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Constructing an outdoor covered plunge bed

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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.

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