Site & structure
Greenhouse foundations and bases
The base determines level, drainage, load transfer, anchoring, door alignment, and how much of the project is actually finished.
Short answer
Before ordering, identify whether the greenhouse needs a supplied base, framed foundation, slab, piers, or another documented support. The answer depends on structure, soil, frost, drainage, local rules, and the manufacturer’s instructions.
What the base has to do
A foundation supports vertical loads, resists movement and uplift, keeps the frame level, and gives the enclosure a durable edge. Oklahoma State Extension emphasizes that foundations must resist overturning and vertical pressure and may need to extend below the frost line. Those are design considerations, not universal instructions.
Choose by responsibility
Separate “included with the kit” from “required for installation.” Ask who supplies the base, who levels the site, whether the threshold needs a particular elevation, and whether anchoring attaches to the base. Price and schedule work that is not in the box.
A simple site brief
Write down soil and drainage, frost exposure, slope, delivery access, finished floor height, utilities, and the exact exterior footprint. If you cannot answer those yet, the responsible result may be “prepare first.”
Common mistakes
- Measuring only the glazing footprint.
- Assuming a flat-looking yard is level enough.
- Putting a permanent structure where water pools.
- Choosing foundation material before reading the manual.
A judgment call
A seasonal film house may use a lighter, well-drained base; a permanent rigid house may justify more substantial work. Neither label decides the answer alone.