The choice of a specific type of roofing material for a garage roof begins with an analysis of the condition of the concrete floor slabs and the angle of inclination of the slope, since it is these parameters that dictate the need to use weld-on or traditional materials. If there are already cracks on the surface or the old layer is cracked, ignoring this fact will lead to the fact that even the most expensive material TechnoNIKOL or Bikrost will break in the first season due to movement of the base. Many owners make the mistake of buying material with a fine coating for a flat roof, where water will accumulate, which inevitably leads to rotting of the cardboard base and leaks.
For reliable protection, it is necessary to take into account that roofing felt is a collective name that covers dozens of modifications with different bases: from short-lived cardboard to fiberglass and polyester. Incorrect choice of markings, e.g. use of underlay RPP-300 as a finishing layer, will reduce the service life of the roof to 2-3 years instead of the guaranteed 10-15. It is important to immediately decide on the installation method, since the fused technology requires a gas burner, and mechanical fixation with nails is only suitable for cardboard-based materials with coarse powder.
The modern market offers solutions that completely eliminate the need to cook bitumen mastic, which was the norm twenty years ago. A key factor in durability is not only the thickness, but also the type of top protective layer, which takes on the impact of ultraviolet radiation and mechanical loads from snow or walking when servicing antennas. In this article, we will look at how to read the labels so as not to overpay for unnecessary characteristics or, conversely, not to save on critical parameters.
Main types of bitumen-based roofing materials
Traditional roofing felt, which has been used for decades for waterproofing, is based on roofing paper impregnated with bitumen. This is a budget solution that is still relevant for temporary buildings or garages with a steep slope, where water does not stagnate. However, the cardboard base Rubemast or classic RKK-350 tends to absorb moisture at the slightest damage to the protective layer, which leads to swelling and ruptures when water freezes in winter. Such material requires mandatory protection from above, for example, painting or laying slate, since it itself is vulnerable.
A more modern analogue is fused materials based on fiberglass or fiberglass, often called euroroofing felt. In their structure, cardboard is replaced with a rot-resistant frame, which radically changes the performance properties. The bitumen mixture here is modified with polymers, which gives it elasticity at low temperatures and resistance to fluidity when heated by the sun. For a garage roof, this is the best choice, allowing you to create a monolithic roof without seams.
There is also a gradation based on the type of topping, which directly affects the scope of application. Coarse-grained slate or basalt toppings protect against mechanical damage and the sun, while fine-grained or dusty ones are intended exclusively for lower layers or temporary protection during transportation. Using a material with a dusty coating as a top layer is a gross mistake, leading to the rapid destruction of bitumen under the influence of UV rays.
⚠️ Attention: Never use materials marked "P" (pulverized coating) as a top finishing layer on a roof in the sun. They are intended only for base layers of waterproofing or temporary solutions.
When choosing between classics and modern analogues, it is worth assessing labor costs. Working with cardboard often requires a multi-layer cake with mastic, while glass base allows you to cover the roof in one or two layers using the fusing method. This reduces work time and reduces the weight of the structure, which is important for old garage cooperatives with limited load-bearing capacity of the walls.
Decoding the markings: how to read abbreviations
Understanding the letters on the end of the roll is the first step to purchasing the right material. The marking is based on the principle of three letters and numbers, where each position carries specific technical information. The first letter always indicates the type of material: R - roofing felt. The second letter indicates the type of base: K (roofing cardboard), C (fiberglass), T (fiberglass), E (polyester). The third letter characterizes the type of top layer: K (coarse-grained), M (fine-grained), P (dust-like), H (scaly).
The numbers at the end indicate the density of the base in grams per square meter. For example, in marking RKK-350 the number 350 means that the weight of one square meter of cardboard base is 350 grams. The higher this indicator, the stronger the material and the higher its breaking load. For a garage roof, the minimum acceptable value for cardboard is 350 g/m²; the use of 300 g/m² is only possible in a multi-layer cake as a lining.
The differences between the fundamentals are significant. Fiberglass (T) has high tensile strength but low elasticity, so it is good on stable substrates. Fiberglass (C) less tensile strength, but more elastic. Polyester (E) is the most expensive and reliable option, capable of stretching and returning to shape, which is ideal for roofs subject to temperature deformation.
- 🏷️ RPP-300 - lining material on cardboard with dusty topping, used only as a bottom layer.
- 🏷️ RKP-350 - roofing material on cardboard with a dusty coating, requires mandatory protection or a top layer with dusting.
- 🏷️ RKK-400 - classic roofing felt with coarse-grained topping, suitable for the top layer on pitched roofs.
- 🏷️ Bikrost TCH - a modern material made of fiberglass with coarse-grained coating, intended for fusing.
It is important not to confuse the purpose of layers. Lining marks (often with a second P or third P) do not have UV protection. If you cover the roof with such material as the final layer, after one summer the bitumen will dry out and crack. Always make sure the top layer has an index K or M with protective properties.
Comparison of characteristics: cardboard versus glass base
The choice between cardboard and glass base is a choice between savings today and durability in the future. Cardboard materials such as Ruberoid domestically produced, they are much cheaper, but their service life rarely exceeds 5-7 years even with high-quality installation. They are heavier, require more bitumen mastic for gluing and are more labor-intensive to install, since you often have to boil the mastic in a barrel.
Fiberglass based materials such as Bikrost, Linocrom or Bipole, belong to the class of surface-surfaced ones. Their installation is faster: the roll is rolled out and heated with a gas burner until the bitumen melts. Adhesion to the base occurs at the molecular level, creating a sealed membrane. The service life of such coatings is 10-15 years, and when using polymer modifications - up to 20 years or more.
The table below will help you systematize the differences and make an informed decision about which roofing material to choose for your garage roof in your case.
| Characteristics | Cardboard base (RKK, RPP) | Fiberglass/Fiberglass (TKP, HKP) | Polyester (EPP, ECP) |
|---|---|---|---|
| Service life | 3-7 years | 10-15 years | 20-25 years |
| Installation | On mastic, nails | Burner fusing | Burner fusing |
| Elasticity | Low, cracks in the cold | Average | Tall, stretches |
| Price per m² | Low | Average | High |
It is worth noting that for garages located in the shade or under trees, where there is a high probability of mechanical damage from branches, fiberglass (T) will be preferable to fiberglass (C) due to its tensile strength. However, if the garage is on subsiding soil and the walls are “walking,” it is better to take polyester material that can stretch and not burst.
Main conclusion: For a permanent garage, saving on a cardboard base is impractical - the overpayment for a glass base will be recouped by the absence of repairs within 10 years.
Substrate preparation and installation technology
The quality of installation directly depends on the preparation of the surface. Concrete floor slabs must be cleaned of debris, old toppings and dust. The presence of swelling or peeling of the old coating requires their mandatory removal. If the surface is wet, you cannot fuse the material - the water will boil under the bitumen layer and tear off the coating. In such cases, it is necessary to let the base dry or use special primers that work on a wet base.
Priming with a primer is a mandatory step that is often ignored. The primer (bitumen emulsion) binds residual dust and improves the adhesion (adhesion) of the material to concrete. It can be applied with a roller or brush, allowing it to dry completely until the stickiness disappears. This takes from 2 to 12 hours depending on the weather.
☑️ Roof preparation checklist
Fusing technology requires uniform heating. Using a gas burner, both the surface of the base and the underside of the roll are heated. An indicator of proper heating is the melting of the bitumen layer and the appearance of a characteristic shine. When rolling out a roll, it is important to ensure that no folds form and that the overlap of adjacent strips is at least 10-15 cm.
⚠️ Attention: When working with a gas burner, follow safety precautions. Have a fire extinguisher on hand and wear thick clothing and shoes. Do not heat the material excessively - the bitumen may catch fire, and the base (especially polyester) may burn out.
Laying is usually done in two layers. The first layer (lining) is laid with an overlap, the second (finishing) - perpendicular to the first or with a large overlap to cover the seams of the lower layer. For flat roof garages, one layer of quality material such as Technoelast or two layers Bicrosta.
Selection and installation errors that reduce service life
One of the most common mistakes is laying the material in the cold season or during rain. Bituminous materials lose their elasticity in the cold, and when rolling out a roll, microcracks may form on the surface, which will become sources of destruction. The optimal temperature for installation is from +5°C to +25°C. Working in hot weather is also undesirable, since the material may deform under the installer’s feet before it cools down.
Insufficient heating of the seams leads to the formation of “pockets” where water flows. In winter it freezes and expands, breaking the connection. Visually, a high-quality seam should squeeze out a bead of bitumen mastic 1-2 cm wide along the entire length of the joint. The absence of this roller indicates underheating or insufficient pressure.
Ignoring connections to walls and ventilation pipes is another fatal mistake. Water often flows not through the center of the sheet, but along the perimeter. To seal vertical surfaces, it is necessary to use a weldable material extending into the vertical at least 20-25 cm, forming a fillet of mortar at the junction corner.
Secrets of long service
Experienced roofers recommend that before laying the finishing layer, sprinkle the joints and junctions with talcum powder or fine sand (if technology allows) to prevent sticking when storing rolls, but the main thing is not to walk on the newly laid hot coating, so as not to disturb the structure of the coating.
It is also worth mentioning the mistake of saving on the number of layers. One layer of the most expensive material may be less reliable than two layers of material in the average price category, since the probability of a through defect in a two-layer system tends to zero.
Alternatives and modern solutions for the garage
Although the question “which roofing felt to choose” remains relevant, the market offers alternatives that may be more convenient in specific conditions. For example, liquid rubber (sprayed waterproofing) creates a seamless coating of any shape, ideally flowing around pipes and antennas. However, its application requires special equipment, which makes the method less accessible for DIYers.
Membrane roofing (PVC, TPO, EPDM) is another option that is gaining popularity. It is mounted mechanically or with ballast, without fire. It is safe and fast, but the cost of materials is significantly higher than bitumen analogues. For a standard garage this may be redundant, but for a used roof (for example, if there is a terrace or recreation area planned there) this is the best choice.
However, classic weld overlay remains the gold standard for garage co-ops due to its price, availability and proven technology. Properly laid Bikrost or Linocrom will keep your garage dry for a decade, requiring only periodic visual inspection.
Helpful advice: If you are making a roof yourself without an assistant, cut the roll into sheets of the required length in advance. Rolling out and heating a heavy roll alone is extremely inconvenient and dangerous.
Is it possible to put roofing felt on an old coating?
Technically it is possible if the old coating is not swollen and holds firmly. However, experts recommend removing old layers in order to see the condition of the slabs and avoid a “pie” of many layers of bitumen, which can float in the summer from the heat. If you decide to lay on top, be sure to use a gas burner to heat the old layer.
How many layers of roofing felt are needed for a flat roof?
For a flat roof (slope up to 3 degrees), a minimum of two layers is required. The first layer is a lining layer (for example, Bikrost HPP), the second is roofing with protective coating (for example, Bikrost TCH). One layer is allowed only for temporary structures.
What is the difference between Bikrost and Ruberoid?
The main difference is in the base and installation method. Roofing felt is usually made on a cardboard base and glued to mastic. Bikrost has a base made of fiberglass or fiberglass and is mounted using the fusing method (melting the bottom layer with a burner), which provides better tightness.
Do you need a slope for water drainage?
Yes, even a minimal slope (1-2 degrees) is necessary. On a completely flat roof, water will stagnate, forming puddles that will accelerate the destruction of bitumen and increase the likelihood of leakage through microcracks. The slope can be created with a screed during repairs.