Our Greenhouse

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Right from when we were planning the terracing of our garden, it was clear to us that we wanted to build a greenhouse. Claudi got her inspiration from Pinterest: greenhouses made from old windows. When I saw the pictures, I thought: we’ll never manage anything that beautiful.

The Terracing

Before I get to the greenhouse build, let me say a few words about our big garden design project. Our garden is just over 1,600 square metres, but most of it is on a slope. This meant the largest areas were only good for mowing and a few old fruit trees.

“Shall we add one more level?” quickly became “Let’s terrace the whole garden – otherwise we’ll never be able to get the digger back up when we want another level some day.”

What came out of it, from the top of the garden down to the bottom: a path along the edge of the woodland with honey and blueberries. Below that, a large area with lawn and a fire pit. Further down, the snacking level with raspberries, red currants, strawberries and columnar fruit trees. Then the level set aside for the greenhouse and raised beds. Right at the bottom was our existing bed, which gained considerably more area.

The terracing took two years, from summer 2016 to summer 2018. We built dry-stone walls, with no concrete except for a water feature. Just as the walls in the local vineyards were built hundreds of years ago. The difference is that we laid drainage pipes and used a fleece to stop silt from washing into the backing of the walls. A fine spot for slow worms, lizards, mice and spiders.

The Windows

As early as spring 2017, Claudi found the windows through classified ads. All for free. A decent load of similarly sized windows from an old timber-framed house, plus a few smaller ones. We brought them home together with a door in a trailer that was, volume-wise, slightly overloaded.

Before that, she had already bought a beautiful window, well over 100 years old, that had once been above the entrance door of a villa. This window is the reason the roof of our greenhouse is so steep.

The Planning

The rough width and length were already dictated by the terrace. Claudi did the planning on paper. An important task here was to arrange the windows so they would fit, since each had a slightly different width. So we numbered the windows and assigned each a position. It also mattered which ones could only open (tricky with tomatoes in front of them) and which ones could also tilt.

I did the more detailed planning in Tinkercad, a free 3D tool normally used for creating 3D prints. Here I could model everything precisely, which proved very useful later. We could take measurements directly from the 3D model and build from them. Whatever we built, we then measured and adjusted the plan wherever there were deviations.

The Basic Structure

Our greenhouse stands on a strip concrete foundation. On top of this sits a wall of paving bricks. The stability of the timber structure comes not from the windows but from a frame of 12x12 cm beams, into which the windows are screwed. The fairly high roof is supported by a gable with rafters. We chose sturdy twin-wall polycarbonate sheets as the roofing material.

The Foundation

Before we could dig the foundation, we first had to create a level surface. We had to move leftover soil from filling the raised beds. Then we had to scrape away soil in places where we had driven over it countless times with the digger, leaving it very compacted. The best approach was to scrape it away with a hoe (* Affiliate) (we have a slightly different one) after lightly moistening.

First, Claudi measured out the outer dimensions of the future walls and drove in wooden pegs – not right at the corners, as those would be dug out for the foundation, but extending each side about 20 centimetres outwards. This lets you run a string line, as you can see in one of the photos. It’s important that the string wraps around the correct side of each peg, otherwise the peg’s thickness either gets added or subtracted. Mark the correct side of the peg to be sure.

After measuring, we cut the outer edge of the foundation with a spade – a few centimetres outside the line, as the foundation should be slightly wider than the wall. We dug one spade’s width down. And again I had to move soil…

Since our terraces are deliberately slightly sloped, the foundation would either have protruded enormously above the ground on the lower side, or the wall would have disappeared into the ground on the higher side. Since the wall shouldn’t stand in damp conditions, and since a visible foundation on the bed-facing side probably wouldn’t have looked great, our foundation has two different heights. On the lower side it is exactly one stone height plus mortar thickness lower. At the front this is hidden by the door opening, and at the back it doesn’t matter.

On the lower side we used a slug fence as formwork, as we didn’t want to buy shuttering boards. The other side we poured directly against the soil.

To reinforce the foundation we put construction steel rods in the middle – the reason being that we had terraced quite recently and couldn’t rule out that the soil at the very front edge might settle a little.

The Wall

We didn’t want the timber to start at ground level. It would likely have rotted quickly there, and inside it would also always have been quite muddy from watering. So we built a wall about 50 centimetres high.

To separate wall and foundation, we laid a damp-proof course of roofing felt between two layers of mortar. This prevents water from wicking up from the foundation into the wall and crumbling the mortar after a few years. On the higher side the ground level is slightly above the wall. There we cut the soil a few centimetres below the top of the foundation and filled it with gravel so water can drain away.

I then laid up the wall with my amateur skills. A long spirit level was very helpful here, as I could check long stretches including around corners.

The Timber Frame

The entire upper part of the greenhouse is carried by 12x12 cm beams. We only used these vertically at the corners and on either side of the future door, as well as for the gable. Horizontally, on the wall and above the windows, we used 12x6 cm beams – partly because these are simply resting on supports and 12x12 cm would have been massively over-engineered, and partly because the window frame sits directly against them, adding another ~6 cm. Visually that would have been too heavy. The uprights to the gable and the rafters are also this size.

I wanted as few visible screws and brackets as possible. I managed that.

At the corners I sawed half (3 cm) out of each horizontal beam so that both beams together are back to the full thickness when overlapping. In the centre of this joint I drilled a hole and drove in a 22 mm dowel. The dowel is a few centimetres longer than the joint, so it extends into the vertical corner beam. Nothing should shift.

To stop the whole assembly from sliding on the wall, the horizontal beams are bolted to the wall with heavy screws.

At the corners I used a router to create recesses for large brackets. This let me additionally bolt the horizontal and vertical beams together. The brackets sit where the window frames would later be mounted, so they are hidden.

The Windows

We knew we’d have to refurbish the windows. Sand down the old paint and repaint – if only it had been that simple.

The old timber-framed house the windows came from had shifted over the years. To make the windows fit there, most had been sawn into parallelograms. So they were usually the same width top and bottom, but completely skewed. Refurbishing the windows turned out to be quite an undertaking.

After sanding, I trimmed the window frames with a circular saw (* Affiliate) so that with an added strip on each side they would again have the right dimension. This let us bring almost all the windows – which we had assumed would have various widths – back to largely the same width. In some cases the frame was also damaged at the bottom or top; I used the same technique there. I glued and screwed the extra strips on. All screws are countersunk so I could fill over them.

Claudi painted all the beams and windows one by one. First oiled, then primed, and finally two coats of linseed-oil-based paint.

We screwed the windows into the existing timber frame. The window frames are also screwed to each other.

Later, a beam was added above the windows to support the roof structure. Since the windows weren’t all exactly the same height, I got a hand plane and adjusted them to fit.

The Roof Structure

This got a bit fiddly. We had to connect several different levels. At the front, the door is a different height from the windows beside it. Above the door we installed a window lying flat, opened by an automatic opener (* Affiliate) whenever the greenhouse gets too warm. At the back, the central window is taller. Above it the very old window finds its place. Since it is quite high, we had to make the roof very steep. With hindsight, one advantage of this is that the greenhouse doesn’t overheat in summer.

With just the side beams in place but no gable or roof, the greenhouse went into its winter break. Passers-by always looked rather puzzled about what it was going to be.

Claudia’s Illness

In December 2020 we received the shattering diagnosis. Claudi has cancer.

From that point everything became uncertain. Our good friend Bettina had an idea and planted it in my mind: she pictured Claudi standing in the greenhouse in spring, starting off the seedlings.

The Roof

So work resumed on the building site as early as March 2021. We mounted the gable.

We puzzled for a long time about how to work on the roof at all. At first we wanted to build scaffolding around the outside. Then came the realisation that scaffolding on the inside would be much simpler and more practical. But it turned out to be even simpler, more practical and cheaper. I bought six timber planks, slightly longer than the greenhouse is wide. Three screwed together gave a platform that we could slide around inside the greenhouse as needed.

I miscalculated on the rafters. They are a centimetre too short, leaving a gap. I covered this on the front and back of the greenhouse with a plank in between.

The many small openings at the front and back gable ends I filled with twin-wall polycarbonate sheets. These can be cut wonderfully with a circular saw using a fine-toothed blade. I fixed them with triangular wooden strips on both sides. Since buying that many pre-made triangular strips was too expensive, I simply bought wide boards about 2 cm thick and cut them into triangular profiles myself, alternating between 45° and 90° cuts.

The polycarbonate sheets rest on the rafters on rubber profiles. Retaining profiles are screwed from the outside. Normally this is no problem for a roof pitch like a typical canopy or carport – you can slide up on the profiles using shuttering boards. But at our angle that was impossible. Here the nimble body control of our friend Pablo saved the day; he managed to get even the uppermost screws in.

Interior Layout of the Greenhouse

A concreted-in raised bed separates the growing area from a paved area. Growing happens in a large strip on the left side and along the back wall. The smaller paved area gives enough room to stand and has space for a table for starting seedlings and pricking out.

For the floor covering we used large slabs of white granite that Claudi once managed to get hold of at a building site. In spring she had regained enough strength to lay them herself.

From some “already-there” wood and a few of the planks from the roof build, I made a table. I gave it a good sand and treated the working surface with worktop oil, the kind we normally use in the kitchen.

Along the long left side we fixed two heavy battens with screws every 10 centimetres. On the screws we can hang short chains, and strings are attached to these. We train the tomatoes up the strings. As soon as a string gets too tight from the tomato plant winding around it, we let out one chain link.

In spring and winter we hang wire baskets from chains. Plants can overwinter in them, or in winter you can grow things like spinach and lamb’s lettuce. This extends the greenhouse over several levels when there are no tomatoes in it. To stop the temperature dropping too low in winter, we got a gas heater (* Affiliate).

On the right side, between the windows, we can hang shelves on wall rails. This gives us a shelf for seedlings we start ourselves along the entire length of the greenhouse, above the table.

Water

The greenhouse itself has no water supply. If it did, we would have needed planning permission. Since we have a Gardena pipeline system (* Affiliate) running through the whole garden, we have water almost everywhere. Behind the greenhouse runs one of these pipelines, to which we connected an iron pipe. This runs along the outside of the greenhouse and we have a handy tap right next to the door.

Our pipeline system is fed from an old cistern, which we supply via a pressure pump. When the cistern is empty, we can switch to mains water, which fortunately hasn’t been necessary often.

We obviously didn’t want to waste the rainwater from the roof. So we fitted small gutters and a tank of just under 300 litres on each side. These are connected underground and have a hose connection in the wall facing the bed. This lets us water the lower bed using only water pressure, no pumping needed.

The Door

This also needed a good amount of refurbishment. Part of it had a galvanised metal sheet, which isn’t easy to paint. We had a piece of glass cut to size and fitted it with traditional linseed-oil putty.

The pintle hinges (the metal pins a door hangs on) for the door we screwed into the timber beam and at the bottom into the masonry. We made a matching strike plate from a metal plate, which I routed into the left door beam.

The Old Window

I did mount the door before the old window, but the window has its own significance – especially for Claudi. So I’ll end this building report with it.

The lower part of the window was completely rotten and beyond saving. Fortunately – otherwise the roof would have been even steeper. I removed it and kept the coloured glass panes. We had these cut to size and fitted them left and right as infill windows beside the tall window.

To protect the old window, we had a large pane of safety glass cut to size. It is mounted from the outside and protects the old window from the weather. It also closes off the areas where the old window has its curved sections.

Claudia

In spring 2021, Claudi was still able to start the later plants in the greenhouse. She was able to fully enjoy the first growing year in the new greenhouse. Tomatoes, peppers, chilli and a watermelon. And lots of parsley…

From autumn and winter 2021 our situation deteriorated dramatically. The seed-starting in the greenhouse in spring 2022 was done by me (Thorsten), as she was in hospital almost continuously. Claudi was often there via headphones or video call.

I wrote this text in hospital while accompanying Claudi as she was dying. On her last day, I read her the rough draft.

Impressions