Modular homes are built in factory-made sections, transported to the building site, lifted onto a prepared foundation, joined together, connected to utilities, and finished through inspections and site work. The process has nine main stages, although the work is usually divided into more detailed construction steps. Most interior and exterior construction happens in the factory. Site work covers the foundation, module placement, connections, utilities and final finishes.
Modular Home Installation at a Glance
| Stage | What happens |
|---|---|
| 1. Design and approvals | Plans are adapted to the site, local building code, foundation type and transportation requirements. |
| 2. Site preparation | The lot is cleared, graded and prepared for drainage, access, utilities and the foundation. |
| 3. Foundation construction | A basement, crawl space, slab or other approved permanent foundation is built. |
| 4. Factory construction | The home sections are framed, enclosed and fitted with finishes, plumbing, electrical and HVAC components. |
| 5. Delivery | Specialized trucks transport the completed modules to the property. |
| 6. Crane setting | A crane places each module onto the foundation in a planned sequence. |
| 7. Module connection | Crews join the sections structurally and seal the roof, wall and floor connections. |
| 8. Utility connections | Electric, water, sewer or septic, gas and HVAC systems are connected or completed on site. |
| 9. Inspections and finishing | Officials inspect the work, then contractors complete stairs, porches, siding, grading, landscaping and other site work. |
1. The Home Is Designed for the Site
Before construction begins, the manufacturer, builder, architect or engineer adapts the home design to the property.
Planning usually covers:
- Local building and zoning requirements
- Foundation design
- Soil and drainage conditions
- Snow, wind, seismic and flood requirements
- Road access for delivery trucks
- Space for the crane and module staging
- Locations for electric, water, sewer, septic, gas and telecommunications connections
- Setback, height and lot coverage restrictions
In the United States, a modular home generally must comply with the building code adopted by the local jurisdiction where it will be installed. That code is often based on the International Residential Code.
Modular homes are regulated differently from manufactured homes. A modular home is built to the applicable state or local building code. A manufactured home is built on a permanent chassis under HUD's Manufactured Home Construction and Safety Standards.
2. The Building Site Is Prepared
The builder prepares the property before the modules arrive. This work may include clearing vegetation, removing unsuitable soil, establishing temporary access and grading the lot so water drains away from the home.
The contractor may also install:
- Temporary construction access
- Driveway or crane access
- Stormwater drainage
- Underground utility trenches
- Retaining walls
- Erosion-control measures
- Temporary electrical service
Access can determine whether delivery and crane setting go smoothly. The modules still need a safe route from the delivery truck to the foundation, even though most of the home was built at the factory.
The delivery team may need to check turning radii, overhead utility wires, road restrictions, bridge limits and the amount of space available for staging.
3. The Permanent Foundation Is Built
The foundation is completed before delivery. Depending on the design and property, it may be a:
- Full basement
- Crawl space
- Concrete slab
- Pier or beam system
- Engineered perimeter foundation
The foundation must match the modular home's structural plans. It must also account for local soil, frost depth, drainage, wind, snow, seismic and flood conditions where applicable.
A modular home is not placed on bare ground. The foundation provides the permanent structural support, and the modules are attached according to the approved engineering documents and the manufacturer's instructions.
HUD guidance for factory-finished modular dwelling units describes the units as being transported to the site, set on conventional foundations and joined together.
4. The Modules Are Built in a Factory
The manufacturer constructs the sections inside an enclosed factory. Depending on the design and contract, a module may leave the factory with much of the following already completed:
- Structural framing
- Exterior sheathing and siding
- Roofing
- Insulation
- Windows and exterior doors
- Drywall or other interior wall finishes
- Cabinets and flooring
- Plumbing lines
- Electrical wiring
- Heating and cooling components
- Bathroom and kitchen fixtures
The factory does not always complete every connection. Plumbing, heating and electrical systems may be installed in the modules but still need to be connected after the sections are placed on the foundation.
Factory-built sections are inspected through the applicable state or local approval process. Some construction cannot be inspected after the walls and ceilings are closed without opening them, so regulatory review may include factory plan review and inspection.
5. The Completed Modules Are Delivered
After factory construction is finished, each section is loaded onto a specialized trailer and transported to the property.
The delivery team normally coordinates:
- Truck access and turning radius
- Utility-wire clearance
- Road restrictions
- Delivery timing
- Police or traffic control where necessary
- Weather conditions
- Crane arrival
- Temporary module storage, if required
The delivery order matters. Some sections must be placed before others so the crane and installation crew can reach the foundation safely.
A delivery plan may also account for narrow roads, steep driveways, low branches, parked vehicles and nearby buildings. If the site cannot accommodate the trucks, the builder may need to change the access route before delivery day.
6. A Crane Places the Modules on the Foundation
A crane lifts each module from the trailer and lowers it onto the foundation. The module design and manufacturer's instructions determine the lifting points and rigging procedures.
As each section is placed, the installation crew checks:
- Position
- Elevation
- Alignment
- Bearing points
- Foundation connections
- Temporary bracing
- Clearances between sections
Volumetric modular construction uses enclosed, three-dimensional building units that are joined at the final site to create the completed structure.
Not every off-site home uses this method. Some projects use wall panels or smaller prefabricated components that are assembled on site. A crane-set modular home is the most recognizable example, but the installation process depends on the construction system.
7. The Modules Are Joined Together
After placement, the crew connects the sections so they function as one home.
This work may include:
- Bolting, welding or fastening structural connections
- Joining floor, wall and roof assemblies
- Connecting electrical wiring
- Connecting plumbing lines
- Connecting HVAC ducts
- Sealing the joints between modules
- Completing roof transitions
- Installing exterior trim and siding at connection points
- Repairing or finishing drywall, flooring or ceilings affected by the joints
The connections between modules, and between the modules and the foundation, are important parts of the approved modular design.
The crew may also complete work that could not be done at the factory because it depends on the final position of the sections. This often includes roof sealing, exterior weatherproofing and interior finish work along the module joints.
8. Utilities Are Connected on Site
Once the modules are secured, the home is connected to the property's utility systems.
Typical connections include:
- Main electrical service
- Water supply
- Sewer or septic system
- Natural gas or propane
- Heating and cooling equipment
- Internet and telecommunications
- Stormwater systems
Factory-installed plumbing and electrical systems do not eliminate site work. Connections between modules and connections to the property's utility infrastructure generally have to be completed or verified at the site. HUD documentation describes factory-installed systems as being field connected after the units are set.
The contractor may also install permanent utility meters, connect exterior equipment and complete any required testing before final approval.
9. Inspections Are Completed
The project must pass the inspections required by the local authority having jurisdiction, often called the AHJ. Requirements vary by state and municipality.
Inspections may cover:
- Foundation and anchoring
- Structural connections
- Electrical work
- Plumbing
- Mechanical systems
- Fire safety
- Energy-code compliance
- Egress and other safety features
- Final site work
The approval process depends on whether the state has a modular or industrialized building program. Some states conduct plan review and inspections through a state agency. Others rely more heavily on the local jurisdiction or approved third-party inspectors.
The builder should know which inspections are required and who is responsible for scheduling them. A home cannot be treated as complete until the required approvals have been issued.
10. Final Exterior Work Is Completed
After the modules are secured and connected, the builder completes work that could not be finished at the factory.
This may include:
- Steps and entry landings
- Porches and decks
- Garages
- Chimneys
- Exterior connection trim
- Final siding and roofing details
- Skirting or foundation enclosure where applicable
- Driveways and walkways
- Final grading
- Landscaping
- Permanent utility meters
These items may be separate from the factory-built home price. The purchase contract should state which work is included, who will complete it and how changes will be priced.
How Long Does Modular Home Installation Take?
The on-site set and connection work is usually shorter than conventional construction because much of the house is completed before delivery.
The full project schedule also includes:
- Design and engineering
- Permits and approvals
- Site preparation
- Foundation construction
- Factory production
- Utility work
- Transportation coordination
- Crane setting
- Inspections
- Exterior finishing
The foundation and site preparation can take longer than the crane setting itself. Weather, difficult access, special engineering, permitting delays and utility connections can extend the schedule.
The best way to estimate the timeline is to separate the factory schedule from the site schedule. The home may be ready at the factory while the property is still waiting for its foundation, utilities or final approvals.
What Is the Difference Between Installing a Modular and Manufactured Home?
| Feature | Modular home | Manufactured home |
|---|---|---|
| Main construction rule | Local or state building code for the final site | HUD Manufactured Home Construction and Safety Standards |
| Typical structure | Factory-built modules joined on a permanent foundation | Factory-built home constructed on a permanent chassis |
| Installation | Modules are set and structurally joined on the foundation | Home is transported, leveled, supported and secured according to installation requirements |
| Foundation | Commonly designed as a permanent basement, crawl space, slab or other engineered foundation | Foundation and support requirements follow applicable HUD and local requirements |
| Code authority | State or local building authority | HUD standards for the home, with local rules for site work and installation |
The terms are sometimes used interchangeably, but they describe different regulatory and structural systems. The International Code Council identifies modular housing as subject to the code requirements of the final jurisdiction. Manufactured housing is subject to HUD standards and is built on a permanent chassis.
What Should a Buyer Confirm Before Ordering?
Ask the builder or manufacturer for a written breakdown of the following:
- Foundation responsibility: Who designs and builds the foundation?
- Transportation: Are delivery and transportation permits included?
- Crane setting: Is the crane included in the quoted price?
- Utility work: Are water, sewer, septic, electric and gas connections included?
- Site access: Who pays if trees, utility lines or road improvements must be addressed?
- Exterior completion: Are stairs, decks, porches, garages, siding and roof transitions included?
- Inspections: Which party coordinates state, local and third-party inspections?
- Weather delays: How are delivery and crane days rescheduled?
- Warranty coverage: Which company handles factory defects, transport damage and site installation issues?
- Final completion: What must be finished before the home is ready for occupancy?
Bottom Line
The crane setting is only one part of modular home installation. Site access, foundation design, utility planning and a clear contract often determine whether the project stays on track. Confirm who is responsible for each item before ordering, especially foundation work, delivery, crane services, utility connections, inspections and exterior finishing.