Flat Roof Repair Costs

It can be easy to repair a felt flat roof depending on the problem. If you’ve got an old-style pour-and-roll felt flat roof, you might be starting to run into problems, but even if you have a newer torch-on felt roof, issues can occur. You might find cracks, lifting, leaking flashings or dips and hollows in the felt. Luckily, there are some easy fixes – but the best thing to do to prolong the life of your felt flat roof is to get a professional to look at it.

If your felt flat roof only needs a small repair, you might be able to get away with using a paint-on fix from a tin that you just brush on. However, if you want a more permanent fix, you’ll need a few more tools and supplies.

You can use a patch of torched-on roofing felt over the crack or leak, but if your flat roof is very damaged or wet it might not take it. You can also buy liquid systems for felt roofs, but again, there is a possibility that your roof might not take it. Also most of the high-quality liquid systems are only available for trade customers, so you might be better off asking a roofing pro to do it for you.

How to repair your flat garage roof will depend on what it’s made from. Lots of flat garage roofs are made from EDPM rubber, asphalt or felt. We’ll explain how to carry out repairs on your garage roof here.

EDPM rubber flat roof repair

EDPM rubber is an excellent choice for a flat garage roof and should need little maintenance. But if you do need to repair it, there are a few easy fixes. If it’s a small crack or tear, apply some lap sealant to the area, but don’t use too much. If you go for a more professional repair later, the sealant will need to be scraped off, so if there’s too much it might cost you more in labour.

If you need to repair the flashing, buy some malleable flashing tape so you can form it into the right shape. Clean and dry the area that needs repairing, then apply an EDPM primer. When that’s touch dry, stick the patch of flashing tape down from the centre outwards with a roller.

Repairing an asphalt flat garage roof

Asphalt is also very hard-wearing, and when it does need fixing, the fixes often last a long time. So if you do get cracks or blisters, you can use a paint-on fix from a tin as a temporary repair. When it’s time for a more permanent fix, you can add a small patch of torched-on roofing felt or use a liquid system, but the high-quality ones are often only available to trade customers.

How to repair a felt flat garage roof

Felt can be repaired in a similar way to asphalt flat garage roofs. For small cracks or a temporary fix, try a paint-on treatment from a tin. But for something more permanent, use a patch of torched-on roofing felt or a liquid system. If these don’t stick, unfortunately it means it’s time for a new felt garage roof.

If you do need a new flat garage roof, leave it to the professionals who will ensure that your new roof will last for years.

Blisters are most common on membrane roofing systems. Lots of contractors will tell you that if there are no signs of further damage, there might not be any need to repair flat roof blisters. They form when pockets of air or water get trapped between layers of the roof’s membrane or between the membrane and the frame. When the sun is out and it heats the pockets expand and stretch the membrane. If you do want to repair your flat roof blisters, there are a few ways to go about it.

If you have a membrane flat roof, cut away the membrane until you reach a place where the membrane is still stuck tightly to the roof. Reapply as many new membrane layers as you cut away over the blistered area. You might even need to do more. To make sure your patch remains watertight, you’ll need to leave at least 6 inches around the edges of the blister.

If you’ve got a felt roof, you can cut an X shape through the blister. Peel back the triangles that you’ve made and let the timber frame dry for a while (so don’t do this when rain is forecast!). Then, coat the area with lots of bitumen adhesive and leave it to dry until it feels tacky. Then press down the triangles of felt firmly into the adhesive.

After that, you’ll need to add more bitumen adhesive to the cuts you made. If you’ve got any spare roofing felt, cut a square that’s about 100mm bigger than the cuts then lay this over the adhesive. If you’ve not got any felt, it’s cheaper to use a self-adhesive flashing strip. Once you’ve laid the strip or patch over, seal the edges with more bitumen adhesive.

Tar and gravel flat roofs are popular because the gravel weighs down the surface of the roof so it doesn’t blow away and it also protects it from sun damage. The tar makes the roof watertight, so you won’t get any leaks. However, sometimes problems occur and you’ll get cracks and leaks. So how do you repair a tar and gravel flat roof?

If you notice leaking coming through your flat roof, try to find the source of the leak. Since water can travel easily, it might not be where you think it is. The first place to check is the flashing, then any parts of the roof with gravel missing. Once you’ve found the crack, sweep away any remaining gravel and clean the area.

Apply a primer to the area and allow it to dry. Then, apply a tar and gravel roof patch that you can get from most DIY shops. Patch 2-3 inches around the damaged area, creating layers, and ensuring that there aren’t any air bubbles or gaps. Then you should cover the entire patch with gravel.

Before you try to repair a tar and gravel flat roof yourself, consider how much of the roof needs repairing. Professionals often say that if cracks and faults make up 25% or more of the roof, then you should look to replace it. It might be tempting to try and replace your tar and gravel roof yourself, but it’s best left to the specialists. They will ensure that your new roof is watertight and strong enough to withstand sun damage and storms.

How much a flat roof costs to repair depends on a few factors. Is your flat roof on a garage or an extension? What is the flat roof made from? It’s always best to get a few quotes to compare prices, but we’ll give you a rough idea here.

If your flat roof was installed in the 1990s or earlier, it’s likely that you’ll see some leaks or damage soon. Felt flat roofs used to be installed completely flat, which meant that water couldn’t run off. That means that water pools and can create moss and damp. Sun exposure can also damage the felt, causing damage and eventually holes that lead to leaks.

If you’re lucky enough to have got away with just needing a flat roof repair, this should set you back an average of £100 per square metre. If your roof is sagging due to the weight of it putting pressure on the timber frame, you might need additional joists – which could cost anywhere between £1,000 and £2,000, depending on how many you need. But if the problem is due to the internal part of the roof system becoming waterlogged, you could be looking at over £5,000.

If your roof is severely leaking or the timber joists are rotting, it might be more cost effective to replace your flat roof. If you keep forking out for repairs, it will eventually be cheaper just to replace the whole thing, which could cost around £2,000.

Yes – you can repair a flat roof in the winter. Contractors will still be able to help you repair leaks, and it’s a myth that they will charge more. Most won’t have any additional costs just for coming out in the winter.

You'll have to wait for any snow and ice to melt before you can repair your flat roof. Depending on what type of flat roof you have, some repairs might have to wait until temperatures reach a certain level above freezing – some coating products won’t adhere (stick) in low temperatures, but a roofing professional will be able to advise you on what is best to use in the winter. If you have an EDPM rubber roof, most of the adhesives won’t mix in cold weather, so you might have to wait until temperatures rise to get a proper repair to your flat roof.

The best way to avoid needing to repair your flat roof in the winter is to inspect it at regular intervals. During the summer, even in the UK’s mild weather, the sun’s UV rays can damage and weaken flat roof surfaces, potentially causing cracks and holes. As autumn approaches, take a look at your flat roof and see if you notice anything untoward. If you do, speak to a reputable roofer who can repair your flat roof for you before winter arrives.

Fibreglass, or GRP, flat roofs are very durable and should last you years, but over time they can become brittle and you might see some cracks or holes forming. Luckily, you can repair a fibreglass flat roof and it doesn’t have to be too difficult.

Cracks in a fibreglass flat roof

If you notice long cracks in your fibreglass roof, you can often use a fibreglass crack sealant. Simply clean the area, squeeze the sealant into the crack, then smooth it off. If you want it to look neater, you could coat the entire roof with a restorative coating which will make it look new again.

Hole in a fibreglass roof

If you notice a hole in your fibreglass flat roof, you’ll want to get this repaired as soon as possible to avoid any rainwater getting into your home. There are lots of fibreglass roof hole repair kits on the market, both online and in DIY stores, so you shouldn’t have trouble picking one up. They usually contain a mouldable UV cured patch that you can stick onto the hole. It will harden and become instantly weatherproof, so is the perfect emergency repair solution.

Fixing pin holes in a fibreglass flat roof

Unfortunately, if you find pin holes in a fibreglass flat roof it’s often because the installer didn’t use enough resin during the fibreglassing process. Luckily, if you can’t get back in touch with the installer or you only notice after a few years, you can fix this yourself.

Sand down the roof back to the clear resin layer. Clean the entire roof with acetone and reapply some GRP roofing resin. Ensure that all the pinholes are filled – you might need two coats.

How to repair a hole in a flat roof depends on what material your flat roof is made from. If you have an asphalt, felt or EDPM rubber roof, the repairs are quite simple, whereas it’s a bit more tricky if you have a fibreglass flat roof.

How to repair a hole in an asphalt flat roof

If you’ve got a small hole in your asphalt flat roof, you might get away with using a paint-on fix from a tin. It’s best to use this as a temporary measure to tide you over until you can get in touch with a professional. If the hole is on the flashing, you can add heat-applied flashing tape to it, or use a patch of torched-on roofing felt. There are liquid systems you can use, but usually they’re only available to the trade.

Repairing a hole in a felt flat roof

It's a similar process to asphalt roofing if you want to repair a hole in a felt flat roof. Use a paint-on fix for a temporary solution, but the best way to repair a hole is to use a torched-on piece of roofing felt to cover the hole and make it watertight again.

How to fix a hole in an EDPM rubber flat roof

If the hole in a rubber flat roof is small, you may be able to get away with applying some lap sealant to the hole. Only use a small amount, as if you go for a more permanent repair later down the line all of this will need to be scraped off. You can also use a malleable piece of self-adhesive flashing – clean the area, add EDPM primer and stick the patch on from the centre outwards. Add sealant to the edges if you want to give it more water protection.

How to fix pin holes in a fibreglass flat roof

If you find pin holes in your fibreglass roof, it usually means there wasn’t enough resin used at installation. To repair the holes, you’ll need to sand down the entire roof back to the clear resin. Then clean the area with acetone and apply GRP roofing resin – the acetone ensures that the resin sticks. You might need two coats of resin to get rid of all the holes.