A developer’s guide
Understand the options, what arrives from the factory, and what your team still needs to deliver.
01 / The big picture
Factory-built and prefab broadly describe buildings—or parts of buildings—made off-site and assembled or installed at the project location. A factory might deliver home sections, room-sized modules, panels, or individual components.[1]
The difference is what happens in the factory and what remains to be done on-site.
Also part of the picture: Kits, pods, and prefabricated components.
02 / What arrives from the factory
These common labels describe different aspects of factory-built housing. Start with what the factory supplies, then confirm the product’s approvals and delivery scope.[1][2][3][5]
Manufactured is not another word for modular. Manufactured housing follows the HUD Code; modular buildings follow the applicable state or local building-code pathway. Both still require attention to site and installation requirements.[2][3][4]
03 / Three practical questions
The category is only the starting point. Understand what you can design, how it gets made, what you are buying, and who completes the work.
Once the design and scope are coordinated, factory work and site work must come together. The split depends on the building system, the package purchased, and the project team.
Establish the agreed inputs for factory and site work.
Produce sections, modules, panels, or components.
Prepare the site, foundation, and connections.
Bring the parts together at the property.
Complete connections, remaining work, and required inspections.
Factory work and site preparation may overlap when approvals and the project sequence allow.
A production method does not determine the material. Factory-built systems may use wood, steel, concrete, or engineered assemblies.[3] Explore materials and panel types.
“Steel” describes the structure. “Modular” describes the production approach. Neither describes the whole package.[3][6][7][8]
A familiar label is a starting point. Verify the actual product, approvals, included scope, and remaining work.[1][2][3][9][10]
You can start with a factory design, a site and project goals, or drawings you already have. The right path depends on what you bring and how the manufacturer works.[5][6][13]
Choose an existing manufacturer floorplan or product family and explore the changes it supports.
What happens nextEvaluate site fit, permitted changes, specifications, and the remaining project scope.
Question to askWhich changes are supported for this design and site?
Bring your site, intended unit mix, target sizes, and development goals. Work with a manufacturer and design team to develop a configuration around the factory’s building system.
What happens nextExplore configurations, coordinate the design, and confirm technical fit and scope.
Question to askWhat site information and project goals are needed to explore a configuration?
Bring an existing concept or architectural design for review. Determine what fits the manufacturing system and what may need to change.
What happens nextThe manufacturer helps adapt or develop the design around its building system. Confirm which architectural, engineering, fabrication, installation, and site-work responsibilities it takes on and which remain with your project team.
Question to askWhat needs review or revision before this design can move forward?
Example floorplans can show what a building system can do; they are not necessarily a fixed menu of products.[13]
A factory package is not always a finished building. Compare what is included and what your project team still needs to complete.
Physical building package The assemblies, materials, fixtures, and finishes delivered.
Project support services The agreed design, engineering, coordination, logistics, or installation support.
What arrives and what support the manufacturer provides are separate questions.
Factory may includeFraming, structural panels, or other load-bearing assemblies.
Project team may still completeEnclosure, building services, finishes, and site work.
Factory may includeStructure and enclosure assemblies, potentially with insulation, windows, or doors.
Project team may still completeRemaining assembly, building services, interiors, foundations, and site connections.
Factory may includeInteriors, fixtures, and building services completed within individual modules.
Project team may still completeInstallation, foundations, utility and module connections, remaining finishes, and inspections.
04 / The complete project
Before comparing manufacturers, make sure you are comparing the same scope. Ask what arrives completed, what remains on-site, and who is responsible for each part.
A concept can support an initial conversation. Provide GroundUp with drawings, specifications, and scope decisions to get project-specific pricing and production.[5]
Confirm what has been reviewed. GroundUp helps determine which local, installation, and site-specific requirements remain.[4]
05 / From understanding to evaluation
GroundUp helps you understand not just which factory can serve your site, but how its building system, design flexibility, and delivery scope fit the project you want to develop.
Whether you start with a factory design, a site and project goals, or existing drawings, GroundUp helps organize the inputs, evaluate preliminary fit, and coordinate the next steps with suitable manufacturers.
This guide explains the wider factory-built category. Available GroundUp options depend on your location, project requirements, and participating manufacturers’ verified capabilities and approvals.
The factory and project design team confirm the technical design, scope, and production requirements. GroundUp supports evaluation and coordination; it does not replace them, the permitting authority, or the installation contractor.
06 / Keep exploring
No. Prefab is a broad description of off-site production. Volumetric modular is one approach; panels, kits, and components are others.[1][10]
No. The result depends on the site, design, factory scope, logistics, and remaining work. Compare total development cost and the complete schedule, not only the factory package.
No. Confirm what the approval covers and which planning, site, installation, and other local requirements still apply.[4]
Do not assume that from the name or appearance. Check the specific product’s certification and intended use. Park-model RVs are designed for temporary recreational, camping, or seasonal accommodation, not as an interchangeable category of permanent housing.[12]
Definitions and product scopes vary. Review the referenced sources and confirm the requirements for your actual product and location.
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Your next project
Bring your site, project goals, or existing drawings. GroundUp helps you evaluate preliminary fit and prepare the next manufacturer conversation.
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