Please do not hesitate to contact us on 0330 123 1885 or email your requirements to [email protected] where we would be happy to provide you with the most up to date lead times or work with you to find suitable alternatives.

A Guide to Bituminous Felts for Flat Roofing


18th April 2018

There are many different types of flat roofing systems available, each one with their own pros and cons. Roofing felt is one of the oldest available options and advances made in the past decade or so have begun to move more towards the 'torch-on' approach. This is now one of the most widely used systems across the UK.

We’ve put together a guide to flat roof felting to help you learn more about this material. Learn how it's laid, the cost implications and the benefits it could offer you below.

What is Bituminous Felt?

Bituminous felt is a form of waterproof sheeting that is used to cover flat roofs, 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.

Roofing-Felt-SIG - Laying Roofing Felt - Roof Stores
Laying Roofing Felt

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.


FIX-R FXR009CR Roof Performance Resin Clear 9kg

FIX-R FXR009CR Roof Performance Resin Clear 9kg

FIX-R FXR009CR Roof Performance Resin Clear 9kg
Buy online now

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 for professional contractors is 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: Whether you expect the roof to experience high levels of foot traffic, or very little at all, you will want it to stand the test of time. 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. Felt roofing is also not the most expensive option, so as a mid-tier solution it offers an affordable and cost-effective alternative. This can also be seen in the low-level maintenance required over time, which reduces the need for repairs and associated costs.
  • Versatility: While this article is concerned with flat roofing, the versatility of torch-on felt roofing must also be discussed, as it can be used on pitched or curved roofing if required. Therefore, it remains one of the most popular options on the market for numerous professional installation companies.

How to Install Roofing Felt

Follow the steps below to learn more the basics of roof felt installation and what is required before undertaking this type of roofing project:

  1. Remove any debris that may interfere with the installation process.
  2. Secure metal flashing at the edges of the roof before primer is applied. This will enable the felt to bond with it more easily.
  3. The first bituminous membrane sheet should then be positioned onto the roof before being secured to the surface, typically using a nail gun.
  4. 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.
  5. 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.
  6. Once the bitumen is rolled back into position on top of the membrane, the two can begin to bond together.
  7. The same process is repeated across the entire surface of the roof.

Note: If there is any old roofing material in place, in some cases torch-on felt can be applied directly on top. Please check with a professional before setting out on a DIY roofing project.

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.

Roofing-Felt-SIG - Torch-on Bitumen Felt - Roof Stores
Torch-on Bitumen Felt

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?

Browse the links below for the most up to date pricing of roofing felt products available at Roof Stores.

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 AndersonTotal Torch Vapour Control Layer is a popular choice for this type of installation and isn’t prohibitively priced.

The torch-on felt solution relies on a three-layer system, which will require two levels of underlay underneath the cap sheet. Anderson Toptorch SBS SB2 Torch-on Underlay is a solid option, with rolls that cover 16m length, 1m width and have a thickness of 1.5mm available for a manageable outlay.

Anderson Tecnatorch SBS 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, so ensure you measure correctly. However, even for larger projects, this is still an affordable option.

How Much Bituminous Felt Does a Typical Flat Roof Require?

Unfortunately, there isn’t one answer that can solve this query for everyone. You must calculate the total area of your roof in metres squared to understand how much material will be needed. More complex roofs with several planes will use more material than normal to produce an even finish.

It should also be born in mind that the costs listed in our roofing felt section only account for the felting material itself and doesn’t factor in the tools needed for the installation process.

When you contact an installation company they should offer a free site visit to estimate the scale of the job. Once they produce a quote this will also include all the material and labour costs. This will help you assess how it fits in with your budget.


© Roof Stores 2020 - Part of SIG plc