Design and Selection

Published on January 22nd, 2013 | by Shelley Awad


Preparing for Your Greenhouse Site

How to Select & Prepare Your Greenhouse Site

Do your homework!  Careful planning will avoid any disappointment with the greenhouse location that you select.  Be sure your greenhouse will be easily accessible to your utilities including electricity, water, heating, ventilation and cooling.   Also, plan for the type of heating you will require:  Will it be gas, propane or electric?   Will you be installing lights?  Bringing water underground up through the greenhouse flooring is very convenient.  Be sure to place any water lines below your frost line.  What is the position of the sun?  A southern exposure is preferred, and greenhouse experts recommend that the top ridge of the greenhouse run from east to west for best results. During the winter months, this angle will provide the maximum sunlight exposure for your greenhouse.  And, this will also help reduce heating costs.  Do you have trees or any other objects that could block sunlight.  If your trees are deciduous, don’t worry.  They will drop their leaves in the fall, allowing sunshine to come through…and they also provide needed shade in the summer, keeping your greenhouse cooler.
A free standing greenhouse can be placed anywhere in your yard, whereas a lean-to style unit needs to be attached to an existing wall, whether it be your house, your garage or any other structure.   It is also possible to attach a free standing unit to an existing wall, if you prefer that shape to the 3 sided lean-to.  The back gable end can be removed, and it can be attached to your existing wall.  If this is the option you want, be sure the company that you are purchasing from allows for this option.  Usually the end being gable attached requires modifications to attach properly to the wall.
You will need to take note of the maximum height that you have if you are attaching a lean-to or free standing greenhouse to an existing wall.  Will it fit under your soffit?  If not, consider attaching the greenhouse structure direct to the end of the soffit.  This gives you a slightly larger greenhouse (larger by the width of the soffit).  You can then place “infills” under your soffit to enclose the entire area in.  Check with your greenhouse supplier to see if they can provide you with “infills” that will match your greenhouse structure.  If not, you will need to build your own using the building material of your choice.
Plants that are resting or that are dormant, still require a minimum of six hours of light daily. Remember that grow lights can be installed to supplement natural light in order to meet the requirements for your greenhouse.


Many greenhouse bases are optional.  The base is the structure required to support all of the greenhouse framework.  You can purchase a greenhouse base if available, or you can build your own using rot resistant or pressure treated wood.  You can also attach the greenhouse to a raised foundation wall if you need additional height, a wise idea if you are growing taller plants or small trees.  If you do want to build a raised foundation wall, you can use any material you like.  Check with your greenhouse supplier to see if they offer a “door drop” service.  This means they will drop the door back down to ground level for you.  Many companies offer this as a free service, while other greenhouse companies do not offer this option at all.  If they do not offer this option, it is not practical for you to purchase from them, as you would need to build steps leading up and down from your greenhouse door.  You can even attach the greenhouse structure to a concrete pad.
Special Note if you are attaching to pressure treated wood as your base:  Pressure treated wood now required a 10mm polyethylene barrier between the wood and the aluminum sill of the greenhouse.  This is necessary to prevent corrosion of the aluminum.  This requirement has resulted from a chemical change in the way pressure treated wood is processed.
  • A hobby greenhouse under (100 sq. ft.) can usually be fastened to a 4″ x 4″ or 4″ x 6″ treated wood timber foundation.
  • For a larger greenhouse a 6″ x 6″ beam is recommended. Wooden timbers can be stacked to increase the height of the greenhouse.
  • For a more permanent site, concrete slabs or concrete footings may be installed.  Bricks or masonry blocks may also be used, but ensure the top bricks are closed off, so it a flat surface to fasten the greenhouse to.
  • All foundations must be level and square for easy installation of the greenhouse structure.
  • Check your local building codes regarding site requirements and to determine whether a building permit is required.

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About the Author

Greenhouse Consultant, Shelley Awad, provides everything you need to know about greenhouses. Whether you are buying a greenhouse or you already own one, you’ll learn tips and tricks on greenhouses and how to grow year-round. Questions always welcome.

4 Responses to Preparing for Your Greenhouse Site

  1. Lauren says:

    Hi, there. I am looking at installing a 6 x 6 aluminum and fiberglass greenhouse over an existing concrete slab in my backyard. I am planning to add drainage to the slab with a hammer drill and cover it with 2″-3″ of soil, then grass and raised garden beds, and the greenhouse. It is cost prohibitive to remove the slab, as it measures approximately 30′ x 60′ in it’s entirety. I am trying to figure out the best way to secure the greenhouse, as there is quite a bit of wind at times in my area, and I’m nearly certain the weight of the greenhouse would not be substantial enough to secure it. I am considering building a frame from either pressure treated lumber or pallets, attaching that to the slab, bringing in dirt, and attaching the greenhouse to the frame. I’m just not certain if this is the best method, or how to attach the frame to the concrete. Do you have any suggestions? Am I on the right track here, or should I do something else to get this thing installed safely? Thank you for your reply!

    • Shelley Awad says:

      I recommend that you keep the existing concrete slab. This will keep the greenhouse more secure and also helps to keep it warmer in the winter, because the concrete heats up from the sun. It is wise to put in a drainage hole in the middle of the greenhouse. I am not sure why you are covering the slab with soil and grass? I wouldn’t do that. Just build your raised garden beds on each side of the greenhouse, and at the back if there is room, and leave a narrow walkway down the center that gives you access to all raised beds. You could always remove some of your large concrete slab and just keep what you need for the greenhouse. You definitely have to secure the greenhouse, otherwise it will blow away. You can do this two different ways — you could drill holes through the bottom of the frame and secure it directly to the concrete, or, as you suggest, you could use pressure treated lumber to make a frame, attach the wood to the concrete, then secure the greenhouse to the wood frame. Special note: if you are using pressure treated wood, you must use a 3mm plastic barrier on top of the wood so that the aluminum frame is not in direct contact with the wood. There is a chemical in pressure treated lumber that will erode aluminum. Also, keep in mind that the larger your wood frame is, you will have to step over that frame to get into the greenhouse door. Sounds like you are on the right track. Let me know how your project goes! If I can be of further assistance, don’t hesitate to ask!

      • Lauren says:

        Thank you. This is really helpful. I’m thinking of going the wood frame route, but didn’t know about adding plastic between wood and greenhouse — thank you! How much should I be concerned about drainage? I’m not sure I see any good ways for this to drain, as adding a drainage hole in the concrete is nearly impossible.

        I would keep the concrete uncovered, but this slab covers about 75% of our yard, and as we have children and pets, I would like a safe place for them to play. Granted, grass over concrete is still not soft, but there are fewer skinned knees. 🙂

        Thank you again for your help.

  2. click here says:

    I hope to read more from you! totally agree with this.

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