Flat roof outlets – what do roofers need to know?

When it comes to flat roofs, efficient drainage is essential to prevent water pooling, which can lead to serious structural damage and costly repairs. Understanding flat roof outlets and their role in your roofing system is crucial.

In this blog, we’ll cover the basics of flat roof outlets and highlight some of the outlet options available from Lancastria, all tried and trusted by our flat roofing customers.

What are flat roof outlets?

Flat roofs are a popular choice for many commercial, industrial, and residential buildings due to their modern aesthetic, cost-effectiveness, and efficient use of space. When designing and specifying a flat roof, it is important to consider proper drainage.

The unsung hero of the flat roofing world, flat roof outlets are designed to ensure adequate drainage of water from flat roofs, preventing water accumulation that can otherwise cause leaks, structural damage, and other issues. By specifying the right outlets, roofing designers and contractors can ensure the longevity and durability of their flat roof project.

The risks of improper drainage on flat roofs 

Allowing water to pool on flat roofs can compromise the integrity of the roof and, in the worst-case scenario, the structure of the building. Water pooling increases the likelihood of water seeping through roofing material, joints and seams, or through skylights and vents, leading to damage to walls, ceilings and insulation. It can also act as a thermal bridge, impacting the energy efficiency of the roofing, or even causing damage if it freezes and expands during the winter months. Left unchecked, excessive pooling can cause deflection of the structure, outlet blockages, or lack of access to roof mounted plant.

Compliance with Building Regulations is also a key driver in ensuring proper specification of drainage on flat roofs. Guidance and standards for rainwater drainage are provided in Approved Document H of the Building Regulations for England and Wales and Building Standards Part 3 in Scotland. The National House Building Council, (NHBC) standard 7.1.5 also provides guidance on the design of drainage for flat roofs, balconies and terraces. All of these documents require that flat roof drainage is designed in accordance with BS EN 12056-3.

Key considerations for choosing flat roof outlets

Factors such as rainfall intensity, roof area, and building life influence drainage design. However, it is also important to consider the design and durability of the outlet, to ensure that it drains water effectively.

• Outlet material: consider the material that your outlet is made from. Outlets can be constructed from different materials, including PVC, EPDM, or metal.
• Water volume: how much rainwater does the outlet needs to be able to handle. Is there likely to be heavy rain? Must it handle run-off from another structure? Do you need a solution that can handle a high flow rate?  Choose the outlet (and the quantity of outlets) according to your roof specification, location and size. A massive part of the flow rate is down to the correct leafguards being specified. Using the correct leaf guard can massively increase the flow rate.
• Roofing membrane: Also ensure you speak to your supplier to ensure that the outlet is compatible with the roofing membrane that you plan to use – this is an important step in ensuring the integrity of your waterproofing system. And consider maintenance too. Does the outlet need a leaf guard to prevent blockages?
• Installation: always ensure outlets are positioned at the appropriate place on the roof to facilitate natural water flow. It is also essential that the seal between the outlet and the roofing membrane is watertight to prevent leaks.
• Maintenance: regular inspection and cleaning of the outlets and leaf guards will help ensure the roof performs as planned.

Recommended flat roof outlets from Lancastria

Lancastria offers a range of high-quality flat roof outlets and accessories designed to meet all flat roofing outlet needs, applications and budgets on new build or refurbishment projects.

Our flagship range of outlets are the SBS, PVC or plain Metal flanged stainless steel spigot outlets. These offer excellent durability as well as being able to be bonded and sealed very easily by design. These outlets with there range of flanges will suit almost any system with the correct one specified.

These are also available as a parapet outlet, which is the perfect solution for through-wall applications or outlets positioned close to an abutment. Available in three sizes, and with a flow rate of 0.32 litres per second, the outlet features a heavy-duty stainless-steel spigot. There is no ‘lip’ at the entrance to the spigot which reduces the risk of ponding.

Our EPDM Black Flat Roof T-Pipe drainage outlet is suitable for use with Torch On felt. The ribbed push-in downpipe provides a completely leak-proof connection to the pipework.

Cost effective alternatives include the EDPM sump flange outlet, for use on flat roofs with EPDM, felt and bituminous membranes, or the EPDM Square Parapet or Balcony rainwater drainage outlets, which offer weather and UV resistance for use with EPDM, bituminous or felt membranes and materials.

The EPDM Mechanical Fix Flange Outlet comes with an integrated leaf grate. Designed to be easy to fit, the roofing membrane is dressed over the outlet flange and secured by the mechanically fixed clamping ring over the threaded stainless-steel studs – creating a secure, leakproof seal between the roofing membrane and outlet.

Unsure which outlet is the right one for your application, or need advice on how many outlets you need to ensure adequate drainage? Speak to our friendly team, who will be happy to help. Call us on 0161 777 9009 or email sales@lancastria.com