Venting The Roof - General Priciples
The principle of roof venting is as follows: with the help of sun the air inside of the roof is heated. Based on difference in temperatures of the air layer and the exterrior it comes to the rising (ascending) hot air stream that tends to be exhausted by the vents placed in the upper part of the roof (usually the ridge vents or venting fans placed near the ridge line).
In the second step of the same process the fresh (and colder) air is taken in through the intake vents (soffit intake vents usually).
This is very important as the hotter air can absorbe more water (vapour) and when contacted with the cold surface, the vapour would
condensate (become water again) and moisture the roof.
Orientation of the roof for better passive roof ventilation
Strength and direction of the wind is also very important with the roof venting - the intake vents shall always be oriented towards the windy side of the roof.
In order to achieve the proper roof air ventilation it is necessary to make the air between the roof layers within the roof jacket flow following the above mentioned principle without any substantial obstacles.
Roof ventilation effectiveness
The roof ventilation effectiveness dpends on the following factors:
- the pitch of the roof;
- the active surface of the roof;
- the (in roof kept) air volume;
- the shape of the intake and exhaust roof vents;
- the dimension of the intake and exhaust roof vents;
- the location of the intake and exhaust roof vents;
- the distance between the intake and exhaust roof vents;
- the coverage of the intake and exhaust roof vents;
- the relative humidity of the interrior;
- the diffusive resistance of the roofing (surface);
- the orientation of the intake roofing vents towards the windy side of the roof;
