Bituminous Felts for Flat Roofing for Annexe

Roofing felt for annexes is one of the oldest available options and advances made in the past decade mean the ‘torch-on’ approach is the best option for many. This is now one of the most widely used systems across the UK for annexes with flat roofs.

What is Bituminous Felt?

Bituminous felt is a form of waterproof sheeting that is used to cover flat roofs on annexes, or as an underlay beneath slate or tile roofing. The substance itself is made from bitumen which comes from the distillation of crude oil that has been either mixed with sand or crushed limestone.

This is then applied to a fibrous membrane which is typically made of fibreglass, polyester or hessian. An extra coating of sand or fine gravel can be added on top to improve the aesthetic appeal.

The two main methods of its application are pour & roll and torch-on.

What are the Benefits of Roofing Felt?

Torch-on felt roofing has become increasingly popular in recent years – these are the main advantages of this method:

  • Installation: One of the main benefits of bituminous felt is the ease of installation. The same can also be said about repairs which, while rarely required, can be seen to quickly and efficiently. Torch-on felt roofing is very much an all-year-round application as its installation cannot be affected by the temperamental British weather.
  • Durability: Felt roofing is a highly durable option that holds up well to UV rays and excessive heat during warmer periods of the year. This is equally true in wetter seasons. Limited foot traffic across a felt roof won’t cause any serious issues and it should not be pierced or damaged by any falling debris.
  • Value: Felt roofing always offers a great return on investment. While not the cheapest option on the market, the quality of its material allows it to provide real long-term value. This can also be seen in the low-level maintenance required over time, which reduces the need for repairs and associated costs.

How to Install Roofing Felt

  • Remove any debris that may interfere with the installation process.
  • Secure metal flashing at the edges of the roof before primer is applied. This will enable the felt to bond with it more easily.
  • The first bituminous membrane sheet should then be positioned onto the roof before being secured to the surface, typically using a nail gun.
  • The first layer of modified bitumen is then laid over the membrane before being cut to size to fit the surrounding area. The membrane used must have a polyester carrier to ensure good tensile strength.
  • Half of the bitumen is then rolled up before the flame torch can be used to fire into the underside. Take care to evenly heat the bitumen.
  • Once the bitumen is rolled back into position on top of the membrane, the two can begin to bond together.
  • The same process is repeated across the entire surface of the roof.

What is the Lifespan of Roofing Felt?

Much of this will depend on how well the material is maintained over the years. Although felt requires relatively low-level checks, it can still be prone to damage in extreme weather. The local environment, footfall and how quickly any repairs are dealt with will also be determining factors.

The durability of felt is one of its main plus points. Depending on the manufacturer, the minimum guarantee you will receive is 10 years. However, it is commonly thought amongst roofing experts that torch-on felt can last beyond 30 years in many cases. Of course, this is as long as the roof is well maintained.

How Much Does Roofing Felt Cost?

It’s always helpful to have a good idea of cost before you commit to a roofing project. While roofing felt isn’t the cheapest, it’s one of the most effective systems. The prices are certainly within most people’s budget.

Roofs that feature insulation on the outside of the structure will require a vapour control layer to prevent the rise of condensation.

The torch-on felt solution relies on a three-layer system, which will require two levels of underlay underneath the cap sheet.

Torch-on Mineral Felt Capsheet is used as the final layer of the felt roofing process. It’s available in rolls that are 8m long and 1m wide, with a thickness of 4.2mm (Mineral) or 3.8mm (Sand). Of course, how many rolls you need will depend on the size of the roof.