Installation of Bituminous Membrane on a Gradually Sloping Roof

Installation of BMI Icopal bituminous covering

Waterproofing of gradually sloping roofs is normally done using bituminous membrane, a durable and flexible material. Bituminous covers are a so-called continuous type of covering, which means that their seams can withstand water pressure. As the term is used here, a “gradually sloping” roof is a roof with a pitch of 1:10 or less. To ensure drainage of water, even flat roofs should always have some amount of inclination towards the roof drains.

Waterproofing for a sloping roof should always be installed by a bitumen roofing professional

Installation of waterproofing on a sloping roof requires professional expertise, and as such, the installation described here should always be carried out by a professional who specialises in waterproofing bituminous roofs. Hot-work is normally required in this type of installation, so the installer must have a valid hot-work card and hot-work permit.

Installation instructions for bituminous membrane

On this page, you will find some illustrative instructional videos on the waterproofing of gradually sloping roofs. However, you should always follow the installation instructions – i.e. the work instructions – when installing bituminous membranes. The videos are not a substitute for the instructions on waterproofing of sloping roofs, or for waterproofing structures designed by structural engineers.

Installation of bituminous membrane – Instructional videos

Installation of thermal insulation on a gradually sloping roof

Underneath the thermal insulation is a vapour barrier membrane and a flat substrate. The thermal insulation should be installed on top of the vapour barrier membrane. Arrange the thermal insulation panels in place using a method known as “brick-stacking”, wherein the seams of the panels do not form a grid pattern. The seams of the thermal insulation layers should not be in the same spots – instead, they should be installed in such a way that they overlap each other. Work the thermal insulation into the proper shape using a wool-knife and a handsaw.

Slant adjustment on a sloping roof

A gradually sloping roof is never perfectly flat – it always has inclines that allow water to drain. As a general rule, such inclines are already built into the roof’s structure. In some cases, the slant of the roof is adjusted during the renovation of the roof, in order to ensure (e.g.) adequate sloping in the direction of the roof drains.

The slant is adjusted using expanded clay, on top of which grooved mineral wool or thermal insulation layers are installed. The waterproofing is installed on top of the thermal insulation layer.

Hot-gluing a bituminous membrane to a sloping roof

Some bituminous membranes are attached to their substrate by adhesive bonding. Melted bitumen is used as a bonding agent. Special care is required when working with hot bitumen – Stelox blown bitumen can be used at temperatures of 200 - 230°C, and Vedagum EBH rubber bitumen can be used at 170 - 210°C. The temperatures specified for the use of these materials must not be exceeded.

When you are working with/near a bitumen pot, certain equipment needs to be used, such as special “pot gloves” with long shafts for the arms to fit in, and tightenable openings to ensure that no molten bitumen gets on the inside of the gloves.

Welding a bituminous membrane to a gradually sloping roof

Welding of a bitumen membrane involves melting the protective plastic on the underside of the membrane and heating the bitumen to a molten state. Press the seams tightly into place; when doing this, ensure that a small amount of bitumen squirts out to a distance of at least 10 - 15 mm from the seam.

If one uses the stripe-welding option, only the stripes on the underside of the bitumen membrane should be melted. At the end-seams, the membrane should be heated so that it adheres to the substrate over the entire area of the seam.

Installing an upright section of membrane on a sloping roof

Upright sections serve to prevent water from getting into (e.g.) the joints between the roof and the wall structure. Upright sections are installed separately for the base and surface membranes, respectively. Base membrane: at the wall or eaves, bring the base membrane up to the top edge of the triangular lath, and press it tightly into place. Cut a separate upright piece from the membrane, as well, according to the dimensions of the wall or eaves – though it should be at least 300 mm – to be placed on the vertical surface at the joints of the wall.

Install the upright piece tightly against the eaves or wall, and also make it overlap with the roof surface. Secure the piece’s attachment using fasteners at the top. Surface membrane: weld the upright pieces on top of the base membrane pieces. They should extend a longer distance than the upright pieces of the base membrane, both on the roof surface and on the wall/eaves. At the eaves, turn the upright piece of the surface membrane so that it goes over the eaves, forming a so-called “flood” membrane.

Installing a roof drain on a sloping roof

A roof drain should be installed on a hard substrate. If the substrate is wool, then a separate sheet of plywood should be installed, attached using fasteners at the corners, to serve as the base for the roof drain. Install a LaippaPolar outlet-sealing membrane, with the gauze surface facing downwards, where the underside of the roof drain will be. Install the drain in place, and seal it, with another LaippaPolar membrane, which you should install with the gauze surface facing upwards this time. Thereafter, affix the base and surface membranes around the drain according to the instructions.

Installation of an underpressure vent, or other outlet, on a gradually sloping roof

Cut a hole in the substrate according to the size of the outlet you are installing. On the underside of where the outlet will be, install LaippaPolar outlet-sealing membrane, with the gauze surface facing downwards. Instal the outlet in place, and seal it, with another LaippaPolar membrane, which you should install with the gauze surface facing upwards this time. Thereafter, affix the base and surface membranes around the outlet, according to the instructions.

Installing an overflow pipe on a gradually sloping roof

Attach the base membrane at the eaves, extending it up the top of the triangular lath. In the eaves structures, make a hole for the outflow pipe. Cut a piece of the LaippaPolar outlet-sealing membrane to place where the underside of the outflow pipe will be, and weld it in place with the gauze surface face down.

Cut a hole in the LaippaPolar membrane for the outflow pipe. Install the outflow pipe in place, and seal it with another LaippaPolar membrane, which you should install with the gauze surface facing upwards this time. Thereafter, affix the base and surface membranes around the outflow pipe, according to the instructions.

Installing a drip tray on a gradually sloping roof

In the case of a clear-coloured tray, the surface should be roughened and pre-treated with a bitumen solution. In the case of a painted tray, the surface should be roughened. The drip tray should be installed 20 - 30 mm away from the end of the eaves. In double-layer covering structures, the drip tray should be installed between the base and surface membrane. The tray should be mounted with screws at intervals of 100 mm, in a zig-zag pattern.

At the continuation points, cut a 30 mm piece from off the drip edge of a panel to be inserted on the inside, and insert the cut panel into the other panel’s profile. Cut the corner points according to the profile of the panel, so that the panels will overlap with each other. Weld the surface membrane to the drip tray, and press it tightly into place.

Installation of expanded-clay roofing

Installation of expanded clay:
The grain size of expanded-clay roofing should be selected according to the thickness of the expanded-clay layer. Load the expanded clay into a lift-van and pour it, in an even layer, onto the area to be filled. Ensure that there is sufficient expanded-clay filling in the narrow and shallow spaces by shovelling the expanded clay into place. Finally, level the expanded clay according the top edge of the sloping laths.

Pouring a concrete slab:
Place the casting fabric under where the concrete casting will be, and add more fabric as the casting progresses. Pour the concrete in an even layer, and spread the concrete mix into an even and uniform layer. Level the surface of the concrete casting according to the edges of the drain, in such a way as to ensure that there will be adequate sloping in the direction of the drain.

Safety on the job

When one is working on a roof, safety is of paramount importance. Always follow the safety instructions for the job site where you are working, and do your part to make sure that it is safe for others to work on the site as well. In the installation of bituminous coverings, besides the general safety instructions, one should also take special care and caution when working with hot bitumen and when otherwise doing hot-work.

Icopal Katto Oy – general safety orientation

Everyone working on a construction site is responsible not only for their own safety, but also for the overall safety of the site. Watch the video to see Icopal Katto Oy’s general safety orientation.