How to Build a Flat Roof?


Roof 1

Flat or slope roof is a type of roofing that is widespread both in the US and all around the World. You can see such roofs on residential low-rise houses and extensions, on multi-apartment buildings, on commercial real estate, shopping centers, industrial and office buildings of any size.

In addition, you can spot flat roofs on sheds, garages, balconies and terraces. Such roofs are usually covered with bitumen and asphalt, rubber or EPDM, PVC membranes, sheet metal or even solar PV-panels.

DIY or Roofing Contractor

At first glance, an average flat roof seems like a simple structure you can build yourself, but in reality it is not an easy task.

Even a minor mistake in the calculations or during the installation of the roof frame, underlayment material or roofing material can lead to permanent leaks, wind uplifts, cracks and fractures. As a result, you risk causing damage to your inner house property and building structure.

Therefore, if you are planning to build a flat roof, but you do not have experience in the construction of roofs and the corresponding skills, we strongly recommend contacting professional roofers.

When choosing a roofing company, look at check list: whether the company has licenses and permits for the installation of flat roofs, what materials the roofers use and what guarantees they give when everything is done. Ask the experts of roofing contractor to come up with an estimate. Usually it’s free.

Step by Step Guide

Attention! The specific list of construction works depends on the type of project and the selected roofing material.

  1. Firstly, even before the construction of the roof frames, consider whether a flat roof is suitable for the selected project. Consider the architectural and structural features of the building, as well as the climate and weather in the region. Your main task is to make a reliable roof for ages that will not let water get inside your house and that will withstand wind and snow loads.

When completing roof design, consider additional but still optional elements on the roof – chimneys, skylights, ventilation system, utilities, and so on.

  1. The next step is to build stable and secure roof frame with joists. Usually they spaced 1-1.5 feet apart but it depends on the project. Joists must be fastened, as they will hold the main load of the whole roof.

The particular scheme and material of the frame depends on the project, the area of ​​​​the flat roofing, the weight of the roofing materials, as well as your plans. If you plan to use the roof as a furnished terrace, the frame needs to be strengthened accordingly.

Despite their name, ‘flat’ roofs are not completely flat. Usually roofers make a slight slope during the construction of the roof frame, so that the water accumulated on the surface goes directly into the gutters. The angle of inclination of the roof surface depends on the area and the roofing material. It can be invisible to the eye, or it can be quite discernible.

  1. Sheathing and underlayment is something to think about in the next step. The roofing material is attached not to the frame, but to a special sheathing. Most often, plywood or similar materials are used. They can be additionally reinforced with fiberglass backing, rigid foam and other materials.

In addition, builders install special underlayment materials like insulation, waterproofing, vapor-control or breather membranes that protect the interior of the building from water, moisture, heat loss (in winter) or heat (in summer), condensation and etc.

The specific set of underlayment and deck materials depends on the type of roof – warm, cold or a so-called compact roof. Each type of roof has its own advantages and disadvantages.

  1. Installation of covering flat roof materials. When the underlayment is ready, the flat roofing materials are mounted on the top. Depending on the material chosen, roofers use one or another installation technology – some materials are mounted using the torch-down method, others are adhered or screwed using special fasteners.

Roof 2

What Material to Use When Building a Flat Roof

Several types of materials for flat roofs are used in our country. The choice of material depends on several criteria – the type of building and roof itself, your individual requirements for appearance, your budget, climatic features of the region, and so on. When choosing a material, consider its service life, need for maintenance and maintainability as well as weight and other parameters.


Common materials in this category are rubber, EMPD, TPO, PVC. Each material has its own characteristics, service life limitations, its own level of waterproofing and resistance to mechanical damage. Membranes can be just laid down on the roof surface, fully adhered, fastened by adhesive, solvent welded and so on.

Modern membrane roofing materials are the best choice if you are looking for a durable, environmentally friendly and energy-efficient solution.


There are many roofing materials based on bitumen (or based on more modern polymer analogues of bitumen). Their main advantage is low cost, so these materials are most often mounted on commercial or industrial buildings. Bitumen roofing can be mounted using cold, hot or torch-down methods. BUR, one of the oldest roofing technologies, also uses gravel, asphalt and bitumen.


Despite the fact that metal, including corrugated metal, is more often used in the installation of sloping roofs, sometimes metal sheets are also used as roofing material for flat structures.

Sheets of galvanized steel, aluminum or copper are used as roofing material. As a rule, they are attached to the roof with special fasteners and connected with special waterproof seams with each other.

PVC or wood decks

These materials are ideal for exploited roofs, terraces, outdoor patios. They are mounted over rubber, EPDM or PVC membranes that protect the building from water.


A flat roof can be a compliment and a highlight of your property. If it is designed and built correctly, a flat roof will reliably protect your property from any negative elements such as rain, wind and snow. In addition, if everything is done correctly, the roof will last 20-30 or even 50 years without the need for major repairs. All you have to do is check the perfectly installed roofing material a couple of times a year for damage or leaks.

How to Build a Flat Roof? was last modified: by