How to Build a Greenhouse Foundation

Building a greenhouse, for those who are attempting it for the first time, involves more than just building the structure, even if it's a pre-built greenhouse. There are several factors you'll need to evaluate, one of which will be your new building's foundation. You'll have a number of foundation options, each with its own challenges and advantages:

Choice A: Wood Foundation

You could lay a floor of railroad ties with a narrow space (no wider than 1") between them. Another type would be a platform constructed of spaced 2 X 4's fastened to a base of 4 X 4's. With either of these floor types the spacing of the boards (or ties) would give you good drainage. Disadvantages will be in coping with weeds and mold likely to grow between the boards.

Choice B: Concrete Foundation

With a concrete foundation, much like some homes built on a slab, you will not have the challenge of weeds or mold, but if you have little or no experience with pouring, leveling, and smoothing concrete you'll likely find this option to be more challenging.

But whether you choose a wood or concrete foundations, each will require different tools, equipment, and material.

If you go the concrete route, you'll need some of the basic tools, equipment, and materials. But unless you're experienced with concrete work you're likely to find yourself using materials you're less familiar with, such as rebar, conduit, concrete surface hardener, expansion joint spacers, etc.

Here are the basic tools and materials you'll need:

  • Squaremouth shovel
  • Hammer
  • 16 penny nails
  • Level
  • Screed
  • 2 X 4's (for forms)
  • 1" X 4" X 12" wood pieces
  • 1" X 2" X 12" wood stakes  
  • Trowels
  • Water hose and water
  • Concrete mix

Build Your Concrete Foundation in 4 Steps

  1. Planning
  2. Laying out your conduit and rebar systems
  3. Building your concrete forms
  4. ouring and finishing the concrete

If you're planning for a larger greenhouse you might need the help of a contractor or electrician to help you lay out a system of conduit for electrical, data, and telephone lines you'll need embedded in your floor. With a smaller building you might be able to mix your own concrete, whereas with a larger one you'll likely need it delivered premixed to your site

Complete construction of your concrete foundation might take two or three weekends, depending on how big your floor is, how many helpers you have, and what kind of concrete tools you might have handy.

You should be able to build your concrete forms, even if you have no experience. Your biggest challenge will be in finishing and curing the concrete, but if your floor is to be no bigger than a two-car garage you should be able to mix, pour, and level your concrete with guidance from someone who has at least some experience with concrete construction. If your floor is to be larger, you'll be wise to get help from experienced concrete workers.