A design for small, low-cost demountable homes with full facilities (cooking, washing, shower and toilet).
© Plateau Group
This H4H design is available to any volunteer groups for non-commercial use, but please make a formal request.
H4H Fabrication Details
[Lowest Skill Level]
Ply sizes aren't always available, and costs vary extraordinarily. Generally these days, any real plywood (as distinct from core-board, etc.) is relatively water tolerant, and therefore usable in every part of the house other than the Water Closet and Divider Cupboard backing where we strongly recommend the use of the more expensive Marine Ply. The main component of ply costs, therefore is the quality of the surface finish, and in this application this is a secondary consideration.
The standards for ply quality include the selection of resins used to glue the veneers together. The Marine Ply comes from America so it is in an Imperial (rather than Metric) standard, usually of 2440x1220) The veneer surface quality has a two-alpha designation. AA is premium quality: BC has one surface (B) with good continuity and the other (C) not so good; CDis often called "Structural" because while the ply is just as strong, neither surface is without blemishes. (The minor gaps in the veneer will be filled and sanded, but acceptable if you paint over them.
On the Internet you will find a totally confusing range of plywood sizes advertised. This is because the importers are anxious to bring in cheap ply by the container load from anywhere in the world, but this doesn't mean that the sizes you choose will necessarily be available when you go to buy.
Our experience is that the only size consistently available is the 1200x2400 standard for lining and structural ply and 2440x1220 for Marine Ply.
Ply thicknesses and the number of veneer layers are also highly variable. 3mm "three-ply" is OK for the ceilings, but 4mm would be better for wall linings. The 15mm five ply is strong and rigid enough for floors, beds and tables.
This is a fold-up panel (1800x285) of 15mm ply which is hinged just forward of the back edge of the floor. When erected it sits on the floor-panel, not on the frame.
This carries the weight of the Shower-tray and Raised Dry Area floor. These raise floor panels are the last to be added during the erection, and both have ribs added to their underside which fit both sides of the Inflection and lock it in place.
The inflection panel also has two side 'tabs' which lock behind the vertical 'Inflection Attachment' timbers in what is otherwise the Utilities underfloor cavity.
As with all of the main frames, the dimensions have been carefully chosen to make maximum use of standard timber sizes. The ply is significantly expensive, so we have aimed for a design which utilises the full uncut sheets of ply whenever possible. Offcuts of the framing timber can generally be used for battens, and offcuts of the ply are also useful.
[Note: When assembled, both the Side Wall panel and the Front Wall panel sit on the floor's frame, not on the floor ply.]
Floor Ply Dimensions:
Ideally, the 15mm plywood floor (3.0x1.8) would be cut from a formwork ply sheet of 1.8 x 3.3 m. It would then have been cut to create the main floor length of 3015mm with a cut-off inflection of 285mm.
Ply of these dimensions is not easily found in Australia so we propose making the floor up from three sections cut from two 1200x2400 ply sheets, with the inflection cut from another panel.
The ply gauge used for the floor could be the lighter 12mm thickness, but we tend to think it will feel flexible and therefore insecure.
The inflection will be hinged upwards at a point close to 3000mm along the floor length. This is a ply-thickness distance from the end of the main floor ply.
CHECK - The distance of the raised inflection from the end of the whole unit is about 600mm, while the raised floor is 700mm wide. This means that the raised floor will have an 100mm overhand forward of the inflection support. This is deliberate.
Inflection air gap The inflection will introduce air-gaps above and below the 285 height, and since these are at foot level, these may be an annoyance in cold climates. The bottom gap should be easily fixed by adding a batten to the end of the frame directly behind the hinged inflection. The top gap is not likely to produce an air-gap problem if the two raised-floor sections (the shower-tray and the dry-area floor) are given ribs (for both strength and position stability) on either side of the inflection.
Electrical feed notch:We need to bring the electrical feed into the unit in some safe way, and the way the electrical system is handled will be of key importance in gaining any local council approvals of these cabins. The main incoming electrical feed is via a standard off-the-shelf builder's extension cable with an earth-leak safety protection switch. The incoming cable goes initially to the Step-box box which becomes the distribution point.
Therefore cut a small (but deep notch = 8mm wide x 20mm deep) into the top of the inflection at the mid-point, so that the incoming cable enters the unit at a point which is high off the ground, directly under the raised floor, and behind the Divider Cupboard (rather than the Step-box itself).
We have positioned this cut behind the Divider Cupboard not behind the Step-box because a cable entering directly behind the step point it is likely to be easily kicked or displaced. The depth of the cut is to allow for the supporting/positioning battens on the underside of the shower-tray and dry floor area.
Also, we suggest that you:
This seemingly trivial detail is important: We are concerned that the cable could be accidentally jammed between the inflection and the raised floor/shower-tray timbers. The erectors won't necessarily think to protect the cable if the string tie-down isn't already in place and ready to be used. This is the way accidents happen.
Erection on site:
The floor is obviously the first panel to be set in place at the site, and it establishes the potential amount of roof rain flow-off when setting up outdoors. Since there is no inherent slope in the roof itself, you need to get this angle right, especially where torrential rain can be expected. Don't bother with spirit levels: the best judgement of the slope angle will be a flat (baking?) tray of about 30 cms with a cup-full of water, or a length of transparent PVC tubing with both ends blocked. This will show you clearly how well your choice of slope will perform.
If you are erecting the home outdoors, you should drive steel star-pickets deeply into the ground at all four corners, and perhaps also across the back and sides between the corners, before you add the other panels. Lock the floor down with wire (and later with some flat metal straps. Later after the side panels have been assembled you should also lock down their back corners near the Stub Legs. Fencing wire is a good material for tie-down.