Constructing an outdoor covered plunge bed

[annew]

I’ve had some requests to describe how I made my 2 new plunge frames, so I hope the following will help.



Despite being a Yorkshire person, only the slabs used for the base were recycled, all the other materials were bought specially. I don’t think my dad would have approved. He would have used pallet wood and old window frames, I think!

[annew]

The frame base is made of concrete paving slabs set on edge, sunk 15cm and packed around with soil, then tied together using strips of copper piping, hammered flat, and bolted to the slabs. Do not try to drill into the slabs closer than about 12cm from the top or they will break. If you do break one, stick it back together with superglue and drill lower down. That’s what I had to do. (Lesson 1)


The sides of the frame are lined with polystyrene sheeting to help insulate the frame, and also to absorb some of the expansion, should the contents freeze.
The base is lined with porous fabric to keep worms out, then 15cm of large gravel to prevent capillary absorption from the groundwater. Another sheet of landscape fabric tops that, and then the sand is placed on top. I used ordinary sharp builders’ sand.

[annew]

To construct the supporting structure for the lights, I used 75x50mm timber for the 2 vertical king posts, 35x35mm for the 8 diagonal braces, 50x50mm for the ridge, and 150x20mm planks for the sides, all tanalised.
First the 150mm wide planks were bolted to the sides of the frame, using coach bolts and nuts. They stood proud of the upper edge of the slabs by 30mm.

The king posts (cut with a v-notch at the top into which fitted the ridge, positioned diagonally), sitting on the top edge of the end slabs, were attached to the slab using an offcut of timber. The ridge pole was then screwed into the v-notch in the king posts.

[annew]

Next came probably the trickiest bit for a beginner woodworker like me. The diagonal braces are fitted between the side planks and the ridge pole. They are positioned in line with the king posts at the end, and to come directly beneath the join between the lights, 8 in total.

Before fitting, the timber has a narrow groove routed out about 8mm from each side on what will be the upper surface, to discourage rainwater from seeping across from the gap between the lights down into the frame beneath. The bottom end of each brace must be cut to fit in the corner between the side plank and the top of the slab, and the top end cut to fit snugly against the underside of the ridge pole.

A spirit level must be used to make sure the ridge is not pushed up or pulled down or the lights will not open and close properly (Lesson 2). This is REALLY fiddly, and is ideally done with an extra person to help. A mitre saw was used to do the main cutting, and a belt sander to fine-tune the angles. Keep all the braces marked with their positions and cut them all to size before permanently attaching any (Lesson 3).

When you are happy that they all fit properly, they are screwed to the side planks and ridge, countersinking the screws.
Finally, the top edge of the side planks is beveled using an electric planer or belt sander, so that it carries on down the angle of the diagonal braces.

[annew]

Now for the lights:
The lights (covers) are made of 700mm wide, 10mm thick double-wall polycarbonate sheeting from roofing suppliers. Hinges are the loose pin type as I need to remove the lights in summer and replace them with shading material slung over the ridge pole and weighted down with battens. The trick is remembering where you put all the pins when you need to put them on again (Lesson 4). Also, each light needs to be permanently coded so that it goes on in the same position every time, or the hinge halves won’t match up (Lesson 5).

2 kinds of edge mouldings were used for the polycarbonate sheeting: The U-section is used to seal the cut ends of the sheeting, and is applied over porous metal tape, which is called teabag tape. The side with the ridge along is used for the upper surface to deflect rain from the gaps between the lights.
The F-section is used for parts where I needed to attach hinges etc. The flap part can be cut off if necessary to leave a deep U shape and a flat strip, which are needed later.

Cut the polycarbonate to size. The lights should overhang the ends of the frame by about 80mm. I had to take some off the width because my frames were too close together, and when the lights were all raised there became too little room between them to walk along (Lesson 6). Tape the cut edges and apply the u-section plastic moulding, mitering at the top end.

[annew]

To attach the hinges to the top of the lights, first I attached the F-section along the top edge, mitering into the corners. Hinge postions were marked and a single pop rivet is applied to the part holding the polycarbonate, to avoid the moulding from being pulled off the light.

One half of the hinge is then attached to the flap part using small countersunk machine screws and nuts. The rest of the lights are constructed in the same way, 2 hinges per light.

[annew]

Before attaching the lights to the ridge, the attachment points for the stays must be fixed. The flap part is cut off an 80mm piece of the F-section moulding, and the resulting deep U-shaped piece is used to attach the stay to the lower edge of the light. It is slid into position in the centre of the lower edge, and rivets applied from upper and lower sides, into a channel in the polycarbonate, at each end of the moulding piece to anchor it to the light.

Now the aluminium sections come into play. A 25mm piece of the wider aluminium is cut and the cut corners rounded off. A 6mm hole is drilled through the 2 sides towards one end, and 2 smaller countersunk holes in the bottom of the channel. This is then riveted to the piece of moulding you have just attached to the light, so that it is on the underside of the light and the holes in the sides are towards the lower edge of the light.


You will need to use a spacer to apply these rivets, as the nose of the rivet-gun will not fit into the channel (Lesson 6). I used a 50x10mm piece of flat aluminium with a 2mm hole drilled at one end. The long narrow part of the rivet goes through this, and then a small nut before inserting it into the rivet-gun. The thicker part of the rivet is then pushed into the predrilled holes and the rivet is applied in the usual way.

[annew]

Tea-time, more later.

[ronm]

Will u build me some please?  They look 'the business'. We are down the road!

[Martinr]

Truly impressive Anne. When you've finished at Ron's you can come a bit further down the road

[Tim Ingram]

Anne - that's tremendous; all the detail is so valuable. You should write it up for the Journal, or as an article for the opening section of the website. Another project to fit in with the prospective tufa garden. It would be good to have such a plunge bed to help increase some of the nursery plants, especially bulbs (and snowdrops!). Up to now I have either grown plants in the garden setting or from seed, but a plunge like this would allow much more control over watering and pests.

[ronm]

Its amazing Anne. Joking apart it really is what I envisaged as the ideal for my potted plants. I'd like to see someone better it! Now can I follow your instructions .. although they are thorough I'm not so good  . Will certainly be trying though. Thank you!

[ronm]

What do you consider each one cost Anne?

[angie]

Anne that's brilliant and to have it showed with so much detail is perfect. Better than my effort that blows away every time its windy.
Is Aberdeen to far to come  

Angie  

[annew]

Will u build me some please?  They look 'the business'. We are down the road!

Ha!! Judging by how long it took me (8 weeks), you couldn't afford me!
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