This H4H design is available to any volunteer groups for non-commercial use, but please make a formal request.

[Low Skill Level]

Note: See the two separate Side-Frame sections for finishing off; with the lining, shelving and fit-out details.

Fabrication details:

All wall studs are the same height so the roof is flat. Outdoors in weather these units will need the floor panel to be slightly raised on scrap-wood chocks under the front of the floor-panel to provide some rain run-off.

Overall length of these frames are 3.6 metres - which is the length of the top and bottom plate timbers. The roof overhangs the front by a further 0.3m. The side walls are all 70mm in width and insulated for most of the length with glass-wool insulation. We have not included any noggins, mainly for reasons of simplicity in the fabrication, and the need to nail, etc.

We don't think this is potentially a problem because of the size, but we anticipate that this may be a criticism levied by tradesmen. We would stress that conventional building techniques are not directly transferable to flat-pack demountable homes, which will be trucked around and erected on both indoor and exterior sites; flexibility is not normally a major concern in house building.

The uncut sheets of 3-4mm plywood used as a liner also help fix the timbers in place and maintain the squareness and rigidity of the walls. The Studs (upright timbers) on both sides are further held in place by hinged shelving which serve as major longitudinal strength members.

The frame sizes are chosen to allow the plywood sheets to overlap onto the sawn timber by 10mm. This overlap is just enough to allow the ply to be glued and tack-nailed. The ply is a major diagonal strength component as well as the inner liner surface. Note that this 10mm of overlap leaves 20mm of bare frame timber around the ply, and this avoids double-framing and is a key factor in keeping material costs low, and simplifying construction techniques.

Note also that all Studs are the same 2080mm length which means that the roof has no "pitch" to allow rain-water run-off. This makes the units easier and more fool-proof to fabricate, better for indoor use, and for also easier handling when demounting for storage.

Outdoors in the rain, we assume that timber off-cuts, flat rocks or a brick, etc. will be used to provide the necessary rain 'pitch' by tilting the whole building backwards a fraction. [See assembly details] We have also included provisions for staking the cabins down to handle rough weather.

Ideal Fabrication Sequence:

Ideally, you would fabricate both side frames at the same time. They are identical until we begin adding lining, and then they become mirror images.

Check all timber lengths. The four longitudinal Plates should be 3.6m, and the 14 vertical Studs should all be 2080mm.

If you can, you should arrange for the timber to be delivered precut; if not arrange with some handyman with a docking saw to cut the timbers uniform and square.

The only timber that requires precise cutting is the horizonal Raised Floor Supports, which leave the gap between studs able to accommodate both the Water Closet unit (700mm wide) and the fixing angle-iron and tie-down. It needs to be 710mm in length.

Mark-up stud positions:

1. Lay the four plates together (flat). Raise them on a couple of battens above a sheet of plywood. The idea is to use the ply as a squareness gauge, so you can align and then mark all four together with a guaranteed precision.
2. You need to mark the position of the studs at each end. Mark all stud positions using the "|X|" sign. This provides obvious lines for both Stud sides, and the "X" is a universal sign for the attachment mid-point.
3. Begin at the front. Then mark positions for Studs 2 to 5 which are spaced at 600mm centres (The gaps between them should be a uniform 570mm)
4. Now work from the back Stud 7. Position Stud 6 by using your Raised Floor Support (710mm) timbers as a spacer for the gap between these last two studs. The Water Closet fits here between these studs, so the separation here is important.
5. Now drill two screw holes for each stud (about 20mm in from each side) at the centre points of the |X| markings. These drill gauge should be the same as the screws shafts. There is nothing gained by making the holes 'tight'; the screws should slide comfortably through the holes.
6. Now counter-sink each of these holes. You want the head of the screws to be at, or slightly below the timber level. You should be using 55-60mm countersunk wood screws, and you want them to be tightened down to the point where the head is not 'proud' (projecting). [Note:This is far more important with demountable homes than would normally be the case (where they'd be nailed) because the wood will shrink during storage and the frames will be flexed during transport.]

Now fix the studs in place.

• The screws should drive into the Stud ends relatively easily with fresh timber, but you may need the volunteers to drill smaller guide holes (this necessitates a lot of drill changing if you are driving the screws with the drill's screwdriver bit).

• Nail the spacer batten to Stud 7 to create the underfloor utilities cavity (For 30mm timber = 240mm. For 35mm timber = 230mm.) The spacer also strengthens the support under the WC, so glue and nail it in place.

• Now add the Raised Floor Supports (710mm) between Studs 6 and 7. The top of the support should be 300mm from the bottom of the bottom plate. (use the Inflection Attachment to keep it level with the spacer)

• The Inflection Attachment should be positioned (on our calculations) 600m from the back edge of the frame, but only put the Attachment lightly in place with a single screw until you get a chance to check it against the actual floor. The back of this timber stub should align with the back of the raised Inflection itself
  [But remember the side panel over-hangs the floor panel by 10mm at the front]

• [Important and easy to forget:] Drill larger holes through the bottom of both Stud 5 and 6 at about 200mm from the base level. These are needed to pass the electrical power cable through to the main room space (The cable will descend in the cavity, then later penetrate the plywood liner just in front of the inflection, and run across (behind the Divider Cupboard) to the safety switch unit inside the Step-Box.)

Now Square the frames:

At this point we suggest that you add the first sheet of ply liner to one of the frames ... beginning at Stud 1 ... and checking that it covers to the mid-point of Stud 3. This sheet of ply liner will square the whole building, and it needs to be glued and tack-nailed (use 20mm flat head panel nails spaced every 300mm) on all four sides -- and also along the mid-point of Stud 2.
CHECK ON STUD 1 that you have 20-25mm of uncovered frame timber since the angle-gal junction attachment, slots in here.
We will add the rest of the ply liner during the finishing stage later.

Check the frames against each other:

At this stage just do a quick check to see if both Side Frames match, and that there is no significant misalignment. By adding the liner to only one frame you have established which is to be the Bed-side frame, and which the Table-side frame. So now add the first liner to the other frame.

Cross-bracing

There is some doubt as to the necessity of cross bracing on these side walls with strap (also called 'hoop') gal flat-iron since the ply liner will be so effective in providing diagonal rigidity. This is probably true (extra cross bracing is not essential) except possibly outdoors for the area from Stud 5 to 7 on the Bed/Water Closet side. We suggest cross-bracing here ON THE OUTSIDE of the panel. Note also: By crossing Stud 5 slightly above and below its butt joints, the straps can also strengthen the actual butt joints at what is their weakest point along this wall.

If the units are to be used mainly outside, there would be value in doing this to both side walls.

To get the maximum value out of cross-bracing you should always screw the brace-iron to every timber crossed. Also, in potentially windy locations, you may consider pop-riveting the mid-points of some of the outer cladding to the bracing to stop it rattling.

Add the two Stub Legs:

These are screwed onto the bottom of Stud 7 using a couple of screws spaced well apart. These two stub legs carry the weight of the Back Wall panel onto the ground surface (there is no floor panel here). The Back Wall has its own 30mm thick Bottom Plate, so the top of these Stub Legs should align with the underside of the Raised Floor Bottom Plates.

The original idea was to find some way of making extendable legs, but we have settled on adding these two Stub Legs made with an easily removable 'foot/pad'. This is just a pad of, say, 100x50 15mm thick hardwood which is added to the bottom of the 70x30 Leg with a single screw so it can be easily removed or replaced with something thicker or thinner, or nothing if you want to tilt the cabin back for water run-off.

The overall length of the Stub + Foot/pad should be 340mm so it projects below the frame by the thickness of the Floor Frame (70mm). It needs to attach to the INSIDE of each Stud 7, so that the Back Wall plate (30mm thick) can sit on top.

Fixing some potential problems

The junction of the Bed-side Wall frame and the Front panel has a potential problem because of the need to provide fairly strong supports for the bed plank with its battens and hinges. We suggest that both Side-walls need a length of solid batten timber behind the ply in these front corners.

Ideally, full-height lengths of good batten timber (say 25x15) should be glue-nailed to the inside of Stud 1, providing enough face on the plywood side for a hinge attachment. Drill the battens through the 25mm timber 'crosswise' and use some jolts or longer-than-normal nails + the glue. This wider face alongside the ply surface will provide extra attachment points for the ply liner, shelf hinge, and the bed support battens.

[Note that the joiner angle-iron (green) is fixed from the outside to the front of Side-Wall frame at Stud 1 during erection of the walls, and from the inside at the back to Stud 7.]

Indented Back Panel on Table-side

We want to be able to assemble the cabins from the inside, so that a cluster can be erected in close proximity, and if necessary up against a wall. On the bed side the space between Stud 6 and 7 is unlined because it is occupied by the Water Closet, which fits back into the wall and occupies the cavity space.

So on this side there is no problem; the Back Wall frame can be tied to the Bed-side Wall frame using the gal angle-iron joiners from inside the cabins, because the erectors will have full access to Stud 7, and therefore be able to add the three screws which join the panels together.
 

On the Table-side Wall frame we wish to both line and insulate the space between Stud 6 and 7 for reasons of appearance, utility, heat retention and strength. However with conventional lining ply nailed and glued to the frame-facing, the erectors would not have access to fix the angle-iron joiner to Stud 7.

For this reason, we use 25 or 30mm batten timber nailed and glued to the surrounds of the cavity between Studs 6 and 7 (also top and bottom) against the outside cladding. Then cut and fix the liner to this, thus creating an indented area while still allowing access to the angle fixing area.

We suggest that this indented space could also be used to protect a wall mirror (which is important to female occupants). The two longitudinal shelves on this side of the cabin cross this indented space at heights of 400mm and 1220mm above the Raised Floor level. They rest on battens on the Back Wall (no hinges on Stud 7.) so allowance could also be made here to add some extra shelving and perhaps a narrow "make-up" table by using plug-in shelf supports (or even a small hinged drop table on light chains) provided these don't block access to the angle-joiner space close to the three attachment holes.

A 'ladder' of narrow shelves can hang on chains or thin strong cord from a couple of hooks on the underside of the top-plate. This is ideal for toilet and makeup items.