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Foundations for Attached Greenhouses

Your new attached greenhouse will be a permanent addition to your home, so the foundation requirements are a bit more involved than they are for our free standing greenhouses. We recommend consulting a local builder before you begin constructing the foundation. A local builder can consider your needs and inspect the site where the greenhouse will be attached.

The main requirements of the foundation are outlined below:
* The base must be level and on one plane.

* The wall and ridge supports must also be on one plane. This must be constructed so there is exactly a 90 degree angle between the base and the wall members.

If your siding is uneven, such as clapboards or cedar shingles, this may require building a 2" x 4" frame on top of the existing siding. This will ensure a level plane for mounting the greenhouse frame. (For Northern Light Greenhouse models only.)

* The base foundation must be constructed so frost heaves will not affect it. Ideally, the base should be insulated to reduce the heat requirement in winter.

The requirements above are no different than those necessary for any deck or construction project added on or around your home. Time spent creating a quality base and foundation for your attached greenhouse will not only make the actual assembly of the unit easier, but it will ensure a long and trouble-free life for your greenhouse as well.

The construction process is similar to the one used for building a deck. So, if you are in an area that is not affected by frost heaves, concrete piers can be used in place of poured concrete.

Again, we recommend discussing this project with someone nearby who is familiar with the local building requirements and can help you design a suitable foundation.

Warning: If you live in an area prone to frost heaves and do not set-up a proper foundation, damage to the greenhouse can result, possibly tearing it off the wall.

Make your foundation to these dimensions for Northern Light Greenhouses:
101 3/4" (8 x 8)
201 1/2" (8 x 16)

Width:(from house wall)
96 1/2" (8 x 8; 8 x 16)

93 1/2" (8 x 8; 8 x 16)

The flashings required for your attached greenhouse are like most used for structures being attached to existing buildings. As with the foundation, we recommend consulting a local builder to find out the best method of sealing and flashing your unit to protect it against drafts and rain water.

Note: Flashing needs to be installed prior to installation of panels!

Most hardware stores carry the light gauge rolled aluminum flashing that is ideal for this application. It is also inexpensive and easy to use. You will need to bend the flashing to fit over the ridge and onto the siding on your house. Do this by bending the material over the edge of a 2" x 4", much the way you would fold a piece of paper across the edge of a desk.

Lead flashing is quite acceptable and in many cases is easier to work with, although it is more expensive than aluminum. If you wish, you may use a roof sealing mastic, applying it as you would on asphalt shingle roofs, around chimneys and plumbing vents. Again, obtaining professional advice is recommended.

A draft/weather seal can be used behind the frame members prior to fixing in place. This seal can be purchased at any local hardware store. The easiest seal to apply is an adhesive backed foam tape which can be stuck to the frame members prior to installation. The type of flashing and/or sealing is dependent on how permanent you wish your installation to be and what exact base/wall detail exists.

When properly installed, your attached greenhouse will be virtually free from drips, leaks and drafts. However, this unit is designed as a greenhouse and not a living space, so if you intend to use it as a sun room, please use outdoor furniture.

If you have questions or need assistance, please call our technical service staff at 800-688-5510 or e-mail us at:

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