The short answer
Most flat roofs are designed for occasional access by someone clearing leaves or checking an outlet, not for regular foot traffic. GRP and lead tolerate it better than bitumen felt or thin single ply sheet. If you want to sit out on the roof, it needs a purpose-built balcony or terrace build-up, with proper guarding and a decking or paving system, rather than a covering never meant for it.
Occasional access and regular use are different things
Every flat roof is built to resist rain, wind and the weight of snow. A designer does not assume people will cross it every day unless the brief says so. Occasional visits to clear a gutter, replace a bulb in a rooflight or reach a chimney are another matter, and a sound covering can cope with those if the person is careful and wears soft-soled shoes.
Regular use is a different category. Carrying furniture, planters or a barbecue onto a roof loads the structure and wears at the surface. If the roof was never designed as a floor, moving it into that role risks damaging a covering that is still working, so we would rather talk it through before it happens.
Think about who will go up and how often. A roofer clearing outlets twice a year is a very different load from a family using the roof most evenings in summer, and the covering, the deck and the edge protection should reflect that honest difference.
How the main coverings cope
GRP, or fibreglass, forms a hard, jointless shell that tolerates light foot traffic well, which is one reason it is chosen for small balconies and dormers. Our page on flat roof materials sets the main options side by side.
Lead is tough but soft, so it needs boards or a walkway over it where people will tread, or it will crease and stretch over time. Bitumen felt is easily scuffed in warm weather and is the covering most at risk from heels and dragged tools. EPDM rubber is flexible and forgiving but can be punctured by sharp objects, and thinner single ply membranes need protection from heavy traffic.
MyBuilder's flat roof guide, updated on 21 August 2026, gives national price bands for reference: felt £70 to £100 per m², EPDM £90 to £130, GRP £95 to £150 and lead £150 to £200 or more. The tougher coverings cost more, and some of that extra buys resilience underfoot.
Weather changes the picture as well. A wet roof is slippery whatever it is made of, algae and moss make it worse, and a frosty morning can turn a smooth membrane into an ice rink. Even on a covering that tolerates traffic, pick a dry day, keep both hands free for a ladder and have someone else at the bottom.
When you need a walkway
A walkway is a hard-wearing path laid over the covering to spread the load and protect it. On a membrane roof it can be a row of rubber or concrete tiles on pedestals, or a protective sheet stuck over the surface, running from the access point to whatever needs visiting, such as an outlet, an air-conditioning unit or a solar panel.
The walkway should end somewhere sensible and be easy to see, so the person maintaining the roof knows to stay on it. It should not trap leaves against an outlet or block the run of water, a point that matters on any roof prone to pools, as our page on ponding describes.
Edges and trims can also be damaged by being stepped on, so check that any metal edge strip is firmly fixed before anyone relies on it. Our notes on flat roof trims show what a good edge looks like and why a loose one is a warning sign.
Turning a roof into a balcony or terrace
A balcony build-up is a different construction from a simple covering. The deck has to be designed for people, with enough strength and a well-drained surface. Above the waterproof layer sit supports, then decking or paving, with joints that let water run away without leaving a puddle. The perimeter needs guarding to a safe height, and the structure must be able to carry the load.
This almost certainly touches the Building Regulations and may touch planning, particularly if neighbours overlook the space. Ask the planning team at the council for your address, which is Swindon Borough Council inside the borough, and your building control body, before any work starts. The permitted development rules for roof additions exclude a verandah, balcony or raised platform, so do not assume yours is allowed.
Any new balcony also raises the matter of waterproofing at the door threshold, where a step up is often needed and a rooflight or French door can complicate the detail.
Drainage deserves thought too. Decking or paving sits above the membrane, so leaves and grit collect underneath where nobody sees them, and outlets need an access hatch or a removable panel so they can be cleared. A terrace that cannot be inspected is a terrace that will eventually leak unnoticed.
Our advice before you step out
If the roof feels soft or springy, stay off it. A rotten deck can fail without warning, as our page on a spongy flat roof explains. If you only need access now and then, we can recommend a covering and a short walkway that suit the use. If you want a proper sitting-out space, we will tell you whether the existing structure can take it or whether a purpose-built deck is the right answer.
Whatever the outcome, you receive pictures taken on your roof after the visit, then a written quote, and the workmanship guarantee that backs finished work lasts ten years and is set out on paper. Get in touch on 01793 626096, through WhatsApp or by the enquiry form. Our flat roofing page lists the other work we do on roofs of this kind.