Loft Ventilation

Keeping A Loft Conversion Well Ventilated

by: Craig Ellyard

Converting the loft will automatically change the roof space from being a ‘cold roof' to a ‘warm roof'. This will greatly effect the ventilation in the roof and is often overlooked when a householder begins work on that new loft conversion project.

The original purpose of any loft was to act as a cold ventilation space that would expel any damp caused from rain or condensation. This cold roof space was then effectively sealed from the rest of the house by laying down layers of insulation material.

Of course, when a loft is converted, that barrier of insulation must be removed to the new roof level ceiling. And it is above that new ceiling where the loft conversion ventilation patch must be sited. If there is no ventilation above the new loft room than eventually the timbers will begin to rot because of dampness.

Making A Loft Ventilation Path

Before the new course of insulation is fitted a 50mm air space has to be left below the underfelt of the roof tiles. This allows air to escape from the roof space before it forms condensation by creating a ventilation path.

However, on its own a ventilation path will not afford adequate protection. To encourage a proper air flow there should be a small gaps or holes cut along the length of the eaves of the roof. This allows the air to enter from one side before exiting from the opposite side of the roof.

If the angle of the roof is more than 35 degrees than ridge vents may well have to be fitted; this would in effect form a vacuum which would suck up air from the eaves. However, if the house does not have any underfelt beneath the roof tiles, and this is often the case in older properties, than the air will escape naturally through the tiles meaning that ridge vents are not necessary.

Other Things To Consider About Loft Conversion Ventilation

Timber stud walls are used extensively in loft conversions to create storage space along the eaves. The interiors of the cupboards will obviously be well ventilated but they may be sitting on insulation from the bedroom ceilings.

This can cause black mould but won't be a problem as long as plastic ducts are fitted above the soffits. This allows the eaves to be ventilated but also retains that important insulation.

To allow adequate air flow where skylights have been fitted ventilation holes should be drilled into the rafters on each side of the window.

Loft Ventilation Technology

As with everything else the use of new technology makes many of the old rules obsolete and this is true enough in the case of loft conversion ventilation.

Most new roofs are now built with insulation boards installed above the rafters. The use of the insulation boards negates the need for ventilation by creating a warm roof space. The use of new breather membranes as underlay in the roof also means that the need to create ventilation paths is greatly reduced when converting the loft.

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