What is inversion roof

The overwhelming majority of mansions and cottages in Moscow and the Moscow region have pitched roofs. Flat roofs are rarely used and are most often used to cover protruding parts of a house, terraces, etc. Structurally, a traditional flat roof, often referred to as a “soft” roof, consists of a load-bearing slab on which a heat-insulating material (mineral wool slabs) is laid over a vapor barrier layer, protected from atmospheric precipitation by a waterproofing carpet based on bitumen-containing roll materials (Fig. 1).

However, this design has a number of disadvantages. It is not always possible to ensure the complete tightness of the vapor barrier layer, as a result of which water vapor penetrates into the thickness of the insulation and accumulates in it, since the dense waterproofing carpet prevents moisture evaporation. Over time, a lot of moisture accumulates in the insulation, which flows down, forming wet spots on the ceiling.In addition, at negative temperatures, water freezes, increases in volume and tears the waterproofing off from the base. During operation, the waterproofing carpet is exposed to climatic and mechanical influences, which leads to cracks through which water enters the room; leaks are formed, it is very difficult to establish and eliminate the cause of which.

Fig. 1

1 – floor slab
2 – fastening the insulation
3 – vapor barrier
4 – insulation
5 – waterproofing carpet
6 – additional insulation

Fig. 2

1 – overlap
2 – waterproofing carpet
3 – insulation made of extruded polystyrene foam
4 – filter material
5 – a layer of gravel with a thickness of at least 50 mm

There is an alternative constructive solution for a flat roof – the so-called. inversion roof, practically devoid of these disadvantages. Its difference lies in the fact that the insulating layer is located not under the waterproofing carpet, but above it (Fig. 2). This design protects the waterproofing layer from the damaging effects of ultraviolet rays, sudden temperature changes, freezing and thawing cycles, as well as mechanical damage, which provides an increase in the service life of an inverted roof compared to traditional (so-called “soft”) roofing. The design of the inverted roof allows you to use it as an exploited flat roof on which you can sunbathe, put a table and chairs, plant grass or arrange a flower garden.

On the reinforced concrete slab of the covering, along the screed (or without it), arrange a waterproofing carpet of two layers of “Filisol” or one layer of “Rooflite”, on top of which the insulation slabs are laid. A carpet of filter material is laid on the thermal insulation, and then gravel is poured. If the roof is in use, then paving slabs can be laid. Recommended slope of inverted roofs 2.5-5%.

During the operation of the roof, melt or rainwater flows down through the gravel layer, passes through the filter material, partially through the joints between the insulation plates and flows down the waterproofing carpet into the drainage devices.

Insulation for inversion coatings

For insulating an inverted roof, only non-hygroscopic materials are applicable that can maintain high thermal insulation characteristics in a humid environment. These requirements are met by extruded foams with closed pores, which have close to zero water absorption, good heat-shielding characteristics in a humid environment and sufficient strength..

Insulation protection in inverted roofs

To protect the insulation from floating, exposure to ultraviolet rays and strong winds, it is loaded with a layer of washed rolled gravel measuring 16-32 mm. Sand or gravel mixtures are not used as a loading material. The thickness of the gravel layer is taken depending on the thickness of the insulation slabs.

You can also use paving slabs or cobblestones as a weight. If you arrange a lawn or a small flower garden on the roof of the house, then the soil will play the role of a protective layer. This design is shown in Fig. 3.

The gravel layer is laid on a special filtering material (fiberglass, “Taipar” material, etc.), which passes water well, but is an obstacle to the passage of solid soil or sand particles. The filter material prevents the top (soil) layer of the exploited roof from being washed out and protects the insulation plates from siltation.

Fig. 3

1- reinforced concrete floor slab
2 – primer layer
3 – waterproofing carpet from roll materials
4 – extruded polystyrene foam
5 – filter material
6 – drainage layer of gravel
7 – filter material
8 – soil

Fig. 4

1 – reinforced concrete floor slab
2 – primer layer
3 – waterproofing carpet from roll materials
4 – extruded polystyrene foam
5 – filter material
6 – drainage layer of gravel
7 – metal apron
8 – cap of the drainage funnel
9 – additional layer of waterproofing

Structural elements of inversion cover

An important structural element is the junction of the drain funnel to the coating. Along the perimeter of the hole, it is necessary to lay an additional layer of waterproofing material, install a metal apron and ensure the slope of the waterproofing carpet towards the drain funnel (Fig. 4).

In order to ensure a reliable abutment of the inverted roof to the outer wall of the house, additional layers of waterproofing material are arranged in the junction zone, which are attached to the outer wall above the level of the coating (Fig. 5).

Fig. 5

1 – reinforced concrete floor slab
2 – primer layer
3 – waterproofing carpet from roll materials
4 – extruded polystyrene foam
5 – filter material
6 – drainage layer of gravel with a diameter of 4-8 mm
7 – drainage layer of gravel with a diameter of 16-32 mm
8-paving slabs
9 – soil layer (optional)
10 – outer wall
11 – non-hardening sealant
12 – metal apron
13 – outer wall cladding
14 – additional layer of waterproofing material

Fig. 6

1 – reinforced concrete floor slab
2 – primer layer
3 – waterproofing carpet from roll materials
4 – extruded polystyrene foam
5 – filter material
6 – a layer of gravel with a thickness of at least 50 mm
7 – drainage bed of fine (4-8 mm) gravel
8 – paving slabs flooring
9 – thermal insulation material

To improve the thermal insulation properties of the coating, as well as to exclude the likelihood of cracking in places where the waterproofing carpet bends, near the outer wall and parapets on the floor, it is advisable to make a bevel of thermal insulation material (Fig. 6). Protection of the insulation layer from mechanical damage and an increase in the resistance of the gravel layer to the effects of increased wind loads are achieved by laying concrete (sidewalk) tiles around the perimeter of the coating (along the parapet and the outer wall).

As already noted, the bulk of the water that enters the roof during rain or is formed as a result of melting snow flows through the gutters. However, a certain amount of moisture inevitably seeps into the gap between the insulation and the waterproofing carpet, from where it subsequently evaporates outward, passing through the joints of the insulation plates. Therefore, when installing an inverted roof with a top layer of materials with low vapor permeability (earth, concrete slabs, etc.), it is necessary to provide a drainage layer over the extruded polystyrene foam that does not interfere with the diffusion of water vapor, for example, a layer of crushed stone or fine gravel with fraction 4 -8 mm and a thickness of at least 20 mm (fig. 7).

Fig. 7

1 – overlap
2 – primer layer
3 – waterproofing carpet
4 – insulation
5 – filter material
6 – drainage layer of gravel
7 – paving slabs

Fig. 8

1 – the main layer of insulation
2 – waterproofing carpet
3 – an additional layer of insulation
4 – filter material
5 – ribbed floor slab

In cases where the supporting structures of the floor are made of thin ribbed slabs of small thickness, condensation may form on the inner surface of the floor due to the ingress of cold water under the insulation layer. To avoid this, it is recommended to provide for the installation of two layers of insulation material: one above the waterproofing carpet, the other (additional) – under it (Fig. 8).

Insulation of existing flat roofs

As one of the methods of insulating an existing flat roof, we can recommend converting it into an inversion roof. This type of insulation is possible only if the supporting structures are sufficiently strong. If there are no leaks, a layer of insulation is laid directly on the surface of the waterproofing carpet, if the waterproofing is in an unsatisfactory condition, it should be replaced or an additional layer of rolled waterproofing material should be laid. Slabs of extruded polystyrene foam are laid on the restored waterproofing carpet, on top of them – filtering material, followed by loading with a layer of gravel at least 50 mm thick (Fig. 9); it is also possible to arrange an exploited roof, as described above.

Fig. 9

1 – surcharge gravel layer
2 – filter layer
3 – insulation
4 – restored waterproofing carpet
5 – existing coverage

Fig. 10

1 – floor slab
2 – primer layer
3 – vapor barrier
4 – insulation of the existing roof
5 – restored waterproofing carpet
6 – an additional layer of insulation
7 – gravel backfill
8 – drain funnel
9 – wooden bar

Particular attention should be paid to the tightness of the waterproofing carpet in the place where the pipe passes from the drain funnel. If the existing roof did not have insulation, the funnel junction node is performed in accordance with Fig. 4; in the presence of an old insulating layer, the insulation material is selected along the perimeter of the funnel, and a wooden bar is laid on this place (Fig. 10).

Before inverting the existing flat roof along the perimeter of the covering, it is necessary to arrange a parapet with a height of at least 500 mm, which can be made of monolithic reinforced concrete.To do this, at the location of the future parapet in the reinforced concrete floor, holes are drilled into which the anchor rods are monolithic, The reinforcement frame of the parapet is connected to the anchor rods , install the formwork and fill the structure with concrete.

Fig. 11

1 – floor slab
2 – primer layer
3 – vapor barrier
4 – available insulation
5 – waterproofing carpet G – new thermal insulation (extruded polystyrene foam)
7 – gravel
8 – drainage layer (gravel with a diameter of 4-8 mm)
9 – paving slabs (along the entire perimeter of the roof)
10 – wedge made of heat-insulating material
11 – internal insulation of the parapet (extruded polystyrene foam)
12 – wooden beam
13 – fastening profile
14 – covering metal profile
15 – external thermal insulation of the wall and parapet
16 – hinged facade

Only after the parapet has been erected can work on the inversion roof be started. To exclude the possibility of freezing of the concrete floor, all surfaces of the parapet should be thermally insulated (Fig. 11).