VENTILATION

                     Eave to Eave Ventilation                                                        Eave to Ridge Ventilation

The principal of all ventilation methods and systems is to allow a passage of air into the loft space, circulate and then leave, taking any water vapour from within the loft space to the outside. A basic method is to allow air to enter at one side at the eave, and leave at the opposite side.  A more reliable method is to allow to enter at one or both eaves, circulate and the to leave via the ridge.

To insulate a loft space effectively, the insulation material should be taken into the eave area. This has the effect of creating an air tight seal which  does not allow for any air flow. To prevent this problem preformed corrugated plastic trays are fitted to suppress the insulation allowing a passage of air between the underside of the roof covering and the insulation. Air can be allowed into the loft space by a ventilated soffit strip (diagram), over fascia ventilators or by soffit ventilators.

Ventilation at high level can be provided by ridge vents. These are purpose made units made by all the leading manufactures to complement their range of ridge tiles. These units may also be used to ventilate a soil vent pipe via a flexi pipe. Alternatively a 'dryfix' ventilated ridge system could be used which provides a continuous line of ventilation across the ridge. 

The roof area must be properly ventilated to control condensation in accordance

with The Building  Regulations 1985 (amended 1990). The need for ventilation

is a consequence of modern building materials and methods, higher

standards of insulation, increased draught proofing and our lifestyles.

Condensation is caused by water vapour generated by washing machines,

showers, baths, central heating systems and by ourselves. Warm air is able to

hold more water vapour than colder air. Able to pass through brick, plaster

board and insulation materials, water vapour will rise through the property

into the roof space. The roof space is generally the coldest place within the

property and the air and water vapour will cool. Trapped within the roof space,

 this cold air can not hold the quantity of water vapour as when it was warmer

and so the water vapour condenses into water. This is called the 'dew point'. 

The effects of persistent condensation can cause severe damage in several ways:

• Timber: Causing swelling and distortion. Prolonged exposure may result in potentially dangerous weakening of the roof structure due to  rotting timber
• Insulation: Many insulation materials will lose their insulating properties when wet. Prolonged exposure may result in mould or fungal growth.
• Ceilings: In severe cases condensation may soak through ceilings into the habitable area causing damage to fixings, fittings and electrical installations. An unsightly dark gray band may appear around the edges of the ceiling.

THE NEED FOR VENTILATION

VENTILATION METHODS

EAVE VENTILATION (LOW LEVEL VENTILATION)

RIDGE VENTILATION (HIGH LEVEL VENTILATION)