DIY Greenhouse Knee Walls

Knee walls are a part of a DIY greenhouse foundation built above the footing to 28″ above finish grade. The greenhouse base frame sits directly on top of the knee wall.

Any style of greenhouse can be built utilizing a knee wall, but some types are more suitable and will benefit more from a knee wall.

Advantages of Greenhouse Knee Walls:

  • It increases the headroom in the barn style or A-frame greenhouses;
  • It adds more space for hanging plants in peaked roof greenhouses;
  • Higher greenhouse ceiling improves the air circulation;
  • It provides space for additional insulation at the ground level, substantially saving on heating costs;
  • It hides clutter, like pots and bags of soil, normally placed below benches;
  • Knee walls can be built of any type of construction material, allowing the owner to make it to fit his or her house architecture and material;
  • Improves esthetics of the greenhouse, if made of attractive material, such as stone or brick;
  • Protects the glass or other type of glazing from debris from lawn mowing or weed whacking.

Greenhouse Knee Wall Disadvantages:

  • The wall blocks some light coming to the greenhouse and plants cannot be grown below benches or at the ground level;
  • It adds to the cost of the foundation, regardless of the material.

Construction of a Greenhouse Knee Wall

The construction of a knee wall depends on the material you plan on using (lumber, brick, cinder blocks or stone.) If you make your

DIY Greenhouse Knee Wall

knee wall of stone, brick or concrete, it would make it easier to attach the greenhouse base frame to it if you install a sill plate made of a pressure treated pine or some weather-resistant wood like cedar or cypress.

The knee wall has to be completely square and level, especially if it will provide foundation to a glass-glazed greenhouse. If the foundation or knee wall are not level, the doors, windows or vents might fail to open, or will get frequently stuck. Glass panels might crack under pressure of a frame that is being twisted.

Before building a knee wall, check with your local code enforcer to see if you need the permit to build it, and if they allow non-professionals to do that type of work.

Knee Wall Door Issues

You have to specify to your greenhouse manufacturer that you wish to place the greenhouse on a knee wall, and ask them to adjust the door height so that the door opens at ground level. Some models of greenhouses kits are designed with the knee wall in mind, and most high quality greenhouse manufacturers will custom fit the greenhouse to adapt to the height and type of the knee wall of the customer’s specification.

A knee wall makes any greenhouse look like more permanent structure and make it fit in much nicer with the existing house and its architecture. This is particularly important if the greenhouse owner plans on using his greenhouse not just for growing plants, but for spending time in it during the winter or treating it as a conservatory.

A knee wall is very popular with attached greenhouses, where the material for the knee wall should be the same as the house walls.

Building a knee wall for your DIY greenhouse might add to the cost, but if your greenhouse is an important part of your life and you spend a lot of time in it, a knee wall will significantly add to its appeal and function.

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