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Pitched roofs.

Case study: flat roof surface renewal

Renewal of large flat roof felt surfacing - Holbeck, Leeds

The approach

There are several different types of flat roofing systems available, each one with its own pros and cons. Roofing felt is a tried-and-tested option. Technical innovations in the past decade have made it even more reliable. The 'torch-on' method is now the most widely used method, replacing the poured bitumen approach.

The materials

The underlay layers of bituminous felt are comprised of a fibrous membrane made of glassfibre or polyester impregnated with bituminous bitumen.

The top surfacing layer, referred to as 'mineral felt' additionally comprises a mixture of sand and fine gravel. This layer is available in either green or red colours.

Durability

Torch on felt covering can be applied at any time of the year.

The material has good durability characterists: limited foot traffic across a felt roof won’t cause any serious issues and it will not be damaged by any falling debris.

Felt roofing is a mid-range cost option; neither the most expensive nor the cheapest. It provides real long-term value because of its durability and low maintenance requirements. If the roof suffers local damage or modifcations are required (such as penetration by new services) localised repairs are easy to make.

Application

On new roofs a bonding agent is applied to the substrate for the first layer. On roofs previously covered in felt, the upper layers are stripped off to establish a secure surface with which to bond.

The first two layers of felt are rolled on using a torch to activate the bituminised adhesive coating. These layers are waterproof but vapour permeable.

Each of the three layers is rolled out so that the joints are staggered.

Upstands and other features are modelled and interlaced with the felt layers.

Finally the top layer of mineral felt is 'torched-on'.

Make sure you hire a contractor that is experienced (and insured) for torch-on processes.

The gallery below illustrates the whole procedure.

DWGRoofing.

Replacing felt on an old flat roof - Holbeck, Leeds

 

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Finally, top coating of solar reflective surfacing.

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