Skip to main content
Coppered oak rooftop design

If a roof is not capable of tolerating the additional weight of a terrace, what steps can I take?

If you do face this problem, there are two main ways to rectify it. Firstly, you can reinforce the walls or introduce beams to strengthen the original structure. This can be costly but is often the best course of action. The second option is to build a steel frame on top of the existing roof to take the weight of your new development. This ‘floating frame’ distributes the weight of the terrace evenly across the walls and protects the existing building from load damage.

What waterproof protection do I need to include in my plans?

Rooftop terraces and gardens built directly onto a roof will need to include a protective layer to prevent water damage. If the waterproof layer is not resistant to root penetration, then a root-resistant layer should be added. This root-resistant layer will be covered by a protective board to keep tools and machinery from penetrating the layers below. The waterproof layer should be replaced during redevelopment if it is nearing a lifetime of approximately ten years old.

What drainage measures will be necessary?

A simple way of removing water is to include a drainage sheet between the waterproof layer and the soil or flooring. Drainage sheets have a slight gradient that carries water away to the gutters of the original building. In rooftop gardens, a filter layer is included to prevent soil from collecting in the drainage sheet. On unusually large rooftops, it might be necessary to include gullies and water conduit systems.

What are the first steps of laying a floor on a roof deck?

Your construction will determine your floor-laying options. When using a floated-steel frame, the flooring can be laid directly onto the frame itself. When laying directly onto a roof, the most common method is to use pedestals. The benefit of a pedestal system is that it allows for drainage elements and other services to run below the flooring. Pedestals can be used for paving or decking.

Is it better to use paving or decking?

The short answer is that both types of flooring have pros and cons. Concrete slabs are generally easy to maintain and can be laid directly on top of pedestals. However, they do seem to be the default in many roof designs and that can make the installation feel a little uninspired. Decking boards can look beautiful but require a substantial gap underneath them as the wood will need to breathe to slow down rotting. Wood will also need annual anti-algae treatments to prevent the boards from becoming slippery. Alternatively, Millboard decking has zero timber content and can be installed lower to the ground, making it the ideal choice for rooftop terraces. It also requires little maintenance, and won’t degrade or host algae as timber would.

What is an extensive roof?

Extensive roofs, or ‘living roofs’, are easy to install and manage. These installations turn roof-spaces into elevated meadows. A thin layer of soil is laid onto the roof surface and sown with low-maintenance plants. This layer insulates the roof, which reduces energy bills and noise disruption. The extensive roof is not designed for walking on.

What is an intensive roof?

Intensive roofs are the most common type of rooftop renovation. They include seating areas, dining areas and more elaborate gardens than those found on extensive roofs. The options available on an intensive roof are limited only by the strength of the building and the size of the budget. With some intensive roofs including soils depths of over a metre, it is not uncommon for the final design to have a final weight well over 650kg/m².

What else can I do with my roof space?

Rooftops can also be used for water collection, allotment space and energy generation. In fact, rooftops can be adapted for almost any concept you can think of – so long as the main elements (weighting, waterproofing and drainage) have been considered.

Back to top