Intermediate fl oors

8.4.1 Concrete

Min 100mm bearing onto concrete core

Top of concrete pour Floor finish as required

Figure 8.11 Precast/in-situ plank fl oor cast into an ICF wall.

Support must be given to the edges of the infi ll blocks or pots, the support being provided by the core and not the polystyrene formwork. The bearing provided by the concrete core should not be less than the bearing provided by the fl ooring system support beams (see Figure 8.12).

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73 Bearing of outer block

to be a min of ‘X’ but not greater than Z

2

X

Z

Figure 8.12 Precast beam and block fl oor to an ICF wall.

Timber joisted fl oors are most easily fi xed by simply cutting slots in the formwork, into which the joists are directly inserted, and the joists cast in during the pour. The joists should have a minimum bearing of 50mm, or reach halfway across the core, whichever is the greater (see Figure 8.13).

If there are joists on both sides of the wall, they should be staggered to ensure the joist ends are not in contact, and any cut ends specifi ed as treated with preservative. Irregular-shaped composite joists and concrete beams can also be installed in this manner, but extra time and care will be needed to make good around the more complicated cut-outs.

8.4.2 Timber

Floor joist with straps inserted into preformed pockets Horizontal and vertical

reinforcement

Termite shield

Exterior finish

Finished ground

Figure 8.13 Section through wall with embedded timber

fl oor.

The ICF method is well-suited for casting in the fl oors as part of a continuous pouring sequence. The pour can be stopped temporarily just below the level of the underside of the joists, to be continued after any fi nal adjustments to the fl oor. In such cases, the lift should be terminated 50–75mm below the joist-bearing level. If the fl oor is propped, this will allow the continuation concrete pour to fl ow beneath the joists, giving a full bearing and solid fi xing. Alternatively, the joists can be levelled and bedded onto mortar packs before the next lift is resumed.

8.4.3 General

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If the fl oors are not to be cast in with the walls, or if the fl oors are required to be separated from the walls, e.g. to improve acoustic performance, a timber stringer can be used to support the joists. The timber stringer is fi xed to the walls by cast-in J- or L-bolts, which then supports the fl oor. This provides a true simply supported fl oor structure (see Figure 8.14).

Because the stringer is supporting the fl oor, it is essential that it is connected directly to the concrete and not fi xed through the polystyrene formwork. This is to avoid any possibility of movement caused by compression creep of the polystyrene over time. The direct bearing to the concrete is achieved by cutting out pockets from the inner formwork face behind the ledger before the core is concreted. The stringer is fi tted with the J-bolts, aligned with the cut-outs and positioned against the formwork. The pockets fi ll with concrete when the wall is poured, casting in the fi xing bolts, and ensuring solid support to the back of the stringer as shown in Figure 7.6.

An alternative method, which is ideally suited for taller structures where the wall section is reduced for the upper storeys, is shown in Figure 8.15. A similar effect, useful where the wall section is not reduced, can be achieved by the use of corbel sections, referred to previously in Figure 8.5, which showed its use for supporting external brickwork.

Reinforcement

Cut out foam

@ 45 deg.

ICF forms

Anchor bolts as per spec

1st floor joist

Joist hanger 2 x timber ledger

7’’ (178mm) (min)

Figure 8.14 Section through ledger support.

Floorboarding

Floor joists

Rim joist

Treated sill plate

Hand cut tapers

Figure 8.15 Floor support by internal corbel system.

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Where the joists run parallel to the wall, restraints to prevent lateral movement must be provided. In masonry construction, this is usually achieved by retro-fi xing L-shaped steel straps to the underside of the joists, and screw-fi xing them to the face of the wall below.

In ICF construction, retro-fi xing to obtain a direct connection to the concrete core would involve stripping away part of the formwork.

A more convenient method, when fl oors are not constructed at the same time as the supporting walls are cast, is to fi x the straps to the upper surface of the joists/concrete beams during the installation of the fl oor, and locate the vertical leg upwards into the centre of the concrete core above the joist level, to be cast in with the next pour (see Figure 8.16).

8.4.4 Lateral restraints

Screed

30 x 5 galvanised M.S. straps

FFL

1stpourContinuationpour

Figure 8.16 Example of a lateral support tie.

A robust fi xing is provided by drilling the wall plate to take rag, J- or L-bolts. After fi tting the washers and bolts, the wall plate and bolt assembly is located at the top of the form immediately the pour is completed, ensuring the bolts are fully immersed and the plate is solidly bedded onto the fl uid concrete – see Figure 8.17. The locations of the holding-down bolts should be specifi ed so as not to interfere with the rafters and joists. This method of fi xing the roof structure to the walls dispenses with the need for the holding-down straps used in masonry construction.