Create a roof garden retreat

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Planning to turn a flat roof into outdoor living space? Follow Michael Holmes’ advice on creating a roof garden, including advice on planning permission, structural requirements and costs.

Roof terrace with hardwood flooring and birch and gingko trees

ABOVE: The blue Yorkstone of the planters, along with birch and gingko trees, contrasts well with the stylish ipe hardwood flooring of this roof terrace in London.

Will you need planning permission?

A change of use to form a terrace or balcony from a roof will need planning permission, unless it has already been established for at least four years, in which case it is lawful to retain it. The authority’s main consideration will be the privacy of neighbouring properties. The distance it can project to the rear may be restricted, or it may be necessary to build a wall to obscure views to the sides.

Converting a flat roof into a terrace is notifiable under Building Regulations, so you must contact your local authority building control department and submit full plans or a building notice application, along with a fee of around £300-£400.

Roof terrace with hollow planters

ABOVE: The hollow planters on this terrace allow light to flood in from the west.

What structural work is necessary?

In addition to a doorway to access the terrace, the floor structure is likely to need upgrading to take foot traffic – a structural engineer can advise on this. Balustrading must be erected to a height of 850mm and fixed securely to the floor, walls or both. Popular solutions include masonry walls to match the house, iron railings or toughened glass.

The floor surface must be non-slip and suitable for foot traffic. Some flat roof coverings such as bitumen with stone chipping can take traffic, but decking or tiles look better and protect the roof. Decking is ideal as the firring strips between the deck and roof surface can be cut to level out any slope of the roof. Water must be able to flow over the flat roof and drain away, and an upstand of at least 75mm must be maintained at the door threshold to stop water getting inside.

What will it cost?

Expect to pay around £600-£700 per m² plus VAT, including strengthening the roof structure, replacing the roof covering and installing hardwood decking.

Roof garden with stone table with curved oak and stainless steel bench

ABOVE: An oak and stainless steel bench curves around a stone table in this roof garden.