Choosing a flat roof is not simply a matter of picking a material and getting it installed.
A small roof over a home extension has very different requirements from a large commercial roof containing plant and service areas. An existing roof that needs replacing may present different challenges again.
The right choice depends on the building, the roof design, how the area will be used and what the finished roof needs to deliver.
At C&S Roofing, we install a range of flat roofing systems for residential and commercial projects, including single ply, hotmelt, bitumen and torch on felt roofing.
So, what should you consider before choosing one?
Start With the Building, Not the Roofing Material
It can be tempting to choose a roofing system because you have seen it used elsewhere or because a particular option has been recommended to you.
The building itself should come first.
Some of the main factors to consider include:
- Whether the project is residential or commercial
- Whether it is a new roof or replacement
- The size and shape of the roof
- Insulation requirements
- Drainage and outlet positions
- Roof access and expected foot traffic
- Plant, rooflights and other penetrations
- Whether the roof will support a green roof, terrace or other feature
- The amount of detailing around walls, edges and changes in level
- Budget and long term plans for the property
Once these points are clear, it becomes much easier to decide which roofing system is likely to suit the project.
Single Ply Roofing
Single ply roofing uses a lightweight synthetic membrane to create the waterproof layer of the roof. The systems installed by C&S Roofing use PVC membranes, with adjoining sheets joined using hot air welding to create a continuous waterproof surface.
Depending on the specification, the membrane can be mechanically fixed or adhered.
One of the main advantages of single ply is its low weight. The membrane is also flexible, making it useful where a roof includes different shapes, junctions or interfaces with existing parts of a building.
Installation does not require an open flame, which can also be an important consideration on certain projects.
Single ply may be worth considering where you want:
- A lightweight roofing system
- A relatively straightforward installation process
- Flexibility around roof details
- A solution for either new build or refurbishment work
- A clean and simple finished appearance
It can be used across residential properties as well as much larger commercial roofs.
Hotmelt Roofing
Hotmelt roofing uses a waterproofing membrane that is applied hot to a prepared structural surface.
The material bonds directly to the surface beneath it, creating a continuous waterproofing layer that follows the shape and detailing of the roof.
This makes hotmelt particularly useful for roofs with more involved layouts or architectural details. It can also be incorporated into green roof projects and other roof constructions where additional finishes will sit above the waterproofing layer.
Hotmelt may be worth considering for:
- Roofs with complex shapes or detailing
- Green roof projects
- New build or refurbishment work
- Projects requiring a fully bonded waterproofing layer
The complete roof construction still needs to account for factors such as insulation, drainage and anything that will sit above the waterproofing system.
Bitumen Roofing
Bitumen roofing has a long history in flat roofing and remains widely used across residential and commercial properties.
Modern bituminous membranes generally contain reinforcement, such as polyester or glass fibre, within the waterproofing material. This gives the membrane additional strength and stability.
Bitumen roofing is a broad category rather than one specific product. Different systems can use different membranes, layers and installation methods.
Torch on felt, which we look at next, is one form of bituminous roofing.
Bitumen systems may be worth considering where the project requires:
- An established flat roofing solution
- A system suitable for residential or commercial use
- Reliable waterproofing
- New roof or refurbishment work
The appropriate bitumen system will depend on the roof itself and the specification required.
Torch On Felt Roofing
Torch on felt uses bituminous membranes with an underside that is heated during installation so that the membrane bonds securely to the prepared roof surface.
C&S Roofing installs the Paralon torch on felt system, an APP modified bitumen waterproofing system with a stated life expectancy of more than 30 years.
The system can be used on new builds and refurbishment projects, as well as podium decks, balconies and terrace waterproofing.
Depending on the project, it can form part of warm, cold or inverted roof constructions.
Torch on felt may be worth considering where the project calls for:
- A multi layer bitumen waterproofing system
- New roof or refurbishment work
- Balcony or terrace waterproofing
- Warm, cold or inverted roof construction
- A proven bituminous roofing approach
Because heat is used during installation, the building and site conditions also need to be considered when deciding whether it is the appropriate system.
Do Not Look at Waterproofing in Isolation
Choosing between single ply, hotmelt, bitumen and torch on felt is only one part of planning a flat roof.
Insulation, drainage and detailing can have just as much influence on how well the finished roof performs.
With a warm roof construction, for example, insulation is installed above the structural roof deck. This helps reduce heat loss while keeping the deck on the warmer side of the roof construction.
Drainage also needs to be planned carefully. A flat roof is not completely level. It requires appropriate falls so that rainwater is directed to outlets rather than remaining on the surface.
Details around outlets, walls, upstands, roof edges, pipework and changes in level deserve particular attention. These are often the areas where problems begin if a flat roof has not been properly designed or installed.
The roofing system and the rest of the roof construction therefore need to be considered together.
Think About How the Roof Will Be Used
Two roofs of a similar size can require very different systems depending on what happens on them after installation.
A roof that will rarely be accessed has different requirements from a commercial roof containing plant that needs regular maintenance. A roof supporting vegetation has different requirements again.
Before selecting a system, consider questions such as:
- Will people need regular access to the roof?
- Will there be plant or equipment above it?
- Are there numerous rooflights, pipes or other penetrations?
- Will a green roof or terrace be installed?
- How easy will future maintenance be?
- What type of insulation is required?
Looking at how the roof will actually be used can help narrow down the available options considerably.
What If You Are Replacing an Existing Flat Roof?
A replacement project should start by establishing why the existing roof needs work.
Age may be one reason, but recurring leaks, damaged waterproofing, poor drainage or problems with the original installation can also be involved.
Replacing the existing covering with the same type of system without considering what caused the problems may simply recreate some of the weaknesses already present.
A replacement gives you an opportunity to review the waterproofing, insulation, drainage and important roof details together.
For homeowners, our residential re roofing service covers the options available when an existing roof has reached the end of its useful life.
For business premises and larger properties, C&S Roofing also provides commercial re roofing solutions based on the condition and requirements of the existing roof.
Getting the Right Flat Roof for Your Project
Single ply, hotmelt, bitumen and torch on felt all have applications where they work particularly well. The important part is matching the roofing system to the building and the job the roof needs to do.
Roof size, shape, access, insulation, drainage, detailing and future use should all form part of that decision.
At C&S Roofing, we work across residential and commercial flat roofing projects and can assess these requirements before recommending a suitable system.
If you are planning a new flat roof or replacing an existing one, get in touch with C&S Roofing to discuss your project and the available options.
