Your Property Wizard

Flat Roof Repair and Replacement

Despite the name, flat roofs aren’t flat but pitched at a small angle. If they were completely level, water would pool on the surface of the felt, degrading the material and leading to leaks.



Flat roofs are common across the UK, particularly on garages and extensions, largely due to their low cost. However, they’re notorious for leaking, so you should be prepared to either patch or replace your roof every 15 years or so.

Maintenance costs shouldn’t be that expensive, and your roof should keep out the weather for years to come. But, beware of the all too common bodge jobs; these won’t only damage your bank balance, but your home too.

This article will go over all the important factors you need to know when it comes to repairing and replacing your flat roof, from how much it costs to repair or replace a flat roof, what affects the cost of repairing or replacing a flat roof, how to save money on repairing or replacing a flat roof, what’s involved in repairing or replacing a flat roof and how to find and hire a roofer.

For our top tips on roof repair, keep reading to find out the most cost-effective way of getting the job done.

How Much Does It Cost to Repair or Replace a Flat Roof?

Depending on the material you choose for your flat roof, the price you can expect to pay for its repair or replacement will differ. Here are the main materials and their associated costs, as well as the expected labour time:

Felt roof £40 to £60 per square metre 1 to 2 days
Rubber roof £60 to £85 per square metre 1 to 2 days
Fibreglass roof £70 to £90 per square metre 1 to 2 days
Lead roof £90 to £105 per square metre 1 to 2 days

For a standard felt roof, expect to pay between £40 and £60 per square metre for replacement material. If you have opted for a rubber roof, this cost will rise to be between £60 and £85 per square metre.

Moving up the scale again, a fibreglass roof will enter at between £70 and £90 per square metre; while a lead roof will be between £90 and £105 per square metre.

For each roofing material, you can expect to have labour costs of around £15 to £30 per hour, depending on the skill and geographical location of your roofers, which equates to between £120 to £240 per day.

It’s good to note that roofers often operate in pairs for safety, so your price for labour will most likely be doubled for this reason, as our costs are listed as per person.

Most jobs will take between one to two days to complete, which is something to bear in mind when working out your labour rate depending on the type of roof you choose.

Replacing a Leaking Garage Roof Costs

If your garage roof is leaking significantly, you’ll have to get it replaced.

For an average double garage with four walls, quotes should be in the region of £750 to £1,000 outside of London, and between £925 and £1,300 in the capital.

Replace a Leaking Extension Costs

The cost of replacing a flat roof on an extension is unfortunately higher. However, it’s worthwhile paying the extra cost if you don’t think a patch job will work – because the last thing you need is a flood every time it rains.

The average cost for a roof that’s approximately 1.5m larger than a double garage roof should be between £975 and £1,500, with prices in London around £500 more.



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What Affects the Cost of Repairing or Replacing a Flat Roof?

There are a few factors that can increase the cost of repairing and replacing a flat roof, with the ability to make your costs skyrocket if you’re not savvy.

Rotten Timbers

If the felt’s pulled back and you discover rotten timber, you’ll have no option other than entirely replacing a flat roof.

In many cases, flat roofs are installed as a cheap and short-term option. As a result, low-cost chipboard or ply is often used.

Replacement decking timbers of a decent grade will cost between £40 and £55 each, including their installation.

Water Pooling

If you realise that water’s pooling on your roof instead of running off into a gutter, you must have the pitch (the angle at which your roof is laying) altered.

Luckily, this only requires a couple of inches of timber and shouldn’t increase costs too much. It’s important to seek advice from your builder as to how much the roof should be elevated, and it’s a job that shouldn’t be put off as standing water will destroy felting quickly.

Additional Costs

Flat roof replacement costs can vary wildly because there are many different factors.

For example, you might not like the look of felting and want stones or chippings added. This can also protect the felting material from UV light, prolonging its life as a result.

In addition, if it’s an extension roof, you have to pay for the costs of insulation, too.

Beware Rogue Builders

There are many builders out there who, unfortunately, will offer to fix or replace your roof without really knowing what they’re doing.

You musn’t allow contractors to leave existing felt in place and simply cover it over, not only because the resulting seal isn’t tight, but because you can’t inspect the roofing timbers.

In addition, be wary of anyone who says they’ll seal your roof with liquid tar. This will only last a couple of years at best before cracks and splits allow water back in.

How Can I Save Money on a New Flat Roof?

Preservation Is Key

What you do to your flat roof from the moment it has been originally laid will greatly impact how it performs over its lifetime.

With regular maintenance and cleaning, you’ll keep on top of any hairline problems when they start, instead of finding out when you have a huge leak in your garage.

Proactive vs. Reactive

Caring for your roof will also save you from having to be reactive in the event of a sudden leak or breach of the material.

If you’re keeping on top of snags as they happen, you’re likely to know if something is going to break soon, allowing you to plan your repair instead of having to call someone up to come out straight away, which will incur higher fees than something that you’re able to plan a little more in advance.

Use Local Traders

It’s no secret that local traders will be more competitively priced than nationals, simply because they don’t carry the overheads of the latter.

They may be less readily available, but if you’re fine to wait a little longer to get someone to see you, they can be an effective cost-saving route, as well as championing local tradesmen, too.

Thoroughly Vet Traders

If you’re having a flat roof put in from new, you must get professional traders who know what they’re doing. If they pitch the roof incorrectly or use the wrong sealing materials, the integrity of the roof will be jeopardised from the beginning.

While we can’t turn back time, we can always make sure that moving forwards we use reputable traders who will get the job done right the first time.



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What’s Involved in Repairing or Replacing a Flat Roof?

When repairing or replacing a flat roof, your contractor will first come out, assess the situation and ascertain whether or not it’s a patch job or a full replacement.

They’ll come and remove any stone chipping and existing felt, inspect the roof timbers and, if these are not rotten, install the new roof.

This includes adding an underlay to the existing timber decking, fitting the new felting and installing drip edges and upstands. Your builder should also take any waste materials away for you – but this is something you should always check, and not just presume.

On an extension, there’s often poorer access and scaffolding may be required. In addition, due to the join with the main property, you’ll need to have lead overlaps installed as well as wall upstands.

If it’s not a first storey extension, it’s also harder to remove waste material, and because it’s a habitable room beneath, additional felting and insulation are required.

How Do I Find and Hire a Roofer?

Seeking recommendations from family, friends and neighbours is a great place to start as it helps you kick-start your search with some pre-vetted, trustworthy candidates.

Especially if someone on your road has had similar work done recently, make sure you ask them if they’d recommend their trader. Even if they tell you not to work with them for whatever reason, you’re still ruling out someone and making your ongoing search much easier, which is a great positive.

Using an online search tool like HouseholdQuotes can help to streamline your search as you just have to use one website instead of keeping track of what you’re doing across multiple pages. What’s more, the quotes obtained on this site can help to save you up to 40% – which is a huge saving when it comes to roofing repair and replacement.



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Ensuring the Professional Is the Right Fit

The most important piece of advice is to ask your builder questions so you know what your quote includes:

  • Will the old felt be removed and the new felt added?
  • Is there a separate breakdown of timber costs if they’re needed?
  • Will old materials will be taken away?
  • And, if required, how much will scaffolding cost?

Second to this, once you’ve settled on a trader you want to ask for a written quotation. This is something essential to refer back to in the event of any disagreement or misunderstanding during the job, which gives both parties a point of reference which isn’t just relying on someone’s memory of a conversation you both had weeks ago.

You’ll want to seek out the trader’s experience, as well as their references from relevant and recent jobs. Although a trader might have a glowing back catalogue of work, it’s best to check the year in which it was completed, as regulations can change, skills can improve or decline or working teams may change, meaning what you see in someone’s portfolio mightn’t necessarily be what you get.

All traders should carry insurance to cover both themselves and you in the event of any issues, so just cover all bases and check for proof of this before agreeing to work with an individual. If they refuse to show you or make a fuss about you even asking, it’s best to take it as a sign to step away, as if they’re withholding this information what else might they be hiding?

Final Checklist

If your flat roof has seen better days and you’re sick of damp interiors and extreme weather-proofing solutions every time it rains, then getting your roof repaired or replaced can be the best way to go.

Here’s what you need to consider before getting the job booked in:

  • Take a look for yourself and take stock of the problems you’re having – as not all leaks will require an entire re-roofing which can save you money – and time!
  • Find a reputable trader using HouseholdQuotes to save you up to 40% on your quote, as well as saving you time from searching on different websites
  • Ask your trader to check your roof is correctly pitched to avoid pooling
  • Make sure you get a written quote and make sure that your trader shows proof of their insurance before getting started on your job.


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Frequently Asked Questions

What Are Some Signs My Roof Needs to Be Repaired or Replaced?

Generally speaking, you’ll know if something is awry with your flat roof. From tears on the surface to movement in the fabric; holes or lifting; to more obvious signs like flooding and a permanent damp-smelling space.

Not all cases will need an entire replacement – usually patching an area will suffice as a mend – but if something keeps coming loose after many patch repair jobs, it might be time to move onto a full replacement.

Is It Better to Repair or Replace My Flat Roof?

In general, if you have a significant leak, you need to be prepared to replace the entire roof. If the water’s collecting in a puddle, the felt is sagging or cracks and UV damage have destroyed the roofing material, making a few repairs is not a long-term solution.

However, there are a few instances where you might be able to patch, including:

  • Felt has come away from the wall (such as on an extension)
  • Small rips have been caused by falling roof tiles or third-party damage
  • Water is leaking under the roof where the felt meets the guttering

In these cases, you might be able to get away with a small fix. This is normally an easy DIY job, and you can repair your flat roof for less than £50 if there are only a small few tears or cracks.

Most roofs are covered in felting has got bitumen on the rear side. When a blowtorch is used, the bitumen melts slightly and becomes attached to the wooden roof structure. Unfortunately, until felting is torn off, there’s no easy way to establish if the wooden struts and beams need replacing too, so you must consider the extra cost of this when you budget repair and replacement costs.

How Long Do Flat Roofs Last?

If well-maintained and properly installed in the first place, a flat roof should last you between ten and fifteen years before it will require a full replacement.

How Often Should You Seal a Flat Roof?

Generally speaking, and if there are no significant problems with leaking or pooling water, every five years should be sufficient for re-sealing your flat roof.

Even if you’ve had no problems with your roof over its lifetime, that’s not a reason to skip on re-sealing it – you need to keep up the maintenance to make sure the roof maintains integrity and stays in great shape for years to come.

How Much Does a New Roof Cost?

There is no one-size-fits-all answer to this question, as it depends entirely on the material you choose, your location, as well as a whole other host of other considerations.

For a full answer and indicative costs, see our dedicated page on roof replacements here.

How Much Does Roof Cleaning Cost?

Roof cleaning mightn’t be your first choice for maintenance, as the adage out of sight, out of mind will remind us. But it is an important part of maintaining the health of your roof, no matter if you can see it or not.

For full information on roof cleaning and associated costs, see our dedicated page here.



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