Building a new Greenhouse - Part 1 - Six-on-Saturday

In the early spring of 2013, we built our large greenhouse using 14 shower panels we'd picked up on the cheap.   

This 12' x 6' 6" (3.6 x 2.0 m) building has served us extremely well for the last seven years, but during the winter we made a decision to demolish it and re-use the glass panels to make a similar smaller greenhouse in a slightly different location.  There were a few reasons for this :-

• some of the greenhouse roof beams are suffering from rot which may soon become a structural problem, so they'd have needed replacing anyway.

• we want to reclaim the corner of the garden where the larger greenhouse is currently sited.  With the greenhouse removed, it's a large paved area surrounded by a concrete plinth, so it's an ideal place to plant some shrubs either in large pots and / or by selectively removing a few of the paving slabs and planting directly into the ground.

• by building a smaller greenhouse than the original, we can re-use all of the glass panels and make it glass-sided all around - at present, the back (north) wall is made from timber, and although we'd faced the panelling with reflective aluminium foil insulation, the back side of the greenhouse is still a little dark. 

I could have removed all the glass panels, and then just modified the existing carcass to make a smaller greenhouse, repairing the roof in the process, but I think that's actually much more work than building a new framework from scratch.  It would also have been very heavy to move, even though it's not far to drag it over to its new position.

So, before our recent holiday, I'd drawn up plans for a new 8' x 6' (2.4 x 1.8 m) greenhouse and prepared a base using paving stones I'd recovered from elsewhere in the garden.  

new greenhouse base area cleared and levelled ...

paving stones laid and retaining wall section renewed ...

The implementation plan is to first construct & erect the new greenhouse framework, transfer all the glass panels over, and then demolish the old one afterwards.

Again before our holiday, I'd bought 45-off 3.6 m lengths of 75 x 38 mm treated timbers, as are sold as fence rails.  It's much more wood than is needed for the greenhouse, the remainder will be used for retaining walls and raised beds.

During laying of the new greenhouse base, I'd used some of this timber to replace a section of the short retaining wall that runs along the north-east side of the garden, and will be behind the new greenhouse.  When the old greenhouse has been demolished, I'll also renew the rest of this timber wall - there's no access at present with the greenhouse in-situ.

We generally followed the same construction techniques as for the old greenhouse, pre-fabricating the building as five frame sub-assemblies; front, rear, LH side, RH side with door, and finally the roof.  

The frame timbers were cut to length using the cut-off saw, and all connections were glued and screwed.  A simple tip when building square or rectangular frames, to ensure you've built them with square corners (essential for fitting glass afterwards), is to just measure across the two diagonals and make sure the measurements are equal.  If you need to adjust them, use thin wooden battens fixed temporarily across the frame timbers using screws, and leave them in position until the glue at the frame joints has completely dried.

And if you've more than one frame to make of basically identical overall dimensions, then build the subsequent ones directly on top of the frame below, so you can see that everything's correctly aligned.

glue drying, from the bottom: front; rear; LH side, RH side & door ...

We painted all of the frames with two coats before erecting them, using Wilko's garden furniture paint - less than half the price of the Cuprinol stuff.  Painting all the frames actually took longer than it did to construct them !

I pre-installed the door surround in the RH frame assembly, using three stainless-steel fire door hinges.  I added a bracing strap from aluminium flat bar, to keep the door frame square when the glass panel is fitted - those panels are 6 mm toughened glass, and very heavy.

So then it was a case of joining the five frames together, first lifting the rear and LH side frames into position on the base and using screws to fix them along the corner.   With these first two frames screwed together, they became self-standing and so attaching the LH side and front frames was easy.

When the four vertical frames had been assembled, we lifted and aligned the roof frame and then screwed that down onto the top of the front & rear frames.  

The pre-fabbed frames have been designed with ventilation openings all around the base and at the top of the rear section, and these will all be covered with louvred grilles, to stop rodents, birds and butterflies etc from getting inside the greenhouse.   

ventilation openings at the highest point at the rear ...

and all around the base ...

Further ventilation is provided at the top of each side, where the roof slightly overhangs the side frames - the fall of the roof means the front of the roof frame is lower than the rear, and this creates two open wedge-shaped spaces protected by the overhang which allow warm air to escape.  We'll likely make up something with a fine mesh to cover these openings.

frame assembled - enough work for this week ...

We'll give everything yet another coat of paint before we continue, but not today - it's sunshine and showers here, so not ideal for painting.

It was great to get out in the garden during a week of fine weather - this was my exercise for the week during the lockdown !  

We'll post again when the remaining works are completed - we're still only halfway through this project ...

And head over to The Propagator's site, the host of Six-on-Saturday, and check out what other gardeners around the world have been up to this week.