Condensation encourages rot and mould growth.
Roof space ventilation building regulations.
If a building is less than 10 metres wide and the roof pitch is less than 35 degrees then 10mm eaves ventilation is required.
Then aim for about 1 sq.
Cold roofs versus warm roofs.
Ventilation 2010 edition incorporating 2010 and 2013 amendments ref.
Roof insulation thermal resistance at roof perimeter should be equal or greater to thermal resistance of exterior wall.
The building code lets you reduce that by half under some conditions but more roof ventilation is usually better.
And current best practice.
Ventilation is not required to a warm roof system which is where the insulation is placed above the joists or rafters.
The air gap dimensions shown on the drawings are the minimum widths required for clear continuous ventilation air paths at the eaves.
Otherwise ventilation is required and this is known as a cold roof system.
Therefore it s important that the ventilation slots aren t blocked.
Ventilation of attic spaces is required by most building codes as well as by roofing material manufacturers and the national roofing contractors association nrca.
In of vent opening per 150 sq.
When ventilating a roof the air should be able to enter at one end and travel through to the other end where it can exit.
Duo pitch roofs greater than 200 pitch or greater than 10m span should have additional ventilation at the ridge to assist airflow through the roof void equivalent to at least a 3 mm wide continuous gap.
Isbn 978 1 85946 679 7 pdf 683kb this file may not be suitable for users of assistive technology.
If the attic is equipped with high and low ventilation openings the requirement is 1.
Around 25 per cent of heat loss occurs through a building s roof but high levels of insulation in historic roofs can be counter productive sometimes even accelerating heat loss in the long term.
Roof voids must be ventilated in order to stop warm air condensing on cold surfaces.
In many pitched roofs a ventilation slot is built in along two opposite eaves so that air can flow across the roof space.
You can also contact your local municipality to check on building code in your area.
Attics must have a minimum of 1 square foot of ventilation openings for every 150 square feet of floor space.
Cold roof with impermeable hr underlay if a building is 10 metres wide or more or the roof pitch 35 degrees or above then 10mm eaves ventilation is required together with 5mm ridge ventilation.
The recommended ventilation ratio to provide for vented attic assemblies when an air barrier is present is the 1 300 ratio as specified by most building codes.
The open area of a vent is sometimes listed on the roof air vent as nfva net free vent area.
Both building regulations and nhbc require ventilation to be provided in roof spaces.
Jonathan taylor s article unpacks the key issues including the role of moisture ventilation and buffering.
1 300 ventilation ratio recommended.
