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How to felt a flat roof Roofing

How to felt a flat roof

Posted on 24 September, 2021

Fitting felt to a flat roof is a big task but one which must certainly be undertaken. Additionally, with a little support, research and preparation it is something you will be able to get the hang of and successfully do.

Positively, felt is a lightweight and affordable way of preserving your home and making your garages and sheds more long-lasting whilst simultaneously protecting your property by keeping the space dry. Felt prevents water damage from seeping into spaces. If water is allowed to impact roofs then it could cause rot or damage which in the mildest way might lead to dampness but most seriously could cause structural problems.

In this article, we will discuss how best to felt a flat roof and the most effective ways to fit the material, whether you are doing it for the first time or replacing it.

What do you need to felt a flat roof?

Sometimes aspiring handymen can get over-excited by the prospect of doing this project and buy only the felt. However, in order to successfully install the felt you will need a few important tools so make sure you check your toolbox and if anything is missing, add it to the shopping list.

What we will need:

  • Felt
  • Hammer
  • Felt adhesive (choice is yours but ask for recommendations)
  • Galvanised nails
  • Tape measure
  • Paint Brush
  • Gravel (if you would like)

Preparing the roof

Once you have acquired or found all of these items you can start preparing the roof. Before fixing the felt, you need to make sure that the roof is in a good condition and there are no signs of rot or water damage. If you find any problems, the roof may need to be tended to before attaching the felt. This is particularly true if the building in question is made of timber such as a garden shed.

Secondly, measure the roof accurately. The last thing any builder wants is to cut the felt and find out they’ve wasted a large proportion of it as the measurements were wrong. Triple check the length and width of the flat roof before starting.

Thirdly and this may sound odd but check the weather. Not only will spending a day outside in the cold and rain be rather miserable it could also have an adverse impact on the overall process and the longevity of the felt. The purpose of the felt is to protect roofs from water damage, however, if you begin working on the roof whilst it rains it could allow for rot to set in and even make the process volatile and unstable. Pick a warm or at least dry day to start the task and not only will this be more enjoyable but more sensible as well.

Adding the felt

Having measured the felt, cut it out and lay it on the roof surface for 30 to 40 minutes before hammering in the nails. This will make the process easier.

Primarily, place one layer on the roof and holding it firmly hammering the galvanised nails into the roof, starting at the centre and moving along. Once you have done this, you will want to add a layer of adhesive. You must add the second and third layers on top, repeating the step of adding adhesive in between. The key here is to make sure there are no air bubbles when you place the felt upon one another.

Once this has been completed walk over the roof to flatten it and add a final layer of adhesive. At this point, you may consider adding gravel however this is optional and maybe an aesthetic choice. Additionally, some people like to add solar paint to the roof. This can prevent the roof from overheating however, this is not a necessity but will likely increase the lifespan of the felt and delay having to replace it.


Hopefully, you can see that fitting felt isn’t as complicated as you might have imagined but it does require patience and planning. If you follow the steps above and buy all the materials you need in advance then there is a good chance you will be able to complete the task competently and effectively.

However, if you do have any further questions or want some recommendations, feel free to get in touch with our team and we would be happy to help.

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