An expandable container house is a transport module whose side sections slide or swing out after delivery, so the erected building is wider than the box that arrived on the truck. Buyers meet the format in camp and site accommodation catalogues, usually promoted on floor area per transported unit. CDPH does not manufacture expandable container houses. The CDPH range is built on a bolted steel module supplied as a completed unit, packed flat for transport, or bolted for later demounting. This page explains what the expandable format is, what to verify before specifying it from any supplier, and how the CDPH bolted module answers the same underlying brief.
What the format is
In an expandable unit, a container-sized core carries hinged or sliding wall and floor sections. On site, the sections open out and lock, and the internal width grows beyond the transport width. The moving sections carry their own seals, hinges and locking hardware, and the roof and floor loads of the opened building pass through a frame that changes shape between transport and use. That moving structure — not the concept — is what a buyer has to evaluate.
What to check before specifying one
- Load path in the open state. Ask which members carry roof and floor loads once the unit is expanded, and request the design load table for the opened building, not the transport box.
- Joint sealing. The moving joints are the weather line of the building. Ask how they are sealed, how the seals are inspected, and what replacement involves after repeated openings.
- Cycle rating. If the unit will be expanded, closed and moved between projects, ask how many cycles the mechanism and seals are rated for.
- Fire and compliance evidence. Request test evidence for the complete expanded unit in its erected configuration, for the market the building will be used in.
- Clear dimensions in both states. Confirm internal width and height opened and closed, so transport planning and room layouts are based on the same figures.
The CDPH alternative: area by combination, not by mechanism
CDPH gains floor area by combining standard modules side by side and stacking them — single, double, triple or more storeys, in I, U, L or courtyard layouts — rather than by opening a single unit. The modules are 6055 × 2990 × 2896 mm or 6055 × 2435 × 2896 mm, on a galvanised cold-formed steel frame (t=3.0 mm, SGH340), with roof live load 1.0 / 0.5 kN/m², floor live load 2.0 kN/m² and wind load 0.6 / 0.5 kN/m². Electrical circuits are pre-fitted in the roof, water supply runs along the walls and drainage is wall-side. Where transport volume is the binding constraint, the flat pack format ships the same standard box packed flat for assembly on site; where the building must move again, the detachable bolted format is demountable and reusable. Neither format has moving structural sections; both are bolted constructions that can be taken apart and re-erected.
Expandable format vs CDPH bolted module
| Question | Expandable unit (wider market) | CDPH bolted module |
|---|---|---|
| How floor area is gained | Sections of one unit open out on site | Standard modules combined and stacked |
| Moving structural parts | Hinges, sliders, seals and locks | None — bolted connections only |
| Transport efficiency | One wide room per transport unit | Flat pack format packs the standard box flat |
| Relocation | Close, transport, re-open; cycle rating applies | Unbolt, transport, re-erect |
| Evidence to request | Loads and fire evidence for the opened configuration | Module load table and category certifications |
Talk to CDPH about the brief behind the format
Most expandable specifications are really a requirement for area per shipment or a wider clear room. Send the room sizes, headcount and transport route behind your specification to the CDPH engineering team; every project is quoted individually after engineering review — there is no standard MOQ — and the team replies within one business day with a concept proposal and a budget range. If, after comparison, an expandable unit is still the right answer, the checklist above will help you specify it from a supplier who manufactures the format.