In colder climates or wherever you want to grow vegetables and plants when the weather is not ideal, a greenhouse is the way to do it, but in order to support it you will need to build a greenhouse foundation. A greenhouse consists of a metal frame with either glass or composite panes. Although not nearly the weight of a garage let alone a house, a greenhouse nonetheless needs a good support system to stay level and workable. There are a number of different materials you can use to build your greenhouse foundation. Concrete, brick and timber are the three that will be discussed here, briefly outlining the pros and cons of each.
Laying a concrete foundation for your greenhouse will be the most durable option. A concrete foundation benefits from its inherent strength and uniformity. Properly framed, a foundation made from concrete will last a long time, and if it is correctly sealed, it will be protected from the elements. For large greenhouses, a concrete foundation makes the most sense as the greater the weight of the frame, the more important it is to have a solid structure supporting it.
On the other hand, pouring a slab of concrete large and thick enough to support a greenhouse can be both time consuming and expensive. If you were to hire a contractor, it could easily run into the thousands of dollars. Doing it yourself may save you some money, but the labor involved is extensive.
Another option for a greenhouse foundation is brick. With a properly smoothed and leveled bed of earth, interlocking brick pavers can be laid that offer support for a greenhouse comparable to concrete. Although labor intensive, it is less so than pouring your own concrete foundation. And unlike concrete, if ever a section of brick were to crack, replacement is a matter of changing out the necessary number of bricks.
You can opt to simply fit the bricks together in an interlocking pattern or use mortar to secure them. Using mortar will require more labor and cost, but it will give you an even firmer base upon which to build a greenhouse. The initial cost of brick may exceed the raw materials required for pouring a concrete foundation, but there is a mutual tradeoff of labor vs. cost between the two options.
A timber foundation, or one constructed out of lumber, is yet another option. For homes, garages and other buildings, the lowest level of lumber is always secured to a concrete foundation. Thus, merely laying out a few slabs of wood for a foundation will work only for the smallest of greenhouses. If the land is very flat and level and the greenhouse is of modest size, constructing a foundational frame out of pressure treated wood is a viable option. Use 4 to 6 concrete support blocks with brackets built in. These in turn support 4x6 floor beams which support the appropriate number of 2x6 floor joists. Atop these go plywood or another type of sub floor, followed by any linoleum or flooring of your choice. If your greenhouse is not too big, this is a very workable idea that won’t cost you as much as hiring a concrete crew or purchasing hundreds of interlocking bricks.
Several different materials are available to you for your greenhouse foundation. Concrete, brick and lumber all present an effective way to support a greenhouse, whatever its size. Cost, labor and strength are all factors to consider before you make a choice.