Building a Lean-To Greenhouse on a Stone Cabin

It seems, after two years of experimentation with the seed starting to harvest cycle, that every serious gardener needs a greenhouse.


With few windowsills, or light for that matter, we found it difficult to successfully germinate seeds inside the house and keep them alive afterwards.

As Spring is one of the main sowing seasons, it happens that there is a lot of light and warmth during the day, then the temperature drops in the evening, which many more Mediterranean vegetables like aubergines and tomatoes can’t handle.

Some people combat this by bringing their seedling trays indoors in the evenings and outside again in the morning. For a few trays, this is a reasonable method. For 10+ trays, it’s unsustainable. And there’s just not enough room indoors anyway.

When some prized Turkish aubergine seeds shot out of their little holders and into the air, only to bend over and start rotting in their potting mix a few days later, we knew something had to change.

Our house is an old barn conversion, made from stone walls with a little wood store on one side. This wood store was south-facing, with a terracotta tile roof and some rotting eucalyptus trunks holding the whole thing up. Worryingly, it looked liable to fall down at any minute. Those tiles crashing down on an innocent wood-collector’s head does not bear thinking about.

sturdy and safe

As they say in permaculture, the problem is the solution.

We had two problems:

  1. no place to put seeds
  2. wood store fatal danger

The solution: rebuild wood store as lean-to greenhouse for seed starting.


This plan was actually over a year in the making, as the idea was floating around back when my Mum came to visit in May 2018.

There were a lot of processes, including: finding some second hand windows to upcycle for the exterior; designing around those sizes; agreeing on the aesthetic, and actually building the thing.

Our first window donation came from the same guy who sold me the van, he had a kind of junkyard guarded by three dogs on permanent leads, and Nik spotted these windows leaning against one of the metal shacks. Antonio happily loaded them into the back of our new purchase along with twenty bottles of questionable-looking Cava. Though not so questionable that we didn’t drink it.

The rest came from a listing with no image on, a useful site for finding second hand stuff. They were all completely free. Success!

Next, the design. I really struggled to find any plans on the internet of a lean-to greenhouse on the side of a stone wall cabin. All the plans I found involved a perfectly straight and level wooden or cement-type wall. For this reason I have decided to go into detail about how we built ours.

For the fellow cabin-dwellers with a wood store to revolutionise! 

First, we removed the old structure by taking off all the tiles using a ladder and sitting on the house roof. (Kind of dangerous, could be a better way). Then we took away the posts and slats and as much wood as possible, just leaving the two large beams embedded in the rock for potential structural support later.

We then measured the space and designed the structural frame to fit. Instead of digging vertical posts into the floor, we decided to build the outer side onto a flat, level piece of wood for ease and simplicity. The ground there is wonky so the floor beams are supported at one end by bricks to make it level.


We made our main exterior wall by screwing four large pine beams together as a rectangle. We then hoisted this into place and temporarily screwed it to the old wood store beams to keep it upright. We were very grateful for some much needed help from experienced friends during this crucial stage.


Next, we angled the roof beams to mark up where they’d go into the wall, making sure the slant was enough to allow rain run-off.

Raf’s pneumatic drill, or jackhammer, was incredibly useful for the next stage, saving hours of work with a hammer and chisel. We power-chiselled the old beams out of their holes, then hammered out new holes in higher places by removing large rocks from the wall. We did this in four equidistant points across the wall, in a more or less straight line.


The pine beams were then inserted into the new spaces, screwed into the rectangle frame and cemented into place. Voila, first day of work, and the hardest part was over.

After this it was really just a case of putting in the time to attach the roof, windows, doors and finishing touches.

The windows are screwed in and unopenable, which is fine because there’s a large gap for air flow between the top of the frame and the roof. We plan to attach mesh here to minimise snail entry.

The roof is made out of 10mm thick polycarbonate sheets, cut to size using a jigsaw and attached with screws into the roof beams and slats, waterproofed by plastic stoppers.

The roof was the largest expense at about €250 for the sheets and u-connectors. It was a lot more than we’d anticipated but considering the whole greenhouse was built and furnished for less than €500, we can’t complain.

On the topic, the 2nd largest expense was actually exterior weatherproof varnish. At €30 a tin, it’s a lot, full of evil chemicals, impossible to make at home, but on the whole worth it to turn our cheap pine into durable posts. Extra expense was added by my accidentally knocking a whole tin of it onto the floor. Cry.

We made the doors by using the two windows from Antonio. Thin planks were screwed side by side to a frame the same size as the window, we then attached the windows to their consecutive boards, painted all the wood green and added some handles from an old cupboard. We then mounted them to the large structural frame using metal hinges from the local agricultural shop.


To continue fulfilling the space’s purpose as a wood store, Nik had the ingenious idea of leaving part of the south facing side wall open as a wood store, with access outside and inside via a cupboard door. In the design phase I thought this too good to be true/ wasn’t confident enough in our building abilities. But now this is a working reality.

The rest of the gaps are filled with beautiful trunk offcuts, all different shapes and sizes, screwed onto the outside to help seal it. They’re a really effective and easy method of filling in spaces. It’s not too complicated and still provides a foresty-fairytale effect.

Inside, we made the wood store cupboards using the same technique as for the bottom of the doors, though we had to make the sides touching the ground slanted so they’d fit the wonky floor.

The book I just read talks about ‘Spontaneous Architectural Principles’: working around the materials you’ve got. I like these principles. Less exacting, less time consuming, more varied and perfectly imperfect. (As long as it doesn’t fall over, of course).

Nik then made a garden bed out of the old roof tiles, layering them upright to form a snug little cove in the corner of the room, which he then filled with earth and leaves.


I made a table-cupboard in the other far corner as a potting surface and tool store. Finally we can move the hammer, drill and various screwdrivers that clutter the fireplace into a tidier home.


The last things to do are now to seal the remaining gaps, build some shelves and give the windows another coat of paint. They’re still outstanding, but it looks finished and those things can wait for less rain-filled days.

We collected some wood from the fallen-down trees by the waterfall and have sawn, chopped and stacked it in the new store.

So that’s pretty much it! Has it inspired you to do the same on the side of your home? A sun-filled space to sit and read, whilst also keeping your plants happy.


If you do end up building something like this, and want some more detailed information such as measurements, list of materials, tools etc, or any other thing, please do not hesitate to get in touch at

We’d love to hear from you!

A little note:
Apparently, this greenhouse does not officially qualify for the title of ‘lean-to’, because a lean-to has to be supported specifically by the act of leaning on a wall. So this is technically just a ‘greenhouse attached to the side of a house’, which is actually more sturdy, but doesn’t sound as good.

4 thoughts on “Building a Lean-To Greenhouse on a Stone Cabin

    1. That’s an understandable worry – I heard from a friend that polycarbonate roofs aren’t that long lasting, so I expect that would be the first thing to go, but he said they usually last 4-5 years. Who knows! We’ll have to see. Hopefully it lasts longer.

      As for the structure, we built it very sturdily and the previous one (the woodstore) had been there for around 25 years if I understand correctly, and had been made with untreated wood. It was falling apart but still just about going by the time we took it apart.

      I forgot to add that some of the bottom beams are covered in EPDM to stop water damage from the ground.

      The beams are halved planks of pine from the local wood yard, and hopefully the varnish should help to make them last longer.

      Great that you already have the windows. Good luck with your build!


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