Flat Roof Upstand: Everything You Need to Know

What flat roof upstand height is needed for a flat roof installation? It’s a fairly simple question with a fairly simple answer – 150mm above the finished roof level. But often this guidance can be misunderstood or incorrectly interpreted, due to many different regulations. So, to clear this up and for more information on the minimum upstand for flat roof buildings, continue reading.

What is an upstand on a flat roof?

Before we dive into the flat roof upstand detail, let’s first highlight what an upstand is on a flat roof. An upstand on a flat roof is a raised section or edge where the roofing membrane continues vertically up a wall, parapet or around a roof feature like a skylight or vent. It’s typically 150mm or more above the roof’s surface.

The purpose of an upstand is to:

• Prevent water ingress: Upstands stop rainwater from seeping into joints between the roof and adjacent walls or structures, especially where surfaces meet at 90° angles.
• Ensure waterproof integrity: By turning the waterproofing membrane (like EPDM) up and over the upstand, you create a continuous and sealed system that resists pooling water and wind-driven rain.

• Comply with building regulations: Including building codes like BS 6229, BS 8217, and the NHBC Standards 2025.

Exceptions to UK building regulations

The NHBC Standards 2025 normally defines a minimum upstand for flat roof height as 150mm. But this is unless it serves as an accessible threshold, where this height can be reduced to 75mm. An accessible threshold is a doorway or opening that provides step free access between internal and external spaces. It is typically used for entrances and patio doors with accessibility needs, or openings to balconies and roof terraces. The standard 150mm upstand ensures waterproofing integrity, but at door thresholds, it creates a step that hinders accessibility. The upstand height may be reduced to 75mm to allow easier passage for wheelchairs, pushchairs and people with limited mobility.

Because lowering the upstand can make the area more vulnerable to water ingress, additional detailing is needed, such as a high performance EPDM membrane that’s carefully sealed around thresholds.

Waterproof your upstand with EPDM

When it comes to flat roof waterproofing, upstands are an extremely important detail. EPDM (Ethylene Propylene Diene Monomer) rubber makes sealing them simple and effective. Made from a blend of natural gas and oil, EPDM is a synthetic rubber formed into tough and flexible sheets. It’s the ideal material for creating a watertight seal across your roof and upstands, whether you’re working on a garage, extension, shed or bay window.

Because EPDM is a complete roofing system, it easily accommodates upstands and detailing without the need for complex joints or additional flashings. You can find supplies for your flat roof in our shop if you are comfortable handling installation yourself. Alternatively, we offer flat roof installation services too to guarantee a professional and durable finish.

Why choose EPDM rubber for your flat roof?

• Exceptionally durable: EPDM can last for decades with no cracking, blistering or splitting.
• Weatherproof and UV resistant: Performs reliably in the UK’s harshest weather, from freezing winters to heatwaves.
• Fire-resistant: Offers excellent resistance to fire, UV rays, ozone and temperature extremes.
• Low maintenance: Once installed, it requires very little upkeep.
• Cost effective: With its long lifespan and minimal maintenance, EPDM is one of the most budget friendly options available.
• Ideal for low pitch roofs: Perfect for shallow gradients where traditional tiles aren’t suitable.

Ready to install a flat roof upstand?

Whether you’re planning a DIY flat roof project or looking for expert installation, the team here at Alvadac has you covered. We supply premium EPDM rubber roofing systems across Yorkshire, ideal for waterproofing upstands, thresholds and all flat roof detailing. Need help with your installation? Our experienced team offers a full fitting service to ensure your roof is sealed, secure and built to last.

Contact us with enquiries or if you would like to keep reading, you can check out our guide: Is EPDM Rubber Roofing Better Than Felt Roofing?