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How to felt a flat roof

Ever wondered how to felt a flat roof? Our handy guide is here to help, with instructions, repair tips for leaks, and answers to your FAQs.

Using felt to protect shed and outhouse roofs is very popular, and it isn’t hard to see why. Felt is affordable and very lightweight, making it easy to install and repair, even for those who aren’t experienced in DIY. So, if you want to learn how to felt a flat roof, you’re in the right place.

This guide is designed to teach you how to felt different types of flat roof, from garages to extensions. You’ll also learn what the best felt to use is and how to repair a leaking flat felt roof.

How to felt a flat roof

Choosing felt as a cover for your flat roof is a great decision. It looks great whilst not breaking the bank. Plus, where felt installation used to be complex, it’s now simple enough for any budding DIY enthusiast.

best felt for flat roof

Before you start learning how to felt a flat roof, you’ll need to collect a few essentials. These include:

  • Felt
  • Hammer
  • Felt adhesive
  • Tape measure
  • Gravel (optional)
  • Galvanised nails
  • Paint brush for use with the adhesive

When you have everything you need to hand, you should properly prepare the old roof. Do this by removing any old pieces of felt, checking for damage to the roof or timber and making any necessary repairs. Next, you can begin by following these steps:

  1. Carefully measure your flat roof with a tape measure. Check you have enough felt to cover the space at least 3 times.
  2. Lay out your felt on the roof surface and wait about 30 – 40 mins before continuing. This will make installation easier.
  3. Place your first layer of felt on the roof and make sure you hold it tightly in place. Hammer your nails through the felt into the roof, starting at the centre of one side and moving along the edges in 5cm intervals.
  4. If you need to add another sheet of felt, then lay this next to the first sheet with a 5cm overlap. Again, nail down the felt.
  5. Next, cover your felt sheets with a thin layer of felt adhesive.
  6. You can then position the second layer of felt over the first. Make sure you flatten the felt, removing any air bubbles, then nail it in place.
  7. Add another thin layer of adhesive and lay the third and final sheet of felt over the top of the second layer.
  8. Again, make sure there are no air bubbles and that your final layer of felt overlaps the flat roof by more than 5cm.
  9. Walk over your newly laid felt to completely flatten the surface.
  10. Finally, add one more layer of adhesive and consider adding a layer of gravel over the top.

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repairing a flat roof with feltHow to felt a flat shed roof

Felt is a very popular covering for shed roofs, protecting the contents of your shed from the elements and looking great. If your old shed covering is damaged or worn, now’s the perfect time to learn how to felt a flat shed roof. As shed roofs tend to not be designed to support the weight of an adult, using a steady ladder is a must for this project.

Use the following tips to cover your shed:

  • Measure twice before cutting your felt to size. Human error is always a risk when using a tape measure so be certain you have measured correctly.
  • Ensure you allow enough felt to overhang the edges of your shed roof on three sides.
  • Use layers of felt to create a durable waterproof surface.
  • When it comes to finishing the edges of your shed roof, use our ‘how to felt edges and corners of a flat roof’ section below.

How to felt edges and corners of a flat roof

When you are laying felt, it’s important to know how to felt the edges and corners of a flat roof. This may seem a little tricky at first, but you’ll soon get the hang of it. The most important thing is to allow an overhang when felting your roof.

Once you have finished laying your felt you can use a sharp utility knife to cut away any excess felt. You can then neatly fold the felt in the corners and nail it in place.

How to felt a flat roof on a garage

If you’re planning to learn how to felt a flat roof on a garage, you’ll need to ensure you purchase enough of the material to cover the large surface. You’ll also need to properly prepare the roof by removing any old roofing materials, then sweeping up any debris and ensuring the surface is dry.

Also, ensure anytime you switch to a new piece of felt you leave at least a 5cm overlap to prevent leaks in your garage. Once you’re ready to begin, follow the steps in our ‘how to felt a flat roof’ section.

How to felt a flat roof extension

As with garage and shed roofs, laying felt on a flat roof extension needs to be done correctly to prevent future issues. Wondering how to felt a flat roof extension? Use the instructions in our ‘how to felt a flat roof’ section.

What is the best felt for a flat roof?

It can also be useful to know what the best felt for a flat roof is. There are three separate types of felt for flat roofs to choose from. Below is a brief summary of each type:

  • Shed felt: Perfect for garage or shed roofs, this type of felt looks great and is easy to install but will need to be waterproofed.
  • Torch-on felt: You’ll need a blow torch in order to install torch-on felt, so this isn’t the best option for DIY beginners. It is however brilliant for creating a watertight seal and is installed in three layers.
  • Self-adhesive felt: Thankfully, you won’t need a blow torch for this type of felt, instead it adheres to your roof without the need for felt adhesive. Self-adhesive felt is also long-lasting and affordable.

Felting a roof Repairing a flat roof with felt

When your roof covering is in need of repair, this can lead to leaks and rotting timber, causing damage to your shed and its contents. As such, repairing a flat roof with felt is a good option to protect your possessions and shed.

There are a few methods of repairing a flat roof with felt, the most common of these are:

  • Extra layer: It’s possible to add a new layer of felt on the top of your flat roof. The best way to do this is to use torch-on felt, although this can be dangerous. Hiring a professional to tackle this hazardous job is a fantastic option.
  • Patch repair: If the damaged area is small, a patch repair may be the most suitable option. The way to do this is to add your patch ensuring it overlaps the current felt layers by about 5cm and use felt adhesive to fix it in place.

How to repair a leaking flat felt roof

If water starts to drip into your shed or garage, particularly after it rains, you unfortunately have a leak to deal with. The first step is to locate the leak. This can be tricky because leaks often run under the felt and along the roof of your shed before finding a hole to drip through.

You’ll usually be able to spot a torn or damaged area in the felt that needs to be repaired but if the felt is in poor condition in general, it may be better to replace the whole thing. Once you’ve spotted the leak, you’ll need to learn how to repair a leaking flat felt roof. There are a few types of damage that may need to be repaired, below is a summary of the two most common issues:

  • Tears: Carefully check the roof is not damaged under the tear, then clean the felt around the split. Add a layer of felt adhesive under the tear and push flat while it sets. Next cut a patch of felt that’s big enough to overlap the edges of the split by 5cm. Finally, use adhesive to stick the patch over the tear and press down.
  • Bubbles: Again, clean around the blister, then create a crosscut in the blister using a utility knife. Gently lift the four flaps and ensure the roof underneath is clean and undamaged. Stick the felt down using adhesive or a hot gun. Then cover with a patch, allowing a 5cm overlap before sticking in place.

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using blowtorch to felt a flat roofFAQs

How do you put roofing felt on a flat roof?

As described earlier, felt is a great covering for any type of flat roof. Wondering “how do you put roofing felt on a flat roof?” Well, just follow the steps in our ‘how to felt a flat roof’ section.

Can you felt a flat roof?

Yes, you can felt a flat roof. In fact, this is a brilliant option if you’re looking for an affordable, easy to install way of protecting your garage or shed.

How many layers of felt should a flat roof have?

Adding several layers of felt to your roof will help to create a waterproof covering, protecting your possessions from the elements. But how many layers of felt should a flat roof have? We’d recommend using three layers for great results.

Professional flat roof felting

Felting a flat roof used to be a complex, hazardous process but luckily it’s now much simpler. While we’ve designed this guide for people with different skill levels, this can still be a little too difficult for beginners. If you do feel out of your depth, it’s better to seek help than do a substandard job, which could cause untold damage to your flat roof.

Thankfully, using our handy search feature is the perfect way to reach a range of local professionals. Just enter your postcode and let us do the hard work for you.

How much does refelting a roof cost?

If you plan to use an expert to refelt your roof, you may be interested in how much this will cost. The price you pay will of course depend on a number of factors and our refelting a roof cost guide covers these and so much more.

Alternatively, another excellent resource is our replacing roof felt under tiles cost guide. This article is also bursting with tips and guidance to help with your project.

Typically you can expect to pay:

  • The average cost of refelting a roof is £600 for a medium-sized shed.
  • The average cost of replacing roof felt under tiles is between £2,000 – £7,300.

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