Greenhouse Foundation Calculator
Work out how much concrete, gravel, pavers or lumber you need for your greenhouse foundation. Enter the size of your greenhouse base and pick a foundation type.
How it works
How much concrete or gravel does a greenhouse foundation need?
Every foundation comes down to volume: length × width × depth, converted to cubic yards. One cubic yard is 27 cubic feet.
Cubic yards = Length (ft) × Width (ft) × Depth (in) ÷ 12 ÷ 27
| Foundation | Best for | What to know |
|---|---|---|
| Concrete slab | Glass greenhouses, garden rooms, paved floors | Most stable and easiest to keep clean. An 80 lb bag of mix makes about 0.6 cubic feet. |
| Footing or stem wall | Larger greenhouses, in-ground beds, more headroom | Dig below your frost line. Many Victorian and Orangerie models are designed to sit on a low wall. |
| Gravel pad | Polycarbonate greenhouses, good drainage | Cheaper and drains well. Gravel weighs about 1.4 tons per cubic yard. |
| Pavers | A finished floor that drains | Lay on compacted gravel and sand. |
| Timber base | Small, light greenhouses | Quick to build, but it must be level, square and well anchored. |
Questions
Greenhouse foundation FAQ
What is the best foundation for a greenhouse?
For a glass greenhouse, a concrete slab or a footing with a low stem wall is best because glass needs a perfectly level, rigid base. Polycarbonate greenhouses can sit on a gravel pad or a timber base that is level and anchored.
How much concrete do I need for a 10 x 12 greenhouse slab?
A 4 in slab for a 10 x 12 ft greenhouse needs about 1.5 cubic yards, or around 74 bags of 80 lb concrete mix, including 10% extra.
How thick should a greenhouse concrete slab be?
4 inches is standard for a hobby greenhouse. Thicken the edges to 8 to 12 inches, or add a footing, for large or heavy glass greenhouses and in areas with deep frost.
Can I put a greenhouse directly on the ground?
Small polycarbonate greenhouses can sit on a base frame anchored into the ground, like the Riga foundation frame. Glass greenhouses should always go on a level, solid foundation.
More tools
Other greenhouse calculators
- Heater Size CalculatorHow many BTUs it takes to keep your greenhouse warm on the coldest night.
- Heating Cost CalculatorWhat a winter of heating will cost with electric, propane or natural gas.
- Fan and Ventilation CalculatorThe exhaust fan CFM and vent openings that keep summer heat down.
- Snow Load CalculatorHow much the snow on your roof weighs and when to brush it off.
- Greenhouse Size CalculatorHow big a greenhouse you need for the plants you want to grow.
- Shade Cloth CalculatorThe right shade percentage and cloth size for your greenhouse.
- Grow Light CalculatorHow many grow lights it takes to give your plants enough light in winter.
- Rainwater CalculatorHow much water your greenhouse roof can collect for your plants.
Want a second opinion?
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