Flat Roof Repair & Replacement Costs in 2019

For a small fix, such as a minor tear in the felt or membrane, then the cost to repair the flat roof is likely to be around £50. It should be a reasonably simple task for a competent DIY exponent, meaning the only real cost would be in purchasing the appropriate sealant for the roof type.

On the other hand, for a larger repair job for more extensive damage or a big leak, then you can expect the cost to rise substantially; mainly because you will likely be looking more towards a replacement job rather than a patching-up exercise.

Replacing an entire flat roof on your property, typically an extension on the building, can cost in the ballpark of £1,000 to £2,000.

Similarly, if it’s a garage roof replacement that’s required, then expect to pay anywhere between £750 to £1,500.

Repair Or Replace Entirely?

So, how do you determine whether you can get away with patching up the old roof, or having to bite the bullet and go for a full replacement?

It’s a tricky one, and there’s really no definitive to answer, with each case offering a different response. On the one hand, and especially in older roofs, if you have detected a leak, then this should be a warning sign that it’s on the wane, with any patching merely a case of putting off the inevitable need to replace.

However, this is not always the case. For instance, you could fix the roof perfectly successfully if meets these other general conditions:

  • Apart from the leak, there is no other identifiable sign of damage and the rest of the roof looks to be in good condition
  • It is a newer roof with no real sign of wear and tear
  • The damage is very small
  • The cause of the damage was from an unforeseen event, such as debris striking it in a storm.

If this is the situation at your property, then it’s likely that a simple repair will suffice. However, if you’ve any doubts, or if another leak appears within a short period after the repair has been carried out, then it might need a call to a specialist for advice and a quote.

Carrying out a Roof Repair

Like with any home improvement or DIY task, to successful undertake a flat roof repair you need to ensure that you follow the correct procedure so that you stop the water entering the building and prevent further damage.

While there are similarities to the repair procedure, whichever type you have, before you start the job it is worth noting what your roof is made from so that you can use the appropriate materials.

It is, of course, worth noting, when carrying out any work on your flat roof, that caution and care is needed to ensure that you stay safe. If you are using a ladder, then ensure they’re in good order, and that they are firmly placed and secure. Preferably, however, you should consider scaffolding for a safer working environment at height. While you will obviously want to repair the leak in the roof, your safety and those of anyone working with you, is of paramount importance.

Common Types of Flat Roof

  • Build Up Roof (Bur) – also known as tar & gravel, it’s a common roof type in both the UK and USA, comprising of layers of flat roof felt laid out and overlapped on the surface, which are then coated over with hot, melted tar. Typically, the tar is then be covered by a layer of gravel, which provides an added layer of protection against the elements, particularly UV rays from the sun, that can deteriorate the tar over time.
  • Bitumen – Similar to a build up roof due to the fact that it is comprised of layered asphalt rolls laid across the surface, with a base sheet and a cap sheet. It’s installed one of four different ways:
    • With hot tar, again similar to a BUR
    • By a solvent-based adhesive
    • Open flame to melt the sheets together
    • Self-adhesive base and cap sheets
  • EPDM Rubber – These are tough black rubberised materials that will be stretched tight over a fibre board or insulation board. A rubber flat roof, when perfectly installed, provides exceptional waterproof qualities. They are installed either by ballasting or being weighed down with large stone, or adhered to the boards with a special glue. To protect the rubber material, typically you would cover the roof with stone.
  • Polyurethane – This method involves spraying a high-density polyurethane foam evenly across the surface. This is then protected via an elastomeric topcoat that provides the surface with waterproofing; usually coloured white or light grey.
  • Thermoplastic Membrane – This provides a single layer solution that is usually installed similarly to rubber, either by application of a strong adhesive or held in place with screws and plates.

Identifying the Leak

As any owner of a property containing a flat roof will tell you, water can be one of the major areas of concern and something that must be protected against. Even the smallest kind of leakage can cause costly damage to the property and should be addressed and repaired as soon and as fast as possible.

Such is the threat posed by water damage, skimping or cutting corners on your maintenance and repairs should be an absolute no-no, and we would always recommend that you use good quality materials and appropriate processes; or seek the services of a reputable professional.

Just as you would with a sloped roof, you need to clearly identify where the leak is located. For this, you need to take care and attention because the point at which the water seeps into the property is not always the source of the leak itself.

For instance, if the leak has come about due to damage to the membrane, the water will likely travel some distance before it finds a way into the property.

Therefore, you need to be sure that you can accurately locate the source of the leak so that you can isolate it and stop the water coming in. You can follow some simple steps to help you.

  1. From the point where the water is visible inside the property measure out the distance to the closest two walls
  2. Take those measurements as starting points on the rooftop
  3. While we refer to them as flat roofs, the reality is there is generally a slight slope to allow for runoff. Therefore, having located the water’s entry point into the property, work back up to slope
  4. Check the roof for any rips, general signs of wear and tear, blisters, punctures or other signs of deterioration or damage in the membrane
  5. If no damage is detectable, then check the flashing, pipes and vents, looking for any structural damage or breakages in the caulk
  6. If you still have no joy in locating the source of the leak, then you need to call in the experts, who will carry out a thorough search.

After You Have Located the Leak

Having found the source and cause of the leak, the first call of action might well be to refer to the warranty in place. A flat roof will generally have some kind of warranty ranging from 5 years up to 20 years.

Therefore, if you find that your roof is covered, then contact the manufacturer to arrange the repair.

However, if the roof is not within warranty then you need to work out the best route to restoration.

If the damage you’ve identified is severe, then a seeking a professional roofer would be the sensible option. They will have the experience, the know-how and the tools to ensure that the leak is repaired, providing you with the comfort that your property is not going to suffer from water seeping inside.

As part of your search process, it might be a good idea to consider taking photos of the damaged area, which you can pass onto the roofing company so that they have an understanding of the problem which can help them offer both a solution and a cost to repair the roof.

It goes without saying, of course, that you should do your research when it comes to hiring someone, with recommendations from friends and online reviews providing good pointers. We’d also suggest getting a few quotes to compare prices and recommendations.

If You Decide to Tackle the Repair Yourself

If you think that the damage is relatively minor and that you are able to tackle the repair yourself, then we’d suggest taking the following steps, according to the type of roof you are dealing with.

Small Damage

For minor damage that cause leaks, then you might find that you’re able to make a fix by applying an appropriate sealant over the crack, tear or puncture. Similarly, if you’ve identified degraded caulk around a pipe or vent as the problem, then this too can be repaired by re-applying over the effected area.

If you have a BUR or other felt and tar-based roof, then re-tarring the damaged area can provide the seal over the problem area.

It should be noted that, dependent on the extent of the damage, the age and condition of the roof, these ‘quick’ fixes might offer only a temporary solution, and more extensive repairs or even replacements might be required to resolve the issue permanently.

Larger Rips and General Damage

You can follow a similar process of applying sealants or other protective barriers over larger rips and tears in your flat roof, again providing a temporary solution.

However, if these are excessively large then it suggests that there may be a more serious issue with the roof, and it might be time to call in the experts; and possibly that the roof is in need of replacing rather than repair.

Be Cautious

If you do have need to call a roofer to deal with a leak, then we can only stress again the need to be proceed with caution and ensure that you have someone established with a good reputation.

A roof that fails and causes major leakage is a fear for all homeowners, meaning that it can be easy for more unscrupulous tradespeople to apply the scare tactics in order to get you to replace your roof, when a simple repair is all that’s needed.

Understanding the type and the condition of your flat roof can help you make a more informed decision on the best course of action when you have damage and a leak, which can ensure you get the appropriate level of work done, in the correct fashion, without being forced into unnecessary expense along the way.

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