Modular Construction

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Modular construction uses sets of standardised parts in the construction of buildings, vehicles, ... Several systems exist, each with their own parts catalogue.

Examples

Why use standardised parts ?

When using standardised parts (such as standardised beams, sprockets, bearings, ...) you reduce the amount of variation your structures can have. So why use them ? For example, with gridbeam you can only use beams with a size of 1,5-3 inch and a length of 2, 4, 6, or 8 foot. If you don't use any standardised set, you can make designs that use beams (and other parts) that can have any size and length.

The answer is that, the more different types of parts you use in designs, the less valuable each part becomes (as you'll use each specific type of part less often in all of your designs). So once you take the design apart (i.e. when it becomes no longer needed and thus obsolete) each part will be less usable in the other designs and thus less valuable (lower resale value). In practice, that often means that parts no longer get reused at all and ultimately destroyed.

So, using a set of standardised parts is definitely a good idea, but a balance needs to be found so that it uses the least amount of different parts, but still enough of them to allow enough variation of the designs.

What system to use ?

Several systems exist (see examples). Many of these have beams in different standardised sizes. To allow to also make the different parts yourself (rather than always needing to buy them from a manufacturer), it makes sense to use a system that has beams in a size that stays close to the industry component sizes (and these industry component sizes vary per country, so various grid beam systems exist, but the imperial one is still the most common).

For wood-based beams, that means 2x2's (= 2 inch x 2 inch or 5,08 cm x 5,08 cm; actual size is more like 3,8 cm x 3,8 cm though). For metal beams, it makes sense to use whatever industry standard that is closest to the wood-based beams. That means using metal pipes with a 38 mm diameter.

Since gridbeam uses 3,8 x 3,8 cm wooden and metal beams (they're called the 1,5 inch gridbeams), it's easiest to use this commercial system. When making it yourself, you can either buy standard 2x2's (or 38 mm metal pipes) and cut them yourself (to 2, 4, 6, 8 inch length or even any length between 1 and 8 foot, with increments per 1/2 foot).

When making spherical objects, it is best to use a system designed specifically for that. A system with spaceframe nodes is perfect for this. It is useful for polytunnels (greenhouses), ... A system such as the Deltrastructures Axent system could be used.

Features of conventional building materials

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 of modular systems

  • 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.

In practice

  • 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.

This modular construction concept is based on standard practice from the following references:

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

New or alternative concepts can be compared to this reference design, and if found better, then become the new reference design.

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.