Roof waterproofing: materials and methods of installation

Recommendation points

• Waterproofing tasks
• Types and scope
• Application of coating waterproofing
• Installation of membranes
• Using roll materials
• Matching the type of roofing

Roofing is not the only barrier against moisture penetration into the supporting system and insulation cake. The basis of protection against condensation and residual penetration of atmospheric precipitation is provided by waterproofing. What it happens and how to correctly perform the installation are the main topics of our today’s review..

Waterproofing tasks

Roof coverings, with very few exceptions, do not provide absolute protection of the roof from getting wet. The organization of an additional hydro-barrier immediately under the crate has several goals at once:

1. If it is possible to shift the dew point to the border of the roofing, condensation drops on the rafter system and insulation are excluded;
2. When using such coating materials as slate, seam roofing or metal tiles, the seepage of rain or melt water flowing down them is excluded;
3. Protection of mineral insulation from weathering is provided;
4. Eliminates the risk of damage to the roof system due to damage to the coating or installation errors.

The need for a device under a waterproofing coating is determined by considering two general cases of the type of roof – cold or warm. In other words, waterproofing must be present in the composition of the warm roof cake, that is, with a thermal protection belt. An exception to this rule is roofs, the insulation of which was carried out according to a careful thermal engineering calculation, in which the dew point coordinate range is entirely inside the hydrophobic layer..

In the case of a cold roof, waterproofing is usually not required. If the installation of the coating is performed in accordance with the manufacturer’s recommendations, the only source of moisture in the space under the roof is condensation from daily temperature drops. Its formation can be neglected only if intensive ventilation of the under-roof space is provided..

Types and scope

When choosing the type of waterproofing, one should move from general cases to specific ones. In general, materials for roofing waterproofing can be classified according to the following criteria:

1. Mounting method. This can be adhesive, hardfacing, spraying or mechanical fixing. This criterion must correspond to the type of insulation (it is impossible to fuse over polystyrene foam) and the material used for the roof covering.
2. The ability to pass water vapor. In some cases, it makes no sense to make a complex crate system with two ventilation circuits, it is much easier to ensure the removal of moisture-saturated air through a diffuse or superdiffuse membrane capable of passing steam and retaining water droplets falling on the outside.
3. Optimal thermal mode of operation. The material must be resistant to heating of the roof from sunlight and at the same time retain its properties at low temperatures.
4. Mechanical strength and maintainability. During the installation of the roof covering, the waterproofing can be subjected to significant loads, it must maintain its integrity until the completion of the flooring.
5. Seamlessness. For slopes with a slope of less than 15 °, this is a mandatory requirement, because in case of a leak, water will have time to find a way under the roof. In the case of using rolled and welded materials, it is required to provide a solid overlap value – about 20 cm, which ultimately results in a significant overspending of materials.

Application of coating waterproofing

The most specific type of waterproofing is considered to be seamless coatings applied to a continuous sheathing or base. Three main types can be distinguished here:

• bituminous mastics of atmospheric hardening;
• bituminous melts;
• spraying materials.

In the first two cases, the application takes place according to a relatively simple scheme. The main thing is to ensure a high adhesion rate by removing dust, dirt, oil stains from the crate surface. Sometimes it is practiced to grind the wooden base before lightening, it is also possible to process with primers, which are compatible in composition with the waterproofing material.

Mastics and bituminous melts are among the most proven and effective types of waterproofing. They are mainly used for low pitched roofs as well as flat and inverted roofs. If this type of waterproofing subsequently becomes a finished roofing covering, its thickness should be at least 15–20 mm, and at least two layers of reinforcement with cardboard (tar paper) or fiberglass are required. If the waterproofing will be protected from atmospheric and mechanical influences, a layer of 2-3 mm is sufficient. Reinforcement is required only with a significant drop in temperatures in winter, as a rule, this mark is from -15 ° С to -20 ° С.

Spray-on insulation on the Russian market is represented by liquid rubber and polyurea compounds. The main advantages of this method are high speed of work performance, resistance to negative influences and an absolute degree of water protection, which lasts for at least 20-30 years. You will not be able to arrange such a hydro-barrier yourself; special equipment is required.

Installation of membranes

A feature of membrane materials is their ability to pass steam limitedly, while retaining water in a liquid state of aggregation. Thus, diffuse membranes retain the ability to ventilate the insulation, but qualitatively protect it from condensation.

Installation of membranes should be carried out so that their outer plane is in the ventilated space. In this case, continuous ventilation along the slope from the eaves to the ridge in the vertical direction must be ensured. Since in the classic roofing scheme, the battens are arranged horizontally, using diffuse membranes, it is necessary to fix them with distance battens, leaving space for ventilation and for water droplets to roll down.

Diagram of a roofing pie for a gable roof with a classic wooden rafter system: 1 – roofing material; 2 – skate; 3 – rafter system; 4 – vertical lathing to form a ventilation gap; 5 – horizontal lathing for fastening the roofing material; 6 – waterproofing

With superdiffuse membranes, this requirement is not so strict. Due to their own porous structure, they are able to absorb a significant part of the moisture and then give it to the air during the process of limited ventilation. The air space should not be continuous, small enough gaps due to the relief of the wave roofing material. However, in both cases, the installation of ventilation outlets in the ridge area is mandatory..

The membranes are rolled horizontally from the cornice upwards. The overlap between the membranes is from 50 to 200 mm from different manufacturers and is glued on both sides. Quality materials have an adhesive backed edge hidden under the protective tape and overlap rationing markings. One of the mandatory requirements for the installation of films and membranes is the absence of tension when attached to the rafter system. The free sag helps to neutralize the manifestations of temperature deformations and ensures efficient drainage of accumulated water. There are also recommendations for waterproofing mechanical fastening points by applying universal sealants under the pressure strip.

Using roll materials

Roofing material, waterproofing films and windproof hydrophobic burlap are laid mainly in the vertical direction on slopes with a slope of more than 40 ° and horizontally with more gentle slopes. The main specificity of the installation of roll waterproofing is the thorough sealing of overlaps.

So, when laying roofing material, one edge of an already rolled strip turns away and heats up until black shiny droplets of bitumen appear. Then an adjacent strip is pressed against it and rolled, which, after hardening, folds back onto the rafter system. The disadvantage of roofing material in this regard is high fragility. A more practical alternative is the so-called weld-on roof, reinforced with rotting fibers or a woven base, for example, glass-insulated or SBS-cloth. When laying rolled bitumen materials on a solid crate or flat roof, it is widely practiced to warm up the back side of the sheets for gluing over the entire area.

When waterproofing with polymer films with a homogeneous structure, they are sealed with special adhesives. Since most films have a non-polar polymer structure, their bonding is possible only after special processing to enhance adhesion. In the conditions of construction projects, the most common etching of the glued areas with a chromium mixture or treatment with strong solvents (toluene, trichlorethylene) with a short heating with a building hair dryer After processing, bonding with rubber or polyurethane glue is possible.

PVC films are devoid of the disadvantage of low adhesion ability; they can also have a reinforcing reinforcement, for example, from glass fabric. The cost of such waterproofing is much higher, which is offset by higher strength, service life and installation speed. The fixing of films on the rafter system is carried out by analogy with membrane materials: with sealing of the fixation points and without tension.

Matching the type of roofing

As a conclusion, we note that the choice of the type of roof waterproofing and layer thickness should be determined by the type of roofing used. So, budget options like metal tiles or profiled sheets are largely susceptible to weakening of the sealing washers over time, and therefore the waterproofing under them must be able to withstand a significant amount of incoming moisture. Here, it is preferable to use diffusion membranes and PVC films on a fabric basis..

For slate or bitumen shingles, the use of roofing material or its more modern analogue, glass-insulated, is widely practiced. There is a great risk of damage to the roofing itself, respectively, the flow of moisture can be even more abundant than through the attachment points, especially during periods of thawing of ice and snow masses. Several layers of deposited insulation help to maintain the waterproof properties of the roof before repairs.

For many roofing materials, only the materials recommended by the manufacturer should be used. For example, for soft tiles, the use of third-party waterproofing materials is not allowed, only a branded underlay carpet. This is due to the fact that the roofing materials for which the guarantee is provided are not coatings in the usual sense, but complex roofing systems that can perform their functions efficiently only if all the components are present and the installation technique is followed..