Warm roof ventilation requirements

Warm roofs are a type of roof construction that can include loft conversions, a ‘room in the roof ’ scenario, often created with dormer windows, or simply a roof. The sandwich warm deck roof is the most common type of flat roof. The insulation is placed below the waterproof covering and is either mechanically fixed or bitumen bonded on to the top of the deck. The enclosed void of a warm pitched roof does not require to be ventilated.

With the introduction of vapour permeable (plastics) underlays the need to create ventilated voids above inclined insulation and the requirement to ventilate cold roof lofts may be reduced.

The ventilation requirements of a pitched roof depends on the type of roof membrane used under the tiles or slates and battens to keep moisture or rainwater coming in from outside. If the roof covering or roof membrane is a material of high moisture resistance or impermeable, then the building regulations require a 50mm wide ventilation gap beneath the roofing felt and tiles. Ventilation at the Eaves.

Roof voids must be ventilated in order to stop warm air condensing on cold surfaces. Condensation encourages rot and mould growth. A vapour control layer is required on the warm side of the insulation to combat condensation. The warm deck roof as shown below has the insulation located above the deck.

The requirements will be met by the ventilation of those roofs where the moisture from the building can pass through the insulation.

Roofs with a pitch of 15° or more Pitched roof spaces should have ventilation openings at eaves level to promote cross- ventilation. No ventilation is required for these types of roofs. Warm Roofs To ventilate between the insulation and the underlay where the insulation is parallel with the roof covering through a min 50mm cavity from low level to high level. Always Compare Before You Buy! The Building Regulations demand eaves ventilation in most cold roofs and often high level ventilation as well.

Therefore, if a VPU is used the amount of ventilation should be less than for a bitumen underlay and more than for no underlay. There is no test data to determine the correct level of ventilation. Therefore, the levels of low and high level ventilation should remain unchanged for VPUs. In warm deck roofs , however, the insulation is positioned above the structural deck, and no ventilation is necessary as a result. The roof deck is kept at a temperature similar to the inside of the building throughout the year and this protects the roof structure from the hot and cold extremes, cutting down the thermal movement.

This traditional roof construction uses movement of air through the roof void to prevent the occurrence of harmful condensation. Get quotes from reliable roofers! Save time finding a local roofer.

Our new flat roof has moved from being a warm roof to a cold one. For roof design and specification p. A warm flat roof may require anywhere from 1to 200mm of insulation on top of the roof – depending upon the U-value requirements of the project. This requires a larger fascia detail and may make it difficult to meet planning requirements , as the roof grows in height.

A flat roof should be designed to minimise condensation and a condensation risk analysis should be undertaken taking into account positioning of insulating materials, vapour control layers, ventilation , thermal insulation and the choice of materials. This can be calculated using computer programmes. Pencast – Warm Roof Construction It is perhaps surprising, and certainly unfortunate that some building professionals, and contractors are under a misapprehension as to the precise requirements in order to achieve warm roof , an or cold roof construction.

To understand ventilation in roofs we must first recognise that there are many different roofs types. In Ireland the most common types are pitche lean-to and flat roof construction. Each of these roof types poses different challenges for ventilating a roof space. To ventilate a roof space adequately the type of roof structure must first be identified. Roof ventilation Roof ventilation Soffit vent type C Push in soffit vent Over fascia vent 1m over fascia vent Over fascia ventilation system Corbel vent Roof vent mkRoof vent mkcottage style Roll form eaves vent Insuvent 6m eaves vent pack Eaves comb.

The installation of a well constructed vapour control layer is pivotal to the success of a cold roof solution that incorporates the use of a vapour permeable underlay to achieve a reduction of traditional ventilation requirements. In exceptional circumstances where a warm deck construction is not possible, you may be permitted to install a reduced thickness of Polyisocyanurate (PIR) type insulation between the joists but a millimetre air gap must be maintained over it, where this solution is permitted the roof ventilation will need to be checked and increased to the levels as shown above for a pitched roof with a. INSULATED PITCHED ROOFING INTRODUCTI.