Felt Roofing Guide

How to Lay Felt Roofing

Covering a roof with felt is a tidy and effective way of protecting a roof, especially since good quality felt is extremely durable. Fixing it to a roof can be done quickly and simply when using the correct tools and taking care when planning, measuring and preparing.

If you are installing felt onto a new roof, or if you are replacing old felt, this guide is designed to walk you through each step in completing the project.

Safety – Be Smart.

Even if you think the height you are working at is nothing, no matter what you are doing there is always the possibility of getting injured. To protect yourself make sure that you are wearing suitable protective gear and clothing like shoes with good grip, gloves and a hard hat.

The project will require a large number of nails, so a box to hold all your nails may come in handy before they become a threat to safety.

Being stood on a sloped roof should try to be avoided as you can become unbalanced so easily. To work directly on the roof, you should use boards or sections of ladder that are fixed to the roof, in order to spread the weight across a larger surface area, providing a sturdy platform to work off of.

Materials – More Is Better

Obviously, you will need enough felt to be able to cover the roof, as well as adhesive and nails. Therefore, if you do not know the exact amount needed (more likely than not), then you should always expect to need more than you have calculated.

As well as the materials you will need a number of tools, these include a claw hammer, a crowbar/pry bar, a brush or roller to spread the adhesive, a knife with a hooked blade and a spade if you need to remove heat-bonded felt.

Preparation – Old Felt & Roof Structure

Before you even consider taking the roofing felt off, check that the roof structure is sound and is able to endure the removal of the felt. Also check that the roof substrate is good enough to be re-roofed, if not then a new deck needs to be fitted.

Before you remove all the felt from the roof, first you need to remove the barge boards along the edge of the roof. Any external or decorative objects need to be removed carefully, to do this gently place your crow/pry bar behind and wiggle to pull the nail out of place, before putting it into your box of nails. If removing the nail this way doesn’t work, try using a spade.

If the felt has been heat-bonded, it might be difficult to remove. A big, flat head spade will most likely be the best tool for the job. To remove the felt, scrape the felt using any rises or gaps to get the process started. It is recommended to do this on a cooler day so that the bond doesn’t encounter any more heat. Nails used alongside the bonding system need to be removed to avoid penetrating the new waterproofing.

Felt that has not gone through heat-bonding will be easier to remove and should be able to be taken off without the use of any tools.

With the old felt removed, make sure there are no nails or other objects sticking out of the wood, as this can easily damage the new felt.

Preparation – The New Felt 

Ensuring that you have measured everything correctly is extremely important at this stage since you have to factor in the overlap required. Starting with the width of the roof, you will need to give an extra 50-75mm at the front and back of the roof behind the barge boards.

Roll the felt out onto a level surface and calculate the width required, using the lap joint as a reference to keep measurements level. Starting with the width, you will need to leave 50-75mm at the front and back of the roof behind the barge boards.

After cutting the first section, do the same thing for opposite side of the roof. You should end up with two strips that will cover the width of the roof, but if they do not cover all of it, don’t worry we will explain how to fix this later.

Laying Out The Felt

First of all, you need to calculate the amount of overhang needed at the lowest edge of the roof, this is to prevent water from reaching the underside of the roof. Roll out the felt onto the roof and adjust it as necessary for the overhang on all sides. If you want the felt to stay in place, place a nail at the highest corner to temporarily fasten it in place.

Ensure that you never hammer a nail completely through the timber so it pierces through the inside edge, but hammer it enough for it to sit flush against the felt.

When you are happy that all of your measurements are correct, hammer down the nails and hammer in more on the lap joint at centres of around 150mm. Keep all nails in the upper half of the lap joint in order to leave space for the ridge nails.

Stop nailing as soon as the lap joint is securely fastened, then do the same to the opposite side.

Now begin to fix the felt to the lowest edge of the roof, pull it tight in a corner and fix it temporarily with a nail under the eaves. Work along the edge, nailing at around 120mm centres, making sure that the felt doesn’t fold or ruche up at all.

Now move onto the sides of the felt. Pull it tight over the side of the roof, and starting at the higher edge, fix it in place using nails. Work down to the corner and fasten it in place. This can be done in multiple ways, you can fold the felt into a triangle over the side of the roof, or you can cut at the corner of the felt and cross the two strips.

Bigger nails will need to fasten this in place since it will need to be driven through two layers of felt. Repeat this step for the opposite side.

The Ridge – Laying Felt

Calculate and measure the space that needs covering with a final strip of felt. It should start 10-20mm inside of the outer edge of the lap joint on either side, in order to cover both sides with felt.

Measure the middle and bottom edges of the roof, ensuring that the measurements taken are correct all the way along. Ensure that you have accounted for the overlap required along the front and back of the roof.

Cut the strip and lay it on the roof. Fix it in position for the moment on the side and fold it back on itself, leaving the lap joint uncovered. Ensure the felt is securely folded over and fixed in place.

Apply a good amount of adhesive (slightly more than you think you need) across the entirety of the uncovered joint. Unroll the felt and place it onto the adhesive and fix it in place with nails at around 150mm centres. Fix it with nails at the lower edge, so they don’t hit any other nails previously fixed into the upper half of the joint.

Take out the nails securing the felt at the opposite end, and add the adhesive and fix the felt to the roof with nails. After this the felt can be secured to the front and back by the gable, you do this by doubling the felt over in the top corner. Larger nails are needed to secure the felt here, as it is twice the thickness in this area.

Final Stage – Finishing Touches

You can now replace or re-install the barge boards taken off earlier. Ensure that the felt it sat nicely across the entire roof with no unwanted folds or lumps and that no nails are piercing through the felt or timber.

Covering a roof with felt does not need to be a complex job. Ensure that you take as many steps as possible to reduce the risk of injury and keep to all safety requirements. Making sure that you have the correct measurements and tools for the job will save you time and hassle, leaving you with a tidy and practical roof, protected from the whatever weather is thrown at it.