DIY Greenhouse Project: Building the foundation and frame

DIY greenhouse project

A greenhouse is one of the best investments a gardener can make. They keep the fussiest of houseplants happy and allow vegetables to grow year-round. You can make your own greenhouses with basic DIY tools and cheap scrap materials.

greenhouseTiago Lopes

This guide takes you through the steps of building a greenhouse foundation and frame. Getting this basic structure in place is crucial. Once you have it, you can work on flooring, inserting glass, doors and windows, and adding any electrical fittings.

What is a greenhouse?

inside greehouse Rafael Rex Felisilda

A greenhouse is a structure designed to house plants under optimal growing conditions. They shelter plants while letting in sun-light, insulating heat, and trapping humidity. At one stroke, they offer all the key ingredients for healthy plants.

Greenhouse walls and rooves are made primarily of transparent material, usually glass but sometimes plastic. The frame of the building can be metal, plastic, or wood. They can be freestanding or attached to the side of the house. 

For a more controlled environment, greenhouses can be fitted with fans, shutters, heaters, and ventilators. 

Is it hard to build a greenhouse? 

If you have some DIY experience, you will find the initial step of building a foundation and frame relatively easy. If not, you may need help from a more experienced person. Leveling the site is the only step that will probably require professional help.

Greenhouses can be simple rectangular structures. This guide takes you through how to build a basic framework, without any fittings. 

It is often best to get professional help with leveling the ground for the foundations. This is a part of the job that requires the most labor and expensive equipment. 

Where should I locate my greenhouse? 

Choose the orientation

First, choose the best orientation for your greenhouse. 

For all-day sunlight, a freestanding rectangular greenhouse should be oriented with its two longer sides facing East and West. This makes a heat-trap, catching morning light from the East and afternoon light from the West. 

Consider shade and light

You also need to consider shade. Choose a site that gets the least shade from surrounding trees or buildings, even during the winter when the sun is low in the sky. 

Are greenhouses expensive? 

You can buy cheap, pre-fabricated greenhouses to assemble at home. However, building a DIY greenhouse can save on labor and shipping costs. 

What’s the best time to start a greenhouse?

The best time to start a greenhouse is just before the growing season in spring. Aim to have it ready for mid-February. The unheated greenhouse will be about 4 degrees warmer than the outside, and you’ll be able to sow seeds much earlier in the year with one. 

How do I build my greenhouse  foundation? 


  • Treated lumber
  • Wooden stakes
  • Mason’s string 
  • Compass
  • Carpenter’s square
  • Spirit level
  • Hamer 
  • Saw
  • Plumb line
  • Level
  • Measuring tape

Measuring and marking the foundations

Mark the outline of your foundations using wooden stakes and string before you start leveling and digging. 

There are two stages to marking the foundation. First, you must mark out a perfect rectangle on the site using string and stake. This rectangle is meant to guide you in constructing batter-board corners, which will mark out the final corners of your building.  

To make the initial string-and-stake rectangle sketch, use a compass to find the correct orientation for your greenhouse. Then, use a tape measure to measure out one of the long sides. Mark both ends of this long side by driving stakes into the ground. Join up the stakes with string, or a mason line.

Using a carpenter’s square to measure out precise right angles, mark out the other three sides in the same way. You should now have a complete rectangle made up of four stakes joined up with string. To check ti is a perfect rectangle, measure the length of the two diagonals – they should be exactly the same length.

Now, you can start fleshing out the corners of your string and stake rectangle using batter boards. These batter board corners will indicate exactly where to lay the first concrete foundations blocks. They will also mark the final corners of your greenhouse building.

To build up your corners, drive three stakes in an L shape around the outside of each corner stakes. Place several feet between the original (now inner) four corner stakes and these new outer L-shaped stakes. Connect each set of L-shaped stakes by nailing two batter boards to their outside. 

Finally, remove your initial string-and-stake rectangle. It has served its purpose of providing precise lines and measurements for the corners. To do so, drape mason line between the outer batter-boards so you end up with a string rectangle that sits exactly above the original string rectangle. Weigh these new lines down with stones or other weights, and make a notch in the batter board so that the mason line sits in place.

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