Punched Nail Plate Joists Rafters And Purlins

Initially developed in the USA and Canada for long span floor and flat roof joists, the product consists of an upper and lower timber chord spaced apart by special metal 'V' pressings which at the top and bottom of the 'V' have punched nails similar to the trussed rafter connector plate. When pressed into the top and bottom flanges or chords, these 'V's produce a lattice girder.

The advantages:

(1) The economic use of timber.

(2) A precision engineered component.

(3) Easy installation of services such as electric cables, plumbing pipes, and small ducts through the lattice.

(4) Wide fixing chords for floor and ceiling decking.

Best Rafter Nail

Plywood sarking fixed to top of rafters over entire roof slope. Noggings provided at all unsupported board edges.

Plywood fixed to underside of rafter on sloping ceiling only. Noggings provided at ply edges.

Plywood panels between rafters fixed to 50 x 50 frame fixed to rafters. Fix ply at ends to blocking between rafters. Minimum 25 mm air gap between top of ply and top of rafters.

Line of ceiling slope change.

Plywood panels incorporated to provide continuation of notional line of rafter diagonal brace.

SANG-NAIL.

Fig. 7.15 Raised tie bracing.

Plywood sarking fixed to top of rafters over entire roof slope. Noggings provided at all unsupported board edges.

Plywood fixed to underside of rafter on sloping ceiling only. Noggings provided at ply edges.

Plywood panels between rafters fixed to 50 x 50 frame fixed to rafters. Fix ply at ends to blocking between rafters. Minimum 25 mm air gap between top of ply and top of rafters.

Line of ceiling slope change.

SANG-NAIL.

Plywood panels incorporated to provide continuation of notional line of rafter diagonal brace.

Fig. 7.15 Raised tie bracing.

(5) The same component can be used for joists, rafters, purlins, etc.

(6) No on-site waste because the component is manufactured to a precise requirement.

(7) Can be designed to span clear between external walls without internal load bearing partitions and their associated costs of additional foundations.

(8) Can be designed for top or bottom chords support.

(9) A considerably improved product weight/span ratio compared to solid timber.

One of the first truss system manufacturers to produce a similar product was Gang-Nail who many years ago produced a product called 'Econoflor'. This earlier version of the 'V' lattice beam used timber lattice members connected to the top and bottom chords with the same punched metal connector plates as used for trussed rafters. The labour content in cutting the numerous small lattice timbers and indeed placing them in special jigs made the product less than economically viable compared to conventional solid timber, and at that stage Gang-Nail had problems in convincing the authorities of its performance in fire. Gang-Nail have now reintroduced this construction under the name 'Eco-floor'. They claim it is now a viable product compared to the alternative forms of manufactured joist where the floor zone is limited to approximately 200 mm.

Gang-Nail have since produced a new product called SpaceJoist, illustrated in Fig. 7.16, using the metal 'V' nail plate construction. MiTek have a similar product called Posi-Strut; this is illustrated in Fig. 7.17 showing a typical joint detail for attic roof construction using the Posi-Strut for floor joist and rafters.

Trimming for openings can be simply done as illustrated in Fig. 7.17. MiTek concentrate on the production of Posi-Strut with a few of their fabricators who specialise in the product, investing in the dedicated jigs required, thus making them highly efficient and improving the cost effectiveness of the component.

One of the initial objections to the use of lattice joists as mentioned above is the spread of fire through the floor or rafter void. Testing has been done by both Gang-Nail and MiTek who have developed approved constructions for up to one hour fire

Plywood gusset

Plywood gusset

Chipboard flooring

Clearspan SpaceJoist truss

Fig. 7.16 SpaceJoist attic.

Chipboard flooring

Clearspan SpaceJoist truss

Fig. 7.16 SpaceJoist attic.

ROOFING FLOORING

Type of assembly of truss foot: Posi-Strut with the principal rafter on roof beam and return of load moving horizontally.

Milek Indusrw;s Lis

Fig. 7.17 Posi-Strut details.

resistance for use as floor joists, thus clearing obstacles from the path of those wishing to specify this relatively new building product.

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