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 re-felting is sometimes needed. Today, we are talking about roof felting and how to felt (and re-felt) 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 will get a certain square footage you will 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 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 re-felt 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 whilst 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.
  10. 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 a utility knife, fold the felt around the corners, and nail them down.

Refelting a Flat Roof

Re-felting 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 have 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 re-felt your flat roof with new felt entirely.

Get quotes from roofing professionals to determine accurate re-felting costs for all your roofing requirements including but not limited to garage felt roof and more. Trust our roof felting guides for how to properly install and re-felt flat roofs. Contact us to transform your roof with professional flat roof felting services.

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 re-felting typically costs between £500 and £2,000.

3. How to properly felt a flat roof using cold adhesive?

To properly felt a flat roof using cold adhesive, first ensure the roof deck is clean and dry. Plan the layout and cut felt rolls to size, allowing for overlaps. Apply cold adhesive evenly using a notched trowel, roller or brush. Roll out the underlay, smoothing it and pressing down firmly. Ensure overlaps are securely bonded with adhesive.

4. What are the key considerations when choosing felt for a garage roof?

When choosing felt for a garage roof, key considerations are the weight/density, UV resistance, and warranty period of the material. Heavier mineral felt is very durable. A reputable brand with UV protection and a 10+ year warranty is recommended.

5. What is the cost to re-felt a flat roof, and what factors influence pricing?

The cost to re-felt a flat roof typically ranges from £50-£100 per square meter. Key factors influencing cost include the roof size and pitch, ease of access, number of protrusions like vents, choice of felt material, and professional labour fees.

6. Are there specific techniques for folding felt roof corners during installation?

Yes, there are specific techniques for neatly folding felt roof corners during installation. The key is pre-creasing or cutting the felt diagonally so it can be folded without buckling. Corners should be securely bonded with adhesive to prevent leaks.

7. How much does it typically cost to re-felt a garage roof?

To re-felt a standard single garage roof typically costs £500-£2,000 depending on size. Larger or commercial garages may cost £2,000-£5,000. Pitch, access, materials and labour impact pricing.

8. What are the common materials required for flat roof felting projects?

Common materials required are felt rolls, underlay, adhesive, nails/staples, edge trims, sealant, and accessories like drain connectors. A torch may be needed if using heat-bonded felt. Safety equipment is also essential.

9. Can homeowners undertake DIY felt and re-felt projects, or is professional help recommended?

DIY felting is possible but challenging. Hiring a professional roofer is highly recommended for proper installation, waterproofing and longevity. Mistakes can lead to leaks, mould and enormous repair costs.

10. What are the potential challenges and solutions when felting a flat roof?

Potential challenges include securing the felt on windy days, cuts and tears in the felt, getting clean overlaps, and properly sealing complex joints. Solutions involve taking time and care, plus using adequate adhesive.

11. Is there a recommended maintenance routine for felted flat roofs to prolong their lifespan?

It’s recommended to inspect felt roofs annually, clean debris from the surface, check seals and flashings, and recoat every 5-10 years. This can prolong the lifespan of the felt significantly.

12. Are there environmental considerations when choosing felt for flat roof applications?

More eco-friendly felt options include recycled rubber and EPDM synthetic felt. These have higher upfront costs but longer warranties. Disposing of old bitumen felt responsibly is also important.


Felting and re-felting a flat roof is certainly not an uphill battle. However, even if you know how to felt a flat roof, you will 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 will 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 will reply within the shortest time frame possible.