What is roofing felt

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What is roofing felt

roofing felt

This material has been used for over a century. It is still popular among owners of suburban property. It is used as a roof covering for private houses and apartment buildings. According to many experts, it is indispensable for the arrangement of a layer that protects against water insulation and supporting structures of the roof. The coating has a small thickness, so it can serve as a protective layer in the bathroom and kitchen, where the probability of leaks is particularly high. Now on sale are many analogues that differ from each other in properties, price and appearance. In order not to make a mistake when choosing, it is necessary to understand what is a roofing felt, the size of the roll, its width and length.

Advantages and disadvantages

The ratio of price to quality makes the coating a great alternative to other materials.


  1. The main advantages are the low price and availability. Ruberoid is used everywhere, so it can easily be found at construction markets and in many specialized stores.
  2. Small mass makes the roofing structure easier. This can affect the cost of the entire building, as it will be possible to make the walls thinner, and the truss system less massive.
  3. The canvas is flexible and can be used on slopes with a complex configuration. The slope angle does not matter. This property makes the roofing felt unique. All of its analogues have limitations on these parameters.
  4. The coating is laid quickly. The work does not require special skills and professional equipment. The canvas is laid with an overlap of 10 cm and nailed to the crate. More complicated things are with floating materials. Here a certain skill is required. The work is performed using a gas torch. Bitumen is melted with it, and heated sheets are laid on top of it.
  5. The durability of products on a cardboard base is low. They are prone to rot if moisture penetrates them. In addition, cardboard is easily flammable. Modern varieties based on glass fleece and fiberglass do not burn and are fireproof.


  1. In the absence of mineral dusting and a protective film surface melts in heat and cracks in cold. Compared with the service life of corrugated board or shingles is not great. At best, the coating will last 15-20 years.
  2. The material does not allow moisture to seep, but, unlike concrete waterproofing, it will not be able to protect the basement from waterlogging. This method is not suitable for all types of soils.
  3. Decorative qualities leave much to be desired. To understand what a roofing membrane is, and how it looks, you need to imagine the roof of a paneled high-rise. The black, unsightly surface is hardly comparable to metal or ceramics. The situation is saved by flexible shingles. It does not look as smart as the real thing, but can compete with the usual corrugated board.

Varieties of material

The basis is a fiberglass fleece, glass fabric or a special roofing board. It is impregnated with liquid fusible bitumen, then on both sides applied refractory composition. To roll not to stick, the surface is sprinkled with talc, sand or asbestos. To increase moisture resistance, a polymer film is used. Coarse sprinkling on the outer side increases resistance to mechanical stress and increases service life. Polymer impregnation, increases frost resistance and prevents the penetration of moisture.

To make it easier to identify the purpose of products and get an idea of their properties, they are assigned a code. It consists of three letters, followed by the mass of one square meter of cardboard in grams. Its density and strenght depend on this index.

The first letter “P” always remains unchanged. The second indicates the type. “K” – roofing, “P” – lining. The third informs about the peculiarities of the material and what kind of sprinkling was used.

The labeling of roofing felt

K – coarse-grained;

M – fine-grained;

P – powdery;

CH – in the form of flakes;

E – high elasticity;

C – improved color fastness.

To understand what is the difference between the roofing felt RPP and RCP, it is enough to know where and how they are used. The first version is suitable for the construction of foundations, roofs with a small angle of slope. It performs the function of a waterproofing agent and is laid under the finish coating. The second applies both inside and outside. It is recommended to use only for roofs. They can replace the underlay insulator, but it is not profitable to do so, because it costs more. There are also other types of markings

T – glass fabric is used as the basis. Its fibers are arranged parallel to each other, which improves its characteristics;

X – fiberglass fleece. The fibers are arranged chaotically, which significantly reduces the tensile strength;

E – polyester. Its strength is lower than that of glass fleece;

P – the surface is covered with a film;

K – a mineral crumb.

If there are two letters “P” or “K” in the marking, it means that both sides are treated.

There are two types of waterproofing, differing in purpose – roofing (GI-K) and for the underground parts of the building (GI-G). There is also a liquid mastic – hydroisol PBK, which is applied with a brush. When cured, it forms a solid hard surface.

Products differ in density, type of sprinkling, method of laying and physical characteristics. 

roofing felt

Types of roofing felt

Tol, which is distinguished by a special impregnation that increases its strength. Its surface is sprinkled with stone chips, protecting the soft base from damage.

Pergamin – an ordinary roofing felt, which does not have improved properties.

Rubeemast – in contrast to parchment is a fusible material and is laid with a torch.

It is better to choose a coating based on the price-quality ratio. Tol has all the necessary properties. It protects well against moisture, but asphalt felt is cheaper. A good seal will provide rubemast, but at low temperatures it may have cracks. To avoid their formation, you need a coarse dusting.

There is a separate class of products in the manufacture of which the basis is not cardboard, and glass fabric or glass wool. It is more durable and has a good flexibility. The price difference is significant, but it pays off for a long service life. Glass fiber, unlike cardboard, is not afraid of water and does not rot when it gets inside.

Waterproofing is widely used. It is well suited for roofs, floors and foundations. After the bitumen impregnation, the canvas with one or both sides is covered with a polymer film that increases its resistance to negative temperatures, moisture and mechanical damage. There are varieties that use a sprinkle of coarse mineral crumbs instead of the film.

Good decorative properties have flexible tiles. Its front side repeats the shape of ceramic tiles, and mineral dressing creates a characteristic texture. As the basis is used glass fabric or glass wool.

Typical sizes of roofing felt: width, length and thickness

The thickness of the underlay material is from 2.5 to 4.5 mm, roofing – from 3 to 5 mm. In most cases, the canvas has a length of 10 m and a width of 1 m, but the current technical regulations allow you to increase its area twice. Dimensions are directly dependent on the brands. With a coarse mineral sprinkling, the length of the roll is 10 m, with a fine – 15 m. If the base is made of cardboard, the factory can produce twenty-meter rolls.

Dimensions depend on the mass of 1 m2 of roofing cardboard, glass fleece or glass fabric. With a standard width of 1 m for products marked “300” the area will be 20 m2. At a mass of 1 m2 of cloth, equal to 350 g, its value will be 15 m2. Rolls with an area of 10 m2 are available with a web weight of 300 g.

To find out how many meters in a roll of roofing felt, it is better to study the information on the packaging.

In the production process an error of 5 mm is allowed.