Assess a permanent modular home rental project using the full cost of reaching a lawful, lettable dwelling. The catalogue price, the expected rent and the investment return are three different numbers.
This guide illustrates the arithmetic for a dwelling added to land already owned. All dollar amounts below are invented teaching assumptions. They are not ModuHaus prices, rental appraisals or expected returns for NSW or Victoria.
Set the investment boundary first
An incremental project calculation asks what additional income and cost the new dwelling creates. A whole-property calculation also includes the existing land and home. Both can be useful, but their yields are not directly comparable.
For a land purchase, include acquisition costs and the whole development budget. For an existing property, state clearly that the incremental calculation excludes its existing value. Owning land does not remove its opportunity cost.
Confirm that the intended rental use is permitted before relying on income. Start with the NSW or Victoria approval guide and obtain property-specific advice.
Gather evidence for the inputs
ASIC's Moneysmart property investment guide explains that rental income may not cover loan payments and other expenses. It also highlights vacancy and ongoing ownership costs.
Request a local rental appraisal that considers layout, privacy, access, parking and competition. Obtain written project costs and finance terms. Include management, maintenance, insurance, owner-paid services and any additional rates or charges that apply.
Use a consistent annual basis. Include letting and renewal fees where relevant. Model shared expenses explicitly rather than silently charging them to the existing dwelling.
Worked example: incremental annual cash flow
The example assumes a completed project cost of $250,000, excluding the existing land and home. The $15,000 debt-service amount includes the year's assumed principal and interest repayments. The figures are illustrative only.
| Input or result | Calculation | Example AUD |
|---|---|---|
| Completed incremental project cost | Assumed all-in cost | $250,000 |
| Weekly rent | Assumption | $500 |
| Scheduled annual rent | $500 x 52 | $26,000 |
| Vacancy allowance | $500 x 4 weeks | $2,000 |
| Collected rent | $26,000 - $2,000 | $24,000 |
| Annual operating costs | Assumption, excluding debt and tax | $6,000 |
| Operating surplus | $24,000 - $6,000 | $18,000 |
| Annual debt service | Assumed principal and interest | $15,000 |
| Cash flow before tax | $18,000 - $15,000 | $3,000 |
Gross scheduled yield on incremental cost is $26,000 / $250,000 = 10.4%. The operating yield after the vacancy allowance and operating costs is $18,000 / $250,000 = 7.2%, before debt and tax.
Neither percentage is a total investment return. Neither measures capital growth, sale costs, tax or the return on the whole property. Cash-on-cash return would also require the actual cash equity contribution.
Test the downside in the same model
Now assume rent is $450 a week, eight weeks are vacant, operating costs rise to $7,000 and annual debt service rises to $17,000.
| Downside result | Calculation | Example AUD |
|---|---|---|
| Collected rent | $450 x 44 occupied weeks | $19,800 |
| Operating surplus | $19,800 - $7,000 | $12,800 |
| Cash flow before tax | $12,800 - $17,000 | -$4,200 |
The project now needs a $4,200 annual cash contribution. Test a construction delay separately: it changes the first year's income and holding costs. A stable-year rental model does not capture that automatically.
In the base example, the simple break-even rent is ($6,000 + $15,000) / 48 occupied weeks = $437.50 a week. This assumes those costs stay fixed. If management fees depend on rent, recalculate them as rent changes.
Decide what would make you pause
Set your own limits with the relevant advisers before choosing a model. Useful questions include:
- 01Can available funds cover a delay and a period without a tenant?
- 02Which cost allowances remain unquoted?
- 03Would a lower rent still cover required repayments?
- 04Does the forecast depend on future capital growth?
- 05Could the second dwelling affect the rent or use of the main home?
A permanent building classification does not guarantee lending approval, valuation or resale performance. Have the lender assess the actual property, construction contract and payment schedule. Have a tax adviser assess tax consequences separately.
Turn assumptions into a project brief
Use the NSW/Victoria budget checklist to replace cost assumptions with evidence. Compare suitable Permanent Homes only after establishing the use and site constraints.
ModuHaus investment feasibility can help organise the model, site and delivery questions. This example is general education, not a recommendation to invest or a forecast for your property.
Sources and further reading
Requirements change and can be applied differently by site and local authority. Check the current official sources and confirm your project with the relevant council, certifier or qualified professional.