Artificial Grass for Roof Terraces
A roof terrace is prime outdoor space in the sky, and often a hard, exposed deck. Artificial grass softens it into a green retreat, provided the weight, wind and waterproofing are handled with care.
Roof terraces turn otherwise dead roof space into some of the most sought-after outdoor room a flat or office can have. Covering the deck in artificial grass makes it genuinely inviting: soft, green and warm underfoot instead of bare paving or asphalt. But a roof is not a garden. Everything you add sits on a waterproofed structure, exposed to far more wind than ground level, and the drainage and membrane beneath are doing an important job you must not compromise.
Handled properly, artificial grass is an excellent roof-terrace surface. The key differences from a garden are weight, wind, drainage and protecting the waterproofing, and this page covers each. Roof terraces are larger and more exposed than balconies; for the smaller, enclosed version of this job, see balconies.
Lightweight build-up
Laid over the existing deck with a thin shockpad and no heavy base, for minimal added load on the structure.
Secured against wind
Edges and joins fixed so gusts at height cannot lift or peel the grass.
Membrane protected
The waterproofing layer and roof drainage are kept clear and intact beneath the grass.
A lightweight build-up over the deck
There is no excavation on a roof and no heavy aggregate sub-base, which would add load the structure may not be designed for. Instead the grass is laid over the existing deck with a thin, free-draining build-up:
- The existing surface: usually a waterproofed concrete deck, asphalt, paving or timber decking, which stays in place.
- A drainage or shockpad layer: a thin foam shockpad or a dimpled drainage mat adds comfort, lets water flow beneath to the roof's outlets, and keeps the grass off any standing moisture.
- The grass on top: cut to fit and secured at the edges.
The whole build-up is only a couple of centimetres thick and weighs very little. Even so, on any roof it is wise to be sure the structure can carry the surface plus people and furniture. If there is any doubt, that is a question for a structural engineer or the building's managing agent before work starts.
Wind: the factor people underestimate
At roof level, wind is far stronger and gustier than in an enclosed garden, and it will find any loose edge. A sheet of grass that is simply laid down can lift, flap and peel in a storm. Securing it is therefore not optional on an exposed terrace:
- Edges are bonded down with adhesive or fixed to a perimeter batten rather than left loose.
- Joins between pieces are taped and glued so wind cannot get underneath a seam.
- On parapet-enclosed terraces the sheltering wall helps, but corners and open edges still need fixing.
The fixing method must suit the deck: on a waterproofed membrane we avoid any fixing that penetrates it, bonding to the surface or ballasting the perimeter instead. Getting this right is the difference between a terrace that looks good for years and one that lifts in the first gale.
Drainage and the waterproofing membrane
A roof's whole purpose is to shed water, and the waterproofing membrane beneath the deck is what keeps the building dry. Artificial grass must work with that system, never against it:
- Keep outlets clear. Roof drains, gullies and scuppers must stay unobstructed. The grass and any underlay are kept clear of them so water always has a path out.
- Use permeable layers. A permeable grass backing and a drainage mat let rainwater flow through and across the deck to the outlets rather than ponding under the grass.
- Protect the membrane. The waterproofing layer is not disturbed or punctured. There is no digging and no fixings driven through it, as the build-up simply sits on top of it.
- Allow inspection. Laying the grass so it can be lifted means the membrane and drains can still be checked and maintained, which matters on any flat roof.
If the existing waterproofing is old or suspect, it is far easier to sort that out before the grass goes down than after.
Access, sun and living with a roof lawn
Two practicalities shape a roof-terrace job. First, access: materials often have to go up through a flat, a lift or a roof hatch, which affects how the grass is delivered and handled, and a long roll may need cutting down to get it up. Second, exposure: a roof terrace typically gets full, unbroken sun, so the surface warms up more than a shaded garden and can feel hot underfoot on the hottest days; a rinse or some shade from a parasol or pergola helps. In day-to-day use a roof lawn is as low-maintenance as any other: an occasional brush, clearing debris away from the drains, and a rinse now and then, as covered in our maintenance guide.
Benefits and considerations
Benefits
- Turns a bare roof deck into a soft, green outdoor room
- Lightweight build-up that adds little load to the structure
- No excavation and no heavy aggregate base
- Drains through to the roof's existing outlets
- Edges secured so wind at height cannot lift it
- Laid to keep the waterproofing and drains accessible
Worth considering
- Check the structure can take the surface, furniture and people, and ask an engineer if in doubt
- Wind at roof level is strong; loose-laid grass is not safe up here and edges must be fixed
- The waterproofing membrane must not be punctured or its drainage blocked
- Full sun exposure means the surface warms up and can feel hot underfoot
- Getting materials up to roof level affects access, handling and cost
How a roof terrace is fitted
The sequence differs from a garden because there is no groundwork. The focus is the deck, the drainage and securing against wind.
Assess the deck
We check the existing surface, the waterproofing, the drainage outlets and, where needed, raise any structural load questions.
Clear and prepare
The deck is swept clean and outlets confirmed clear, so water will still flow freely beneath the new surface.
Lay the drainage layer
A thin shockpad or drainage mat goes down for comfort and to keep water moving to the roof outlets.
Fit and cut the grass
Grass is rolled out, cut to the terrace shape and notched around parapets, planters and any fixtures.
Secure edges and joins
Perimeters and seams are bonded or battened down so wind cannot lift them, without penetrating the membrane.
Final checks
Outlets are checked clear, the pile is brushed up and the terrace is left clean and ready to use.
What a roof terrace costs
Roof terraces are quoted individually because access and the deck condition vary so much. There is no groundwork, but getting materials up to roof level, securing against wind and working carefully around the waterproofing all feed into the price. We assess the terrace before quoting.
Key cost factors
- The size and shape of the terrace and the cutting around parapets and fixtures
- Access, meaning stairs, lifts or a roof hatch and how materials reach the roof
- The condition of the existing deck and waterproofing
- The drainage or shockpad layer specified
- Edge and seam fixing to secure against wind at height
- The grade of grass chosen
Frequently asked questions
The grass and its thin build-up are light, only a few kilograms per square metre, so the surface itself adds little load. The real weight on any roof terrace is people, furniture and planters. If there is any doubt about what the structure can carry, that is a question for a structural engineer or the building's managing agent before work begins.
It can if the grass is only loose-laid, which is why we never leave edges free on an exposed terrace. Perimeters and joins are bonded down or fixed to a batten so gusts cannot get underneath. Done properly, the grass stays put through the worst weather.
It should not, because the build-up sits on top of the membrane, with no digging and nothing driven through it. We keep the drainage outlets clear and lay the grass so the membrane can still be inspected. If the existing waterproofing is already old or failing, it is best dealt with before the grass goes down.
Through the grass and across the deck to the roof's existing outlets. A permeable backing and a drainage mat let rainwater flow beneath the surface, so it behaves much as the bare deck did, as long as the gullies and scuppers are kept clear.
Small, sheltered terraces are achievable for a confident DIYer, but the wind fixing and membrane care are easy to get wrong, and the consequences, whether grass lifting in a storm or trapped water on the deck, are more serious than in a garden. For anything exposed or large, we would recommend having it assessed and fitted properly.
A balcony is smaller, more enclosed and often fine loose-laid over the floor. A roof terrace is larger, far more exposed to wind, and sits over a waterproofed roof whose drainage must be respected, so it needs secured edges and a more considered build-up. See our balconies page for the smaller job.
Related services and guides
Planning a roof terrace lawn?
Tell us about your terrace, its size, the deck, the access and how exposed it is, and we will advise on the right build-up and give you a considered quote.