Structural System

Traditional joists and rafters are cut from trees that are on average 75 years old. This is the prime reason for the pressure on old growth forest. The objective is to eliminate the use of joists and rafters, along with their engineered lumber counterparts, without affecting the structural integrity of the building.

The Wentworth Project uses a Polymorph Structural Framing System (PSFS). This is a simple to assemble modular unit, comprised of 8-foot x 8-foot panels for subfloors, roof or walls, along with box beams suitable for structural frames for houses, barns, retail space and workshops.

Load-bearing boxbeam grid being assembled in Wentworth

Framing grid being built at an associated
project using Plant-Era technology

The PSFS saves wood without compromising on strength, and yields cavernous interior spaces. This simplified modular wood framing system reduces both the overall volume and diameters of lumber needed to frame a home.

Further design criteria were longevity, simplicity of installation, and inexpensive enough construction to be affordable to home owners.

The polymorph framing system yields cavernous indoor spaces. This view looks down two stories to the bio-shelter.		The polymorph framing system can be used for exterior walls. Here, pre-built frames are positioned vertically and horizontally with all remaining spaces filled by windows.

PSFS Construction

The PSFS is made up of re-engineered box beams, panels and posts which replace joists, rafters and stud walls. This approach eliminates any need for the 2x10 or 1x12 inch lumber used in traditional joists and rafters, replacing it with box beams made with lumber as small as 2x2 inches. The box beams are set on 4-foot centres instead of the 16-inch centres of traditional framing.

Box beam interior view. The inclusion of joinery allows us to eliminate
double flanging making the beam lighter and simpler to assemble.

The webs of the box beams are made of structurally rated sheathing. The use of the polymorph grid for structural framing eliminates the need for double flanging in box beams and also reduces the height of box beam webs. The web carries the load, while the 2x4 or 2x6 inch beams are nailed into the edge of the lumber. The glue bond of the web gives the box beam its added strength.

Using carrier beams, into which the joist beams plug into at right angle, eliminates the need for long beams. Carrier beams act like a load-bearing wall so cavernous interiors have been realized for open floor plans with no reduction in structural integrity.

Constructing a box beam on-site. Glue is applied to tack down the plywood web,
which will be fastened securely into place using a nail gun.

Continuation of box beam assembly. Plywood web is now being installed.

Benefits

The Polymorph Structural Framing System provides numerous benefits to the owner-builder or contractor.

1. It reduces the wood needed in construction by 35%.

2. Each house built using this system saves half a hectare of mature trees.

3. In fact, the combination of rigid beam and joinery will withstand earthquakes better than conventional wood-framed housing.

4. Costs are under Cdn$20 (US$13) per square foot for an insulated, sheathed structure, with a roof, subfloors, etc.

5. This type of framing also enables easier installation or modification of plumbing and electrical systems, since pipes and wires can run inside the hollow boxbeams.

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Box Beam Joinery

Box beam joinery options that make it easy for even a semi-skilled handyman to assemble the various modular framing components.

Box beam joinery connections between joist and carrier beams. Joinery allows us to use beams of conventional length lumber that lock into the carrier for a cavernous space with no load bearing walls to impede the eye, ideal for open floor plans or contemporary architecture.

Double tongue & extra long.

Electrical conduits or plumbing pipes can be included
to facilitate retrofits or upgrades to the building.

Timber frame look-a-like joinery.		Double lap joinery for heavy loads and single lap joinery for lighter loads.

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Alternatives to Lumber

In some countries, lumber is too expensive to use in construction. Fortunately, those nations usually have an abundant supply of sugar or bamboo cane fibres, which can be used to form the structural sheathing for box beam webs and semi-stressed skin panels.

Advanced polymorph framing is being developed to take advantage of other types of sheathing such as oriented strand board, sugar cane and hemp hardboard, or a combination of sugar and bamboo cane fibre board for use in the box beams, panels, and posts.

The box beams undergo rigorous load bearing tests at
McGill University Engineering Labs.