The building itself is the easy part to price. You design it, you get an estimate, and the number is what it is. The costs that catch people out are the ones around it, and they depend on three things we can't see from a floor plan: your lot, your city, and how far the building sits from your house.
None of this is a reason to wait. It's a reason to get the right people looking at your yard early, before you fall for a design.
Start with the site
Site work is the most variable part of any backyard build. Two identical houses can cost very different amounts to put in the ground, depending on the soil, the slope and the distance to the street. So the single most useful thing you can do is ask a contractor to walk your lot with your site plan in hand.
What they'll price:
- The foundation. A slab or a raised floor, sized to your building and your soil.
- Trenching and utility runs. Water, sewer or septic, power and internet. The farther the building is from the house, the more trench there is.
- Grading and drainage. Especially on a sloped lot, where water has to go somewhere other than your new floor.
- Site access. A clear path for delivery, a fence section that comes down for a day, or a crane if the truck can't reach.
Then the house's own systems
- An electrical service upgrade. Many homes need a bigger panel or a bigger service to add a dwelling, and saunas usually need a dedicated circuit of their own. Check your panel before you assume.
- Appliances, fixtures and heating. A mini-split heat pump is the common choice for a small building.
- Finish work. If you choose the steel shell, the inside of the building is on your budget, not ours.
Then the paperwork
- Permit and plan review fees. Set by your city, often based on the size or value of the building.
- Impact and utility connection fees. Common for a new living unit, and often lower or waived for a small space.
- A stamped permit set and engineering. Your Ekstra plans are design drawings your engineer and builder work from. The stamped set your city reviews is the next step, priced on its own.
- A survey or a soils report. Only some lots need one, usually when the lines aren't clearly marked, the fit is tight, or the city asks.
And the things everyone forgets
- Landscaping, paths, decks and fencing. Often forgotten, always noticed.
- Insurance and property tax. Call your insurer before you build. A new unit can change both your premium and your assessment.
- A contingency. Set aside 10 to 15 percent for the things nobody could see until the ground was open.
Where to start
Design the building first so there's something real to price, then take the list above to a contractor and to your city. Our free Build Ready Guide has the full checklist, and the designer gets you a site plan and an estimate to bring to both.