A Quick Guide on How to Felt (and Refelt) a Flat Roof

Felt is a popular material amongst roofing professionals and DIYers alike since it used for covering a variety of surfaces, including flat, shed, and garage roofs, and porches to name a few. The main reasons why felt is so commonly used are: it is lightweight, easy to install, and budget-friendly. On the downside, felt tends to rip and tear, which is why refelting is sometimes needed. Today, we are talking about roof felting and how to felt (and refelt) a flat roof specifically.

How to Felt a Flat Roof?

Tools and items that you are going to need to felt a flat roof include felt, felt adhesive, paint brush, hammer, nails, and, optionally, gravel. Once you have everything near at hand, follow these steps:

  1. Climb the roof and measure its length and width by using a tape measure. You’ll get a certain square footage you’ll need to multiply by 3 to get the right amount of felt to cover the roof 3 times. However, make sure you purchase some extra felt so you can cover the edges as well.
  2. Once you have purchased the felt, climb up the roof again, unroll the felt, and leave it like that for 30 minutes to 1 hour so that it gets more flexible and easier to manipulate.
  3. Meanwhile, remove ripped pieces of felt or all the felt if you want to refelt your flat roof completely.
  4. Inspect the roof to check if there is any damage that needs to be repaired and move on to the next step if there is none.
  5. Lay down the first layer of felt and start nailing it down with a hammer while making sure the space between the nails is around 5 inches.
  6. Take a paint brush and apply a thin layer of adhesive over the felt. Remove all the bubbles and flatten all the bumps on the felt while going over it with a brush.
  7. Place the second layer of felt over the first one. Yet, don’t follow the same path but make 2-inch overlaps to ensure all of the surface is well covered and protected. Nail the second layer of felt down, and cover it with felt adhesive followed by the third layer.
  8. Cover the final layer of felt in adhesive (it should be dry within 24 to 48 hours, depending on the weather conditions).
  9. Optionally, cover the entire roof and felt with some gravel.

Tar paper is an organic alternative to felt when it comes to roofing, however it is not as resistant to sun and wind. More about the difference between the two can be found on this link.

How to Felt Edges and Corners of a Flat Roof?

To felt edges and corners of a flat roof the right way, leave some felt to overhand when felting the roof itself. Once you have placed all of the layers, cut away excess felt using an utility knife, fold the felt around the corners, and nail them down.

Refelting a Flat Roof

Refelting a flat roof is a must if some of the felt is in poor condition since under-the-felt leaks can damage your shed and water can easily find the way into your home. You can either add an extra layer of torch-on felt or patch the critical areas. We’ve already explained how to felt a flat roof with cold adhesive so make sure to use a hot gun or a paint brush to apply adhesive before adding another layer of felt or a couple of patches. If you discover that most of the felt has aged and became teared down, our advice is to refelt your flat roof with new felt entirely.

Frequently Asked Questions

1. How many layers of felt should be placed on a flat roof?

At least 2 layers of felt (3 ideally) should be placed on a flat roof to create a waterproof barrier and protect the shed and your home from the elements.

2. How much does felting and refelting a flat roof cost?

Felting a flat roof can cost somewhere between £2,000 and £7,500 (depending on the size of the roof) while refelting typically costs between £500 and £2,000.


Felting and refelting a flat roof is certainly not an uphill battle. However, even if you know how to felt a flat roof, you’ll maybe still want to hire a professional contractor for this type of job. If you live in areas such as Beckenham, Chislehurst, Blackheath, and Orpington, we’ll be more than glad to help with any kind of roofing, building, and maintenance job you need to get done. Here, you can find out more about the numerous projects we delivered. Having any questions about our services, contact us via this form and we’ll reply within the shortest time frame possible.