Adding Pitch to a Flat Roof in Florida

adding pitch to a flat roof

Flat roofs are a popular roof choice for many types of buildings. You’ll see stylish modern homes, as well as big-box stores, office buildings, and warehouses built with flat roofs. You’ll also see some older buildings, say in downtown blocks, with flat roofs that don’t perform well over the years. They might leak, or might frequently have pooling water after rains. If that describes your home or building, let’s go over ways of adding pitch to a flat roof in Florida.

Common Flat Roof Materials

You’ll see flat roofs covered with a few common materials, including:

  • Membrane roofs like EPDM, TPO, and PVC
  • Modified bitumen roofing
  • Built-up roofing

All of these can work well and can have a lifespan of 20–30 years. Lifespan depends on the material and some other conditions, though. A flat roof that’s too flat, though, will probably have some pooling water from time to time. That’s potentially trouble, unless the building is located in a very arid climate. But here we’re concerned with Florida roofs, and really flat roofs in Florida are definitely a cause for concern. With all the rain we get, including storms that dump several inches of rain at a time, we need roofs that drain well.

Why Change A Flat Roof?

No matter the type of roofing material that is on your roof, you may find yourself considering adding pitch to a flat roof. Your roof might have a persistent leak, or you might receive a directive from the building department. The updated building code may require you to bring your building’s roof into compliance.

A flat roof, by the way, is usually not truly flat. It will usually have a pitch of 1/12 or 2/12. That means it rises vertically 1 inch or 2 inches for every 12 inches of horizontal run. The common suburban homes you see everywhere, in comparison, usually have a roof pitch of 4/12. 6/12 is quite common as well. A 12/12 roof is pretty steep and is 45°, for you geometry nerds.

A really involved and expensive way of adding pitch is to work on the framing of the building. If the roof framing is structurally deficient, there’s probably no way around this approach. You’ll need to work with a building contractor who does this type of work. A structural engineer will probably be working on this job as well.


If the building’s framing is basically okay, or it just needs some minor tweaks and reinforcements here and there, you can consider another way to add pitch: tapered insulation systems. Take a look at this page from roofing giant GAF and you’ll get the gist of it. They and other manufacturers create rigid foam—polyisocyanurate—in both flat sheets of varying thicknesses and in tapered sheets.

The tapered sheets can be tapered in just one direction or in two directions. Those sheets that taper in two directions and are generally used in larger commercial projects. Those projects involve more complex designs to move water to drains and gutters and scuppers. Those roofs can be hundreds and even thousands of square feet of roof surface.

Adding Pitch to a Flat Roof

For this article, we can illustrate the concept by upgrading a home’s low-slope roof with tapered insulation topped with a membrane. This is a very slick and tidy system that is both functional and cost effective for homeowners.

Your contractor will start by evaluating the condition of your existing roof. The next step is to determine the thickness of foam required to move water from the high side to the low side. The thickness on the high side will be determined by the run, or the horizontal distance the water has to move. Let’s say your roof is 50 feet from the high side to the low side. One-quarter inch of drop per foot of run is the standard minimum drop, so you’ll need 12.5″ of drop on that roof.

As the GAF site shows, the system uses both tapered sheets and standard sheets. The system builds up the high side against either another wall on the house, or against a parapet wall. In our example here, your contractor can build a parapet wall on the high end and on the two sloped sides if your home doesn’t already have those.

What’s A Parapet Wall?

A parapet wall is basically just a built-up edge treatment for a flat roof that provides a place to finish off the membrane edge. There’s no standard height for a parapet wall, so on commercial and big-box buildings you’ll see them at around 20 inches and higher. That visual barrier helps to hide the air conditioning equipment and other mechanical equipment that has to be installed up there.

For your home’s flat roof, aesthetics play a role as well. Your contractor can install a membrane roof without parapet walls, but you may find that you have a more pleasing appearance with parapet walls. They do actually increase functionality, as well. Raising up the outside edge of the membrane helps to keep the water where it belongs, and moving downstream on top of the membrane.

Your contractor can create parapet walls quite simply if your home doesn’t have them already. With a stack of 2×6′ boards on three sides of the roof, for example, he can create this edge treatment quickly and cheaply right on the roof decking. Taller parapet walls require more involved framing.

Insulation and Membrane Come Next

Next the crew installs the tapered insulation system on the roof deck. The crew can either glue the insulation down or adhere it with screws and large washers.After that the membrane goes on, and the crew will typically glue it down. At the parapet walls the membrane turns up and runs vertically. If the parapet wall is really short the membrane will run right up under the flashing cap that covers the top of the parapet wall. A taller parapet wall may have a siding material, as well.

adding pitch to a flat roof
A very short parapet wall with PVC membrane.

Adding Pitch To A Flat Roof With Tapered Insulation

If you’d like to talk about your flat roof options and adding pitch to a flat roof, give us a call at 813-373-9088. Our team has more than 40 years of experience in roofing. You can also use this form and ask us, “What’s the cost for a flat roof for my home?” and we will contact you.

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