What is the Difference Between SBS and BUR Roofing?

Choosing a flat roof covering gets confusing fast once installers start mentioning SBS and BUR. Put simply, the SBS vs BUR roofing choice is a choice between a modern rubber-modified bitumen membrane and a traditional built-up felt system. SBS goes down in two factory-made layers and flexes with the building. BUR is built up on site from several plies of bitumen and reinforcing felt. Both keep water out well, but they behave differently once Irish weather goes to work on them.

Flat roofs turn up all over Irish properties, on kitchen and bedroom extensions, garages, dormers, porches and plenty of commercial buildings. They are also where a lot of leaks start, so the covering you pick matters more than most homeowners expect. The right system depends on the roof size, the deck underneath, how much movement the structure sees, and your budget.

This guide breaks down what each system is, how they differ in build and performance, which one tends to suit Irish roofs, and roughly what you should expect to pay.

SBS vs BUR Roofing Explained

SBS modified bitumen is the modern evolution of built-up roofing (BUR). BUR is the older method, where hot bitumen and layers of reinforcing felt are alternated on site to form one thick waterproof mass. SBS keeps the bitumen but adds a rubbery polymer that makes the membrane flexible, then delivers it as pre-made rolls that are bonded down in fewer layers. Same base material, very different handling and performance.

The practical upshot is that BUR gives you proven, heavy, multi-layer redundancy, while SBS gives you flexibility and faster, more consistent installation. Most Irish domestic flat roofs now use SBS systems, while traditional built-up work still appears on larger commercial jobs.

What Is BUR (Built-Up Roofing)?

Built-up roofing is a flat roof system made from several alternating layers of bitumen and reinforcing felt, assembled directly on the roof deck. It is the original low-slope roofing method, sometimes called a tar and gravel roof, and has been used on commercial buildings for more than a century. The finished result is a dense, heavy, highly waterproof membrane.

A typical built-up roof is put together like this:

• A base sheet fixed to the deck or insulation
• Three to five plies of bitumen-saturated felt, each bedded in hot bitumen
• A surfacing layer of mineral chippings, gravel or a mineral cap sheet for UV protection

Because every layer is applied by hand on site, the quality depends heavily on the crew’s skill and the weather on the day. The multiple plies give real strength, since if one layer is compromised, the others still hold water back. The trade-off is weight and labour. A built-up roof is heavy enough that some structures need checking before it goes on, and the process is slower and messier than laying a membrane.

What Is SBS Modified Bitumen Roofing?

SBS modified bitumen is a flat roof membrane made from bitumen blended with styrene-butadiene-styrene, a rubber-like polymer that adds elasticity. That elasticity lets the membrane stretch and recover as the roof heats, cools and moves, which stops the brittle cracking that ages older felts. It is manufactured into reinforced rolls in a factory and installed in a minimum two-layer build of an underlay and a mineral-finished cap sheet.

SBS is usually applied by torch-on bonding, where a propane torch melts the underside of the membrane so it fuses to the layer below. It can also be hot-air welded, cold-applied with adhesive, or self-adhered. Torch-on work involves an open flame well above 1,000°C, so it should follow the fire-safety controls set out by the Health and Safety Authority and never go directly onto a bare timber deck without proper protection.

One common mix-up worth clearing up is SBS versus APP. Both are modified bitumen, but SBS uses a rubber modifier suited to cold, damp climates, while APP uses a plastic modifier that copes better with intense heat. For Irish conditions, SBS is generally the better fit, which is why it dominates here. When specifying a system, it is worth checking that the membrane and build-up carry NSAI Agrément certification, which confirms the product suits Irish site conditions under the Building Regulations.

Key Differences Between SBS and BUR

The core differences come down to composition, weight, flexibility, installation and lifespan. BUR is a thick, heavy, site-built system with excellent redundancy. SBS is a lighter, flexible, factory-made membrane that installs faster and handles building movement better. The table below sets the two side by side.

Two points matter most for a homeowner reading a quote. First, SBS accommodates thermal movement, so it resists the fatigue cracking that shortens the life of older built-up felts. Second, BUR’s weight and on-site labour make it slower and more demanding to install well, which is part of why it has largely moved to commercial projects.

Which System Suits Irish Roofs Best?

For most Irish homes, an SBS modified bitumen system is the more practical choice, mainly because of the climate. Irish flat roofs face constant damp, wind-driven rain and repeated warm-cold cycling rather than sustained heat. SBS was made for exactly that, and its rubbery flexibility handles the freeze-thaw movement that makes rigid coverings split over time.

BUR still earns its place on large, flat commercial and industrial roofs, where its layered redundancy and heavy, walkable surface are genuine advantages and the extra weight is not a problem. On a domestic extension or garage, though, the labour, weight and slower installation rarely justify it over a modern membrane. A well-specified torch-on felt system gives comparable waterproofing with far less structural demand.

Whichever system you have or plan to fit, the deck condition underneath is what really decides longevity. Rotten or moving boards will fail any covering early, so any honest assessment starts there. That is also why it pays to arrange a proper survey rather than a covering-only quote, and why prompt flat roof repair beats leaving a small split to spread.

How Much Does Each System Cost in Ireland?

A modern SBS torch-on felt system in Ireland typically costs around €50 to €90 per square metre installed, based on current 2026 market rates. For a standard 20m² garage or extension roof, that usually works out at roughly €1,000 to €2,800 in total. Traditional built-up roofing is generally priced per job rather than by a fixed rate, and tends to sit at or above the felt band because of the extra on-site labour and materials.

Several things move the final figure:

• Deck condition, the biggest swing factor, since rotten timber must be replaced before any covering goes down
• Roof size, access and the number of upstands, edges and outlets to detail
• Location, with Dublin and city labour often adding roughly 10 to 15%

Because so much depends on what sits under the old roof, treat any headline rate as a planning benchmark and get an itemised written quote before committing. For a quick starting figure based on your roof size, an online roof cost estimate gives a useful ballpark ahead of a site visit.

[Image: flat felt roof on a domestic single-storey rear extension viewed from above]

Getting the Specification Right

For most Irish homes and extensions, a flexible SBS membrane is the sensible default, while BUR remains a strong option on large commercial roofs that suit its weight and redundancy. Either way, the covering only performs as well as the deck beneath it and the crew fitting it, so specification and installation quality matter more than the label on the roll.

If you are weighing up a new flat roof or replacing a tired one, talk to a qualified flat roofing installer for a site survey and a written, itemised quote so you know exactly what system you are buying and why.