Seven prefab-buying decisions deserve attention before production starts: comparing offers with mismatched scopes, budgeting only for the house, ignoring running costs, skipping certification proof, committing before the plot is checked, signing without a fixed price, and paying ahead of progress. Published prices, a clear contract, payment milestones, and verifiable certificates help you assess each decision. This guide shows exactly how.
This guide is about buyer decisions, not product doubts. If you are still weighing whether factory-built homes hold up in quality, the prefab myths guide answers that with data. If you want the purchase path step by step, from configuration to handover, the buying process guide walks through all seven stages. This article covers something narrower: seven decisions that affect the project budget and the documents that help you assess them. BioBuilds, the European manufacturer publishing this guide, was founded in 2012 and has delivered more than 220 homes across Europe.
Mistake 1: Comparing offers on the headline price
Two quotes for the same floor area can cover different scopes. One includes delivery; the other adds it later. One is turnkey; the other is a weathertight shell. One includes the ventilation system its energy claims depend on; the other lists it as an option.
The fix is mechanical: reduce every offer to price per square meter at the same finish level and the same included scope before comparing anything. Ask each manufacturer for an itemized list of what the price contains and excludes, in writing. Published list prices make this fast: the displayed BioBuilds price covers the module in its standard configuration. Transport is included in Irish storefront prices and quoted separately by destination elsewhere, and on-site assembly is arranged by the client with BioBuilds' local partners at no extra cost. The 2026 prefab price guide breaks down the current per-model and per-square-meter figures.
Mistake 2: Budgeting only for the house
BioBuilds' standard house price excludes land, foundation, unloading and crane, utility hookups, permits, and site works. Check each offer's exclusions before signing.
Plan those costs before you commit, using estimates for your plot. BioBuilds' site-cost estimates start from €47,600 for Wanderlust 48 and from €85,100 for Sanctuary 142. The model numbers refer to nominal exterior areas in m². These estimates exclude land and transport. The site-cost guide itemizes each line. Figures are shown including an illustrative 19% German VAT. Standard VAT rates are 19% in Germany, 20% in Austria, and 21% in Romania; each supplier should confirm the tax treatment of its services.
Mistake 3: Ignoring what the house costs to run
Purchase price is paid once; heating bills repeat for decades, and the building envelope affects how much heat the home needs. BioBuilds' standard models target around 15 kWh/m² per year of heating demand; the project result depends on the site and configuration. For comparison, the Passive House Institute reports heating and cooling energy savings of up to 90% against typical building stock. Savings over 30 years depend on the comparison home, energy prices, heating-system efficiency, and maintenance costs.
To prevent this, compare offers on both numbers: the price of the house and the project-specific heating demand and any performance commitment in the contract. The Passivhaus ROI guide runs the long-term arithmetic in detail.
Mistake 4: Taking "energy efficient" on faith
For a Passivhaus-certified building system, check the issuer, certificate reference, and entry in the Passive House Institute's public registry. If a claimed performance level matters to your decision or your financing, the certificate reference belongs in the contract.
There is also a physical test to ask about. Airtightness, the property most efficiency claims quietly depend on, is measured with a blower-door test at 50 Pascals; the Passivhaus limit is 0.6 air changes per hour. Ask for the result in writing. BioBuilds' MODULAR building system is Passivhaus-certified for the cool-temperate climate, reference 2582cs03. BioBuilds reports tracking more than 2,000 parameters across the system. The external-wall EPD covers the assembly declared in that document; it is separate from Passivhaus certification.
Check the system certificate in the issuer's registry and record the agreed performance in the contract. Agree when your home will be blower-door tested at 50 Pa against the Passivhaus limit of 0.6 air changes per hour, and request the written result.
Mistake 5: Committing before the plot is checked
Confirm that your plot can accommodate the home, its foundation, and delivery access before you sign. Soil conditions, truck and crane access, and the local permit path all belong before the purchase decision, not after.
A land survey and geotechnical report turn unknown soil and boundary conditions into documented inputs. Where the plot is suitable, ground screws keep a poured-concrete foundation out of the critical path, but a structural engineer must design the foundation for the ground conditions and building loads. The foundation guide covers what the ground decides; ask BioBuilds and your local contractors to confirm delivery access to your specific destination before signing.
Mistake 6: Signing without a fixed price
Construction's classic failure mode is the number that grows after commitment. For a prefab purchase, define the product, scope, and price in the contract. BioBuilds' configurator gives an indicative estimate; the personalized offer and signed contract govern the final price.
Insist on this sequence: an indicative configured price, then a personalized offer that confirms the final gross price before you sign, then a contract that fixes it. At BioBuilds, the personalized offer confirms the final gross price before signing, and the individual signed contract governs. Check any price-change provisions in that contract. Ask any manufacturer to show you the equivalent clause; the answer tells you most of what you need to know.
Mistake 7: Paying ahead of progress
The shape of the payment schedule is a risk statement. Money paid far ahead of verifiable progress moves the manufacturer's business risk onto you; defined milestones make payment dates clear but do not by themselves remove that risk. BioBuilds' published schedule is:
Check the final tranche's trigger in the contract: BioBuilds' final 10% is due when the home is available at the agreed destination, with inspection on the trailer before unloading. The earlier tranches total 90% by the production-start notice, so plan funding around these payment dates.
What does a safe prefab purchase look like?
For each decision above, replace assumptions with written information and project-specific checks. Condensed into one pre-signing checklist:
- Like-for-like comparison: price per m² at the same finish level and the same included scope
- BioBuilds delivery: DAP with all-risks cargo insurance; destination-specific transport price, included in Irish storefront prices
- A site-cost budget based on quotes for your plot, with the VAT basis stated
- Project-specific heating-demand calculation, system certificate reference, and agreed performance in the contract
- Survey and geotechnical report done, or the contract conditioned on them
- Final gross price confirmed in the offer before signing, with scope and any price-change provisions stated in the contract
- Milestone payments with the final tranche at your destination, inspection before unloading
- Warranty terms in writing (at BioBuilds: 5-year structural guarantee, in addition to your statutory defect rights)
Use local specialists for the technical and permit checks, and follow the right sequence: compare on scope, budget the whole project, price the decades, verify the certificate, check the plot, fix the price, tie the money to milestones. The configurator is built for step one: the standard models, finish levels, and listed options have public indicative prices, so your comparison starts from numbers instead of a quote form.
