Modular Construction

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The following modular construction concept is based on standard practice from the following references. New or alternative concepts can be compared to this reference design, and if found better, then become the new reference design.

  • American Institute of Timber Construction, "Timber Construction Manual", 3rd edition, John Wiley & Sons, 1985.

Concept Description

  • The system consists of bolted timber framing on a standard spacing, and bolted filler panels of standard sizes. Using bolts allows additions and modifications relatively easily.
  • Timbers and other lumber are cut locally from on-site trees, then dried using an on-site solar kiln. Un-used parts of the tree are left in the forest, or returned after cutting. Some additional nutrients are added to the forest for sustainability.
  • Wood is left untreated to avoid substances like creosote or metallic salts. This requires an above ground foundation to protect the wood from moisture and termites. To keep the system modular, concrete column footers can be used under each wood post. If a building is modified, the footers can be extracted and re-used elsewhere as needed.
  • Truss braces are used as needed for stability, and cut steel plates and welded angles are used where needed for joint strength. Where loads are not as high, frames and filler panels are bolted directly to each other.
  • Roofing, exterior covering, windows, doors, insulation, and utilities can be pre-installed into filler panels. In this case they need to be in standard locations so they line up. Edge overlap will be needed to prevent leakage. Alternately these can be added later, in which case they should be installed with bolts or screws so they can be removed.

Modular Design Features

Conventional building materials are already somewhat modular. USA lumber and plywood come in sizes that are multiples of 2 feet, for example. But if needs change, conventional construction is not easily remodeled or recycled. Two basic features will allow for that: a standard grid and removable fasteners.

Standard Grid - This is to use multiples of a basic unit as the size of parts and the spacing of fasteners. Basic framing lumber has a thickness of 1.5 inches, which is nominally called 2 inch, but that is before drying and sanding. Then cut lengths should be multiples of 1.5 inches, and fastener spacing is also multiples of that unit size. That way pieces will automatically line up.

Removable Fasteners - Nails are fast to install, but hard to remove. If you don't think you will ever need to change or recycle what you are building, they might be suitable. For semi-permanent items, use screws on a standard grid spacing, and for items that will be changed often, use bolts. Not all holes for screws and bolts need to be drilled in advance, they can be added as needed, as long as the spacing is maintained.

Additional Features

  • Where materials are not an exact multiple, such as studs which are actually 1.5x3.5 inches in size, choose one edge and measure the grid from that edge. Choose a convention such as "the starting edge faces the outside of the building", so items will line up properly. If you are making your own materials, you can make them exact multiples from the start.
  • For wood, center screw and bolt holes in each grid square. Thus for a 1.5 inch grid, they would be 0.75 inches from the edge and end. Where extra strength or rigidity is needed, metal connectors and diagonal bracing can be used. For structures where human safety matters, either building codes or engineered designs should be used. As a first approximation, though, the fasteners should not fail before the structural elements. Since ordinary lumber has a design strength of 1000 psi, and common steel is 18 ksi, the area of fastener should be 1/18th of the area of wood for maximum strength. It can be less where only moderate strength is needed.
  • For roof slopes, stairs, and other angled items, choose slopes that result in even multiples of the grid unit.

Example: Modular Framing Panel

Example 122 x 244cm (4x8 ft) Panel

The 122 x 244 cm (4 x 8 ft) framing panel is an example of the modular concept. A standard plywood sheet and dimensional lumber boards are framed flush at the edges. Longer individual boards or beams are added at the top and bottom of the panels to stabilize walls. Since the panel may be installed and removed multiple times, screws and optionally glue are used to assemble the panel rather than nails in conventional house framing. For this example, two countersunk lag screws would be used at each board to board joint. Countersinking the heads of the lag screws keeps the edges of the module flush. The plywood to board fastening optionally uses construction adhesive (glue), and screws also set flush.

Panel to panel connections are bolted. Make a T shaped template the same height as the panel, with alignment holes at regular intervals on the vertical part of the T. Mark or drill through the template into the panel boards. This ensures that panels have holes in the same location and bolts will line up.

If you are cutting your own lumber with a sawmill, you can substitute individual boards at a 45 degree angle for the plywood sheet. Placing the boards diagonally triangulates the frame and makes it rigid.

Items such as doors and windows can be pre-installed into a module, and panels can be pre-drilled for utilities. Module sizes can vary according to the expected assembly crew. For exterior use, items such as tar paper and furring strips can be pre-installed on the panel, and then vinyl or metal siding screwed on after the panels are assembled. Interior finish and insulation can be similarly panelized and installed after structural assembly.

Another Example

Insulated Component Structures makes prefabricated architectural units, like walls and ceilings and whatnot. They have innovative ways of latching the units together so that 1) you don't need fasteners and 2) they can be taken apart again.

Here's more about companies that make prefabricated panels.