A flat roof upstand might sound like small talk for architects, but it’s actually a big deal when it comes to waterproofing performance. In short, it’s a vertical extension of the roof’s waterproof layer. One that keeps rain from sneaking into places it shouldn’t, like wall junctions, parapets, or pipe penetrations.
A bit of detailing in this area can make all the difference. When installed correctly, an upstand protects a building from leaks, supports drainage, and keeps the flat roof compliant with British Standards. Yet, when it’s done badly, even the strongest system can fail and often right at the edges.
Definition and Purpose of an Upstand
A flat roof upstand is the raised edge of the waterproofing layer where a flat roof meets a vertical surface such as a wall, skylight, or parapet. Its purpose is simple: to stop water from running into vulnerable junctions and direct it safely toward drainage outlets.
Good roof upstand details protect against leaks, improve drainage, and help maintain compliance with building standards. Parapet upstands, for example, form a neat, continuous seal that keeps the structure watertight while blending with the building’s design.
When installed correctly, a waterproofing upstand becomes a quiet safeguard. Small in size but vital for long-term flat roof waterproofing performance.
Typical Materials Used for Upstands
The choice of material for a flat roof upstand affects how well it performs and how long it lasts. Different roof types demand different solutions, so compatibility is key. Here are some common materials used in roof upstand details:
- GRP (Glass Reinforced Plastic): Seamless, strong, and ideal for parapet upstands or complex shapes. May feel a little rigid on larger roofs.
- Liquid-Applied Systems: Flexible and perfect for creating a continuous waterproofing upstand around penetrations. Correct surface preparation is vital.
- Lead or Metal Flashings: Traditional and durable, often used to cap the top of upstands. It must be fixed properly to prevent cracking as temperatures change.
- Single-Ply Membranes: Lightweight, clean finish, and quick to weld. Works best on smooth, prepared surfaces.
- Bituminous Felt: Layered and reliable, though it can look bulky if detailing isn’t tidy.
Matching roof flashing and upstands within the same manufacturer’s system avoids expansion issues, maintains warranty compliance and protects the flat roof waterproofing over time.
Correct Upstand Height and Positioning
A flat roof upstand must be tall enough to stop splashback and wind-driven rain. British Standard BS 6229:2018 recommends a minimum 150 mm height above the finished roof level. This clearance helps water drain freely without reaching vulnerable joints.
Upstands should appear wherever the roof meets a wall, parapet, rooflight, or service pipe. Around parapet upstands, the waterproofing layer should rise behind coping or flashing for a continuous seal.
Meeting these upstand height requirements keeps drainage effective, warranties valid, and the flat roof waterproofing system working exactly as designed.
Why Height Matters for Drainage and Weatherproofing
A flat roof upstand protects against ponding, splashback, and wind-driven rain. When it’s too low, water can creep into joints through capillary action and damage insulation below.
Meeting upstand height requirements (usually 150 mm above finished roof level) ensures reliable drainage and proper separation between the waterproofing upstand and any vulnerable wall detail.
Adequate height keeps roof flashing and upstands working together, preventing leaks and maintaining warranty compliance. It’s a small dimension that makes a major difference to the durability of flat roof waterproofing systems.
Upstand Detailing at Walls and Edges
How an upstand connects to walls and edges often decides how watertight a flat roof remains. The junctions between horizontal and vertical surfaces are where most leaks begin, usually from poor finishing rather than failed membranes.
A flat roof upstand should extend neatly up the wall and sit behind any coping stone or metal flashing to form a continuous waterproofing upstand. At the roof edge, drip trims or termination bars help shed water cleanly. A small but key part of flat roof edge detailing.
Good practice includes:
- Smooth transitions between deck and wall.
- Maintaining a 150mm minimum upstand height.
- Matching roof flashing and upstands for material compatibility.
- Properly sealing joints at parapet upstands and corners.
These simple details keep the entire flat roof waterproofing system durable, compliant, and leak-free.
Common Installation Mistakes to Avoid
Even high-quality flat roof systems can fail if upstands are fitted incorrectly. Most problems start with small detailing errors that let water in over time.
Top 5 Mistakes to Avoid
- Low Upstand Height: Below 150 mm invites splashback and voids warranties tied to upstand height requirements.
- Poor Adhesion: Weak bonding near parapet upstands lets moisture creep behind the membrane.
- Mixing Materials: Incompatible roof flashing and upstands expand differently, causing cracks or peeling.
- Over-Tight Membranes: Pulling too hard at corners creates stress fractures.
- Neglected Edges: Missing trims or drip details allow water to cling underneath.
These small faults quickly compromise waterproofing upstands and drainage. Careful detailing and system-matched materials keep every flat roof upstand performing as intended.
Importance for Waterproofing Performance
A flat roof upstand might look minor, but it’s central to reliable waterproofing. It stops water from creeping into the roof structure through capillary action or wind-driven rain, especially around parapet upstands and corners.
When detailed correctly, the waterproofing upstand channels water safely into outlets and protects insulation and decking below. Most roof upstand details form part of manufacturer warranties, ignoring upstand height requirements or incompatible roof flashing and upstands can void such cover.
In short, this small vertical feature keeps your flat roof waterproofing consistent, compliant, and built to last.
Maintenance and Inspection of Upstands
Even the most durable flat roof upstand benefits from a little routine care. Over time, sunlight, temperature swings, and natural building movement can cause small cracks or separations, particularly around parapet upstands and roof flashings.
Inspect the waterproofing upstand at least once a year, and after extreme weather. Lifting edges, surface splits, or discolouration are early signs that water might soon find a way in. Keeping outlets and edge trims clean also helps prevent ponding and ensures the flat roof waterproofing performs as intended.
Professional inspections are well worth arranging. They confirm that upstand height requirements are still compliant and that all materials remain properly bonded. Regular checks like these protect warranties, extend roof lifespan, and help prevent costly repairs later.
If your flat roof upstand shows signs of wear, or you simply want reassurance that it’s performing as it should. Speak with our specialists at AAC Flat Roofing. Our team provides detailed inspections, repairs, and long-term waterproofing solutions across the UK.
Learn more about our flat roofing services or contact us today to arrange an assessment.
