A bituminous covering for flat roofs is still the most common and reliable waterproofing solution in Lithuania, but “bituminous covering” is not a single material — it is a family of membranes that differ in modifier (SBS or APP), reinforcement, thickness, top finish and installation method. This guide explains how to correctly choose a bituminous membrane for a specific project: how SBS and APP modified bitumen differ, when one layer is enough and when you need two, what membrane class and thickness mean, which reinforcement (polyester or glass fleece) suits each case, and how to recognise a quality covering.
If your question is not “how to lay it” but “what to choose”, you are in the right place. The laying technique itself — torching, welding, pressing — is covered in detail in our separate article on bituminous roof covering technology, while here we focus on material selection. For the practical service context, see our bituminous roof covering and flat roof installation pages.
What a bituminous covering is and what it is made of
A modern bituminous roof covering is not the same as the raw tar bitumen used to cover roofs half a century ago. Today’s torch-applied membrane is a multi-layer rolled product: in the centre is a reinforcement carrier (polyester fabric or glass fleece veil), coated on both sides with modified bitumen, with the top surface protected by mineral granules, metal foil or film. The underside often carries a meltable film that shows where to direct the torch flame.
It is the modifier and the reinforcement that determine the membrane’s properties — elasticity, temperature resistance, tensile strength and service life. So when choosing a covering you should look not at the name on the roll but at the specific technical figures. We go through all of them below.
SBS or APP modified bitumen: the main choice
The first and most important decision when choosing a bituminous covering for flat roofs is the modifier type. Pure bitumen is too hard in the cold and too soft in the heat, so polymers are added that greatly improve elasticity and temperature resistance. Two main modifiers are used — SBS and APP.
SBS (styrene-butadiene-styrene) – elastomeric bitumen
The SBS modifier gives bitumen rubber-like properties: the covering becomes highly elastic, can stretch and return to its original shape, and stays flexible even at −25 °C or lower. It is precisely this resistance to cold and to temperature cycling that makes SBS membranes the natural choice for the Lithuanian climate, where the roof goes through many freeze-thaw cycles each year. SBS membranes cope well with structural movement, snow loads and building settlement, which is why they dominate in Northern and Central Europe.
In practice, the cold-flexibility figure on the Declaration of Performance is the single most telling number for our climate: a quality SBS cap membrane should be rated to −25 °C or colder. Anything warmer than about −15 °C points to a low-modifier or APP product that risks cracking through a Lithuanian winter.
APP (atactic polypropylene) – plastomeric bitumen
The APP modifier gives bitumen plastic-like properties: the covering becomes highly resistant to high temperatures and UV and very durable in heat, but in the cold it is stiffer and less elastic than SBS. APP membranes were developed for southern regions with hot climates and strong sun exposure. In Lithuanian conditions a purely APP covering risks cracking in the cold, so it is used here less often — except for specific solutions or as an underlayer.
Practical conclusion for Lithuania: for most flat roofs in our climate, an SBS modified covering is more suitable because of its cold-weather elasticity. APP may be considered for strongly sun-exposed, hot surfaces or in technical details, but it is not the default choice. We describe how this property shows up in service in our bituminous roof repair article.
One layer or two: how much covering you need
How much will your roof cost?
Enter the roof area and covering type to get an indicative price in a minute. Or call us for an instant answer.
- Free on-site inspection
- Reply within 48 hours
- Warranty up to 20 years
Bituminous waterproofing for flat roofs is laid in one or two layers, and this is not purely a cost question — it is a question of reliability and service life.
A single-layer system uses one thicker (often 5 mm or more) membrane. It is cheaper and faster to lay, suitable for lower-responsibility objects, garages, agricultural buildings, or as a refresh layer over an existing roof. The drawback is that the entire waterproofing responsibility rests on one seam system, so a single bad seam means a leak.
A two-layer system is the industry standard for responsible flat roofs. The bottom (base) layer is torched or mechanically fixed to the substrate, and the top (cap, with mineral granules) layer is laid so that its seams overlap the seams of the base layer. This gives a double waterproofing barrier: even if a top-layer seam is permeable somewhere, it is “covered” by the continuous base layer. A two-layer covering is more durable, more resistant to damage and usually comes with a longer warranty. For new construction or full renovation, Eurokas almost always recommends a two-layer system — read more about layer build-up in our compact flat roof installation article.
Membrane classes and thickness: what the numbers mean
When choosing a covering you will often see a marking with thickness (e.g. 3.0 mm, 4.0 mm, 5.2 mm) and the membrane’s purpose (base or cap). Thickness is directly related to service life and durability: the more bitumen above the reinforcement, the longer the covering withstands UV and mechanical wear.
- Base membranes – usually 3.0–4.0 mm, with film or fine granules. Their job is to create the first waterproofing barrier and good adhesion to the cap layer.
- Cap membranes – typically 4.0–5.2 mm, with coarse mineral granules protecting against UV. This is the layer that “sees the sun” and determines the roof’s appearance and service life.
- Reinforced / long-life membranes – with denser polyester reinforcement and higher SBS content, declared for 25–30 years of service.
It is important to understand: greater thickness alone does not guarantee quality if the reinforcement is weak or the bitumen modification is poor. The true measure of quality is the combination of thickness, reinforcement and modifier, reflected in the membrane’s Declaration of Performance (DoP, to EN 13707).
Reinforcement: polyester or glass fleece
The reinforcement carrier is the membrane’s “skeleton”, determining its tensile strength and dimensional stability. Two main reinforcement types are used for flat roofs, and choosing between them is one of the most important technical decisions.
Polyester fabric (PES)
Polyester reinforcement is strong and highly elongatable — it can stretch 40–50 % and return, so it copes excellently with structural movement, thermal expansion and snow loads. It is the choice for cap and responsible layers, especially where movement or deformation is expected. Polyester-reinforced SBS membranes are the most reliable combination for responsible flat roofs in Lithuania.
Glass fleece veil
Glass fleece reinforcement is very dimensionally stable — it barely shrinks or expands, so the covering stays flat and does not wrinkle. However, it is more brittle and less elongatable than polyester, so it copes less well with movement. Glass fleece is often used for base layers, vapour barriers, or where dimensional stability rather than elongation matters.
In practice, the optimal system often combines both: a glass-fleece base layer (for stability) with a polyester cap layer (for elongation and durability). There are also combined-reinforcement membranes that unite the advantages of both.
Not sure which bituminous covering to choose for your roof?
We will assess your roof structure, slope and loads and propose the most suitable SBS membrane system with specific thicknesses and a warranty.
Top finish: granules, foil or film
The top surface of the cap membrane is not just aesthetics — it protects the bitumen from UV rays, which are the main cause of covering ageing. The finish type determines both appearance and service life.
- Mineral granules (slate granules) – the most common cap-layer solution. Fine slate or basalt granules are pressed into the bitumen and create a durable UV protective layer. You can choose a colour (grey, green, red, anthracite), so granules also serve an aesthetic function. This is the standard for occupied buildings.
- Fine (sand) finish or film – used for base layers that will be covered, or where ballast (gravel), terrace slabs or a green roof are planned on top.
- Metallized (copper, aluminium) foil – special membranes with a thin metal layer, used for parapets, transitions or visible edges where both UV protection and an attractive metallic surface are needed.
If a green roof layer is planned on top, granules are not required, but the membrane must be root-resistant — more on this on our green roof installation page. If a solar plant will sit on the roof, it is important to match the covering with the mounting solution — see our solar plant foundation solutions.
Bituminous membrane comparison table
Below is a summary comparison table of the main bituminous membrane types to help you quickly orient yourself when choosing a covering for a flat roof.
| Membrane type | Modifier | Reinforcement | Typical thickness | Best suited for |
|---|---|---|---|---|
| SBS base | SBS (elastomeric) | Glass fleece / polyester | 3.0–4.0 mm | First layer of a two-layer system |
| SBS cap with granules | SBS (elastomeric) | Polyester | 4.0–5.2 mm | Responsible flat roofs in the Lithuanian climate |
| APP cap | APP (plastomeric) | Polyester / glass fleece | 4.0–4.5 mm | Hot, strongly sun-exposed surfaces |
| Self-adhesive SBS | SBS (elastomeric) | Polyester | 3.0–4.0 mm | Combustible substrates, flame-free areas |
| Root-resistant SBS | SBS + additives | Polyester | 5.0–5.2 mm | Green and ballasted roofs |
Overview of installation methods: torch-on, self-adhesive, hot-air
The chosen membrane is fixed to the substrate by one of several methods, and the membrane type often dictates which method fits. Here we give a high-level overview — the detailed laying technique, steps and nuances are in our separate article on bituminous covering laying technology.
Torch-on with a gas burner
The classic and most widespread method: the membrane’s underside is heated with a gas burner, the bitumen melts and the membrane is pressed onto the substrate, creating a continuous bond. It suits most substrates, gives a very reliable result, but requires an open flame and an experienced installer. It is the default method for torch-on SBS coverings over concrete or old bituminous covering.
Self-adhesive membrane
The membrane has a self-adhesive layer on the underside with a removable film — it is bonded without flame, simply by pressing down. This is a safer solution for combustible substrates (timber, OSB, polystyrene insulation) and in places where open flame is prohibited. In cold weather additional surface warming is needed for good adhesion.
Hot-air welding
Used to weld seams with a stream of hot air without an open flame — especially to secure seams of self-adhesive systems or in sensitive zones. Safer than a burner, but slower and requiring special equipment.
Mechanical fixing and ballast
In some systems the base layer is fixed mechanically (self-tapping screws with stress plates) and the cap is torched; or the covering is held down by ballast (gravel, slabs). The method is chosen according to the substrate, wind loads and whether the roof will be used.
How to match the membrane to a specific project
Correct covering selection starts not from a catalogue but from analysing the object. Here are the key questions an experienced roofer answers before proposing a specific membrane system.
- What is the substrate? Concrete allows torching; timber or insulation requires self-adhesive or mechanically fixed solutions.
- Will the roof be used? Walkable surfaces, terraces, green roofs or solar roofs require the most durable and thickest membranes.
- What is the slope and drainage? Low-slope roofs with standing-water risk require two layers and better reinforcement.
- What responsibility and warranty? For residential and commercial buildings — a two-layer SBS system with a longer warranty; for agricultural — a single thick layer may suffice.
- New roof or renovation? When renovating it is important to match the new covering with the existing one and the substrate condition — see our roof renovation solutions.
It is precisely this matching that separates professional work from laying “the cheapest possible” roll. We write about the selection of layers, slope and structure in detail in our flat roof installation article, and about insulation in our flat roof insulation overview.
Quality indicators: how to recognise a good bituminous covering
For a non-specialist it is hard to assess quality when choosing a covering, so here are practical signs worth paying attention to.
- Declaration of Performance (DoP) to EN 13707 – a quality manufacturer provides clear figures: tensile strength, elongation, cold flexibility, watertightness.
- Cold flexibility – a quality SBS covering has a figure of −25 °C or lower; this is critically important for Lithuania.
- Reinforcement type and density – the stated polyester weight (g/m²); higher density means a stronger membrane.
- SBS content and thickness – higher-class membranes contain more modifier, hence a longer declared service life (25–30 years).
- Even granules – on a quality membrane the granules are densely and evenly embedded and do not shed in your hand.
- Manufacturer warranty and certificates – a clear warranty and CE marking are the essential minimum.
Bituminous covering prices and service life in 2026
The choice of bituminous covering directly affects price and service life. Below are indicative 2026 prices in Lithuania, including material and labour. The exact price depends on roof area, access and substrate condition.
| Solution | Indicative price (€/m²) | Service life |
|---|---|---|
| Single-layer SBS waterproofing | 18–28 | 15–20 years |
| Two-layer SBS system | 28–45 | 20–30 years |
| Full build-up with insulation | 45–75 | 25–30 years |
| Inverted / ballasted roof | 70–120 | 30+ years |
| Green roof (with root-resistant membrane) | 90–150 | 30+ years |
For more detailed price lists, see our flat roof price 2026 and torch-on roof covering price-list articles, or our flat roof installation service page.
Common mistakes when choosing a bituminous covering
- Choosing by price rather than by modifier – a cheap APP covering cracks faster in the Lithuanian cold than a properly selected SBS one.
- One layer where two are needed – saving on the second layer on a responsible roof risks the entire waterproofing.
- Ignoring reinforcement – a glass-fleece covering where elongatable polyester is needed cracks from movement.
- Too thin a cap membrane – thin granules shed quickly, and UV starts to break down the bitumen.
- Not matched to the substrate – torching onto combustible insulation without protection is a fire hazard; a self-adhesive solution is required.
Bituminous covering and alternatives: when to consider PVC or EPDM
A bituminous covering is not the only flat-roof waterproofing solution, and it is fair to say when alternatives are worth considering. PVC and TPO membranes are hot-air welded and give very thin, light, single-layer coverings; EPDM is an elastic synthetic rubber. These systems have their own advantages for wide industrial roofs or specific cases.
Nevertheless, SBS bituminous covering remains the most popular in Lithuania for several reasons: it is easy to repair locally with the same method, it pairs excellently with a concrete substrate, it withstands our temperature cycles and is proven over decades. We write more about comparing different covering types on our flat roof installation page.
Frequently asked questions about choosing a bituminous covering
For the Lithuanian climate, an SBS modified covering is almost always more suitable, because it stays elastic in the cold (down to −25 °C and below) and copes well with freeze-thaw cycles. APP covering was developed for hot climates and risks cracking in our cold, so it is used less often and only for specific cases.
Not always. For responsible residential and commercial roofs, a two-layer SBS system is recommended for its double waterproofing barrier and longer warranty. For agricultural buildings, garages or refreshing, a single thick layer may be enough. The decision depends on the object’s responsibility and budget.
It depends on the layer’s purpose. Polyester is elongatable and strong, so it suits cap layers and areas with movement. Glass fleece is more dimensionally stable but more brittle, so it suits base layers. The optimal system often combines both.
Base layers are usually 3.0–4.0 mm and cap layers 4.0–5.2 mm with mineral granules. A thicker cap membrane withstands UV and mechanical wear longer. However, thickness alone does not guarantee quality — the combination of thickness, reinforcement and SBS content matters.
Mineral granules (slate or basalt) protect the bitumen from UV rays, which are the main cause of covering ageing. Without granules, bare bitumen ages several times faster. Granules also provide colour and serve an aesthetic function. They are only unnecessary where the covering is covered by ballast, a terrace or a green layer.
A torch-on membrane is fixed by heating its underside with a gas burner — the most reliable method for suitable substrates. A self-adhesive membrane is bonded without flame after removing a protective film, and is safer for combustible substrates (timber, insulation) and in places where open flame is prohibited.
A quality SBS bituminous covering lasts 20–30 years, depending on the number of layers, the membrane class and maintenance. Single-layer solutions give 15–20 years, two-layer systems 20–30 years. Regular maintenance and timely repair can extend this further.
Yes, a bituminous covering suits solar plants well if the mounting system is ballasted or matched to the covering so as not to damage the waterproofing. For such a roof a thicker, more durable membrane is chosen, and the mounting points are additionally sealed. We cover the details in our solar plant foundation solutions.
Trust the covering choice to Eurokas specialists
A correctly chosen bituminous covering for flat roofs is half the success; the other half is laying it properly. Eurokas selects and lays SBS modified membranes for flat roofs across Lithuania and Europe, works with proven manufacturers’ systems and provides up to 20 years of warranty. We will assess your roof structure, substrate and loads and propose the optimal membrane system with specific thicknesses. Review all our services or contact us for an individual quote — phone +370 698 013 23, info@eurokas.lt.
