"What does it cost to build a custom home?" is one of the most searched questions in home building, and the honest answer is that a single number per square foot tells you little. What a builder needs, and what a client deserves, is a cost breakdown: the budget split into divisions of work, each with its own number, so everyone can see where the money goes and track it as the job runs.
This guide is written for builders. It covers how to organize the divisions, how allowances, contingency, overhead and profit fit on top, how to read cost per square foot properly, and how to compare budget with actual cost while the house is going up.
Why a cost breakdown beats a price per square foot
A price per square foot is a ratio, not a budget. Two houses with the same area can differ by hundreds of thousands of dollars because of the site, the foundation, the window package, the mechanical system or the finish level. A breakdown by division shows those differences and gives you somewhere to put them.
It also gives you a common language with the client. When the client asks why the number moved, you can point to a division, not to a total.
Step 1: Organize the divisions
Use the same divisions on every job so your numbers can be compared from house to house. A typical set for a custom home:
- Pre-construction: design, engineering, surveys, permits
- Site work: clearing, excavation, access, temporary services
- Foundation and underslab
- Framing: materials and labour
- Roofing
- Windows and exterior doors
- Exterior finishes
- Plumbing
- Electrical
- Heating, cooling and ventilation
- Insulation and air barrier
- Drywall
- Interior trim and doors
- Cabinets and countertops
- Flooring and tile
- Paint
- Landscaping, driveway and exterior works
- Cleaning, final and closeout
Inside each division, list lines at the level you buy or subcontract them. If you use cost codes in your accounting, match them, so actual costs drop straight into the same lines.
Step 2: Price each line
Price from quantities and current quotes, not from last year's job. Quantity times unit cost for materials, crew days times rate for labour, and written quotes for trades. Note which quotes have an expiry date. Material prices that move quickly, such as lumber, copper wire and some imported goods, are worth a separate risk note.
Step 3: Separate allowances
Anything the client has not yet chosen goes in as an allowance: a set amount for, say, lighting fixtures, tile or appliances. Keep allowances visible in their own lines so the client knows which numbers depend on their choices. When the selection is made, the difference becomes an overage or a credit. See our guide to selection sheets.
Step 4: Add contingency, overhead and profit
Direct cost plus allowances is not the price. On top go:
- Contingency. A percentage for unknowns. Size it to the risk: an existing structure, a rock site or an early design needs more than a repeat plan on a cleared lot.
- Overhead. Your office, vehicles, insurance, software and your own time that is not charged to a line.
- Profit. The return for the risk you carry.
Be clear about markup versus margin. A 20% markup on cost is a 16.7% margin on price. Mixing the two is one of the most common ways builders under-price.
Sample cost breakdown
The table below is a sample budget for a sample house of 3,200 square feet. The figures are made up to show the structure and the arithmetic. They are not averages and are not a guide to what any house costs.
| Division | Budget | Share of direct cost | Actual to date | Variance |
|---|---|---|---|---|
| Pre-construction | $48,000 | 4.6% | $51,200 | -$3,200 |
| Site work | $72,000 | 6.9% | $70,400 | $1,600 |
| Foundation and underslab | $96,000 | 9.2% | $98,500 | -$2,500 |
| Framing | $168,000 | 16.2% | $163,900 | $4,100 |
| Roofing | $42,000 | 4.0% | ||
| Windows and exterior doors | $88,000 | 8.5% | ||
| Exterior finishes | $76,000 | 7.3% | ||
| Mechanical, plumbing and electrical | $150,000 | 14.4% | ||
| Insulation and drywall | $64,000 | 6.2% | ||
| Interior finishes and cabinets | $170,000 | 16.4% | ||
| Landscaping and closeout | $65,000 | 6.3% | ||
| Direct cost | $1,039,000 | 100% | ||
| Contingency (sample 5%) | $51,950 | |||
| Overhead and profit (sample 18% on cost and contingency) | $196,371 | |||
| Price before tax | $1,287,321 |
At this sample price, the house works out to about $402 per square foot before tax. The number is a result of the breakdown, not the starting point. Variance is budget minus actual, so a negative number is an overrun.
Step 5: Track actual cost against budget
The budget is only useful if you compare it with what you spend. Post every invoice to its division and line as it arrives, and look at variance at least once a month. A small overrun in pre-construction or foundations is worth a conversation early, while there is still time to recover it in later divisions or use contingency on purpose rather than by accident.
Add approved change orders as their own lines so the original budget stays readable. Our guide to change order forms covers how to price and log them.
A short how-to
- Set up a standard list of divisions and use it on every job.
- Price each line from quantities and current quotes.
- Put open choices in allowances.
- Add contingency, overhead and profit, and check markup against margin.
- Calculate cost per square foot as a check, not a starting point.
- Post actual costs to the same lines as the job runs.
- Review variance monthly and record why each division moved.
The free template and the full workbook
Start with the free Custom Home Cost Breakdown Template. It is an Excel workbook with 18 cost divisions and editable lines, budget, actual, variance and per cent of total, settings for your sales tax rate, contingency and floor area, and a summary with cost per square foot and a budget-versus-actual chart. It comes in an example version with sample figures and a blank version.
When you want the full estimate behind the budget, the Custom Home Estimate, Budget & Job-Cost Workbook (CA$99) prices up to 120 lines across 23 divisions, builds the contract price from direct cost, allowances, contingency, overhead and profit, tracks change orders and job cost, and prints a one-page client estimate. A dashboard shows markup, margin and price per square foot against your target range.
FAQ
What is the biggest cost in building a custom home?
It varies by design and site. Framing, mechanical systems and interior finishes are often among the largest divisions, but a difficult site or a large window package can outweigh them.
How much contingency should a custom home budget carry?
That is a judgment based on the risk on each job. Many builders use a smaller percentage for a repeat plan on a cleared lot and a larger one for renovation, rock or an early design.
Should I show the client the full breakdown?
Many builders show divisions and allowances but keep overhead and profit as one line. Decide what your contract type calls for. A cost-plus contract usually needs more detail.
Is cost per square foot useful at all?
Yes, as a check. Compare it with your own past jobs of a similar type. It is a poor way to price a new house.
Do the sample figures here reflect market prices?
No. They are made up to show the structure. Use your own quotes and past jobs.