A prefab garden suite starting from $225,000 sounds simple, until you learn the factory price is only part of the number. Here’s what the rest actually covers.
The Factory Price Is Not the Whole Price
Prefab garden suites are genuinely attractive from a starting price of around $225,000, and factory construction really does deliver cost and schedule advantages over fully custom builds. But that starting figure typically describes the manufactured module or panel package alone, built and largely finished in a factory, not the complete cost of a suite sitting, connected and livable, in your backyard. Homeowners who compare only the factory price across different prefab companies are often comparing very different scopes without realizing it, which is exactly how a “$225,000 suite” can turn into a $340,000 project once every necessary site cost is added.
What’s Typically Inside the Factory Price
The factory or module price generally covers the structural shell, built and largely finished off-site: framing, insulation, windows and exterior doors, interior wall finishes, and often a substantially complete kitchen and bathroom, wired and plumbed to factory-standard fixtures. Some manufacturers include flooring and paint as standard; others price these as options. The factory environment is genuinely efficient for this work, protected from weather, with repeatable quality control, which is a large part of why prefab can start below custom construction pricing for the same square footage. What it almost never includes is anything that happens outside the factory once the module leaves for your property.
The Site-Cost Gap: What $80,000 to $150,000 Actually Covers
The site costs that complete a prefab project, commonly $80,000 to $150,000 depending on your lot, typically include the foundation, whether helical piles or a slab, the full utility trench connecting water, sewer, and electrical from your main house, delivery and crane or flatbed placement of the module itself, on-site assembly and connection of multiple modules if your suite ships in more than one piece, exterior finishing details that don’t survive factory transport well, final utility hookups and inspections, and design, engineering, and permit fees, since even a prefab suite needs a full Ontario Building Code permit application specific to your property.
Apples-to-Apples: The Checklist for Comparing Prefab Quotes
Before comparing two prefab quotes by their headline number, ask each company to confirm, in writing, whether the price includes the foundation, the full utility trench and connections, delivery and crane or placement costs, site assembly if the suite ships in modules, exterior finishing after placement, design and permit fees, and a contingency allowance. A prefab company quoting only the factory module price, without walking through this list, is not being dishonest, but it is leaving you to discover the rest of the number later, at exactly the point in the project when comparison shopping is no longer realistic. Two quotes that look $60,000 apart on paper are often identical once every excluded line item on the cheaper one is priced and added back in.
Where Prefab Still Wins on Total Cost
Even accounting for the full site-cost gap, prefab remains genuinely competitive against custom construction for comparable square footage and finish level, and the advantage often shows up more clearly in schedule than in raw dollars: on-site assembly typically takes days to weeks rather than months, since the weather-dependent, slow parts of construction happen in a factory in parallel with your permit review and foundation work. For homeowners prioritizing speed and cost predictability, factory-controlled construction reduces the number of variables that can surprise a project mid-build, which is a real value even when the all-in total lands close to a well-run custom project.
When Site Costs Erase the Prefab Advantage
Prefab’s advantage narrows or disappears on lots with genuinely difficult access, since a module or panel set still has to physically arrive at the build site, sometimes requiring a crane lift over the main house at real added cost, and on lots with unusual servicing distances or difficult soil, where site costs dominate the total regardless of how the structure above the foundation was built. In these situations, the factory savings on the shell itself can be entirely absorbed by site conditions that would have added similar cost to a custom build as well, which is why access and servicing deserve the same scrutiny in a prefab decision as in a custom one.
Getting a Real All-In Prefab Number
The only way to know whether prefab actually saves you money on your specific lot is to price the complete project, factory module plus every site cost above, against an equivalent custom quote for the same size and finish level. Our prefab garden suites service prices both the factory package and every site cost together under one contract, so the number you receive is the number you’ll actually pay, not a starting figure that grows once your specific yard gets involved. Our companion cost guide walks through the same comparison in more detail if you’re still weighing prefab against custom for your project.
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