Upstand Height for Roof Hatches: Single Ply, EPDM and Protected Roof Interfaces (Without the Leaks)

Those phrases come up all the time because upstand height sounds like one simple dimension. In reality, it’s usually three coordination decisions rolled into one:

• What is the upstand/kerb made from? (timber / concrete / steel)
• Where is the height measured from? (deck, insulation, or finished roof level)
• What roof system is turning up against it? (single ply, EPDM, or protected/inverted)

Get any of those wrong and the waterproofing detail ends up fighting gravity — even with a perfectly good roof hatch.

At a glance (the things that prevent leaks)

• Define the measurement datum: “upstand height above finished roof level” is the only wording that avoids ambiguity.
• Know the baseline expectation: industry good practice commonly references BS 6229:2018 and a minimum waterproofing upstand of 150mm above the finished roof surface (and on protected roofs, the “finished surface” is the top of the protection layer).
• Protected roofs change everything: pavers/ballast/green roof layers can “eat” your visible upstand if you don’t allow for them early.
• EPDM is often two different things: an EPDM roof membrane (waterproofing system) vs an EPDM seal to the hatch lid (product component). Mixing these up causes avoidable RFIs.

The phrases we see every week (and what they usually mean)

These are the real-world phrase fragments that show up in enquiries. They’re not wrong — they’re just incomplete without context:

• “300mm upstand” — is that the product upstand, the builder’s kerb, or the required upstand above finished roof level?
• “concrete upstand” / “timber upstand” — what substrate are we fixing into?
• “curb liner” — typically a formed liner detail to create a clean external face/interface (often referenced on roof hatch details).
• “insulated upstand” / “fully insulated kerb” — do you need thermal continuity at the opening?
• “upstand RAL” — will the upstand/kerb be visible above finished roof level (and therefore needs a specified finish)?
• “single ply membrane” — the turn-up, corners, and termination method need to be shown/owned by the waterproofing specialist.
• “EPDM bubble seal” — usually refers to the hatch lid gasket/seal, not the roof membrane.

Definitions: upstand vs kerb vs curb liner

You’ll see these terms used interchangeably, but they’re not always the same thing. A quick glossary helps prevent crossed wires:

• Upstand / kerb (generic): the vertical rise above roof level that the waterproofing system turns up against.
• Builder’s kerb / structural upstand: a timber/concrete/steel upstand formed around the roof opening.
• Curb/kerb liner: a formed liner that can create a clean external face and interface for weathering materials.

Key point: most “leak” problems happen at the interface — not because someone picked the wrong hatch.

The core coordination issue: what is upstand height measured from?

Upstand height becomes unambiguous when you define the reference line:

• Datum A: structural deck level
• Datum B: top of insulation
• Datum C: finished roof surface adjacent to the opening (the one that matters most in practice)

Critical good practice note: Standard practice commonly referenced in BS 6229:2018 requires the waterproofing to extend a minimum of 150mm above the finished roof surface. On protected roofs, that finished surface is typically the top of the protection layer (pavers/ballast/green roof), not the membrane.

Waterproofing interfaces by roof type

Your waterproofing contractor should always follow the membrane manufacturer’s detailing rules. But you can reduce risk (and RFI churn) by specifying the correct datum and showing the layers clearly.

Single ply interfaces: corners and terminations are where leaks start

Single ply roofs can be very robust, but upstands and penetrations fail in predictable places:

• Corners at square kerbs (the most demanding workmanship)
• Termination level too low (especially if insulation/falls/protection layers increase later)
• Unclear restraint/termination intent (leading to “best guess” site decisions)

What to do in the spec/section:

• Dimension required upstand height above finished roof level (not just “upstand = 300mm”).
• Show build-up thicknesses near the hatch so the roofer can confirm the exposed vertical height.
• Add a simple note: “Waterproofing contractor to detail membrane turn-up, corners and termination to system manufacturer requirements.”

EPDM interfaces: clarify what “EPDM” means (roof membrane vs hatch seal)

This one causes genuine confusion in enquiries, so it’s worth being explicit.

Protected roofs: the critical warning people miss

If your roof is protected (terrace paving, ballast, green roof build-up), the reference point changes. This is where “we designed 300mm” turns into “why is the waterproofing so low?” on site.

• BS 6229 good practice typically requires 150mm of clear upstand above the paving/ballast, not just above the membrane layer.
• Always show the protection layer thickness and finished level on the section.
• Consider a maintenance/inspection zone around the upstand so terminations can be inspected and repaired.

How Surespan roof hatches typically interface with the roof (what’s “by others”)

Surespan roof hatches are manufactured with an integral insulated upstand and an external fixing flange. The flange is intended to be sealed to the roof slab/upstand and mechanically fixed to retain the unit in place.

In a typical build-up, the roof weathering membrane/material is then extended over the fixing flange and dressed up the sides of the unit upstand, before being tucked under the weathering lip and secured in place (final waterproofing detailing by the waterproofing contractor to their system requirements).

This is why a roof section and roof system choice matter more than a single “upstand height” number.

Product context (quick, relevant highlights)

If you’re choosing between a standard access hatch and an AOV with access, these are the interface-relevant points specifiers tend to look for:

• SRHP75 Standard Roof Hatch: Thermally broken lid and upstand, external curb liner, 75mm PIR insulation (material U-value stated as 0.26 W/m²K), integral weathering lip, gas spring assisted opening.
• SRH-PAOV Smoke Vent with Access: Thermally broken, curb liner as standard, upstand height stated as 300mm, and 50mm PIR insulation option with 0.43 W/m²K U-value (PIR insulation performance).

Related links:

• Roof Access Hatches (category)
• SRHP75 Standard Roof Hatch
• SRH-PAOV Smoke Vent with Access

The quote-ready checklist (copy/paste into your enquiry)

If you include the items below, most technical back-and-forth disappears and you’ll get a more buildable response first time.

Geometry & levels

• Structural opening size (width × length)
• Upstand/kerb height required above finished roof level (standard requirement: 150mm)
• Roof falls direction and nearest drainage outlet position
• Is the roof exposed or protected/inverted (pavers/ballast/green roof)?

Roof build-up

• Deck type (concrete / steel / timber)
• Insulation thickness (including tapers where relevant)
• Waterproofing system type (single ply / EPDM roof membrane / other) + manufacturer if known
• Any protection layers and thickness (pavers/pedestals/ballast/green roof build-up)

Interface scope

• Who provides the kerb/substrate (builder vs roofer)?
• Who details the membrane turn-up/termination (normally the waterproofing contractor)?
• Any finish requirements for visible upstands (e.g., RAL)

Next step (fastest route to a correct detail)

Send your roof build-up + a section and we’ll confirm the interface assumptions before you finalise the detail.

• Include the roof system type (single ply / EPDM roof membrane / protected roof).
• State the required upstand height above finished roof level (and confirm whether the roof is protected).

Submit a Roof Hatch Specification Request