A general rule in modern roof covering practice is that beyond the primary layer of covering, there is a secondary line of defence. This is the underlayment, which may consist of roofing membrane and waterproofing sheets, though roofing membrane is the more common solution. The roofing membrane is laid from meter-wide rolls directly over the rafters, with a 20-centimeter overlap, progressing from bottom to top. This membrane ensures that if precipitation penetrates the primary covering due to extreme weather conditions or cover damage, the underlayment directs the water away from the structure. The membrane is secured to the rafters by nailing counter-battens over it. The roofing battens or decking, onto which the final covering will be placed, are then attached to the counter-battens. The free airspace (cavity) created between the counter-battens plays an important role; allowing the area between the primary covering and the underlayment to be ventilated. The benefit of this ventilation is twofold: it serves to dry out water that has penetrated from the outside and moisture that has condensed from the interior space, and provides thermal protection against the overheating of the structure and the interior space.
It is also important to consider the vapour permeability of the roofing membrane. Based on this property, we differentiate between vapour-permeable and vapour-barrier membranes.
-
For simple attics or undeveloped roof spaces, a vapour-permeable membrane can be used, led over the ridge. This allows the vapour generated in the attic space to diffuse through the membrane into the ventilated cavity. This configuration is called a singly ventilated roof system.
-
If a vapour-barrier membrane is used, the membrane must be interrupted near the ridge, and a strip of membrane must be led over the ridge and secured to the upper side of the counter-battens with a 10-15 cm overlap onto the lower membrane layer. This configuration provides additional ventilation for the interior space. This is the model of a doubly ventilated roof.
For modern inhabited attics or converted roof spaces, only the simpler, singly ventilated version with a vapour-permeable membrane is used. Here, we can choose to completely fill the available space between the rafters with fibrous thermal insulation, which is essential for the thermal protection of the interior space. We must also ensure that the thermal insulation between the rafters is protected from the vapour of the interior space; thus, a vapour-barrier membrane is necessary on the interior side, typically in the layer beneath the plasterboard lining.
Another essential element of modern roof coverings is professionally-executed flashing at critical points for the roof covering, such as:
A further key task at the eaves is to collect runoff water in the gutter and direct it away using a downpipe. Gutters and downpipes can be made of zinc sheeting, galvanized steel sheeting, aluminium, or copper sheeting. The flanged sheets of the semi-circular or square-profile gutter are attached to the rafters with gutter brackets. From the gutter, collected precipitation flows to the downpipe through outlet connectors, from which a swan neck is formed beneath the eaves and secured to the wall with clamps and threaded rods. Finally, the underside of the eaves must be enclosed, typically achieved using boarding, tongue-and-groove paneling, or boxing in the eaves.
Installation of small-element coverings:
-
Create space for the eave boarding at the ends of the rafters;
-
Install the eave-line boarding and verge flashing (gable boarding);
-
Install the underlayment by layering roofing membrane and securing it with counter-battens, creating ventilation near the ridge.
-
Secure the eave board and roofing battens;
-
Install the guttering with gutter brackets, at a 2.5-3% slope, assemble the gutter downpipes, form the swan necks.
-
Form the verge flashings and penetrations;
-
Place and secure the tiles. Ventilating tiles are placed near the ridge, and ridge tiles are fixed on the ridge.
-
Position the ridge battens with ridge batten brackets.
-
Lay the ridge underlays and secure the ridge tiles.
