Pitched Roof VS Flat Roof

When your flat roof needs to be replaced

The Three Types of Flat Roofs

At the heart of any flat roof installation is deciding on the type of roof that best fits your home style, intended use, climate, and budget. The three main types of materials and methods used in installing flat roofs offer homeowners a variety of benefits and disadvantages.

Built-up Roof

The most traditional method, the built-up roof consists of several layers of materials that are laid down atop each other, including hot tar (bitumen), gravel, fiberglass, and roofing felt. This type of roof is fire-resistant thanks to the layers of gravel and can last up to 30 years. However, because of the hot tar, the installation of this type of flat roof should always be done by a professional roofer. It is also a very smelly process and is not recommended for occupied homes. The average cost of a built-up roof installation is $3.50-$7 per square foot.

Modified Bitumen

In direct contrast to the layered approach of the built-up roof, the modified bitumen system utilizes only one layer of rolled material, which can be made of various compounds and installed one of two ways.

The traditional installation, known as torch-down application, requires installers to heat the materials on the roll as they lay them down on the roof. A layer of felt is applied to the roof, followed by a primer and the strips of bitumen, which are sealed onto the roof via the flame of a large torch.

Because this is highly specialized and presents a fire hazard, torch-down modified bitumen roofs are rarely used outside of the professional realm. By contrast, the more modern modified bitumen approach, called peel and stick, is a possible DIY project. Both types of modified bitumen roofing systems are notable for their light colors that reflect heat, their up-to-30-year lifespan, and their middle-grade price. In fact, the installation of a modified bitumen roof generally costs between $3-$6 per square foot.

Rubber Membrane

Made of “true rubber” or ethylene propylene diene monomer (EPDM), the rubber membrane roof is literally like a flattened car tire. However, the chemistry of the material is such that this type of roof actually resists sun damage. It is also lightweight, resistant to scuff marks and tears, and relatively easy to patch in the event of a leak. EPDM roofing is available in two colors—black and white—which serve the needs of different climates and budgets. While the black variety absorbs quite a bit of heat, the white material costs 30 percent more on average because of its heat-reflecting properties. While the average cost to install EPDM roofing is between $4-$6 per square foot, it is easy to install EPDM roofs yourself because there are several systems that you can use to secure them according to your skill level and comfort. This includes mechanical anchoring with fasteners or adhesive anchors or ballasting the material with stone.

Common flat roof problems leading to replacement

If you see the following indications, be sure that minor roof repair won’t be enough.

Water Pooling

One of the biggest issues flat roofs face is pooling water, which can result in irregular stress that causes cracks. Over time, the roof may shift a bit, meaning it may not be as level as it was when it was installed. This will most likely result in water pooling in dips and divots. While flat roofs are manufactured to stand up to water, these pools need to be drained as soon as they form to ensure water doesn’t seep into the roof’s layers. When left unchecked, the pools will harm the roof’s surface and shorten its lifespan.

Bubbling, Blistering and Adhesion Failure

Bubbling and blistering are defects that typically result from adhesion failure. The visible bubbles are generally filled with water or air. This could be a result of poor workmanship, bad insulation or insufficient ventilation. When caught early, the problem can be dealt with; left untreated, the blisters will get too large to be fixed. They can later pop and leave holes in your roofing that make your property vulnerable to interior damage. The cause behind this could be that the roof had excess moisture when it was installed.

Moisture and Leaks

Flat roofs face lingering moisture issues that can be handled effectively so long as you stay on top of them. This type of roof, like any other, can leak, as the water doesn’t have anywhere to go but down. This results in moisture seeping into the roof membranes, leading to further problems such as fungus and mould. The best way to deal with leaks and moisture is to have your roof inspected and maintained regularly. If problems aren’t caught early, a professional roofing company will be able to advise you on the best course of action.

Cracks, Splits and Tears

This is perhaps the easiest problem an untrained eye can spot. If a crack or split is left for too long on a flat roof, the plyboard or chipboard will absorb water. This may turn the material to mush so it becomes uneven, making the roof unsafe to walk on and preventing it from functioning at its best. You may choose to have your roof repaired if the problem isn’t extensive.  However, if you notice cracks or splits across the whole surface, it’s best to replace it.


Similar to other materials, flat roofs with asphalt expand and contract with changes in temperature and weather. When left unchecked, this expansion and contraction will cause the flashing to pull away from the corners and edges of the roof, leading to moisture getting trapped and leaks appearing on your ceiling. Failing to address the issue promptly will deteriorate your roof’s flashing, compelling you to replace it.

Organic Growth

Although algae, lichens and moss might not seem like big problems, they signify that your flat roof requires attention. Any kind of organic growth on your roof is indicative of unwanted water retention. Left untreated, it can do extensive damage to your building. If you can’t figure out why there’s organic growth on your roof, have it checked by a professional.

Damaged Top Coat

If you can constantly hear a fluttering sound coming from your roof during windy conditions, chances are the top coating is damaged. As a result, every time it rains or snows the fluttering panels will expose the materials underneath to weather and cause damage. Not addressing this issue could mean that the roof fails completely and causes weather or water damage.

Design and installation

If you have had a modified bitumen felt roof installed for over 20 years, you have benefitted from an extremely exceptional lifespan for this type of roof. One would imagine that it must have been installed with a lot of care and attention and been subject to minimal foot traffic during its lifecycle.

It’s not uncommon for a felt roof to last only just over two years before it needs to be replaced. For many homeowners who opt for a felt roof, they can feel as though they have found themselves with a leak no sooner than they have had the roof installed.

If the roofer cuts back on materials, time or effort when installing a flat roof, this could significantly compromise the roof’s long-term resilience and reliability. Many homebuilders even prefer to forgo flat roofs and instead choose a tiled pitched roof for lower-level extensions and garages.

Indeed, a pitched roof can be guaranteed for longer than many types of flat roof, while a good provider of flat roofs can be a lot trickier to find than a tiler. Therefore, what are the key signs to look for when diagnosing a flat roof? How would you know whether it needs replacing or repairing?

Here is a list of particular defects that could call for a flat roof replacement. However, keep in mind that, in nearly any of these circumstances, it would be advisable for you to call in a professional to survey the roof before you have a new roof installed, as the issue might be minor.

How do you decide?

When it comes to the dilemma of repair or replace, it can be tough figuring out the best course of action. In the short-term, it is usually going to be cheaper to repair the roof. On the other hand, if your roof is bad enough, continuing to repair it becomes a never-ending exercise in futility. And you can easily end up spending more on repairs than you would have spent to just replace the roof entirely.

A good rule of thumb is this: if the material with which your roof was constructed has reached the end of its service life, you should probably replace it instead of repairing it. It is only a matter of time until other problems develop. In addition, if the cost of repair is going to exceed 20% of the cost of a new roof, and if the age of the roof is more than half of the expected service life of the material with which it is constructed, you should probably replace it. The likelihood of having to pay for additional repairs in the future is high enough to justify the additional outset at the present.