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[Moderate Skill Level]

This is an expensive panel since it needs high-quality water-proof ply wood, as does the back of the Divider Cupboard, as two sides of the shower-area. We need to get both pieces out of a single sheet of 1.8 x 2.4 ply sheet (3mm or 4mm thick) and we will need 600mm if we can for the Divider Cupboard.

The construction of the Back Wall Panel has been slightly changed in this Revision 3 of the plans. See the previous design at the bottom of this page - it is still totally acceptable.

The Back Panel needs to be quite strong (especially on the diagonal) since it is positioned over the utilities access cavity, and it needs to be light-weight because it will be added from the inside during erection. This area is a limited space, so it will be difficult to handle in many circumstances.

The outside dimensions are 1.8 x 1.8m which leaves a 300mm gap below the raised floor for the sewerage and utilities. The cladding on the outside will probably overhang this cavity by 50mm to 100mms.

The panel itself is 30mm thick (so use 30x30mm sawn timbers as the frame), except for a 70x30 full-width bottom plate which projects forward and supports the raised floors (including the shower tray). This bottom plate is itself supported on each side by a short Stub Leg (green) which are screwed to the insides of Studs 7 on each side panel frame.

[Check: The bottom plate under the back wall should be level with the Side-Wall Raised Bottom Plate timbers, when everything is assembled.]

Explanation: For most of their length these side walls sit on a 70mm thick floor panel frame. But the Floor Panel doesn't extend as far back as the back of the cabin. For this reason the Stub Legs are (300-30+70) 340mm in total length (allowing for floor-panel thickness. The Stubs includes a removable/adjustable extension pad added to the bottom of each to allow adjustment for slight unevenness in the ground level, or for the need to tilt the whole unit back to introduce rain run-off.

Fabrication:

Basic frame:

It is best to build the full frame first, and then attach the whole to the Back wall bearer (70x30 on the flat).

Start with three of the four uprights of 30x30 by 1.8m of sawn pine, then add the two horizontals (30x30 x 1.8) which we add to the top and bottom, each butt joint with two long wood screws. Counter-sink the screws them so that they can be tightened down, since damp timbers are likely to shrink over time.

Now check the dimensions and then add the last Stud.

Third stud position: Purely to save costs we have made this back-wall from two sections of Marine Ply, with one being the full sheet width of 1220mm + a 520 mm off-cut from the the Divider Cupboard backing

This is a total width on only 1720, so to make up the required width of 1.8m we proposed to add a wide batten of (say) 60+mm for ply attachment on the WC-side vertical. This will be behind the Water Closet so it is not likely to have water penetration problems. The other junction of the sections will be behind the shower curtain.

Check this all out before you insert the last Stud into the wall frame. Don't add any ply at this stage.

[Note: that for full top-to-bottom coverage in the shower area, we need slight more than the 1.8 m. So cut the ply length to 1840mm to give plenty of ply-fixing space at top and bottom.]

AT THIS POINT WE ARE GOING TO DEPART FROM THE NORMAL CONSTRUCTION SEQUENCE.

Add angle joiners

Now add the two gal angle-iron joiners. These need to be 35mm less in height than the 1.8 m wall height because, during erection, they will need to slot into the gap between the top plates and the raised-floor plates of each side wall. (The 700mm-wide WC unit fits in here between Studs 6 and 7). Check this.

The Back Wall needs diagonal strength. This is especially so since it is raised 370mm above ground level and sits just on the Stub Legs attached to the Side Walls. So we need good cross-bracing with strap gal ('hoop') iron, and the best way to ensure strength here is to have the diagonal wall bracing sharing the top and bottom fixing holes with the vertical angle-irons on each side.

Since one of the sides of each angle will need to be permanently fixed to the verticals on the back-panel, we need to add a couple of extra screws: so drill these extra holes in-between the existing ones, but only on the fixed side of the angle. Countersink the 5 fixing holes in the inside of the angle (this side will be screwed onto the new frame, and the 3 holes on the outside of what will become the fixing tongue. We need the screws heads not to project here since the WC needs this 700mm of stud space.

Now fix the angles on to the inside of the frame (directly above the Bearer's floor projection), and make sure that neither angle is lower than the top of each side's Raised Floor Bottom Plate).

Cross bracing.

Lie the frame with its cladding-side down on the sheet of cut ply. Use the ply as a square to check the lengths of the cross-bracing.

You are now going to add the two gal diagonal cross-braces to the inside of the panel ... the side with both the projection and (later) the ply liner.

Drill the end-holes in the cross braces to match those at each of the angles, and you should lock them temporary together at these four points with gutter-bolts to make sure the frame doesn't move before the ply is fixed.

Drill, countersink and screw the cross-bracing straps to the framing timbers wherever they cross any studs (for rigidity), and then you can add (using nails and a good glue) the cut ply over the top of these straps. Obviously start with the narrower ply panel (520) and butt the 1220 ply piece hard against it. The combination of ply liner and cross-bracing screw-locked to the corner angles is all important for diagonal strength (especially if you plan to stack these home units in two layers).

Finishing off:

Side Shelf Supports: Before moving to the outside cladding, we suggest that you add shelf-support battens for the Table-side Wall and then provide a couple of towel racks and the flange end-sockets for the curtain rods that swing out from the top of the Divider Cupboard.

The Shelf support battens should be about 530 long to span between the adjacent Studs (also drill some 3mm holes into the batten for small clothes hooks). The top of these horizontal battens should be at 385 and 1235 mms above the projecting Bearer timber.

Curtain Rods: Two 750mm curtain rods hinge out from the top of the Divider Cupboard, cross the shower-tray, and lock into two matching (screw-fixed) flange/sockets attached to the top wall plate. These two are the main stability sources for the cupboard and they provide a both a shower curtain rail, and a rod for hanger-drying of washed clothes.

See the details in the Divider Cupboard section.

Towel rails: [Optional] Broom sticks can be purchased with a plastic coating. If you cut one into two lengths, each of about 530 mms long, they can span across between the studs somewhere under the shelf-battens. To be useful as towel rails you'll need to space them out from the wall. Just use short wood blocks or cut lengths of pipe. The alternative is to provide hooks embedded into the high shelf batten, but both are better.