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How Often Does A Flat Roof Need To Be Replaced?

Roofing is an area the building industry has placed a lot of emphasis on, and the choices that a homeowner is faced with are extensive. Flat roofs have always offered the prospect of being able to use the space on the top as additional storage or entertainment area.

Flat roofs constructed with older materials such as asphalt and felt are expected to last 15 to 20 years, after which they will need to be replaced. If the flat roof is constructed from a modern material such as EPDM (ethylene propylene diene monomer), it will last 50 years.

A flat roof is not generally considered an efficient roof structure, and while it may be cheaper to install, the short life expectancy, long-term maintenance, and repair costs make it a more costly, long-term solution. But if that’s the case, then why have a flat roof in the first place?

Pros and Cons of a Flat Roof

A flat roof is any roof with a pitch of 15% or less. And they offer many advantages to the homeowner:

  1. Flat roofs are unobtrusive
  2. Flat roofs are generally more affordable than traditional roofing
  3. Flat roofs are cheaper and easier to maintain than traditional roofs

The downsides of a flat roof include:

  1. Insurers are more cautious
  2. They have a finite life expectancy which is less than traditional tiling material or more modern EPDM roofing on a pitched structure

How Long Does a Flat Roof Last?

While the typical life expectancy of a flat roof is quoted as 15 – 20 years,  structures that have been installed very well and then maintained adequately have been known to last up to fifty years.

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It compares well to tiles generally quoted as having a life expectancy of 60 years.

The primary factor influencing the potential life expectancy is the material with which the roof is built.

If older methods such as felt or asphalt have been used, it will reduce life expectancy. If more modern materials such as EPDM (ethylene propylene diene monomer) are used, the potential life could be more than doubled.

Another essential activity for owners of homes with flat roofs is a regular inspection and maintenance routine. And here’s how to do it…

How To Maintain A Flat Roof

You can extend the life of a flat roof for a considerable period by following a simple maintenance routine and resolving any issues as and when they present themselves instead of waiting and eventually requiring much more extensive repairs.

An adequate inspection schedule is as follows:

  1. End of Autumn
  2. End of Spring
  3. After harsh weather conditions, such as storms, strong winds, and heavy snowfall

Unless your roof is specifically designed to be walked on and hold your body weight, you mustn’t walk or stand on it.

Standing on the roof may result in the covering material being compromised, which encourages splitting and leak forming.

Although generally homeowners can fix whatever damage they can themselves, if it involves walking on the roof, it’s strongly recommended that the homeowner hires a professional experienced in flat roof maintenance to do it for you.

This will avoid any damage done while being on your roof. But given this isn’t always the case, here’s what to do if you want to do your own maintenance…

How To Inspect And Maintain The Roof

When you inspect the roof, look out for the following issues.

#1: Check That The Drains Are Clear

The flat roofs are… flat! The downside of this is that it is harder to drain rainwater, melted snow, or ice.

Checking the drains are clear and removing any debris which restricts the water flow is essential and should be done before any heavy rains are forecast.

Typical debris will include leaves, sticks, dirt, or other blockages.

#2: Prune Leaves & Branches Encroaching On The Roof

If there are trees, creepers, or any other foliage creeping onto the flat roof, it is recommended that you prune this back to at least 1 meter away from the roof’s edge.

The purpose of this exercise is two-fold.

  1. It reduces the potential for leaves or broken bark blocking the drainage.
  2. It prevents moss from growing, ultimately impacting the roof material membrane.
  3. It reduces the potential for large branches breaking off (perhaps in a strong wind) and damaging roof surface material.

#3: Check The Roof After A Heavy Storm

Pooling or Ponding on a flat roof needs repair before it creates further damage.

If your home was subject to a heavy storm, a substantial snowstorm, high winds, or heavy icing, it is worthwhile to check the roof to ensure it caused no damage and the excess water has drained.

You should immediately clear heavy ice and snow off the flat roof because it may be imposing vertical loads on the structure which come close to, or even exceed, its design limits.

Remember, excessive snow is heavy, but it eventually melts, which could overload the roof’s drainage system.

#4: Check Inside Your Home

Keep an eye open for stains or other water damage which may appear on the walls or ceiling. Stains are valuable indicators warning that all is not well with the flat roof.

Timeously, attending to these issues will allow you to resolve the problem before it gets more severe and stops the damage from repeating.

A ceiling board that is constantly dripped on will become soft and ultimately need replacing.

Flat roofs constructed using felt materials or asphalt are prone to the following issues:

  1. Pooling or ponding
  2. Splitting
  3. Blistering
  4. Damaged flashing
  5. Impact Damage

If you find any of the above, the following will give you an idea of the work needed to rectify them.

How To Fix A Flat Roof Which Is Pooling Or Ponding

Did you know? While flat roofs are sold as “flat,” they have to include a slight slope in the construction to ensure that water runs off and doesn’t “pond” and accumulate in large puddles.

If the roof is developing large puddles that are not draining, it needs attention as soon as possible.

Water pooling on the roof needs to be cleared as quickly as possible for the following reasons:

  1. It can cause deep concave indents to occur around the roof
  2. If the roof degrades and allows leaks to start, they will stain the inside of your property.

If the indents and pooling are not attended to, they will collect water and behave like mini catchment areas, damaging the material. After a period, the roof will fail at certain positions and allow water to seep through into the interior of your home.

The roof draining system may be blocked with debris, in which case the repair is simple, as all you have to do is clear the drains.

The issue may also arise from debris littering the actual roof and preventing water flow.

If clearing the drainage system doesn’t have the desired effect and the puddles continue to accumulate, it may result from the original drains being inadequate.

You may need to have the drains enlarged and even consider additional guttering around the sides to prevent the water pooling against the edges.

An extreme solution is installing automatic pumps that activate when the water levels build up.

How To Attend To A Flat Roof Which Is Splitting

A common issue with flat roofs is called “splitting.” It happens mainly with asphalt and felt-covered roofs, and it means the roofing material starts to crack or tear.

While it negatively impacts the roof’s look, it could also result in the structure leaking and the possibility that the home will develop a damp problem. In itself, dampness has severe implications for the occupant’s health.

Several situations can cause splits to happen:

  1. People walk on the roof, resulting in stresses that the material cannot handle
  2. The building is exposed to changing temperatures and moisture levels
  3. Extreme climate conditions, including high winds, rain, ice, or snow, freeze-thawing
  4. Water pooling
  5. Poor quality workmanship when the roof was first installed or recently repaired

Water damage on the interior of the walls or the ceiling may be an indication that splitting is occurring.

It is easier to fix a felt roof than an asphalt-covered structure. You don’t have to be a professional builder to fix a flat roof covered with felt and which is splitting. Here’s how you can do it yourself…

How Do You Fix A Split In The Roof Membrane?

The process to fix splits are:

  1. Remove the material which is splitting
  2. Thoroughly clean the exposed area
  3. Fill the space under the split with bitumen adhesive or roofing cement to seal down any loose areas of the felt roof
  4. Lay the new material over the now clean area

Commercially available felt roofing repair kits include large patches, bitumen adhesive, or roofing cement in the kit.

If you are not comfortable performing the fix, it is recommended that you obtain the services of a professional company. They will ensure the fix is done correctly and the roof remains durable and watertight.

QUICK TIP: It’s a good idea to reinforce the repaired area with an additional layer of patch and adhesive.

What To Do With A Flat Roof That Is Blistering

A flat roof is not completely flat; it istill has a slight angle for the rain water to drain away easily.

A flat roof may begin to blister if subjected to excessive heat. It is caused by air becoming trapped between the asphalt or felt covering and the underlying substrate.

As the heat increases the trapped air, the air expands, and the surface starts to bubble up. If the heat becomes excessive, the air bubbles will burst or rupture, tearing a hole in the material.

Once the material’s surface has been compromised, it is vulnerable to water ingress, eventually resulting in a leaking roof.

If your roof is blistering, you must attend to the defective areas as soon as possible.

Whether the blisters are still intact or burst, the affected area needs to be urgently replaced. If a few localized blisters affect a minimal surface, you can attempt to fix these yourself.

How Do You Fix Blistering?

The method to fix and repair blistering on a flat roof is as follows:

  1. Ensure the roof is dry and the weather forecast doesn’t predict rain.
  2. The roof must be completely dry before you attempt the repair.
  3. Identify the blisters to be attended to. If there is more than one, it is recommended that you circle each of them with chalk, which makes it easier to identify the next one to be worked on.
  4. Using a small utility knife, cut the material around the blister.
  5. Make sure that you only cut into the material and not the substrate below.
  6. Fold back the edges you have cut.
  7. Apply bitumen adhesive over the exposed surface and push the edges onto the sealant.
  8. Replace the material you cut away, ensuring it is securely affixed to the bitumen sealant.
  9. Once the patch has been stuck down properly, add more bitumen sealant to the top of the patch.
  10. Apply a second patch that is large enough to completely cover the patch, the edges, and the area around it.
  11. Cover the entire area with bitumen sealant when the two patches have been secured.

Damaged Flashing Is An Indication Of A Problem

A part of a flat roof that is extremely important but generally overlooked is the metal flashing around chimneys, vents, and other fixtures. If this is damaged or even missing, your flat roof will undergo severe moisture damage over time.

Damaged flashing will cause moisture damage to the roof and the underlying substrate.

If caught early, damaged flashing is easy to repair and will stop more extensive damage and save money in the long term.

Look Out For Impact Damage

If your home has been subject to high winds, debris could have been blown onto the flat roof.

If the objects have been blown with sufficient force, they may have caused impact damage, which may have compromised the integrity of the roofing material.

How Much Does It Cost To Replace A Flat Roof?

Replacing a flat roof is an expensive undertaking for the following reasons.

  1. Different states have unique regulations, which can directly influence the cost of replacement.
  2. Different areas have a varied ability to source the required materials, impacting the price.

The cost of a new roof is calculated by taking the following.

  1. Labor costs vary area by area but generally fall between  $40 to $80 per hour. Assuming an average-sized roof takes five days to install, labor costs will range between $1,600 to $3,200.
  2. Material and Installation costs typically range from $250 to $350 per 100 square feet.

The following table shows the average square foot price broken down by material type:

MaterialCost per square foot
Fiberglass$1 per square foot material price and $4 to $6 per square foot installation cost
Rubber$4 to $13 per square foot
Ethylene propylene diene monomer (EPDM)$5 to $13 per square foot
Built-Up Tar$4 to $10 per square foot
glass-reinforced polyester (GRP)$4 to $6 per square foot
Modified Bitumen$4 to $6 per square foot
  • In addition, there is a rubble removal fee which will cost between $1 to $5 per square foot.


A flat roof installed using conventional materials such as felt or asphalt will last 15 – 20 years. If the flat roof has been covered with modern, more robust material such as EPDM (ethylene propylene diene monomer), it should last for a similar time-frame as tiles.

Inspecting and maintaining a flat roof will extend the life expectancy of a flat structure while also ensuring that it performs optimally.