Four building system models on a review table

Building Selector

Choose a Modular Building System for Your Site | Boxx Modular

Pick the constraint that is hardest to change. A crane that cannot reach the pad eliminates a finished volumetric box. A 30 m clear span eliminates a stack of 6 m modules. A sleeping use eliminates a bare site-office fire note. The selector below is a conversation map, not an automated stamp.

Use and overnight occupancy
Wind, snow, seismic basis
Module size versus clear span
Weeks until occupancy

Three constraints that change a shortlist

Consider a sixteen-room school swing campus with a covered corridor. Comparing panel U-values is useful, but the corridor link also affects the thermal bridge and the accessible route. Ask suppliers to mark the envelope boundary and the link on the same plan so both bids include the same transition.

If the hardest constraint is the road, pack a frame. If the hardest constraint is the week people walk in, finish the room in the bay and prove the crane.

A remote camp with a narrow road and a fixed occupancy date illustrates the trade. A bolted frame may fit the truck envelope while adding assembly days. Ask the bidder to break out packaging, field joints and weather protection so the purchase team can compare the installed cost.

A 36 m workshop with an overhead crane runway raises a different question. Have the project engineer review the runway loads, clear span and portal frame before requesting a quote for the shell. Modular offices may still work as attached rooms once the building interface is detailed.

Numbers the sheet asks for

Design wind speed, example band 45 m/s where the engineer uses that figure
Ground snow load, example 1.5 kN/m²
Seismic basis, example 0.30 g or the local category
Wall thickness 50–100 mm on typical occupied modules
Thermal transmittance target inside 0.25–0.60 W/m²·K
Module envelope example 6055 × 2435 × 2896 mm
Knock-down packing often 4–8 units per 40HQ, case-specific
Main steel grade when a PEB is in play, such as Q355 or S355

These are prompts for the file. They are not a design that ships with every inquiry.

System comparison used in the selector. Figures are typical discussion ranges, not a rated product line.
Question	Volumetric module	Bolted flat-pack	Light-gauge panels	Portal-frame PEB
Factory completion	Room, often MEP to an interface box	Frame and pack, more site close-up	Panels and trusses, site assembly	Fabricated members, site erection
Transport	One box per trailer in many cases	Higher count per 40HQ	Dense packs of studs and panels	Long members, escort rules may apply
Span	Tied to module width	Tied to the bolted bay	House-scale spans	Clear span often 18–60 m
Envelope talk	50–100 mm sandwich panel	Same panel choices after the frame	Stud cavity plus sheathing or panel	Purlin, girt and cladding build-up
Code posture	RB or PMC, local file still required	Same, plus site joint quality	Often closer to a permanent house file	Industrial building file, crane loads extra

Limits to read before you fall in love with a photo

A relocatable building can move and can be leased. Occupancy still needs the fire, energy, accessibility and structural review of the place it sits. Permanent modular construction accepts a heavier approval file and a longer life on one foundation. If someone offers a module that “does not need a permit anywhere,” treat that sentence as a reason to stop, not as a feature.

Ask for the test environment (the assembly, including joints and a representative opening), the method named by the reviewer, the duration in minutes, and whether doors were in the specimen. A 60 minute figure on a core sheet, with no joint, is not a result you can hand to a fire consultant. Boxx Modular can line up a sample panel and a drawing review with the project engineer. That review is a check of documents. It is not a certificate with your address on it.

Z275 galvanizing on cold-formed steel (CFS) is a mass, not a decade count in salt air. Cut edges and welds need a repair spec. A painted carbon-steel portal frame can take an intumescent coating where the fire strategy calls for it, and that coating has a thickness and an inspection cycle. If the file is silent on repairs, the selector is not finished.

Many modules borrow a shipping envelope. That does not mean the unit carries an ISO CSC plate or can be stacked in a container terminal. Flat-pack container houses, expandable boxes and volumetric offices are specified as buildings. Ask for the lifting diagram you will actually use, not a shipping-container slogan.