Mounting of roof membranes

This guide shows instructions for:

  • Roof membranes - with high vapour diffusion of an SD-value < 0,1m.
  • Roof foils - with a low vapour diffusion of an SD-value > 0,1m.

By the use of roof foil it is necesary to leave a 2-4cm ventilation gap between the foil and tharmal insulation, through which the overflow of vapour will lead away. It is obligatory to leave open holes in the eaves and ridge for the proper ventilation. While useing a membrane(with high diffusion) we can forget the gap in favor of filling thee whole space with thermal insulation. In both cases it is a must to mak a ventilation gap between the foil/membrane and the roof covering. This remark concerns especially metal tiles, becouse of the large temeperature changes and enhanced condensation processes. Almost all roof foils and membranes thanks, to UV stable additives, can be left for a certain time without mounting the final roof covering. The time is specified individually for each sort of membrane and foil by the producer. Not obeing this requirement can lead to the total disintegration of the foil duue to the influance of UV rays. It is fair to say, that the shorter the time of full exposure to sunlight the more certain the long usage and lifetime of the product. It is also noticable, that the requirement also specifies the covering of the parts of membrane/foil that stand outside the buildings cube from underneath. Not mounting the under eaves covering, can also lead to wreckage due to the influance of diffused sunlight.

The choice between roof foils and membranes depends on, if th construction space of the roof should fully be filled with thermal insulation. While useing roof foil You sould leave some space between the foil and insulation. In practice, the correct way of mounting the insulation with the ventilation gap is somewhat troublesome. In the instance of building an attic without the thermal insulation, there is no need for useing a membrane. The usage of roof foil will be perfectly common and economically excused. When building a loft it is better to use a membrane. When filling the whole „thickness“ of the roof with thermal insulation we achieve better insulation parameters. To insure the windtightness of the membrane or foil it is advised to use special adhesive tapes to seal the overlapings, which will stop the migrating of free air from the outside of the building into the roof.

 

RULES OF MOUNTING PAROTEC MEMBRANES AND ROOF FOILS

 

COVERING THE ROOF WITH STRIPS

The mounting of the foil or membrane should start with a single strip in the bottom of the roof epanse, parallel to the eaves. With just a slight tense, the strip should be secured to the rafters with the help of staples or tacks.

 

 

NAILING THE COUNTER-BATTENS AND BATTENS

Nail the counter-battens and battens through the extensed foil or membrane, the counter-battens should have a strip of foam tape (purotec) between the counter-batten and foil/membrane. The next strips schould be layed with a 10-15cm overlap by roofs with an angle above 20°. By roofs with an angel under 20° the overlap should be larger, about 20cm.

 

 

MAKEING A GUTTER OUT OF THE MEMBRANE

By elements which stand above the roof expanse, there should be a membrane gutter made, this gutter should be then fixed to the battens with for instance butyl adhesive tape.

 

 

MOUNTING THE MEMBRANE OR FOIL ROUND SMALL ELEMNTS THAT STAND ABOVE THE ROOF EXPANSE

By small elements, like: ventilation pipes or masts, the foil or membrane should be cut in the shape of a trapezoid, the free ends should be then fixed to the battens.

 
 

MOUNTING PAROTEC MEMBRANES - FOLLOW UP

 

While useing PAROTEC membranes w deal with only a single ventilation gap, becouse the whole space under the membrane is filled with insulation. This requires the use of other solutions then those by the use of roof foils.

 

LEADING THE MEMBRANE OUT UNDER THE GUTTER

The correct mounting of roof foils at the eaves will ensrue a propper roof ventilation. The surface of the ventilation holes should be at least 0,3% of the whole roof surface but not less then 300cm² for 1m of eaves. Use counter-battens of thickness of 40mm. The shown on the side solution with leading the foil out under the gutter is better and ensures:

  • an early detection of leaks in the roof covering
  • more reliable ventilation, when the gutter and roof are full of snow
  • a limited possibility of snow beeing blown in under the covering.
 

 

LEADING THE MEMBRANE OUT INTO THE GUTTER

The solution with leading the membrane out into the gutter, takes quite an accurate touch. Requires the use of a ventilation profile. The additional fault of this solution, is the possibility, that the ventilation will be blocked by the snow stranded on the roof. Possible leaks can be discovered too late. While useing a membrane instead of roof foil it is not necessary to leave ventilationn gap on the ridge and under the membrane on the eaves.

 

 

CLOSING THE FOIL ON THE RIDGE

On the side You can see an example how the membrane should be mounted on the ridge. The surface of air outlets in the ridge should be as big as ½ of the air inlet holes on the eaves.

 
 

MOUNTING PAROTEC FOIL - FOLLOW UP

 

 

LEADING OUT THE MEMBRANE UNDER THE GUTTER

When useing roof foils it is necessary to make ventilation gaps under and over the foil. Becouse of the need to ensure propper ventilation, the surface of the air inlets at the eaves should be at least 0,2% of the roof surface but no less then 200cm² for each 1m of eaves. The surface of ari outlets in the ridge should be ½ of the air inlets surface. The ounting of the foil should end 5cm from the ridge. The minimal Thickness of the counter-battens should be 24mm. The minimal thickness of the ventilation gap under the foil should have 20mm. For roofs covered with metal tiles etc. The thickness of the countr-batten should change to mnimum 32mm. In proportion with that should also the surface of the inlets be changed.

 

 

LEADING OUT THE FOIL UNDER THE GUTTER

Generally there are two ways of mounting the membrane or foil at the eaves. On the side you can find a scheme of the solution with foil lead out under the gutter. Such solution ensures:

  • an early detection of leaks in the roof covering
  • more reliable ventilation, when the gutter and roof are full of snow
  • a limited possibility of snow beeing blown in under the covering.
 

 

LEADING OUT A ROOF FOIL UNDER THE GUTTER

The second way of mounting the roof foil on the eaves is leading it out into the gutter. This solution does not however ensure the early detection of leaky covering, what could lead to roof damages. By such solution it is very likely to make some mistakes by the mounting like substitution of the eavs vent profile with a common batten, what leads to reducing of the air inlets. The remarks and advice shown in this instruction do not cover all the aspects and ways of mounting foils or membranes.