Vapour Barriers Up-Stands and Skirting for Flat Roofing

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Vapour barriers are applicable to all flat roofing systems

Vapour barriers are important and applicable to all types of flat roofing systems.

A properly installed flat roof system should include a vapour control layer. A vapour control restricts water vapour from the dwelling damaging the insulation in a warm deck scenario ie: where the insulating material is fitted to the roof decking.

Over time condensation can also cause any timber or support joists to rot. Replacing this is an extremely costly procedure, so to avoid this problem a vapour barrier control layer and insulation should always be fitted in your flat roofing system.

When fitting insulation between the roof joist it is imperative the space is well ventilated. Condensation can build up over long periods and will cause the timber structure to rot.

The vapour control layer is the first layer of the flat roofing to be installed. It is installed directly to the roof decking and should be fixed to the decking with clout head nails and sealed on the laps and perimeter. Few are aware of the importance of this layer, but when you consider the amount of moisture that can build up in a standard house you’ll understand why these are necessary.

A typical family home with two adults and two children living under normal conditions can create up to ten Litres of moisture over a 24 hour period. The moisture or water vapour has to go somewhere, and unfortunately not enough properties are adequately ventilated or insulated correctly to deal with this.

The list below highlights some factors that may indicate that your property is at risk from poor ventilation.

  • Noticeable vapour in the inside of your property.
  • Moisture in building materials.
  • Moisture build-up on the floor, windows, or the walls of your property.
  • Black mould usually on external walls.

Excessive vapour and condensation build up is more common in some properties than others. Older buildings usually have walls without insulation or cavities, and traditionally they had adequate ventilation from chimneys, draughty windows and doors. With modern living, home owners seal up the chimneys, fit sealed double glazed windows and doors, and the roof, more often than not, will have been renewed with a non permeable felt underlay.

These new developments cut out all the previous forms of ventilation and heat the property during the winter months. The warmer air will carry higher levels of moisture. Air will shed this excess moisture when it meets a cold surface. This is called the dew point.

Properties with swimming pools will be exposed to particularly high levels of water vapour. Some rooms of every property are also more susceptible to vapour damage than others. Kitchens and bathrooms, for example, are more likely to suffer from problems with condensation.

Controlling moisture in a property is very important. Specialist building contractors will be able to assist and make recommendations. If your property meets any of the criteria that has been highlighted in this article, it is best to get professional help immediately, as delaying it could make matters worse.

Flat roof vapour barrier installations

Up-stands and skirting for flat roofs.

On up-stands or skirting that is not timber or lightweight concrete and is below 300mm in height, two coats of mastic Asphalt are required to create a combined thickness of no less than 13mm.

On up-stands or skirting that is not timber or lightweight concrete and is above 300mm in height, three coats of mastic Asphalt are required to create a combined thickness of no less than 20mm.

Two coats may be acceptable in areas that are not exposed to the outside, for example, tanking rooms or mechanical service areas
 On up-stands or skirting that is timber and lightweight concrete, three coats of mastic Asphalt are required to create a combined thickness of 20mm. This needs to be applied on expanded metal lathing using a separating membrane.

On up-stands and skirting which has expanded metal lathing that is attached to concrete, brickwork or block work, three coats of mastic Asphalt to a combined thickness of 20mm will need to be applied. This includes a separating membrane.

Read more about the different types of Popular Flat Roofing Materials available.

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