Morning Light

Morning Light

6:00 am. The view from the house this morning. Extraordinary quality to the light. The rain clouds have only just lifted a chink and the sun is sneaking under, low, acute, glancing.

The greenhouse greets the dawn. The white lavender is shining in shards of reflected light. Beyond large heads of white dahlias wait for their turn in the sun. Over the hedge Alliums snake skywards. The distant landscape isn’t awake yet.

Making the most of the winter greenhouse

This year my greenhouse is full of promising buds and strident foliage thrusting up from marbled terracotta pots – delightful even before the main display bursts forth.

Greenhouse_spring_bulbs_1

Last summer this greenhouse bed was full of cucumbers, peppers, melons and egg plants. Usually I leave it empty over winter to rest, but this year I decided to plant up a dozen terracotta pots with various spring bulbs – nothing very exotic, just some dwarf narcissi, tulips and hyacinth. I’m glad I did. Continue reading

Greenhouse Design

Why choose a lean-to style?

A lean-to style greenhouse is one that is built against a wall. The benefits of this are many:

  • The wall retains heat keeping the greenhouse warmer for a longer time into the night.
  • A greenhouse attached to a wall will be stronger than a freestanding one.
  • A permanent set of wires can be fixed to the wall to allow plants to be tied in.
  • Aesthetically, a wall in a greenhouse gives a sense of privacy and solidity
  • When the wall is constructed from brick it can be very attractive.

You can see examples of such structures in the magnificent greenhouses of Victorian and Edwardian kitchen gardens. I am most familiar with the ones at West Dean Gardens which have been restored magnificently to working order. These great greenhouses had a big influence on my far more modest design ideas. I knew I couldn’t compete with them in terms of scale or authenticity but I could take some of the design cues and make them work for me.

Aluminium or timber?

The two obvious choices for constructing the greenhouse are aluminium and wood. Aluminium is long-lasting, low maintenance, and because the struts are so thin, lets in a maximum amount of light. However, it is a poor insulator, and to my mind always looks insubstantial, even ugly. There are exceptions; if money is no problem, then you can get an Alitex greenhouse. They replicate traditional Victorian timber greenhouses using cast aluminium and they look fantastic. Their strap line is “Aluminium made beautiful” which it certainly is, but when you see the cost you will need to go and sit down. Or sell the Jag.

So, aluminium is out. What about wood? Wood is warm, tactile, substantial, sustainable. I like wood. But it is far less durable than aluminium, and if you choose badly, it can be high maintenance or even simply rot in a couple of years. The most common durable greenhouse is cedar (western red cedar). It contains natural preservatives that mean it is virtually immune to fungal decay or insect attack. It knocks spots off even the best pressure impregnated softwoods. So cedar it has to be!

What kind of base?

As well as protection from water, timber needs protection from the soil born microorganisms (mainly fungi) that cause decay. So, whilst all timber lasts longer if it is raised above ground level, even timber close to the ground will eventually rot because rain water splashes soil on to it carrying the decay organisms on to the wood. Hence, to protect the cedar it should ideally be at least a foot or more above the ground. This was the main reason I wanted a brick base for my greenhouse, to keep the wood clear of rain splashes.

When I started researching greenhouses it became clear that the standard ‘dwarf wall’ style is not very dwarf at all, standing about 70cm high, half way to the eaves. Manufacturers, I realised, simply leave off the bottom panel of the greenhouse (see fig 2).

Fig. 1: The standard glass-to-ground configuration provides the maximum light, but has several weaknesses. Firstly, and as already stated,  decay is more likely with the timber so close to soil level. Secondly, the lower panes are prone to soiling and algae build up. Thirdly, the lower panes are prone to impact from spades or feet when working near them. Finally, there is minimal insulation.

Fig. 2: In the standard dwarf wall configuration the entire bottom pane is lost, and the structure sits atop a dwarf brick wall, about 70 to 80cm high.  This increases the insulation value of the greenhouse, but considerably decreases light entering. This basically rules out growing anything at ground level. Consequently greenhouses like this are usually used with staging (work benches) all the way round, and little is ever grown below this height.

Fig.3: My solution was to raise the entire greenhouse up about 35cm on a much lower dwarf wall. This maximizes light, whilst protecting the structure from ground contact and rain splashes. It affords physical impact protection at low-level, and increases insulation. It does, of course, increase the cost as the ends of the greenhouse have to be modified. This is a relatively minor adjustment and did not add too much to the final bill – certainly this modification was considerably cheaper than a full bespoke design.

Greenhouse style and rear wall

OK, so far so good, but I wanted a lean-to style – one with a brick wall running along one side. Current planning laws only allow a boundary wall between properties to be 2m high. Any higher and you’ll need planning permission. As my wall was to replace three fence panels which were themselves 2m high I needed a greenhouse design that would work with a wall of this height. Initially I had imagined a lean-to, but this was not as straightforward as I imagined. Lean-to greenhouses (fig. 6) are designed to go against the side of a house or other tall wall, which need to be at least 2.5m high – so that was out. My second idea was the vinehouse (fig. 5) as this can be erected against a wall as low as 1.95m. This seemed ideal, until I started considering the dwarf wall. If I wanted to add a dwarf wall as per fig. 3 above and jack up the main structure than the wall would be higher than 2m and hence need planning permission. 


[Diagrams modified from Gabriel Ash; (c) Gabriel Ash 2010]

Finally I turned my attention to the standard greenhouse design (fig. 6). With an eaves height of 1.55m I could jack the main frame up 0.38m (five courses of bricks), and still be within the 2m height restriction for a boundary wall. So that’s what I did.

Door Options

I decided on traditional swing doors, rather than the standard sliding doors (shown in fig 4 – 6), mainly for aesthetic reasons. As I have said, I wanted to capture some of the feel of the great Victorian greenhouses, and only a traditional swing door will do that. This is, however, a case of style over practicality. The down side of swing doors is that they can get caught by the wind and smashed about if you do not secure them. Sliding doors do not suffer from this. Also, sliding doors can be left ajar just as much as necessary for ventilation, but swing doors are either open or closed (although I intend to install brass hooks to latch them ajar). Having considered all of these options I couldn’t bring myself to specify sliding doors – they are just too ugly. For example, the top track always sticks out beyond the roof line (see fig 4-6) . I have not regretted the decision since.

Painted or natural cedar?

Cedar is often left unpainted. Its initial reddish hues look fresh and inviting, and it seems almost sacrilegious to even consider applying paint to it when it stands before you all freshly and new. However, like all wood the sun will gradually bleach it no matter what you do, and it will change in time to the standard silver-grey of all old wood. True, it will lose almost none of its famous durability but after a couple of years it won’t look half as smart as it did to start with.

For me, there were additional reasons for painting:

  • To borrow from that traditional Victorian vernacular.
  • To match the black and white styling of our house and other garden buildings.
  • To ensure the cedar was protected to the utmost (lets see if we can get a 50+ years lifespan out of it!)

The final design

Here is the final design, and a picture of the greenhouse soon after construction:

Final Thoughts

Added benefits with this design are that the eave height is nearly 2m on both sides of the greenhouse, giving plenty of vertical growing space; In the first season I had cucumbers and tomatoes growing to the full height on both sides of the path. That extra height gives a sense of space and stature. My dwarf-dwarf-wall has proved itself an excellent choice,  protecting the timber from knocks and splashes whilst letting ample light in to the permanent beds. I am pleased I chose a Gabriel Ash greenhouse – their attention to detail reminds one of how good English engineering can be. They provided an excellent personal service from start to finish, and were always patient, courteous and helpful even though I changed my mind (and the design) several times before finally placing my order.

Related Links

The Greenhouse  – (Introduction & Contents page)

Building the greenhouse – the roof

 

The roof is glazed with large 4mm toughened glass sheets that sit neatly between preformed ridges running down each rafter. Powder coated aluminium capping is screwed down into the rafters, holding the glass in place and sealing them with rubber gaskets. At the top end the sheets sit under the aluminium capping – you can see these details in the image above.

At the bottom the panes rest against a ridge on the aluminium gutter, so water running down gets deposited into the gutter and never comes in contact with timber (right).

The roof is fully weather sealed and virtually maintenance free. Yet, if a pane should ever be broken, it is simply a matter of undoing a couple of rows of screws and it can be lifted out.

 Ridge Vent

Running along the entire top of the roof is an ingenious ridge ventilator. It is operated by wax filled cylinders that expand when the temperature rises inside the greenhouse, opening the vents along the entire length of the ridge. Being the highest point where warm air naturally collects this is very efficient at creating good air circulation throughout the greenhouse. The open vents also act like an umbrella, so rain hardly ever gets in – important when you are trying to avoid rain borne diseases like blight.

Building the greenhouse – painting it

Why paint a cedar greenhouse? In my case it was mainly for aesthetic reasons. It fits in with the style of the rest of the garden and, I believe, gives it a more substantial look akin to the great classic Victorian greenhouses. Arguably, it will also protect the timber and extend its life – I’m planning on upwards of 50yr lifespan, so every little helps. When you start considering carefully where water collects – at the edges of the glass, on the horizontal ledges and so on, the appeal of an extra protective layer makes sense.

Before you consider painting a greenhouse, however, think long and hard – the two images above hide the enormous task involved. There are thousands of surfaces and it takes days and days of patient and careful work. And then you realise despondently you need to do the second coat!

The paint we used is an excellent product by OSMO called Country Colour White. We have used this (and the One Coat Only range) all over our house, inside and out. What makes these paints different to ordinary gloss or eggshell, and far superior in many situations, is that they never crack, peel or blister; They don’t need an undercoat and can be overpainted at any time without rubbing down or prepping first. So they are a truly low maintenance finish. Note, however, that they have a silk-matt rather than gloss finish, although OSMO offer other equally low-maintenance ranges if you prefer a gloss look, but I have not used them.

Building the greenhouse – the path

Long planks were staked in place to create an edging to contain the bricks and base materials. A length of DPC was used to protect the outside edge of the wood from wet soil in the beds.

Services, in this case water and electricity, were run in a trench under the path. It is wise to plan for these services during the construction stage as they are so much harder to add later.

Sharp sand was laid between the planks and compacted to create a dry bed for the bricks. The bricks were then laid and tapped down firm and level with the top of the planks. Kiln dried sand is brushed into the joints to lock the bricks tightly together. Note the beds have been dug too!

The finished path is hard-wearing, attractive and free draining. Note the kick boards that were added to retain plants and mulches.

Building the greenhouse – erecting the frame

Once the contractors had finished the base work we started on the DIY task of assembling the greenhouse. It was supplied by Gabriel Ash, a semi-bespoke design based on their model called ‘The Eight’. It arrived in several preassembled panels that cut down on the erection time:

  • 2 end panels with doors
  • 2 side panels
  • 1 ridge vent
  • 4 roof panels
  • All necessary fittings and instructions

These screw together with the supplied stainless steel screws bolts and fittings, all of which are supplied. The entire structure sits on a rot-proof aluminium base (which rests on the dwarf wall in our case).

As we assembled the panels we discovered the dwarf wall was not quite level, but there was enough tolerance and ‘give’ in the greenhouse that it didn’t matter, thankfully. As the provided detailed instructions were for the standard structure (as opposed to our bespoke modification) there was a bit of head scratching from time to time, but to their credit Gabriel Ash were always available on the end of the phone and gave excellent advice and support – even posting out a few extra fittings that we needed.

The stages shown in the photos above took a little over two days. Standard designs would go up quicker, no doubt, but there was a lot of sealing to be done between the timber and the brickwork. Also I prefer to do things well, so spend a lot of time measuring up, checking for square and considering later stages.

In the middle image above you can see the long timber sub frame for the ridge vent – an excellent feature that sets Gabriel Ash greenhouses apart from the competition. This is a very heavy unit which required two of us to lift it into place and fix it.

Structural Strength

As the greenhouse is long (~16ft) it has an aluminium I-beam which gives it strength midway at the point where the timber panels join. The I-beam bolts together and, in my case, bolts to the rear wall, making the entire structure very solid. Running along the top you can see the aluminium ridge piece which as well as strengthening carries the innovative ridge vents (see:  Building the greenhouse – the roof)