The WikiHouse construction system is based on plywood fins, spaced evenly apart according to the selected gauge of the construction grid. Those fins can vary in size and shape. Once connected together and clad they form a robust timber frame structure.
The gauge of the grid (labelled above as 'g') can vary depending on the desired standard construction module in different countries. A 550mm gauge is provided to accommodate plywood sizes of 2400mm x 1200mm where CNC machines cannot cut to the edges of a sheet. In countries using Imperial measurement systems, where plywood sheets measure 2440mm x 1220mm, a gauge of 600mm is standard. Intermediate gauge sizes of 450mm and 900mm (for one-off pieces only) are also accommodated.
Wikihouse components are categorised into series, according to their width. The widths follow a modular grid of 1200mm (1.2m).
Sections 1.2m wide.
Sections 2.4m wide.
Sections 3.6m wide. This is the longest span module.
For sections wider than 3.6m, compound series are used, such as this one.
Theoretically there is no limit to the width of a section, A, B and C modules can be combined in any sequence.
The roof profiles of these series can follow more or less any form, provided it is structurally viable. Equally, footings can respond to sloping topography. One of the future aims of the project is to develop and test two-storey structures.
The following is proposed not as a fixed set of rules, but as a basic introduction to the design standards for WikiHouse. All designers are invited not only to use these rules, but to develop and change them as they improve on the construction set.
WikiHouse uses only one basic material, 18mm structural plywood, in international standard sheets sizes of 2400mm x 1200mm (approx. 8'x4'). There are a number of different sheet materials to choose from, but they must have sufficient structural strength. Parts are cut from these sheets using a CNC milling machine.
All inside corners must have a 'dog bone' indentation, to accommodate the fact that the cutting head is circular, and can only cut rounded inside corners. Mark these 'dog bones' out in SketchUp by drawing an indentation 5mm deep and 10mm long (as shown). When cut, this will form the required 'dog bone' shape.
At present, WikiHouses uses only three kinds of fixings, M8 mild steel bolts (often BZP) which are, if possible, full threaded, and 4mm x 50mm and 4mm x 30mm woodscrews with a cross-head.
Each fin comprises two layers of plywood in an identical profile. Fin members are 200mm deep.
At the moment, a basic S-joint is being used. The aim of future versions will be to develop an all-plywood wedge joint, making the system much less intensive on bolts. S-joints are distributed around the fins. There are 3 basic rules for doing this:
1. No piece may be longer than 2370mm.
2. S-joints should not be located on corners, as these are the areas under the most stress.
3. S-joints on each layer of fin must be staggered and mirrored.
The structure must be bolted around the S-joints. Bolting holes are modelled as 9mm squares in sets of six at the locations shown. This is a guideline only, not a strict rule. S-joints are staggered around the structure, so usually neighbouring S-joints will 'share' sets of bolts.
Hooks and tabs for cladding panels protrude outside the fin profile.
Holes for primary connectors must be located at key strategic locations around the section.
Primary connectors are slotted through, and pegged on the far side, pulling the structure tight. The slot in the primary connector is designed such that it doesn't matter which way the peg is put it in, though the way shown here is neatest.
Secondary connectors are located at key positions where they serve as cills or lintols for windows and other openings, as well as lateral bracing for the structure as a whole.
Secondary connectors are designed to slot into place. Note that most secondary connectors, like most primary connectors, have a 60mm diameter hole in the centre. This is to allow services (pipes, wiring etc) to be run through the house. The notches in the side allow access for a screwdriver, so the sides of the secondary connectors can be fixed into the fins. These screws do not do any significant structural work, they just hold the secondary connectors in place.
As well as an 18mm wide and 30mm deep notch, 3mm squares must be drawn onto the fin as pilot holes for these screws.
External panels are designed to slot over the hooks on the main structure. Note therefore that the holes have to be large enough to allow the hooking-on and slotting-down movement. The hooks on the main structure can then serve as fixing points for cladding if required.
Internally, a flush interior finish is required, so panels only need to slot onto tabs. Many of these internal panels will also need 3mm holes, allowing the interior panels to be screwed to the main structure.
The purpose of the WikiHouse construction set is that the end structure is ready to be made weathertight using cladding, insulation, damp-proof membranes and windows. WikiHouse is still an experiment in its early stages, and these have not yet been prototyped or developed further. All the information shared on WikiHouse.cc is offered as an open invitation to collaborators and co-developers who are interested in putting open source solutions to these problems in the public domain. If you are working on one of these, or would like to know (or do) more, please get in touch.