A glass greenhouse resting on a concrete footing will last for decades.
Many customers opt for a concrete foundation for longevity and easy cleaning.
Our recommendation is that any double glass greenhouse or any greenhouse over 12x20 should rest on a concrete footing.
Types of Footings
You have a few choices when it comes to concrete foundations and oftentimes this decision should be in conjunction with your local city planning department.
Construction Tip: Beveled exterior edges or uneven surfaces can require major modification to the greenhouse or the foundation itself. The foundation must be level and square for the entire area where the greenhouse frame and interior support channels rest. If you are using pour strips, make sure to use them on the inside of the foundation to avoid the greenhouse base hanging over the foundation.
Spot Footings
A spot pad or footing is used to support a single point of contact, such as under a pier or post. Spot Footings are usually a 2x2 square pad, 10-12 inches thick, and made with reinforces concrete.
Continuous Spread Footing
A continuous spread footing is mainly used to provide a stable base around the perimeter of a building. Spread footings are often augmented with interior spot footings. The spread footing supports the weight of the exterior of the foundation walls. The thickness of the footing provides the necessary strength for the support. The width of the footing base provides a large area with which to transfer the weight from the walls to the ground.
Grade Beam Footing
A grade beam footing is a continuous reinforced concrete wall used to support loads with minimal bending. Grade beams are capable of spanning across non-load bearing areas and are commonly supported by soil or pilings. Grade beam footings differ from continuous spread footing in how they distribute loads. The depth of a grade beam footing is designed to distribute loads to bearing points, while the width of a continuous spread footing is designed to transfer loads to the ground.
A Thickened Edge Slab is another type of shallow foundation common with greenhouse structures.
The slab will be about 4-6 inches in thickness, except at the perimeter where it will be thickened 12” to 18” or as specified by an engineer.
In terms of overall depth, the foundation should be planned as you would design a typical outbuilding. It is critical to ensure the concrete foundation is built according to your local climate given that our typical 8x12 glass greenhouse is close to 1200 pounds. The concrete must cure and be level and square for easy installation.
Important: All concrete foundations should include the use of rebar to strength the concrete as well as using steel mesh in the slab options.