What it means
A normal mortgage is secured on a finished, valuable, sellable building. A construction mortgage starts life secured on a muddy plot, which means the lender's security only becomes worth the loan as the project progresses, and that timing gap drives everything else about the product.
Lenders manage that risk through staged drawdowns. An independent quantity surveyor or inspector visits the site before each release and certifies that the work claimed has genuinely been done, so the money follows the value rather than running ahead of it.
Pricing reflects the extra risk. Construction mortgages usually carry a margin above standard mortgage rates plus an arrangement fee, and many are interest-only during the build, with either monthly cash interest payments or an interest reserve set aside from the facility itself.
Two ratios govern how much is available. Loan-to-cost compares the facility to total project cost including land, fees and contingency, while loan-to-value compares it to the appraiser's estimate of the finished building's worth; lenders apply both and lend against whichever produces the smaller number.
The exit matters as much as the build. A single-close construction-to-permanent mortgage converts automatically to long-term terms on completion, while a two-close structure requires the borrower to arrange separate take-out financing, which exposes them to whatever interest rates happen to be doing on completion day.
In practice
Real-world examples.
Example
A couple building a custom home take a construction-to-permanent mortgage of $560,000. They pay interest only on drawn funds during the ten-month build, then the facility converts automatically to a 30-year repayment mortgage on the day the occupancy certificate is issued, with no second set of closing costs.
Example
A small developer builds six townhouses on a $3,500,000 project financed at 70% loan-to-cost, giving a $2,450,000 facility and $1,050,000 of equity. Each of the four drawdowns is released only after the lender's surveyor certifies the stage, and one release is delayed three weeks when roofing falls behind schedule.
Example
A care home operator finances a $9,000,000 extension with an interest reserve built into the facility, so no cash interest is paid during construction. The reserve is exhausted two months before completion because of a cost overrun, and the operator has to fund $180,000 of interest from operating cash.
Formula
Calculation
Interest for a draw period = outstanding drawn balance x annual interest rate x (period length / 12 months). Total build interest is the sum across all periods.
A developer arranges a $1,200,000 construction mortgage at 9% for a twelve-month build, drawn in three stages.
Draw 1 of $300,000 at the start, outstanding 12 months: $300,000 x 9% x 12/12 = $27,000.
Draw 2 of $400,000 at month four, outstanding 8 months: $400,000 x 9% x 8/12 = $24,000.
Draw 3 of $500,000 at month eight, outstanding 4 months: $500,000 x 9% x 4/12 = $15,000.
Total interest = $27,000 + $24,000 + $15,000 = $66,000.
Had the full facility been drawn on day one, interest would have been $1,200,000 x 9% = $108,000, so staging the draws saved $108,000 - $66,000 = $42,000. Adding a 1% arrangement fee of $1,200,000 x 1% = $12,000 gives an all-in finance cost of $66,000 + $12,000 = $78,000 for the build.Case study
Seen in the real world.
What follows is an illustrative, fictional case. Pennygate Developments, an invented small builder, secured a $1,200,000 construction mortgage at 9% to build four terraced units, with total project costs of $1,700,000 and an expected completion value of $2,150,000.
Pennygate's first budget assumed the full $1,200,000 would be drawn immediately, projecting $108,000 of interest. Rebuilding the cash flow around the lender's three-stage release schedule cut the projected interest to $66,000, and that $42,000 saving was enough to fund the landscaping the sales agent said would move the units faster.
The lesson in this fictional example is that on a construction mortgage the drawdown schedule is a real financial lever, not administration. Pennygate deliberately delayed its final draw by a full month, timing it to the kitchen installation rather than taking it early, and saved a further $3,750 of interest on the way to a refinance into a long-term facility.
Watch out
Common mistakes.
- Budgeting interest on the full facility amount for the whole build period, which overstates cost, or budgeting on nothing drawn at all, which understates it badly.
- Ignoring the take-out risk in a two-close structure and assuming permanent financing will be available on the same terms twelve months later.
- Leaving no contingency in the loan-to-cost calculation, so the first overrun forces an awkward request for additional funds from a lender who is already fully committed.
Questions
People also ask.
Does a construction mortgage cover the land purchase?
Often yes, though lenders usually require the borrower to own the land outright or contribute it as part of the equity contribution before the first build draw.
Does the interest get capitalised into the property's cost?
For a business or investment property it generally does under construction interest rules, while for an owner-occupied private home the interest is normally just a cost of the build.
Does an interest reserve mean the financing is free during construction?
No, the reserve is drawn from the facility itself, so the borrower is borrowing money to pay interest and the total loan balance rises accordingly.
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