Friday, 15 March 2013

Building a greenhouse.....

This unplanned major project all started because I was looking for glass panels to build a simple cold frame to start-off vegetable plants under glass.  

However, one listing on eBay was for a shower panel (singular), but it was very poorly listed and described.  After a couple of emails to the seller I established that there were actually 18 panels for sale in the lot, all of the same height but in batches of three different widths, and all of them brand new !

I put in a bid and was lucky enough to get all the panels for the starting price of £20.  It meant a 160 mile round trip to collect them, but we hooked-up the trailer and set off.  When we saw the panels, they were very much more substantial than I'd initially thought – all 6 mm toughened glass within a polished aluminium frame.  They must have weighed around 400 kg or so, but with half in the trailer and half in the back of the car, we got them home OK.

glass panels in the foreground....

So, after measuring up, we decided we could build a new 12'x6' greenhouse using fourteen of them.

We already have a very small greenhouse with an aluminium frame and polycarbonate glazing, shown in the background in the first photo, but decided that the new one would be more permanent.  The deep ring beam lets us fill the space inside with topsoil, rather than planting out in containers which is what we do with the smaller greenhouse.  This will allow us to plant a few perennials which can establish deeper roots, such as grapevines.  We also intend trying to grow semi-tropical vegetables etc, such as ginger.

This new greenhouse is also full height within the entire growing area - no more banging my head on low apex roofs....

As luck would have it, at very short notice a client in France requested I make a visit to their offices for two weeks to start on a new-build project.  We had only just collected the glass panels on the Wednesday, the request came on the Thursday afternoon, the flights were booked for the following Monday, and so we decided to put the foundations in for the greenhouse during that weekend before I travelled. 

I knocked up a quick outline design to establish the dimensions of the foundations.  I had a lot of old bags of cement in the garden that were actually past their recommended 'use-by' date, so we dug out a trench and bought some rough fencing boards to make shuttering to cast a rectangular ring beam. 

shuttering for the foundation ring beam....

By casting the foundations before the trip, it would give them a couple of weeks of undisturbed curing time before we would need to use them.  In the end, it turned out that it took around five weeks from casting the foundation to finally erecting the basic structure, which was fine because concrete takes 28 days or so to reach its working design strength.  

The foundation took 6 full bags of cement, 24 of aggregate and 12 of sharp sand – 12 batches using our small mixer.  To reduce the volume of concrete, we first placed all the old bricks and stones etc we could find into the formwork.  The batches were produced one after the other on the Sunday afternoon so that each fresh batch was placed before those underneath had started to harden, essential if a homogenous concrete mass is to be achieved.  It's not the prettiest cast base in the world, but it's functional.  A week or so ago, we painted the top and visible side surfaces of the concrete beam using a green floor and doorstep paint, to tidy it up a little.

So, after my return from the business trip and completion of the design, we bought 40 x 2400 mm lengths of 89x38 mm CLS 'engineered' timber from which to construct the frame. 

On eBay, we bought lots of corner fixing brackets and simple angle brackets.   These are screwed to the inside of the wooden frames, and then the glass panels pop-riveted in place via their aluminium side frames.

So far, I've prefabricated four wooden frames, the front, back and the two ends.  Each end incorporates an opening door, so we can get better ventilation on the few days a year that warrant extra cooling.  The western door cannot be fully opened for access, since it's too close to our new hedge, but an automatic greenhouse window opener can partially open and close this door when the internal temperature rises and falls.

The pre-fab frames were painted using Cuprinol's 'Garden Shades', which I've used in the past with good results.  This stuff is quite expensive, around £14 for just a one-litre tin at B&Q.  However, on eBay, I found a 5 litre tin for less than £17 delivered - the reason it was so cheap is that the tin was dented, although the contents are fine.  After it was delivered, I immediately bought two more of the same.  The rear panel boards will take a lot of paint with several coats required, and we've also our large front gate to re-paint this year...

After around five weeks, what with work commitments and poor weather, we today erected the four frames and screwed them together to make the basic shell of the building.

the basic shell of the structure...

The lower frame at the front incorporates five ventilation openings, one under the centre of each glass panel.  Again from eBay, I've already bought aluminium vent grilles to cover the holes.  The design of the roof allows warm air to escape at each end, thus drawing fresh air through these base vents.

There's only four anchor bolts in place for now, just to prevent any tendency for the structure to move in strong winds, but I'll put another six in when the roof's on and before we start the glazing.

The rear (north side) of the greenhouse will be fully boarded-out.  It was only partially boarded during the prefabrication phase because otherwise the back frame sub-assembly would have been far too heavy for two of us to lift it into position.  However, the lower boards needed to be fixed beforehand since the retaining wall behind the greenhouse would have prevented access, but the rest can be pre-painted and then assembled with the shell in-situ.

corner brackets & intermediate lugs for
fixing the glass panels in place

from the east end - the door frame is already fitted
on the RH side, but is held closed using
lengths of wood until the construction is finished

We'll need to put a few more coats of paint on the structure now it's in place.

I've still to construct the roof frame - the design was a little tricky, in determining how to deal with the rainwater sealing and run-off, but this is now sorted and I've already cut all the timber to length - we'll prefabricate this final frame when we get the time and a bit of nice weather.

This particular project has stopped me progressing very far with the others I'm also on with, because it's quite time-consuming and we want to get the greenhouse completed by around mid-April at the latest so we can begin planting for this season.

More to follow as this job progresses.....

Update 01 April 2013

Despite the unseasonably bad weather we've experienced during the last month, we've now finished constructing the roof frame...

roof frame in progress and before painting....

And undertaken a trial fit of the five roof panels in the painted frame - we didn't want to erect this structure eight-foot from the ground and then find the glass panels didn't fit !

with glass panels....

We've today ordered the sealing strips for the roof and also bought 350 litres of topsoil for inside the greenhouse.  With a bit of horse manure from the neighbouring farm, this should be enough to get us going with planting in the next month or so.

Update 11 April 2013

A break in the weather coincided with the rubber sealing strips arriving, and so last week we finally erected the roof structure and fully glazed the greenhouse.   Lifting the roof frame into position and then fitting the roof glass panels turned out to be much easier than we'd thought.  We also laid some paving slabs, both for access and inside the building, although they still need levelling up and a dry mortar mix adding between the slabs.

Still a lot of other finishing works to do, what with fixing handles, locks, gutters and trims around the glass etc, plus an internal shelf or two on the rear wall, but it's beginning to look the part...

 And today we added a couple of barrow loads of horse manure to the topsoil we'd already placed, and so it's just about ready for planting.

almost finished....

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