Considerations for Building a Greenhouse on an Older Property

boy digging greenhouse foundation


Tree Roots and Gas Lines: Unexpected Obstacles

The first thing we faced this spring was tree roots. Yes, the trees mentioned in Part 2 and Part 3 of this series, were removed last year after the wind uprooted them. And this May, after the frost was gone, the stumps were ground out carefully, leaving a pile of wood mulch behind. But our trees were 60 years old. The central roots were ground into mulch with a stump grinder, but the distant roots reached right from the main trunk to the garage were pristine. At less than 30 cm deep and 5 metres broad, the old tree roots crossed right across the property in exactly the same place the greenhouse foundation needed to go.

IMG_5990The stumps finally being removed and revealing all the dead roots still underneath our yard.

Gas Lines: Always Check Before You Dig

But even before we started digging, we followed protocol for building and reached out to the Click Before You Dig and found out, in less than a week actually, that the 60-year-old gas line in our back yard also goes right under the planned greenhouse foundation area. The lovely lady marking the lines did not know how deep the gas line went. “It’s not on file, for this age of house” she said. But our experienced contractor tells us gas lines in our area are at least three feet deep but there is no way to know for sure so we should avoid using large industrial diggers and employ hand digging only.

We exhausted two teens over three days with this hand digging task before Helpful Husband, almost 80 years-old, takes over the job. He uses a shovel and a pickaxe and special saw to cut the now-dead roots growing right through our proposed greenhouse foundation. I want to help, but my arm and hand are still swollen from winter and even though I am finally washing dishes and cutting fruit, the agonizingly slow process of healing from a broken wrist stops me from joining the digging crew and limits me to watering and small tasks.

Laying out foundation for our greenhouse
1 Laying out the outline for our greenhouse foundation, after checking to see where our gas lines could be.
digging greenhouse foundation
2 Our helpful teens that started digging the area where our foundation will be built by hand.
Laying cinderblocks for foundation wall
3 We opted for a cinderblock 20" knee wall which needs to be accommodated for in our foundation build.
Helpful Husband finishing up the foundation dig
4 Helpful Husband, finished up the digging of our foundation.

Now don’t get me wrong. Both Greenfield, a previously undeveloped site, and Brownfield, a site set for redevelopment or that had previously been constructed on, yards require the services of “click before you dig” investigation because it saves lives and reduces lines wrecked by large backhoes trying to do a quick job. It is just that in new yards, the chance of encountering roots bigger in diameter than my contractor’s forearm are rare. But this is quite common, apparently, in an older yard or brownfield, so expect the unexpected when building on a brownfield.

Building the Foundation: Considerations for Greenhouse Construction

There is more than one way to build a greenhouse foundation and we have decided on a combination of gravel, treated lumber and cinder blocks. If you have already read part 1 of this series, you will know I chose the very exciting option of a 20” double drop-door for our new greenhouse. This means I will have a higher roofline. And that’s when we remember the lines crossing between the two expired trees are still in place.

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Due to some incredibly careful arborist work, the power lines survived the tree removal. But suddenly I realize these same lines will be in the way of my proposed very tall greenhouse (11 feet.) So, back to the utility company to get the lines moved that cross over our property on their way to the neighbour’s back yard. This situation is called “aerial trespass.” And when we emailed to complain about aerial trespass, we heard back that we were wrong. According to official records, the electrical company has already moved these lines, apparently before we bought the house. Luckily, they said they would pop by to ensure their records are correct. Their records were not correct. As we can plainly see, the lines are, in fact, trespassing over our backyard, again right where the greenhouse is going. And so, we hope they come quickly.


Greenhouse Installation and Interior Layout

Our greenhouse installer is arriving mid-June. In part 5 of “Buying a New Greenhouse” we will see the greenhouse installation, finish the floor of the greenhouse, and discuss the growing layout inside the greenhouse.

Planting inside the greenhouse is the moment I have been waiting for and I can hardly wait! I am planning a late crop of greens for fall because on my trip to the market today I was forced to buy - yes buy- greens for my dinner. After twenty years of greenhouse growing, and months in my new house without a garden I am excited to get fresh greenhouse-grown greens again. Stay tuned.

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