If you have searched for a retractable ladder, ZIP ladder, or a hatch and ladder, most results focus on domestic loft ladders. This page is written for contractors and architects coordinating commercial ceiling and roof access, where the ladder must work with the opening build-up, the ceiling void, and real site constraints.
Important context: “ZIP” is Surespan’s product range name for commercial retractable ladders. Some enquiries use “ZIP ladder” as a generic term. To avoid ordering the wrong product, identify which ZIP model family you are specifying and which measurements apply.
Which ZIP ladder are you specifying?
Most confusion comes from mixing ZIP models. The ZIP8 is commonly specified as a complete assembly with a casing and trap door. Other ZIP models are typically specified differently. Use the table below to set the context in your enquiry.
ZIP model |
How it is typically specified |
What to confirm early |
|---|---|---|
ZIP4 to ZIP7 |
Retractable ladder selection (ladder choice first, then coordinate with the opening and any hatch/lining detail as required) |
Whether you need a separate access hatch or lining detail, and what structural and clear openings are required for the access route |
ZIP8 (this page focuses here) |
Made to order and supplied as a complete unit including casing and trap door |
Structural opening (A and B), floor to ceiling height (C), void depth (D), and whether you need backboard, handrails, or optional operation features |
Quick links
- All ladders
- ZIP retractable ladders (overview)
- ZIP8 retractable ladders
- Roof access hatches
- Internal access hatch
- Fixed vertical ladders
- Companionway ladders
The ZIP8 measurements that actually drive manufacture (plus the site checks that prevent problems)
Most quote delays happen because an enquiry includes “the opening size” and one height, but not the correct height reference, not the labelled opening type, and nothing about void depth. For ZIP8, there is a clear set of dimensions used to manufacture the unit (A to E), plus a small set of site coordination checks that prevent installation issues.
ZIP8 order sheet dimensions (A to E), plus optional backboard (F and G)
Ref |
What to measure |
What it is |
Common slip-up |
|---|---|---|---|
A |
Structural opening length |
The builder’s opening length used to size the unit (minimum applies) |
Providing an overall lid size, or an unlabelled “opening” with no reference |
B |
Structural opening width |
The builder’s opening width used to size the unit (minimum applies) |
Confusing structural opening (SO) with clear opening (CO) |
C |
Floor to ceiling height |
The height range the ladder is made to suit. State your datum clearly. |
Measuring only to suspended ceiling tiles, not to the structure above |
D |
Void depth |
Depth available above the ceiling line, including clashes and obstructions |
MEP clashes discovered after installation stage |
E |
Casing height |
ZIP8 casing height (standard value). Confirm if you need a non-standard build-up. |
Not checking the ceiling build-up and casing relationship |
F (optional) |
Backboard height |
Optional backboard for fixing and finishing, where required |
Omitting backboard requirements until late coordination |
G (optional) |
Backboard width |
Optional backboard width rule relative to the structural opening |
Backboard detail clashes with hatch or surrounding finishes |
ZIP8 sizing note: when specifying structural opening, allow for the unit casing being manufactured slightly smaller than the structural opening. This is normal and supports installation tolerance.
Site coordination checks (do these before you freeze the opening)
- Suspended ceilings: confirm the distance from finished floor to structural soffit (underside of slab). Retractable ladders fix to the structure above, not to a suspended ceiling grid.
- Structural depth at the opening: check slab thickness and any structural downstands. If the structure depth and the ladder casing/lining detail conflict, you may need a liner or extension detail.
- Deployment zone: confirm corridor width, door swings, and a safe area under the access point so the ladder can deploy and be used without creating a pinch point.
Copy/paste ZIP8 enquiry checklist
- ZIP model: ZIP4 to ZIP7 / ZIP8 / other variant (state which)
- Structural opening length (A): ______ mm
- Structural opening width (B): ______ mm
- Floor to ceiling height (C): ______ mm (state datum)
- Void depth (D): ______ mm (describe services and clashes)
- Casing height (E): confirm standard or project-specific requirement
- Optional backboard required? Backboard height (F): ______ mm, backboard width (G): ______ mm
- Suspended ceiling present? Finished ceiling line height: ______ mm, structural soffit height: ______ mm
- Structural depth at opening (slab thickness/downstand): ______ mm
- Deployment constraints (corridor width, door swings, obstructions): ______
- Handrails, guarding, or operation requirements (if any): ______
- Are you coordinating with an access hatch? internal / roof access / fire requirement (if any): ______
Structural opening vs clear opening vs “trap”
The fastest way to slow a quote down is to send one dimension labelled only as “opening”. In specifications these are different measurements:
- Structural opening (SO): the builder’s opening formed in the structure.
- Clear opening (CO): the usable pass-through size once the frame and linings are in place.
- “Trap”: often used informally and can mean the lid, the lining, or the hole. It is ambiguous.
Use this guide to standardise drawings and enquiries: Structural opening vs clear opening vs overall size.
Suspended ceilings are a common trap (measure to the structure, not the tiles)
If the ceiling is suspended (drop ceiling), you typically need two heights:
- Finished ceiling line (for coordination with finishes and the trap door position).
- Structural soffit height (for fixing points and casing alignment).
A retractable ladder must be fixed back to the structure above. If the project has a deep suspended ceiling zone, plan the liner and finishing detail early so the access point is clean and buildable.
Void depth and services: check the ladder box space before MEP is finalised
Confirm the available void depth and mark up clashes. Common issues include ductwork, cable trays, pipework, sprinklers, and lighting that conflicts with the ladder casing or the deployment path.
Also check the structural depth at the opening. If the slab is significantly thicker than the casing/liner detail, the opening may need an extension/lining solution to bridge the build-up cleanly and securely.
Retractable vs fixed vertical vs companionway (select the safest fit)
Retractable ladders are a good fit for occasional access where you must keep an area clear when not in use. They are not automatically the right answer for frequent access or where users carry equipment. If the access route is used regularly, or the deployment zone is constrained, fixed or companionway solutions may be more appropriate.
Access type |
Best for |
Watch-outs |
Internal link |
|---|---|---|---|
Retractable ladder (ZIP range) |
Occasional access, space-saving, keeps routes clear |
Needs structural fixing above; confirm void depth and safe deployment zone |
|
Fixed vertical ladder |
Dedicated access points and consistent access route |
Guarding strategy may be required depending on the situation |
|
Companionway ladder |
More frequent access, easier climbing angle (space permitting) |
Needs a clear run and landing space; check headroom and route planning |
Fire strategy notes (hatch and ladder)
If the access point sits on or near a compartment line, confirm early whether the hatch assembly needs a fire rating. Fire performance is addressed by the hatch specification and the installation detail. Do not assume that “ladder + hatch” is automatically compliant without confirming the requirement and evidence.
Explore common hatch routes here: Roof access hatches and Internal access hatch.
Get a fast, coordinated recommendation
If you want the quickest route to a quote, send a marked-up GA showing A, B, C and D clearly, plus a note confirming whether the ceiling is suspended and what the structural soffit height is. Include any services clashes, corridor constraints, and whether you are coordinating with an access hatch.
Next step: request a coordinated ladder (or ladder + hatch) quotation here: Contact Surespan.
FAQs
Is this guide for ZIP8 only, or all ZIP ladders?
It covers the ZIP range at a high level, but the measurement section is written to match how ZIP8 is ordered and manufactured. If you are specifying ZIP4 to ZIP7, tell us the model and we will confirm the correct measurement set for that ladder.
How do I measure for a ZIP8 retractable ladder?
Provide structural opening length (A) and width (B), floor to ceiling height (C), and void depth (D). If you have a suspended ceiling, also provide the floor to structural soffit height so fixing and lining details can be coordinated correctly.
What’s the difference between structural opening and clear opening?
Structural opening is the builder’s opening formed in the structure. Clear opening is the usable pass-through once the frame/linings are installed. Use this guide to keep terminology consistent: Structural opening vs clear opening.
Is “trap size” the same as opening size?
Not reliably. “Trap” is often used informally and can refer to the lid, the liner, or the hole. For specification, always state whether your dimension is structural opening (SO) or clear opening (CO).
What causes the most delays in retractable ladder quotes?
Unlabelled opening dimensions, missing void depth, and suspended ceilings where the structural soffit height is not provided. Mark up your GA with the dimensions above and note any MEP clashes.
Do I need to specify a hatch separately from the ladder?
It depends on the ZIP model and the project requirement. ZIP8 is commonly supplied as a complete assembly with casing and trap door. Where a fire-rated or specialist hatch is required, that requirement is addressed by the hatch specification and the installation detail. Always confirm the exact requirement early.
