Guide
Planning and site preparation for modular homes
Factory speed does not help if the lot cannot take a truck, a crane, or a septic field. Order perc, survey, and access work before you lock a plant slot. Site cost is priced by the foot and by the soil, not by the floor plan.
What zoning and code checks come first?
Verify modular homes are allowed before you make an offer. Speak with planning and get clarifications in writing. IRC modular and HUD manufactured homes are different classes. Lenders and local rules treat them differently. HUD Code (24 CFR 3280) plus Fannie Mae B2-3-02 matters if you will finance a manufactured home as real property. IRC modular follows the same residential code as stick-built. California lots add Title 24 energy compliance once the dwelling is permitted. Check zoning first.
- Type of home: Modular (IRC) versus manufactured (HUD). Do not order from a ZIP dealer until the data plate path is named. See Home Nation factory-direct.
- Setbacks and easements: Confirm buildable area and underground rights-of-way. A 10-foot side yard can kill a crane pick.
- Flood and environmental: Flood maps, wetlands, contamination. Elevation certificates change foundation type.
Order a professional land survey and soil or percolation tests. Use results to pick the foundation and drainage strategy. r/Homebuilding posts about failed perc after closing are community signal: test before you buy, not after the factory deposit.
Permits and approvals
Expect to apply for building, transport, and utility permits. Apply early. Some jurisdictions require stamped civil drawings before they will schedule the foundation inspection that unlocks delivery.
When do you need a perc test?
A percolation test measures how fast water leaves a hole in the soil. Counties use it to size septic trenches or to deny septic. If the lot has municipal sewer in the street, you usually skip perc and pay a tap fee instead. If the lot is rural, perc is a go or no-go. Failed perc means a mound system, an engineered field, or a different parcel. Budget $400 to $2,000 for perc and soil work on a simple lot, more if the sanitarian requires extra pits.
Clay that percs slowly, high water tables, and shallow rock all change the field. Geotech borings ($2,000 to $8,000) are cheap compared with a foundation redesign after the plant has already framed. Slope adds retaining walls and stepped foundations. Do not bury organic material under slabs. Stumps rot and the house settles.
How wide is the driveway, and what is a crane pad?
Trailers need about 14 feet of clear width and a path that can take 80-foot loads. Vertical clearance of 14 to 16 feet clears most lines. Turning radius failures show up as last-minute crane upgrades or a refused delivery. Improve the driveway before the haul date. Temporary gravel that ruts in rain is not a driveway.
The crane pad is compacted ground or mats at the pick. The crane manufacturer publishes ground-bearing pressures. Soft soils need more stone or a bigger crane parked farther away, which raises the day rate. Neighbor air rights, trees, and overhead service drops constrain the boom. Measure those before you sign the factory contract. California ADU lots fail here as often as rural modular lots. Kit products such as Studio Shed exist because a crane cannot enter. See prefab ADU companies.
Foundation options
Coordinate final foundation design with the modular manufacturer for pier spacing and anchor points. HUD homes that need conventional loans must meet the foundation tests in Fannie Mae B2-3-02. IRC modular follows the plant drawings and local frost depth.
| Type | Pros | Considerations |
|---|---|---|
| Concrete slab | Cost-effective, quick, good in warm climates | Cracking in frost; no underfloor access |
| Crawl space | Utility access; works on slopes | Insulate and ventilate to manage moisture |
| Basement | Extra living or storage space | Higher excavation and cost |
| Pier-and-beam | Potentially cheaper; good access | Protect from frost; insulate water lines |
What do utilities cost by the foot?
Price laterals from the tap or well head to the set points, not as a lump "utilities" line. Rock, directional boring under a driveway, and traffic control on a county road are multipliers. Wells are $8,000 to $40,000 depending on depth. Septic is $12,000 to $50,000-plus after a passing perc. Electric service upgrades on existing houses (common for ADUs) are a separate panel project.
| Line item | Planning range (2026) | What moves it |
|---|---|---|
| Perc / soil / survey | $800 to $8,000 | Geotech, extra pits, wetland flags |
| Driveway (gravel to paved) | $15 to $80 per foot of length | Width to 14 ft, culverts, slope |
| Crane pad and mats | $2,000 to $15,000 | Soil bearing, mats, second pick |
| Electric trench | $25 to $80 per foot plus fees | Transformer, rock, overhead vs buried |
| Water lateral | $30 to $90 per foot | Meter, meter pit, well instead |
| Sewer lateral | $50 to $150 per foot | Depth, pump, traffic control |
| Gas / propane | $20 to $70 per foot or tank package | Utility vs tank |
| Crane day (set) | $4,000 to $25,000 | Tonnage, boom length, idle time |
Use the cost calculator with your trench lengths. Draw-schedule cash and a 20 to 40 percent site buffer are in financing affordability.
How should you sequence logistics?
Site prep 2 to 6 weeks on a ready lot, delivery and set 1 to 2 days, utility connections 3 to 14 days, final inspections 1 to 3 weeks. Raw land adds months. Align the plant ship date to the foundation cure, not the other way around. Confirm crane access and ground conditions before the truck leaves the factory. Walk the site after heavy rain. Water patterns reveal grading needs.
Uncertified expandables from Amazon still need a pad and a crane. They usually fail as dwellings. Read expandable prefab legality before you spend site money on a CE box. Request buyer help if you want a shortlist that matches county soils and access photos.
FAQ
- What site tests should I order before I buy land for a modular home?
- A boundary survey, geotechnical borings if soils look weak, and a percolation test wherever septic is required. Flood maps and wetland flags belong in the same packet. Skip perc only when a municipal sewer tap is already in the street and you have a tap letter.
- How wide does the driveway need to be for delivery?
- Plan for about 14 feet of clear width, 14 to 16 feet of vertical clearance, and turning radii that can take an 80-foot tractor-trailer. Overhead lines, mailboxes, and tight gates are the usual stops. The factory will give a haul route checklist. Follow it.
- What is a crane pad and why does it cost money?
- A crane pad is compacted, level ground (often timber mats or crushed stone) that can carry the crane plus the module pick. Soft clay, a slope, or a neighbor property line can force mats, a larger crane, or a second pick. Pads commonly run $2,000 to $15,000 before the crane day itself.
- How much do utilities cost per foot?
- Planning ranges, not bids: electric trench $25 to $80 per foot plus transformer fees, water $30 to $90 per foot, sewer $50 to $150 per foot, gas $20 to $70 per foot. Crossings, rock, and traffic control multiply those numbers. Wells and septic are lump sums, not per-foot.
- Does HUD versus IRC change site prep?
- Yes. HUD manufactured homes follow HUD Code (24 CFR 3280) and need an eligible foundation if you want conventional financing under Fannie Mae B2-3-02. IRC modular homes need a foundation designed to the plant drawings. Both still need access, drainage, and utilities.
- How long does site prep take?
- Simple suburban lots: 2 to 6 weeks after permits. Raw land with well, septic, and a new driveway: 8 to 16 weeks, weather excluded. Factory production often overlaps, but delivery cannot happen until the foundation and crane path are ready.
- What contingency should I hold for site work?
- Hold 20 to 40 percent of the site budget on unknown soils, rock, or long laterals. Factory cost is more predictable. Site cost is where modular projects overrun. See the affordability guide for draw-schedule cash flow.