How to Replace a Flat Roof

When it comes time to replace your flat roof, there are a number of different factors to consider. It is important to understand each factor before diving into the roof replacement to help ensure that the roof you choose is right for your needs, and for the building, it is being installed on.

Deciding on the right type of roofing material is one of the most important decisions when it comes to replacing a flat roof, but there are other important things to consider as well, including the roof’s slope and the drainage system. The roof’s insulation factor, as well as the roof’s structural support system, should also be taken into consideration.

Here are some things that you should know about flat roof replacement, and important things to consider that will help you to go about having your flat roof replaced correctly.

Roof Slope

While the term “flat roof” often gives the impression that the roof is perfectly flat, even a flat roof needs a slight slope. This is to help prevent water from pooling and causing damage. Most common problems occur on flat roofs when the slope is not taken into account. Poor sloping leads to poor drainage, which leads to roof damage. It’s best to have a roof slope that’s a minimum of ¼” per foot.


Roof drainage plays an important role in how a roof eliminates the water that collects on your flat roof. Even flat roofs that have been properly sloped, need somewhere for the water to go.

  • Internal Drains – Interior drains are commonly found in urban areas. They drain the water through the building, and connect with the drainpipes into the storm drain, or sewer pipes. You should take precautions with internal drains. In the event that the drains become clogged or frozen then break, you could end up with flooding or sewer discharge.
  • Scuppers – Scuppers are drains installed on the side of the roof that lets water-free fall to the ground. If scuppers are wide enough, they won’t get clogged, and since they aren’t connected to pipes for indoor plumbing there is no risks associated with broken pipes.
  • Gutters and Downspouts – Gutters and downspouts are the traditional means of allowing water to drain.

Structural Load

Another important thing to consider before replacing your roof is to consider the structural load. The structural load is the amount of weight that will be placed on the structure. Understanding how much weight your structure can handle will also help you narrow down the choices in which flat roofing materials you can use. Be sure to consult with a structural engineer if there is any doubt.

Repair Vs. Replace

Finally, make sure the roof needs to be replaced. If the cost of repairs has added up to more than the cost of replacing your roof, it’s probably best to replace it. However, in many cases, repairs can be made that will help to extend the life of the flat roof. If you’re uncertain, be sure to call in a flat roofing professional to see what they recommend.

Once you have narrowed down your options, it’s time to call in a professional to have the roof replaced. Depending on the materials chosen, having a flat roof replaced might cost less than you think.