Greenhouse Kit vs. Custom: The Installed-Total Math
The sticker comparison looks settled -- a prefab kit at $1,000 to $5,000 against a custom wood quote at $6,000 to $15,000 -- and it still misleads in both directions. The kit sticker excludes assembly, delivery, foundation, and utility runs. The custom quote usually includes design, framing, glazing, and site labor, but its width hides real scope choices. Carried to the same finished state -- structure standing on a foundation, vents working, water and power connected -- published 2026 totals put a do-it-yourself kit project near $1,000 to $9,000 and a professionally built project near $5,000 to $25,000. This guide does that math line by line, then compares lifespan and names when each lane wins.
Orange County, CA · Updated 2026 · Costs shown as ranges — your quote will vary by installer and scope
Installed totals: the only fair comparison
| Cost line | Prefab kit lane | Custom-built lane |
|---|---|---|
| Structure / core materials | $1,000-$5,000 | $3,000-$10,000 materials |
| Delivery | $100-$300 freight typical | usually inside the quote |
| Assembly / build labor | $0-$2,000 | $2,000-$15,000 |
| Foundation + utility runs | extra on both lanes | extra on both lanes |
| Finished project total | $1,000-$9,000 DIY | $5,000-$25,000 pro-built |
One published example shows the kit lane's real shape: a 10-by-6 steel and polycarbonate kit at roughly $1,300 to $1,700, plus $100 to $300 delivery, lands near $1,500 to $2,000 before ground work. The custom lane runs the other way: one guide puts a professionally built medium greenhouse near $25 to $60 per square foot. Compare only totals that end at the same place.
What the kit actually buys
A kit buys engineering done in advance. Frame members arrive cut and drilled, glazing panels are sized to the frame, the door and vents are part of the design, and the instruction sequence replaces design decisions. Assembly is measured in days for a small footprint. The trade-offs are also fixed: footprint, height, and panel material come from a catalog, the structure is sized to a stated wind and load rating that the site has to match, and a damaged panel years later means ordering a maker-specific part rather than cutting a standard sheet to fit.
What the custom premium actually buys
A custom build buys fit and material choice. The frame -- wood is the common residential lane, published near $6,000 to $15,000 for a mid-size build -- is cut to the yard: an uneven grade, a footprint between catalog sizes, a taller ridge, or glazing split between glass and polycarbonate where each serves best. It also buys component-level repair: a framer can replace a rotted sill or a glazier a single pane without touching the rest of the structure. The premium is time and coordination -- design, foundation, framing, and glazing run in sequence across weeks.
Lifespan: different clocks, same weak points
No lane publishes a fixed service life, so treat any year figure a seller quotes as orientation only. In practice, a kit's clock is its glazing and seals: film coverings are a periodic replacement line, polycarbonate panels age in sun and are replaced as sheets, and door and vent hardware wears first. A custom wood frame's clock is moisture management: paint or finish maintenance and the condition of sills and joints decide how long the frame stands, while glass itself is a long-lived panel that breaks rather than wears out. On both lanes the structure outlasts its moving parts -- budget vents, openers, seals, and coverings as recurring lines either way.
When each wins
- Standard footprint, level pad, comfortable assembling a kit over a weekend or two: kit -- the lowest finished total in the comparison
- Odd dimensions, sloped ground, or a footprint between catalog sizes: custom -- fit is the product
- Wood frame and glass are the look the yard and the HOA review call for: custom -- catalogs rarely offer that combination
- Short timeline: kit -- days of assembly against weeks of sequenced trade work
- Repairability with standard materials over decades: custom -- every member and pane is a standard size a framer or glazier can match
Frequently asked questions
Is a greenhouse kit really cheaper once installed?
Usually, yes. Published totals put a do-it-yourself kit project near $1,000-$9,000 against $5,000-$25,000 for a professionally built project. The gap narrows once the kit lane adds assembly help, delivery, foundation, and utility runs, which kit stickers exclude.
How much does a custom wood greenhouse cost?
Published ranges put a mid-size custom wood build near $6,000-$15,000, with materials across custom projects near $3,000-$10,000 and labor near $2,000-$15,000. Size, glazing choice between glass and polycarbonate, and site conditions move the total most.
Which lasts longer, a kit or a custom greenhouse?
Neither lane publishes a fixed service life. Kit wear items are coverings, polycarbonate panels, seals, and vent hardware; custom wood wear items are finish, sills, and joints exposed to moisture. Both structures outlast their moving parts, which are budgeted as recurring lines.
What does kit assembly cost if I hire it out?
Published do-it-yourself versus pro comparisons put kit assembly and installation labor near $0-$2,000 in the DIY column, while full professional builds carry $2,000-$15,000 of labor. Get assembly priced as its own line -- it is the line kit stickers leave blank.
Can a custom greenhouse be built to an odd size?
That is the custom lane's main advantage: the frame is cut to the site, so footprints between catalog sizes, taller ridges, and sloped ground are workable. A kit comes in fixed footprints and load ratings that the site has to match instead.