What you need to know about flat roofs and the different types of flat roofing

Flat Roofing in Hertfordshire

Flat roofs are known for various problems such as rainwater seeping into the house and water puddles forming on top. Some of the most common problems with flat roofs include poor thermal efficiency, bad workmanship and poor aesthetics. Over the years, however, the materials for flat roofs have improved. There are different types of flat roofs to pick from.

Original flat roof

Original flat roofs are covered with zinc, lead, copper or other pliable metal. Flat roofs from the 1960s onwards have felt covering.

Traditional cold felt flat roof

Flat roofs produced from the 1950s to 60s had various coverings. The most common styles on residential properties were felt chipping coverings. Traditional cold felt flat roofs have ceiling joists on which a decking is placed. Felt is then added in different number of layers as a roof finish. Today, this kind of flat roof is known as a cold deck flat roof. This is because it doesn’t have insulation in it.

Modern traditional cold felt flat roof

Traditional roofs now have insulation between the roof joists to offer energy saving and thermal efficiency. The heat inside your home won’t escape through the flat roof, helping you save on your energy bills as well.

Modern flat roofs

Improvements have been made to flat roofs to meet the needs of homeowners and business establishments that prefer such roofing options. There are different kinds of modern flat roofs to pick from. You can get a mono-ply system, which is a single rubber roof that is popular among developers. Another popular material that is used for making flat roofs is fiberglass. Green roofs or living roofs are also gaining popularity. These roofs are designed to have a grass like flora growing from the roof.

The Basic Design of Flat Roofs

The waterproofing done for a flat roof is sustained by the structural roof deck. This is commonly made from timber boarding and it is supported by the joists. For structures that have a ceiling, it will be directly attached to the bottom of the joists.

In line with the standard building regulations, the roofing over living areas must be insulated. Many practices put this insulation above the ceiling or deck before the waterproofing is done.

In the case of commercial or industrial projects, the waterproofing is placed below the insulation. This practice is restricted to only building structures meant for commercial or industrial purposes.

For a project where RBM has been installed, there will need to be some fortification made to cover the waterproofing as protection from ultraviolet rays and the heat from fire in the case of an accident. There are strict regulations that provide the right practices to be used concerning the potential outbreak of a fire. The common practice is to include a layer of mineral chippings with the compound to the surface of the roof. Another strategy will be the use of a RBM that has been covered with a mineral surface as the upper layer (Capsheet). This is usually the case for projects with liquid applied and single layer systems.


The effectiveness of the waterproofing materials used in a ceiling or rooking deck will be influenced by the methods used to build the roof deck as well as the ceiling. In the building industry, these two types of roofing are known as warm roof and cold roof. The following segment will highlight the features of these types of roof.


In this flat roof, the deck of the roof is always warm due to the placement of the insulation above the roof deck. It is used mostly for residential and privately owned properties. This type of roof requires no ventilation. The insulation is characteristically attached to the membrane, a common feature of this roof type.


In this arrangement, the waterproofing is placed directly on the deck while the insulation is put above the ceiling enabling the deck to become cold. It is commonly used for residential flat roof designs.

Cold roofs are prone to become affected by harsh weather conditions and if there is no ventilation provided to sustain the materials used in the construction, the roof will require maintenance in a short time. Creating the ventilation will require the services of an experienced builder due to the complex nature of this work. The ventilation spaces need to be created above the insulation.

It is not advisable to use the cold roof in areas prone to harsh weather conditions. In places like Scotland, there are regulations discouraging the use of cold roofs and encouraging the use of warm roofs.

In the case of where the cold roof on a building has deteriorated, the renovations carried out should include provisions that will change the roof structure from the cold roof pattern to the warm roof pattern.


There should be special considerations to fortify flat roofs to withstand any form of pressure on it for a long time. This means that the intervals between carrying out maintenance on the roof will be considerably longer. The following guidance is useful to achieve this.

Protection from harsh weather conditions.

  • The recommendations for a completed roof project are a slope of at least 1:80. This is possible with a design fall of 1:40 or 1:60 which is recommended.
  • There should be at least two provisions for drainage from the roof.
  • The common use of gutters should be widely encouraged over the use of internal outlets.
  • The sizes of any internal outlets should be adequate to handle any pressure from storms; they should be fitted with commonly used guards like the leaf or the gavel guards.
  • The acceptable height of the waterproofing is at least 150mm from the surface of the roof. This should never be compromised.
  • An appropriate cover flashing should be used to cover the upper edges of the waterproofing used for every roofing project.

For protection against sun or frost

  • There are many benefits of using insulation. It will lead to a reduction in the consumption of energy because the inner living areas in the home will be cooler during the summer
  • The provisions made by the building regulations must be adhered to when installing or renovating the insulations for flat roofs.
  • It is also important to provide protection for the bitumen membranes from direct exposure to sunlight.

Prevention of condensation

  • The surest way to prevent condensation is by using good ventilation.
  • In the case of warm roofs, there should be an adequate arrangement for a good vapor control layer (VCL) which will be attached to the deck directly.
  • Protection from the Wind

  • The essential parts including the insulation and membrane must be well-fortified against strong winds.
  • The measures that should be used to prevent destruction from heavy winds are well known to professional roofing contractors. It will be a good idea to seek professional advice concerning the protection of your roof from strong winds.

Protection from People

  • The necessary provisions should be made to fortify the roof to withstand the use of your roof by people.
  • There should also be good safety provisions to guard against fire outbreaks.
  • The local institutions that regulate real estate projects should be consulted before you build a new flat roof.
  • Ensure that your roofing contractor is experienced in the building of a flat roof that will meet the required and acceptable standards.

Which Flat Roof Material Should You Choose?

Three layer flat roofing

The most common material for flat roofs is of course bituminous felt set in 3 layers. The first layer is nailed down and the upper two are bonded to the one underneath with mastic bitumen. A solid bitumen-based compound may be heated to make it liquid and then poured onto the underlying felt. However, this can be a complicated job and should only be attempted by and experienced flat roofing specialist

Another popular roofing material is a single rubber sheet that’s custom made for weather-roofing a flat roof. The material is laid onto the roof boarding and is supported by the roof beams. Insulating material is placed in the space between the two.

The new rubber-based flat roofs are a cheaper and more convenient option. It’s also easy to find a supplier of rubber roofing materials. You just need to make sure that there are no gaps between the existing pitch roof and the rubber roof. Run the rubber materials under and up the slates or tiles of the adjoining pitch roof, so any rain that drops from the lower row falls onto the rubber without any possibility of getting beneath the pitch roof.

Find out about the different materials that can be used for flat roofs here