7.1 Slabs and Strip Footings

Site Classification

Site Classifications are generally carried out for new housing developments, be they part of a subdivision or an individual allotment. The purpose of the site classification is to assess the subsurface conditions and therefore enable determination of the most appropriate foundations/floor slabs (i.e. the classification will generally determine the appropriate dimensions for house footings and / or floor slabs).

Site Classification is carried out in accordance with the Australian Standard AS2870-1996: “Residential Slabs and Footings”.

The available Classes include S (slightly reactive), M (moderately reactive), H (highly reactive), E (extremely reactive), or P (problem site). Classes S, M, H, and E refer generally to sites in which clayey soils will form the founding strata. The classification indicates how reactive the clay subsoil is to changes in moisture content. The reactivity (shrinking and swelling) of the clay can have a significant impact on the footings/slabs of a building slab, which need to be designed to counteract the movements of the clay soils.

Sites classified as Class P generally present difficulties for the proposed construction. The Pclassification more often than not suggests deep and/or uncontrolled fill, which cannot provide suitable bearing for the house. In these situations, the house is either founded on the stable materials beneath the fill (i.e. deep footings/piers), or the fill is removed and replaced with compacted, controlled fill.

Slab Design

All Hebel PowerBlock homes must have footings and slabs designed to AS 2870 “Full Masonry”. Local engineering advice should always be sought.

Fig 7.1.1 Isometric Concept House

 Fig 7.1.2:  Slab on Ground

Table 7.1.1 Slab on Ground

GENERAL NOTE: This table is to be read in conjuntion with the requirements of AS2870 and AS3600.

NOTES: 1. A 10% increase in the spacing is permitted where the spacing in the other direction is 20% less than specified.

2. Where the number of beams in a particular direction satisfies the requirements of the maximum spacing given above, the spacing between individual beams can be varied provided that the spacing between any two beams does not exceed the spacing given in the above figure by 25%. These allowances for increased beam spacings do not override the maximum spacings between edge beams and first internal beams as required by clause 5.3.9.

3. For two storey timber framed floor or Hebel floor panel construction, the width of the edge beams must be increased by 100mm and the bottom reinforcement must be increased by one bar of the same diameter.

Fig 7.1.3:  Strip Footing, Double Brick Sub-Floor Fig 7.1.4:  Strip Footing, Concrete PowerBlock Sub-Floor Table 7.1.2 – Strip Footing

GENERAL NOTE: This table is to be read in conjunction with the requirements of AS2870 and AS3600.

NOTES: 1. For all beams 700mm or deeper, as specified in the table above, internal footings shall be provided at no more than 6m centres, and at re-entrant corners to continue the footings to the opposite external footing.

2. Internal strip footings shall be of the same proportions as the external footing and run from external footing to external footing ‘side slip joints’ consisting of a double layer of polyethylene shall be provided at the sides of the footing only.

3. Provide ventilation to the sub-floor in accordance with the BCA.

Sub-Floors On Elevated Sites

Hebel PowerBlock must not be used at or below ground level. When building a Hebel PowerBlock structure on a sloping site that is not suitable for a concrete slab, a solid core-filled concrete block or brick substructure may be erected on a strip footing to raise the building and floor system to a level that is clear of the ground resulting in a level building platform that allows sufficient airflow under the floor.

The first course of Hebel PowerBlocks must be laid on a DPC to stop rising damp and to act as a bond breaker between the different building elements.

Termite Protection

Hebel PowerBlocks are not a food source for termites. Solid wall construction still requires termite protection. There are many methods to protect your home against a termite invasion and a qualified professional pest control should be consulted to determine the most suitable method for your design.

The Building Code of Australia recognises an exposed slab edge to a depth of 75mm above finished ground level as adequate termite prevention.

For masonry sub-floor construction a continuous ant cap installed between the brick/ concrete block work and the Hebel PowerBlock also satisfies the Building Code of Australia termite protection requirements.

7.2 Hebel PowerBlock Walls

Generally, the minimum recommended wall thickness is:

• 250mm for external walls
• 150mm for internal load-bearing walls.
• 100mm for internal non-load bearing walls.

Hebel suggests considering a wall as having top and bottom lateral restraints only (one-way vertical span) and designing the appropriate wall thickness, so that retrofitting or changing the location of the movement joints will not be detrimental to the lateral load capacity of the wall. In determining the appropriate wall thickness, the designer shall consider a range of factors relating to relevant codes and project specific considerations, these factors may include:

• Movement joint location
• Bracing considerations
• Vertical (compression) loading
• Out of plane wind/earthquake (lateral) loading
• Required fire rating level (FRL).

The particular project loading configurations could result in walls that exceed the above minimum requirements.

Ring Beam (for standard trussed roofs)

A ring beam must be provided at the base and top of perimeter Hebel walls. The ring beam is 60mm x 60mm with 1N12 bar centrally located. Shear connection ties are to be placed at the location of control joints at 600mmspacings (vertically). See Fig 7.2.1 for ring beam details.

Fig 7.2.1 Typical Hebel Ring Beam Detail

Bond Beam (for vaulted roofs)

A bond beam is a continuous beam around the perimeter of a building for the purpose of providing lateral stability and bracing to the walls for vaulted/cathedral roofs, to minimise cracking at openings. As a minimum, bond beams are to be located at the top of the walls for each floor level, or at a maximum vertical spacing of 3m. Bond beams are constructed of reinforced concrete which is poured in situ between two Hebel PowerBlocks. The minimum dimension of the bond beam must be 100mm wide and 200mm high. Bond beam reinforcement should be not less than 2 rows of 12mm deformed bars placed top and bottom in the centre of the beam (overlapped at least 400mm where it joins).

Bond beams must be continuous around a built-in corner. The ring beam at the base is still required. See Fig. 7.2.1.

Fig 7.2.2 Typical Hebel Bond Beam Detail

Compression

The assessment of Hebel PowerBlock wall compression capacity in this Design and Installation Guide is based on the scope of this design guide (see Section 6.0 and Table 6.1). Three top support conditions are applicable:

1) Supporting concrete slab above (see Section 14 and Fig. 14.26)

2) Supporting floor other than concrete slab above (see Section 14 and Fig. 14.28)

3) Face supported framed floor (See Section 14 and Fig. 14.27)

No vertical support of the wall is considered as worst case in the compression capacity assessment. Under that constraint and for wall heights up to 3000mm:

• 250mm load-bearing external PowerBlock walls have adequate compression capacity for all top support conditions.
• 150mm load-bearing internal PowerBlock walls to 3000mm height have adequate compression capacity for the first two top support conditions, but is not suitable for face loaded framed floors. If face loaded timber framed floors are designed both sides of the wall, their spans are within 20% and loading is the same, this can be considered top support condition 2. Otherwise 250mm Hebel PowerBlock wall is required.

Roof loading on top of the wall through the top plate is considered top support condition 2.

Bending

250mm Hebel PowerBlock walls up to 3000mm height have adequate bending capacity without edge support in wind classifications N1 to N3.

Table 7.2.1 provides maximum wall lengths between edge restraints for wind classifications N4 to N6 and C1 to C4. Both ends of these walls must have edge support.

Edge support must be an engaged perpendicular wall (bracing wall) or a built-in 89x89x5 SHS column. The designer must detail the plate connections at the base and top of the SHS column and specify adequate ties to the Hebel PowerBlock work.

Shear

Horizontal forces, such as wind and earthquake loading, applied to a building are to be resisted by bracing walls. Bracing walls are located generally at right angles to the walls subjected to these forces. All bracing components in the building shall be interconnected to adequately transfer the imposed loads to the footings.

Table 7.2.1

Refer to Appendix K in AS3700 for total ultimate racking forces for houses in wind classifications up to N4/C2. Those tables are based on wall height up to 2700mm. For wall height greater than 2700mm up to 3000mm, factor up the loads by 15%. Earthquake categories H1 and H2 are covered by N3/C1 tables and earthquake category H3 is covered by N4/C2 tables.

Table 7.2.2 provides ultimate racking capacities of unreinforced 150mm and 250mm Hebel PowerBlock walls. This table does not include sliding which the designer must also check depending on compression loads on wall in all wind cases and dowel action at base of wall through hold-down rods.

Lintels General

The minimum bearing lengths at the end of all Hebel lintels is 150mm or L/8, whichever is greatest. The bearing PowerBlock must extend past the end of the lintel by min. 100mm.

Hebel Lintels

Hebel lintels are reinforced sections similar to panels. The lintels are used as supports over doorways, windows and other opening.

Lintels shall be installed so that the surface marked ‘THIS SIDE UP’ is uppermost, as the section reinforcement may not be symmetrical. Hebel lintels are not to be cut on-site.

Table 7.2.4 presents the range of standard Hebel lintels and the associated capabilities.

For larger spans, use structural steel lintels as designed by the project structural engineer.

Steel Lintels

Can be used to support PowerBlock work above openings. refer to Tables 7.2.5 and 7.2.6.

Control Joints

During the life cycle of a building, the building and the materials that it is constructed from will move. These movements are due to many factors working together or individually, such as foundation movement (shrinkage and swelling), thermal expansion and contraction, differential movements between materials, climate and soil condition. This movement, unless relieved or accommodated for, will induce stress in the materials, which may be relieved in the form of cracking. To accommodate these movements and relieve any induced stresses, control joints (vertical gaps) shall be installed to minimise cracking in Hebel masonry walls.

Location of Control Joints

Where control joints are required they are best positioned:

• At no more than 6m spacing unless more stringent requirements are specified in accordance with AS 2870.1996.
• At intersecting walls and columns.
• At changes of wall height or thickness, or where chases occur.
• To coincide with movement joints in adjacent elements of structure (floor or roof)
• At junctions of dissimilar materials
• Where architectural or structural features create a ‘weak’ section.

Movement joints are not normally required below DPC level.

Construction of Control Joints

Straight, unbonded vertical joints are the most common type of control joint. Typically, the vertical joint is 10mm wide and filled with an appropriate backing rod and flexible sealant.

Where stability of the design requires continuity across the joint, Hebel control joint ties should be set in every second bed joint.

Movement joints must be continuous through the entire block wall and all surface finishes. When the control joint is aligned with a window or door opening, the joint must be continuous and may need to be offset to deal with the lintel spanning the opening. In such a case a slip joint must be provided under that end of the lintel. Control joints must also be continuous through any bond beams which have been installed in the wall. This can be achieved by breaking the bond beam at this joint during it’s construction. To maintain lateral strength and continuity of the bond beam, the reinforcing rods should bridge the joint with one side of the beam having conduits cast in for the rods to slide while still keeping the wall in plane.

The control joints should be installed as the wall is being constructed as the joint ties must be installed in the centre of the block ensuring the tie is fully bonded with Hebel adhesive.

Service Penetration

To penetrate services through Hebel walls, core out an appropriate sized hole (typically 10mm larger diameter than the service) and run the service through. A flexible sealant should be used to seal the gap around the service, this will also prevent any cracking/movement issues that may occur with the stress imposed on the blocks if the services were placed hard against the Hebel PowerBlock.

For penetrations through fire rated walls, an appropriate fire collar must be used with fire rated sealants. To affix the services to the Hebel walls please refer to the fixing guide in this manual.

Chasing Services Into Hebel

• Services should be run through cavities where possible to avoid unnecessary chasing into Hebel.
• Where chasing is necessary some basic guidelines need to be followed.

– All Hebel products 100mm or less must not be chased

– All chases must comply with the BCA

– The depth of the chase must not exceed 25mm

– The width of the chase must not exceed 25mm

– The maximum number of chases allowed is 2 chases per 1 metre length of wall.

– All chases must be backfilled with a material that will adhere to the wall (Hebel Patch or a sand /cement patching mix).

– Chasing can be done with a Hebel Hand Router or a power router fitted with dust extraction.

 Table  7.2.2 Unreinforced Wall

 Table 7.2.3 Top-Plate & Hold-Down selection Table

Table 7.2.4: Lintel Selection – Hebel Lintel

 Table 7.2.5: Lintel Selection – Equal Angles

Table 7.2.6: Lintel Selection – Galintel

7.3 Floor Panel Systems

Hebel Floor Panels are reinforced AAC panels designs as loadbearing components in commercial, industrial and residential construction applications.

A preliminary thickness of the floor panel can be determined from table 7.3.1 in this guide. Contact your local distributor to confirm the selected floor panel thickness is adequate for the design parameters of span, load, deflection, limit and fire resistance level rating.

After the panels are laid, reinforcing bars are placed between the panels in the recess and around the perimeter of the floor to form the ring anchor system in accordance with Hebel specifications.

The joints and ring anchor sections should be lightly pre-wetted, filled with minimum 15 MPa concrete grout, and rodded to ensure complete and level filling of the notch and groove. A mix of CI:S3:A2 (5mm maximum coarse aggregate) with 150mm slump is usually suitable. The grout should completely cover the reinforcing.

The hardness of Hebel Floor Panels is greater than the PowerBlocks. When ring anchors are placed accurately and mortar is poured carefully and screeded properly, the surface is level and smooth.

When Hebel panels are used in external floor areas such as patios or balconies, it is important to use an approved waterproofing membrane.

Hebel Floor Panels provide an excellent, solid, stable base for tile, slate, marble and other hard surface flooring, including bathroom, laundry and other wet area applications.

The smooth flat surface is also perfectly suited to carpet, vinyl, timber boards, parquetry and decorative plywood flooring.

Panels in General 

Panels should not be cut on site unless they are ordered as cuttable. It is preferred they are ordered from the factory at the desired length. Where panels have been cut the exposed reinforcing should be with coated with Hebel corrosion protection compound or an approved equivalent.

Hebel panels are supplied ready for use. They can be simply and easily laid into position with only the joints needing to be mortared. Installation is therefore largely dry and generally no formwork or bracing is necessary. The reinforcing in the panels is custom designed for each project.

Panels installed on Hebel PowerBlock work or steel beans can offer a flooring system that can be laid down exceptionally fast. As well as providing the benefits of rapid construction, differential movement between floors and walls is minimised.

Framed Floors

Hebel PowerBlock construction can incorporate floor construction using joists. Typically the joists are installed onto bearing plates which distribute the floor loads evenly into the supporting blocks. Hebel PowerBlocks are easily shaped to infill between the joists. The infill blocks will provide support for the blocks above the floor framing.

Image 7.3.1:  Installed Floor Panels
Table 7.3.1: HebeL Structural Floor Panels

With Flexible Coverings / No Walls Above (L/250 deflection)

With Rigid Coverings / Walls Above (L/600 deflection)

NOTES TO FLOOR PANEL TABLES:
• Length is calculated based on the minimum bearing.
• Minimum bearing is panel length /80 but not less than 60mm.
• Maximum clear span is panel length less than 2x minimum bearing.
• (Length) is maximum standard panel length in metres.

Image 7.3.2:  Installed Floor Panels

7.4 Decks, Verandahs and Pergolas

When attaching a deck, verandah roof or pergola to your Hebel PowerBlock Wall, the building designer / project engineer must calculate and determine the loads that will be imposed on the Hebel PowerBlocks. For conditions equal to or less than those outlined in table 7.4.2, a timber or steel waling plate may be attached to the block wall as shown in Section 14 details 14.34 and 14.35. This must be affixed using the appropriate number and type of fixings as outlined in Tables 7.4.1 and 7.4.2. The fixings must be either Fischer Injection Mortar 10mm x 80mm long or Ramset Injection Mortar 12mm x 160mm long.

Where the loads that will be imposed on the waling plate exceed the table or the structure is to be detached from the Hebel PowerBlock Walls, a detached post and beam structure may be erected adjacent to the Hebel wall which will ultimately transfer the load directly into the foundation. This type of construction must be designed and certified by the project engineer.

Table 7.4.1 Deck/Verandah Floor Walling Plate Connection

Table 7.4.2 Roof Walling Plate Connection

Note:  Walling plate span capacity to be checked by building designer project engineer. 

Image 7.4.1:  Decks, Verandahs and Pergolas