What is the cheapest flat roof covering available?

Felt is the cheapest flat roof covering on the market, and on the right roof it is also the right one. The trouble starts when the price is cut somewhere other than the membrane.

Wey Valley Roofing is family-run, with work carried out by our own experienced roofers and never subcontracted, and every job backed by a 25-year written workmanship guarantee. Whether you need flat roofing or flat roofing services Godalming, we cover the whole area, from single garages to full warm-roof upgrades.

Call Scott on 07428 300474 for a free survey and a fixed price in writing, with no obligation.

What is the cheapest flat roof covering available?

The cheapest flat roof covering available is felt, either torch-on or built-up in layers, because the materials are inexpensive and the labour is quick. Mineral-surfaced pour-and-roll felt sits at the very bottom on price, with torch-on three-layer systems a little dearer and lasting considerably longer.

That is the short answer, and it is worth understanding what sits behind it. The covering is only one line on the bill. On a flat roof the deck, the falls, the ventilation and the detailing at the edges decide whether the covering lasts eight years or twenty-five, and those things cost roughly the same whichever membrane goes over the top. Cheap becomes expensive the moment the deck has to come off twice.

Felt is the lowest cost per square metre, with conditions attached

Felt has been on British flat roofs for a century and it still works. A modern torch-on system is normally three layers: a vapour control layer, an underlay and a mineral-surfaced cap sheet, all bonded down with a gas torch onto a primed deck. The materials are the cheapest of any flat roof system, and a competent team can lay a garage or extension roof in a day, which keeps labour low too.

The conditions are these. Single-layer or two-layer felt, laid thin over a tired deck to hit a price, is the reason felt has the reputation it has. Blisters, splits at the laps and ponding in a dead-flat area will finish it early. Torch work also needs care near timber, fascias and neighbouring walls, and there are places on a roof where a torch has no business being at all, so cold-applied or self-adhesive detailing gets used instead.

BS 6229 is the standard that governs flat roofs in this country, and it is the reason we talk about falls, drainage and interstitial condensation before we talk about the covering. Whether you need flat roofing or flat roofing in Guildford, we cover the whole area, and the survey is the same either way: lift a corner, check the deck, check where the water actually goes.

What the price difference between felt, EPDM and fibreglass actually buys

Once felt is understood as the floor, the other two common systems make more sense.

• Felt, torch-on or built-up. Lowest material cost, fast to lay, easy and cheap to patch. Realistic life on a well-built three-layer job is around fifteen to twenty years, less if the falls are poor.
• EPDM rubber. Usually a single sheet across a domestic roof, so on a simple rectangle there are no seams to fail. Modestly more expensive than felt, and it tolerates movement and UV well. It is not the cheapest and it is rarely the wrong choice.
• GRP fibreglass. Highest of the three on price because it is a wet-laid resin and matting system that needs dry weather and a sound deck, often a new one. It gives a hard, seamless, trafficable surface, which earns its money on balconies and roofs that get walked on.

On a small garage the gap between the cheapest felt and a rubber roof is often smaller than people expect, because the labour, the scaffold or tower, the trims and the tip run are common to both. That is the calculation worth doing rather than choosing on the material name. Whether you need flat roofing or flat roofing services Woking, we cover the whole area, and we will put both options on the quote in writing so the difference is visible.

The costs that sit underneath every covering

Most flat roof quotes that look suspiciously cheap have left something out. The usual omissions are worth naming.

The deck. If the chipboard or ply is soft, spongy or delaminated, no membrane will save it. Replacement boarding is a real cost and it is not optional.

The falls. A flat roof is never flat. Firrings or tapered insulation are needed to move water to the outlet, and adding them to a roof that never had them is proper joinery, not a top-up.

Ventilation and condensation. BS 5250 covers this. A cold deck with no cross ventilation rots from underneath while the covering above looks perfect, which is why warm-roof upgrades, with insulation above the deck, are often the sensible route on a re-cover.

Edges, upstands and outlets. Drip trims, wall abutments, lead or GRP kerbs and correctly sized outlets under BS EN 12056. Nearly every flat roof leak we open up started at a detail, not in the open field of the membrane.

If you are looking for a flat roofer near you across Surrey and the Wey Valley, someone can usually be on the roof within a few days, and sooner if water is coming in. All of the above is covered in more detail on our flat roofing page.

When the cheapest covering is the right answer and when it is not

Cheap is not a dirty word. On a detached garage with a sound deck, decent falls and no habitable room underneath, a three-layer torch-on felt roof is a perfectly honest piece of work and we will say so rather than pushing something dearer. The same goes for a small porch or a store.

Where we would argue against the cheapest option is over a kitchen extension, a bedroom or anything with plaster and lighting below, on any roof that gets walked on, on a roof with awkward pipe penetrations and multiple upstands, and on a roof where access is difficult enough that doing it again in a decade would cost more than doing it properly now. Coatings over a failed felt roof get asked about a lot, and we do not push them, because painting over a wet deck buys a season at best.

Scott has spent more than 36 years on Surrey roofs, and the pattern does not change: the roofs that need doing twice were the ones specified on price alone. Every job we complete carries a 25-year written workmanship guarantee, handed over before the team leaves, and that applies to a felt garage roof exactly as it applies to a full warm-roof rebuild. If a repair will see you right, we say that instead of quoting a new roof.