of by BC should be covered by building insurance. :unsure:

These were my plans, but appreciate your thoughts!
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Hey Noseall

I think if it was a single dwelling house - the planners would refuse it.

But it's a converted house made up of 2 flats with their own section of rear gardens.

The proposed landing and stairs would replace the existing and is needed by the upstairs flat to get to their garden.....

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