Straight-Route DDA Lift Design for Pavement Vault Entrances

Key Takeaways

• A 1480mm envelope between a façade line and a pavement vault wall can still deliver straight-route wheelchair access with the right geometry decisions.
• The 1400mm straight-route “golden number” is not just a dimensional target; it reduces stress, improves autonomy and simplifies operation.
• Moving a top threshold by 30–35mm can remove pinch hazards, improve tolerances and reduce invasive builders work later.
• A small, controlled shave into the vault support zone (often around 50mm) can be preferable to forcing a 90-degree travel configuration.
• Fixed railings can often remain untouched if the lift footprint is designed around them early.
• Level discrepancies that feel “minor” (10–30mm) are not minor for wheelchair stability and must be designed out.

What problem does a 1480mm pavement-vault constraint actually create?

When an entrance sits above pavement vaults, you are not just fitting a lift into a visible opening. You are fitting a lift into a structural sandwich: heritage steps above, vaults and services below, and fixed edges you cannot move without escalating approvals and cost.

In this type of enquiry, the visible geometry usually forces three competing goals:

• protect the façade line and avoid cutting into the building face
• keep existing railings aligned and undisturbed
• create a platform route that feels natural to a wheelchair user, not “technical”

A key line in the discussion captures the intent clearly:

“We don’t want to cut into the front face of the building.”

Why 1400mm is the heritage “golden number” for straight-route entry

In constrained entrances, it is tempting to accept a turned configuration because it can appear to “solve” the geometry with less pavement interface.

The practical issue is that autonomy suffers. A user who must turn to travel is being asked to manage alignment, door timing, and platform positioning at the exact moment the building should feel welcoming.

The meeting captured that human reality:

“I don’t think the user would want to have to turn 90 degrees when you’re giving them autonomy to get into the building themselves.”

Straight-route entry at approximately 1400mm creates a calmer sequence so is preferred when possible:

• approach in a straight line
• enter without pivoting
• travel without reorientation
• exit straight to the threshold

That is why Sesame Access typically tries to engineer the envelope to meet straight-route geometry first, and only falls back to turned travel where constraints genuinely make it unavoidable.

For related planning sequencing, see early agenda planning for accessibility lift projects.

Problem–Solution: how do you get straight-route access without changing railings or the façade?

The problem

A heritage entrance often includes:

• steps that have worn over time
• a top threshold that is not perfectly square or level
• an envelope that looks adequate on plan but fails once tolerances, trims and pit build-up are added

The solution

A high-value, low-drama move is a small threshold alignment shift, typically 30–35mm, combined with a straight-route footprint that may project slightly into the pavement zone.

This achieves three outcomes:

• improves tolerance at the front face and reduces the chance of “surprise” cutting on site
• removes pinch hazard risk at protruding edges
• keeps railings unchanged because the geometry is resolved inside the available width

The trade-off is that you may need a limited interface with the vault support zone, often described during design as a modest shave. In the meeting, the expectation was that the shave could be minimal and controlled, in the region of tens of millimetres rather than a rebuild.

A verified experience block: why Sesame Access is cautious about these decisions

Sesame Access designs bespoke platform lift solutions for constrained, regulation-sensitive buildings, where small dimensional decisions can trigger big consequences in approval, safety and user experience.

This approach is consistent across heritage entrance assessments:

• prioritise autonomy and straight-line travel when feasible
• remove pinch hazards during the geometry phase, not after fabrication
• coordinate vault structures and services early so the approval route is predictable
• design around existing railings rather than forcing railing changes downstream

A useful companion read is terrace house bespoke moat platform lift, which explores how Sesame treats perimeter edges, interface risk and “moat” conditions in constrained settings.

Technical consultation log: the real trade-off that decides the concept

A recurring fork in the road is whether to:

• shave a small amount of vault support zone to achieve straight-route access, or
• accept a turned configuration, or
• introduce a sensor-monitored transitional element that adds mechanics and complexity

In the meeting, the risk of adding extra moving parts was described plainly:

“It’s bulletproof”

That is the core engineering trade-off:

• structural coordination is often simpler to maintain long-term than mechanical complexity
• fewer moving interfaces typically means fewer service variables
• straight-route travel improves autonomy and reduces operational errors

Common misconceptions that cause expensive redesigns

Misconception 1: a 90-degree turn is “basically the same” as straight-route access

It is not. The user experience changes materially, especially when independent entry is the goal.

Misconception 2: pavement vaults always block platform lift solutions

They rarely block solutions outright. They change the survey scope and the structural coordination, but many vaults sit low enough to allow controlled interface strategies.

Misconception 3: level differences under 30mm can be ignored

They cannot. They create bump-on/bump-off behaviour at exactly the point the user transfers between surfaces.

The meeting captured the concern clearly in practical terms:

“You’ve got a bump on and off.”

Managing worn thresholds and level differences without creating instability

Heritage steps often contain:

• wear dips
• inconsistent stone thickness
• cross-falls intended for drainage

The design objective should be a level platform surface at travel, with adjacent stonework reset locally to meet it. If the platform is sloped, the user must manage braking and alignment while moving, which is not a people-first access experience.

If the entrance includes a worn threshold, the preferred strategy is:

• propose a squared, level threshold as the primary option
• document why it improves safety and reduces pinch hazards
• retain a fallback option if heritage authorities refuse threshold alteration

Right fit / wrong fit: when is a straight-route configuration the right choice?

If straight-route is not viable, Sesame can shift to a turned configuration or a fully bespoke concept depending on constraints, using solutions such as the Bespoke Lift.

Dimensional tolerances reference table

Product integration summary

This scenario aligns with concealed, site-specific entrance lifts where the visible finish must read as “normal steps” while delivering compliant access.

Relevant Sesame Access product references to explore:

• Edinburgh Access Lift for heritage entrances
• Wellington Lift concealed step lift approach
• Westminster Equality Act Lift for constrained civic access
• Bespoke Lift solutions for non-standard geometry

Frequently Asked Questions

What is the minimum space needed for a straight-route wheelchair platform lift at a heritage entrance?

Many teams target around 1400mm for a calm, straight approach, but feasibility depends on trims, tolerances, railing positions and what can be coordinated below the pavement.

Can you keep existing railings in place?

Often yes. The key is to design the platform footprint around the railing line early so the railing does not become a late-stage “surprise constraint”.

Is shaving into a pavement vault wall always risky?

It depends on the structure and the survey. Many vaults sit low enough that a controlled interface can be coordinated safely, but it should always be confirmed by structural review.

What happens if listed building consent refuses a new threshold stone?

A fallback concept can retain the threshold position and adjust the lift geometry, but this can increase mechanical complexity or require a turned platform route.

Why is a 90-degree travel platform less people-first?

Because it asks the user to manoeuvre during travel instead of simply approaching, entering, travelling and exiting in a straight line.

How do you stop “bump on / bump off” transitions?

By designing for a level platform at travel and resetting local stonework adjacent to the lift so the user transitions smoothly.

How do you design a DDA entrance lift when there are vaults under the pavement?

Start with an early agenda plan: confirm the structural datum, vault depth, services, and the approval route before locking the lift envelope. Use early agenda planning for accessibility lift projects as your internal checklist.

What is a “moat” risk around a platform lift and how do you mitigate it?

Moat conditions are perimeter edge risks where gaps, falls or debris ingress can occur if interfaces are not controlled. See terrace house bespoke moat platform lift for design thinking that carries directly into heritage entrances.

Call to action

If you are working on a heritage entrance with fixed railings, worn thresholds and pavement vaults below, book a short Teams review with a Sesame Access Project Manager to confirm the best concept and the approval route.

Book here: https://www.sesameaccess.com/b...