Prefab projects go over budget when surprises cluster at the edges — connection fees, groundworks, kitchen packages omitted from the base quote, or VAT assumptions misunderstood. A modular price per square metre is a starting point, not a budget. This framework helps you build a spreadsheet that survives contact with reality, whether you are comparing three manufacturers or explaining the project to a bank.
Land and purchase costs
If you already own land, record its book value and any remaining mortgage. If you are buying, include purchase price, notary fees, land transfer tax (Grunderwerbsteuer — rates vary by Bundesland), agent commission if applicable and early survey costs. Corner plots with two road frontages may incur higher connection charges later — note that in your assumptions.
Professional fees and permits
Budget for architects or Bauzeichner, structural engineers, energy consultants, geotechnical surveys if required, and Bauamt application fees. Modular manufacturers sometimes bundle planning services; confirm whether stamp-ready drawings for your municipality are included or billed hourly. Permit timelines affect financing interest — a three-month delay has a cost even if fees stay fixed.
Site preparation and foundation
Clearing vegetation, demolition of old structures, excavation, levelling and drainage often sit outside module quotes. Prefab foundations must meet tight tolerances — slab or strip foundations designed to manufacturer specifications. Poor ground conditions triggering piling or soil replacement can move this line significantly. Get geotechnical advice on sloped or fill sites before locking module contracts.
Modules and factory scope
The factory price should list module dimensions, structural shell, windows, exterior cladding, roof completion level and standard interior fit-out if included. Ask explicitly about kitchen, bathrooms, flooring, internal doors, stairs, paint and electrical fit-out — these are common exclusion zones. Compare quotes only when interior finish levels match.
Transport, crane and assembly
Delivery routes may require police escorts or temporary road closures for oversized loads. Crane hire depends on module weight, reach and site access — narrow lanes increase costs. Confirm who schedules assembly day, who insures modules during lift and what happens if weather postpones the crane.
Utilities and connections
Separate fees often appear for water, sewage, electricity, gas if used, fibre and rainwater drainage. Distance from street to house matters. Rural plots may need private wastewater systems with approval costs. Request quotes from local utilities early; manufacturers rarely control these figures.
On-site finishing trades
Even turnkey-ish packages may leave landscaping, driveways, fencing, decking, final painting touch-ups or custom carpentry to you. Traditional trades finishing connections between modules — sealants, interior joints — should be named in contract scope. Undefined "snagging" periods can become expensive if responsibility is vague.
Furniture, appliances and moving
These sit outside construction contracts but belong in your personal budget if you are upgrading size or quality. Modular homes with precise door widths may require planning for sofa delivery — a small line item that prevents moving-day surprises.
Contingency and VAT
Hold ten to fifteen percent contingency for changes and unknown ground conditions. Clarify whether quotes include German VAT (Mehrwertsteuer) at nineteen percent and whether any subsidy reduces net cost after completion rather than upfront. Financing costs — arrangement fees, interest during build — belong in the total picture if you are borrowing.
A simple tracking habit
Maintain three columns: estimated, quoted, actual. Update when you receive each written quote. Flag items with no quote yet in red — those are where prefab projects typically overshoot. Share the sheet with your partner and advisers so decisions reference the same totals.
Budgeting without guesswork is less about precision on day one and more about exposing gaps before deposits become non-refundable. Pair this template with modular home planning and choosing a building partner so financial clarity supports — not replaces — technical diligence.