Tuesday, 28 August 2012

Building a greenhouse (without going broke)

Build a low cost Greenhouse 

Over the years I have built a few greenhouse "on the cheap" - aka - inexpensive.  I learned a few things the hard way and if you are looking to build one perhaps I can offer a few hints.

SIZE - Decide ahead of time how large of a greenhouse will fit your needs (of course) but also keep in mind that to keep costs down you have to plan to use basic material sizes.  What I mean is, plan on using say a 2x4 8' long instead of 8 1/2' long - because that extra 6" means you have to buy a 10' 2x4.  Big difference in the cost!

MATERIAL - You don't really HAVE to build a greenhouse out of glass.  Or acrylic panels.  If you go to a garden centre you may find one that has "greenhouse plastic" to cover the roof and walls.  Very expensive. And the  first time I covered mine with that expensive plastic it cost something like $125 for enough to cover it.  And to make matters worse, it never came close to lasting the 5 years it was supposed to, but cracked and deteriorated in certain areas that I think must have been because the supplier had it stored with the end of the roll in the sun.  My previous greenhouse was 27' long, which was a mistake as I never thought about the length of  plastic I would need to cover it.  25' would have been just fine and the plastic that I used was available in 100' rolls.  You DO NOT need to buy the expensive stuff - go to the lumber yard and buy a roll of  6 mil VAPOUR BARRIER.  It is protected  with ultra violet inhibitors to stop reduce sun damage.  (Don't ask me why vapour barrier in the walls has to have ultra violet protection!)
Locally, here in Duncan, I can get a 102" x 59' roll of 6mm Clear Poly Film for about $36 (plus tax).
Larger sizes like 120" are available too, but of course they cost more.

DESIGN - You may have a choice of free standing or "lean to".  My previous greenhouses were free standing but this time I was able to save a lot by doing it using the south facing wall of a storage shed as one wall.  You may be able to do a similar one using a solid fence as one wall, perhaps 6' high fence plus an addition to get it high enough to have a sloped roof.  The pictures below will give you a better idea of what I am trying to explain.

BASE - You need a base for your walls and raised beds.  In the past I have used concrete but it means a LOT of work and expense.  However, it is much more permanent.  This time I used pressure treated landscape ties.  They now make them with safer chemicals but you can also line them with plastic to keep the chemicals away from your soil and plant roots.

I  designed it so the beds would be 24" wide inside - easy to reach the whole bed that way.
Shown is the wall of the shed and the start of the raised beds.

This shows the final height of the raised beds.  The sheet of plywood leaning against the wall is 3/4" pressure treated to prevent it rotting.  I split the sheet of plywood lengthways and used it as a barrier to protect the wall of the shed from the dirt & moisture.   Plastic can be stapled to it to separate it from the dirt to prevent chemicals from touching the soil.

I decided the greenhouse was not large enough for all I wanted to plant and I also wanted to plant pole beans and raspberries so I added outside raised beds.  The left one is 24" inside by 8' long.  The right width for a row of raspberry canes.  I tried to keep the dimensions in multiples of 24" as the landscape ties are 8'.  The middle bed is 4' and is for strawberry plants.  The right hand bed  is off size being 5' inside as I wanted the right hand wall to match the wall of the greenhouse.  I am finding the 5' is OK but a LONG stretch when weeding and planting.

View of the greenhouse framework.  The shed is 16' long which fit very nicely for material lengths.  The width of it is 92" in order to have 2 beds of 24" plus the width of the landscape ties and also that fits in nicely with the rafter length of a bit under 8'.  The outer wall a bit over 4' high for two reasons - first to keep the roof slope the same as the shed and secondly the thickness of the top and bottom plate of the wall section.

The nearly finished project.  This gives you an idea of how it looked and I later added a door with a screened opening and at the other end a window with a screen.

I won't try to tell you exactly how much it cost (can't remember, my memory isn't what it used to be) hahaha
However,  it is fairly easy to do rough calculations once you figure out the size you need.  Also, prices vary a lot from one area to another.

In my next blog I will post some pictures of how it turned out and what it looked like as things grew over the summer.

Happy building!


  1. I follow your blog for a long time and must tell you that your posts always prove to be of a high value and quality for readers. Keep it up.

  2. I bought one of those screen shelters for the summer. It has a pop up mental frame with pegs. If I bought some of that vapor barrier and covered it with that would that work as a greenhouse?