This do-it-yourself small greenhouse is something that we started to put together in the beginning of September 2014. We worked it on and off for the next two months finally completing it on November 6, 2014, just before our first real freeze here in Washington State.
The structure itself is all wood construction with the foundation base being 4″ x 8″ treated twenty-year ground contact lumber. The Framework is naturally rot resistant 2″ x 4″ and 4″ x 4″ Cedar and the roof structure 2″ x 6″ fir. As an added measure of protection the Cedar was given a generous coating of Kilz primer/sealer as construction went along. Since this is going to be a damp environment hopefully the high-grade primer will make it more trouble-free for maintenance.
The transparent panels in the overhead are (3) 4’ x 8’ sheets of polycarbonate that were purchased at Home Depot for $32 apiece. To try and save money I designed the openings in the roof to be 2’ x 4’ so I could just cut one panel in half and fill 2 openings. In hindsight it might’ve been better spend the extra $96 and carry each panel all the way to the end of the roof. This would’ve put water runoff from the roof further out from the greenhouse.
For the windows we went to our local glass company with the dimensions for what we needed. Arguably this was the most expensive part of the project coming in at about $400 for all the windows. All we did to mount the windows was use three-quarter inch quarter round fitted into the raw opening on each side of the glass. The quarter round and glass were then caulked using a high-end paintable and clear caulks.
The door was something I came up with in my own fertile mind and is a Dutch door, which separates at the bottom of the window for aesthetic purposes. The doors are constructed from 2 x 6 and 2 x 4, 1 ½ inch Cedar material that was routed out to accept the glass in the upper part of the door with 5/4″ x 3″ decking used for the insert on the lower door. Both the upper and lower parts of the door were biscuited, glued up with a waterproof glue and then caulked.
The lower portion of the greenhouse exterior is 7/16 OSB covered with a 6 inch Cedar lap siding which we purchased at our local lumber store at about $.72 a linear foot. After installation the siding was then caulked at the ends and top with OSI caulk, one of the best on the market.
Since I have a tendency to go overboard with things, the interior is insulated with R14 insulation where it could be and then sheathed with a light plywood panel. The panel was then painted with exterior high-quality paint. We will see if this approach will stand the test of time and moisture.
For the floor we used 1 yard of 5/8 and minus washed gravel which for the 8’ x 8’ structure worked out to be just about 3 inches deep. We suggest if you decide to use this approach to stay with the washed gravel since the regular crushed gravel would result in a dust problem inside the greenhouse until it all filtered through to the bottom. The washed gravel still forms in a strong base and is easy to walk on.
Tips to keep in mind.
- I decided early on that electricity was going to be a must in my new greenhouse so we ran a new 20 A line from my home’s main panel. I must stress here though that unless you know what you’re doing around electricity find someone who does or hire an electrician.
- Make sure that your receptacles are covered as if they are going to be outdoors and protected with a GFCI. Don’t scrimp on this remember water and electricity don’t mix.
- If you live in a colder climate you’re going to want to keep the inside your greenhouse from freezing up and destroying everything you’re trying to accomplish. I find that to use of an upright oil filled heater accomplishes this just fine. They are cheap, around $49, and they last for years. You will also need a 12 to 14 inch fan mounted in the overhead to circulate the air inside the greenhouse to distribute the.
- Place one or two 32 gallon black trash cans filled with water inside the greenhouse. Not only will they absorb the heat during the day they will give it back at night. They will also give you a convenient place to get water for watering your plants.
- Invest in a cheap ($14 at Home Depot) wireless max/min thermometer to keep track of the temperature inside your greenhouse during the cold weather.
- This is going be a damp space and as such will have a tendency to grow mold and mildew. Make sure that all surfaces are covered with a generous two coats of high quality exterior paint. This will make wiping down and cleaning a much easier job.
- Again moisture will build up and if it builds up too far condensation could become a problem. We decided to install a cheap bathroom exhaust fan in the overhead that is tied back to a timer. The fan comes on six times a day for about a half hour and pulls out the moist air and brings in new. So far seems to be working well.
- We decided to use exterior screws when constructing the framework of the greenhouse. We did this because I make mistakes and when I make mistakes it’s much easier to back out a screw and fix it the mistake than to bang out a nail.
- Always check to make sure your construction is level and re-level if necessary immediately. This will save you from looking at your pride and joy after’s you’ve completed it and saying “That looks like it is running downhill.
- One thing I can’t stress enough here is the use of a good high-quality paintable caulk such as OSI for the structural elements. As far as the glass windows and polycarbonate are concerned a high quality clear caulk like Lenoxx is a must especially if you’re expecting any moisture on the caulk shortly after installing it.
- If you look at something and think it could be a leak problem caulk it, you’ll be glad you did later.
There you have it a not so brief brief rundown of our little journey to create a second greenhouse in our backyard for wintering over plants and getting our seedlings started early. It may look like a lot of work and yes the entire structure cost us $3000 almost to the penny, but what we got is something that is sturdy, attractive and will hopefully outlast any kit we could have purchased.
If you have any questions please leave them in the comment box below and I will try to answer them in short order.