substrate options - the nuances of choice and use, + photos and prices

The metal is absolutely waterproof, but this does not mean that waterproofing the roof of the house is not necessary for decking. Even when the sealing of the roof joints and attachment points is done correctly, and the roof in these places is not leaking, there is still condensation on the inner surface of the metal sheet. And it appears almost daily due to daily temperature fluctuations, atmospheric pressure and humidity. And although the waterproofing does not protect the seamy side of the professional sheet from moisture (as some authors claim), it removes it from the roof, does not allow the insulation and the elements of the supporting roof structure to get wet. From the article you will learn about materials for waterproofing, the rules for their selection and use.

substrate options - the nuances of choice and use, + photos and prices

The abundance of condensate is a characteristic feature of the roof from the profiled sheet

Waterproofing of various types of roofs

Decking as roofing Coatings are used in two types of pitched roofs:

  • non-insulated ;

  • insulated .

You can still talk about flat roofs, but there the profiled steel sheet is used as a flooring on which the entire roofing pie is laid. And in this case, according to the scheme of the device of such a roof, bitumen rolled materials and mastics (coated or sprayed), which are on top of the corrugated board and not under it, are responsible for waterproofing. And in order to move the "dew point" from the inner surface of the sheet, such a roof is insulated from the outside, protecting the insulation from the vapors from the side of the room by vapor-hydro insulation, which is spread over the ceiling.

substrate options - the nuances of choice and use, + photos and prices

Waterproofing is supplied and integrated into one "whole" with a drainage system

In sloped roofs, multilayer polymer films are used as waterproofing which almost completely displaced the ruberoid and its more modern analogues (rubemast, stekloizol and others) from this sphere.

In the “upper” part, the insulation scheme for corrugated roofing is the same:

  1. Rafter legs .

  2. Waterproofing .

  3. Counter-rail (remote rail).

  4. Lathing .

  5. Decking .

Important! In this scheme, a special place is given to the remote rail. It "sets" the air gap in the under-roof space, due to which the fumes are eroded beyond the roof, be it evaporating condensate and excess moisture from the insulation.

substrate options - the nuances of choice and use, + photos and prices

The standard ventilation scheme for the roof of the roof, the cold attic and the room

And here are the features of mounting the "lower" part of the scheme, as well as the choice materials for corrugated roofing, depends on the nature of the attic and even the slope of the slope. And above all, it concerns vapor-permeable waterproofing properties.

On our website you can find contacts of construction companies that offer the service of designing and conducting roofing works of any complexity. Directly to communicate with representatives, you can visit the exhibition of houses "Low-rise Country".

Materials and installation features of waterproofing

There are two main types of roof waterproofing films for decking:

  • with limited vapor permeability;

  • waterproof but with high vapor diffusivity.

Manufacturers refer to the first type of vapor-water insulation, the second - to the membranes.

substrate options - the nuances of choice and use, + photos and prices

The breathable membrane has microperforation

The choice of the type depends on the presence or absence of insulation.

Non-insulated roofs

A metal profiled roof (profiled sheet and metal tile) in a non-insulated roof behave completely differently than slate, ondulin or soft tile. Under these materials may not lay waterproofing at all - on their inner surface of the condensate is not formed. Although the manufacturer of ondulin and advises to lay a film Ondutis to improve the tightness of the roof (and this is understandable - he is an interested person).

Films with limited vapor permeability, that is, vapor barrier, are used as waterproofing of a cold roof made of corrugated flooring. This allows you to "cut off" most of the humid air in the attic from contact with the roof.

substrate options - the nuances of choice and use, + photos and prices

For waterproofing profiled sheets in a cold roof, it is better to choose a vapor barrier with an anti-condensate surface
Note! Attic of a cold roof must be well ventilated with its own natural ventilation system.

Waterproofing installation looks like this:

  • Laying start from below horizontal stripes. The film should sag slightly between the rafters, but not more than 2 cm. Sagging is necessary for collecting and “transporting” to the condensate cage.

  • Preliminary fixing of the film is performed with a stapler.

  • If necessary increase the length of the strip, the next segment overlap.Overlapping strips - more than 15 cm. The joint should lie on the rafter leg, and in addition it is sealed with tape with a double-sided self-adhesive strip.

substrate options - the nuances of choice and use, + photos and prices

With the tape also glue the joints with the adjacent surfaces, chimneys and pipes of the ventilation system
may be interesting! In the article on the following link read about materials for a soft roll roof.
  • The lower edge of the first band is put on the drip drop of the drainage system and secured with tape.

  • The next strip from the eaves is rolled out with an overlap of relative to the previous one. The size of the overlap - more than 15 cm. The joint is additionally taped.

  • Finally, fix the film with a lath that is nailed to the outer end of the rafter foot. The rake should be treated with antiseptic. On the side of the rail, facing the waterproofing, stick sealing tape.

  • On the slats they mount the crate for sheeting. The pitch of the batten depends on the slope of the roof and the type of profile.

This is an algorithm for working for one slope - for example, for waterproofing a roof of a balcony for decking.

For gable roofs and hip roofs, there is also a ridge area where the waterproofing installation of each ramp ends up not reaching 5-10 cm before it. This gap is necessary for ventilation of the entire attic and the gap between the roof and the waterproofing.

substrate options - the nuances of choice and use, + photos and prices

The gap in the ridge is then closed with an additional element

Waterproofing of the valley houses is carried out separately for multi-gable roofs:

  • film roll out in the direction of the valley end;

  • fix the film with a stapler to the floor valley and the neighboring truss legs (but not further than 30 cm);

  • the edge of the waterproofing of the right ramp leads beyond the leftmost board of the valley at 15 cm (excess cut);

  • the edge of the waterproofing of the left ramp leads to the far right endova board by 15 cm (the excess cut);

  • edges glue the connector hydrochloric ribbon and fixed to the rafters.

substrate options - the nuances of choice and use, + photos and prices

This is how the waterproofing scheme looks >
Important! The installation of a vapor-waterproofing film is carried out smooth side to the professional sheet. The rough side (with anti-condensate properties) is turned towards the attic.

If they plan to convert the cold attic later into the attic, then a membrane is chosen for waterproofing.

It may be interesting! In the article on the following link read about the structure of the built-up roof.

Insulated roofs

For waterproofing insulated roofs, diffusion or super diffusion membranes are used.

Diffusion membranes have a “medium” vapor permeability. And they can not "cope" with the load on weathering the excess moisture from the insulation. Especially if it is a metal roof. And with a small slope of the roof due to the slight difference in height and pressure between the eaves and the ridge, the intensity of ventilation may not be high enough to weather condensate. Therefore, for a metal roof, a laying scheme with two gaps under the roof is recommended:

  • Insulation is placed between the rafter legs so that a gap of 4-5 cm remains until their end. Second option - insulation is laid over the entire height of the rafters, and they are packed with a distance rail 4-5 cm thick.

  • A membrane is rolled over the distance rail with a slight sag 2 cm), and fasten with a stapler.

substrate options - the nuances of choice and use, + photos and prices

Waterproofing scheme for a metal roof with two ventilated gaps
  • per distance rail over the membrane, attach the counter rail with the sealing tape glued.

  • Next - mounting of the batten and sheeting.

The first gap is needed for ventilation of the insulation, the second - for ventilation of the “inside” of the roofing (condensate weathering).

Important! A scheme with waterproofing with a “conventional” diffusion membrane and two ventilated gaps is recommended for roofs with a slope of more than 35 °.

Super-diffusion membranes are laid in a different way - without a gap on the side of the insulation. They can be used on all pitched roofs covered with corrugated flooring, with a slope of 5. 5 °. In addition to the lack of a remote rail, membrane sagging and the presence of one ventilated gap, the rest of the installation of waterproofing is similar to the previous versions.

substrate options - the nuances of choice and use, + photos and prices

Two mansard roof schemes: with full insulation and waterproofing right up to the ridge, with its small “cold” attic
It can be interesting! In the article on the following link read about the passage of the chimney through the roof.

Major Manufacturers and Prices

“Intra-Specific” selection often depends on cost.And the price of waterproofing under the roofing on the roof is influenced by the density of materials, the number of layers, the strength of the ultimate load in the transverse and longitudinal direction, water and vapor permeability.

The most "simple" is water and vapor barrier films. They consist of two, three or four layers. The more layers, the more expensive the material.

Diffusion membranes, unlike vapor-moisture insulating films, have microperforation. “Holes” are capable of passing steam, but retain water due to the surface tension of water. If we talk about the differences between “ordinary” membranes and superdiffusion membranes, the difference lies in the number of holes per unit area and their diameter - the smaller the hole diameter, the greater the “height of the water column”, the larger the holes, the higher the vapor permeability. Naturally, superdiffusion membranes are more expensive than normal.

substrate options - the nuances of choice and use, + photos and prices

In the domestic trademark Izospan, one of the largest assortment of films and membranes

The ultimate strength depends on the density of waterproofing and the presence of reinforced layer of polypropylene mesh. Such materials have three or four layers. In addition, they may include as one of the layers:

  • at the vapor barrier and membranes - flame retardant fillers (for roofs with increased fireproof requirements);

  • for membranes — an additional anti-condensate layer or thread impregnated with carbon black (with an increased ability to hold and discharge condensate).

For the selection of diffusion membranes, see the following video:

The following is a list of some of the main brands of roof waterproofing for corrugated flooring, which can be bought in the domestic market:

  • Steam and hydro insulation for cold roofs. Izospan D (double-layer, unreinforced) - from 1500 rubles. per roll 70 m 2 . Izospan DM (three-layer, reinforced, with anti-condensate surface) - from 3000 rubles. for a roll. Ondutis RS (reinforced) - from 2190 rubles. per roll 75 m 2 . Yutafol H 110 Standard - from 2470 rubles. per roll 75 m 2 . Yutakon (four layers, reinforced, with anti-condensate surface) - from 4500 rubles. for 75 m 2 .

  • Waterproofing diffusion. Izospan A - from 1500 rub. over 70 m 2 . Ondutis A 120 (with double self-adhesive tape) - from 2070 rubles. for 75 m 2 . Yutafol D 96 - from 1560 rubles. for 75 m 2 . Yutafol D 110 - from 2470 rubles. for 75 m 2 .

  • Superdiffusion membranes . Izospan AM - from 2070 rubles. over 70 m 2 . Izospan AS - from 2900 rubles. over 70 m 2 . Izospan AQ proff - from 3890 rubles. over 70 m 2 . Ondutis Smart SA115 (with self-adhesive tape) - from 3100 rubles. for 75 m 2 . Yutavek 85 - from 3050 rubles. for 75 m 2 . Yutavek 115 - from 4000 rubles. for 75 m 2 . Yutavek 135 - from 5000 rubles. for 75 m 2 .

A clear overview of waterproofing materials can be found in this video:

It might be interesting! In the article on the following link read about the project of a cozy cottage in the Art Nouveau style on the ocean.


Even such a succinct description of various options for waterproofing a roof under corrugated flooring allows us to conclude about the complexity of its structure. Taking into account the nuances of the choice of materials of the required characteristics and properties, only professionals can design and carry out installation. Errors lead to wetting of the structural elements, insulation and overlap. And this is fraught with the loss of the bearing properties of the truss system, not to mention such “trifles” as the loss of the insulating qualities of the roof and the ceiling.


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