Using a Wooden Foundation for Your Greenhouse
A wood foundation is an inexpensive way to quickly setup your greenhouse and provides the support and stability it will need throughout the year. Wood is a very cost effective material to use for the foundation and is easy to work with for most homeowners who already have the tools needed to install it. Wood also enables you to avoid the extensive digging and framing that other foundation options like concrete require, and can save you time and money.
Take Time to Prepare the Site
When building your DIY greenhouse foundation out of wood, there are a few things you’ll need to do to prepare the location before you start. Since a wood foundation is normally built to sit directly on the ground, you’ll need to remove any grass, plants and mulch from the area you plan to locate the greenhouse. Once these materials are cleared, you next need to level the ground and remove any roots and rocks from the surface. In most cases you can complete this preparation with a shovel, rake and carpenters level. You should also consider adding a thin layer of gravel to provide a stable base for the foundation. When you have the ground level, be sure to compact it as much as possible to help avoid settling later on. This compacting can be done by hand or with the help of a mechanical vibrating compactor that you can rent by the hour from your local hardware store. You may also want to lay out a weed barrier on the ground before continuing with your foundation. You can always do this later, but by laying it down now you’ll be sure to protect the entire floor of the finished greenhouse.
Be Sure To Square Your Frame
Once the ground is level and compacted you can start to lay out the foundation for your DIY greenhouse. Most greenhouse plans will include the outside dimensions of the finished greenhouse and these will help you build your wood foundation. Remember that your finished foundation should be about an inch wider than the outside perimeter of the greenhouse. This allows for adequate protection from the elements and provides a good mounting surface for the structure. For smaller greenhouses you can use treated 2X4 lumber to build the foundation. Larger buildings will need treated 4X4 or 4X6 lumber instead to provide a more stable base. Start by laying out the boards on the ground to form the perimeter of the foundation and attach them together to form the frame. Before securing the boards too tightly, measure the diagonals to make sure the foundation is square. Once you have these diagonals equal you can attached the boards together permanently and add as many layers as you need to accommodate the desired height of the foundation.
Provide Adequate Anchoring
Once you have this foundation assembled you’ll need to anchor it to the ground to prevent damage to the DIY greenhouse from heavy winds. To do this you can drive 24” rebar into the ground about every 2 feet and anchor it to the foundation. This extra step will help prevent the foundation from moving and twisting the sensitive walls of your greenhouse in severe weather.
Pressure treated lumber can cause steel and aluminum to corrode over time so you’ll need to install a sill plate on your wooden foundation to anchor the greenhouse. This sill plate can be a standard wooden 2X4 or any one of the many composite lumber products available. It needs to be securely attached to the top of the foundation and then secured to the walls of the greenhouse structure. This connection should be very tight and will help to prevent water and unwanted pests from entering your greenhouse. To help create an even tighter connection you can apply a bead of calking along the edge where the DIY greenhouse frame meets the sill plate.