INSULFORM EXPANDED POLYSTYRENE HEAVY DUTY THERMOPLASTIC BRIDGE BLOCKS DESIGN INFORMATION
7. DESIGN INFORMATION
The Insulform polystyrene blocks are used to form load bearing walls, beams and
columns where the blocks act as formwork that remains permanently in place as
insulation. Polystyrene blocks have the following advantages.
1. Light to transport and lay.
2. Large modular size, while easy and quick to lay.
3. Provides a very light and smooth walled block that is easy to inspect and
4. Provides a high insulation value to the structure.
5. Provides a wall that is easy to concrete thereby ensuring that concrete does
not hang up as on the likes of concrete blocks.
6. Provides a stable base for approved external plaster systems.
7. Provides a stable wall for fixing internal linings to.
8. Concrete cures inside the polystyrene without losing its mixing water rapidly
like other forms of concrete or concrete block construction. There is
therefore no risk of shrinkage stresses reducing the strength of the concrete.
The expanded polystyrene block faces, and the heavy duty thermoplastic bridges of the
blocks can be expected to satisfy the N.Z.B.C. B2 requirements, provided the blockwork is
prepared and coated with an approved external plaster and covered with internal linings
that are properly maintained for the life of the structure.
The reinforced concrete core has the same durability as a reinforced concrete wall of the
same thickness as the core.
As with all expanded polystyrene the blocks must not be exposed to ketones, esters,
chlorinated hydrocarbons, benzene, fuels, turpentine, ether, or solvents. The approved
coating system must not be over coated with any material that forms a vapour barrier.
Only approved plaster and coatings are to be used to allow the blocks to evaporate any
moisture from within the wall.
The expanded polystyrene melts with excess heat, so should be separated by a ventilated
cavity or concrete, from chimneys, ovens, heaters and other hot items.
The Insulform block wall system is suitable for all types of residential, commercial, and
The blocks are formed from fire retardant polystyrene so that the polystyrene shrinks and
melts away from a normal ignition source without catching fire. However where an
intensely hot ignition source such as an oxyacetylene flame jet is concentrated onto the
foam, and melted foam, it is possible to get the vapours to burn.
7.4.1. Outbreak of Fire
Insulform Polystyrene Block Reinforced Concrete Walls contain combustible
components. To meet the performance requirements of NZBC C1 they need to
be protected from heat sources such as chimneys, solid fuel heaters and flues.
Manufacturers of these products must be consulted to determine the appropriate
protection measures (e.g. ventilated cavity) so that the Insulform blocks are not
subject to temperatures above 50°C.
7.4.2. Spread of Fire
Insulform Polystyrene Block Reinforced Concrete walls can be used to meet the
relevant provisions of NZBC Clauses C3.3.1, C3.3.2 and C3.3.5 when the
Internal surface finish requirements shall be as required by Table 4 of NZBC
C3/AS1 where used for SR or SH Purpose Group buildings no special
Where used in Purpose Groups SC and SD special requirements apply. These
special requirements are detailed in Clause 4.5 which follows and include the
mechanical fixing of internal linings to timber inserts or the metal webs of the
Insulform blocks. These fixing requirements apply to both sides of internal walls
and to the inside only of external walls.
The external surface finish requirements shall be determined from Table 2 of
NZBC C3/AS1. These are governed by the surface finish type, building height (as
defined in the Annex to the Fire Safety Documents), the distance from the
relevant boundary and the properties of the cladding system.
Insulform walls finished with Insulclad Plaster System for EPS block walls
and coated as required below may be used wherever an Ignitability Index of 0 is
required in Table 2 of C3/AS1.
External Insulform Polystyrene Block Reinforced Concrete Walls, finished
with an approved Plaster System for EPS block walls will have an Ignitability
Index of 0 provided they are coated with approved plasters or one of the following
? Insulcote 100% acrylic paint.
? Formstone acrylic plaster.
? Colorplast pre-coloured plaster.
There are no requirements for External Polystyrene Block Reinforced Concrete
Walls, covered with a solid plaster in accordance with N.Z.S.4251:Part 1:1998 and
finished with a latex based paint coating system which is less than 1.0mm thick.
The special requirements applying to Insulform walls used in Purpose Groups SC
and SD are as follows:
? One layer of 12.5mm thick standard Gib plasterboard or better must be
installed in accordance with requirements to give at least a one way Fire
Resistance Rating (FRR) of 15 minutes. Suitable details are contained in
Winstone Wallboards Ltd’s Gib Fire Rated Systems, dated July 1997. This
detail calls for the plaster board to be mechanically fixed to timber inserts
anchored to the concrete substrate. The minimum size timber insert shall be
200mm x 50mm anchored with a minimum of 2-100mm FH skew nails. There
is an alternative fixing for these purpose groups shown on Page 29.
? The EPS must be totally sealed from the interior areas of the building and any
ceiling cavities by fire stopping. Any penetration passing through the fire rated
wall must be fire stopped to a FFR of no less than that required for the building
element in which it is installed.
? In multi-storey buildings (i.e. more than two floors) fire stopping must be
provided at each floor level at the junction of floor and external wall.
7.4.3. Fire Resistance Rating
Insulform Polystyrene Block Reinforced Concrete Walls have a fire resistance
rating (FRR) based on the thickness of concrete walls as follows:
Wall Concrete Thickness FRR
100mm thick wall 90/90/90
150mm thick wall 180/180/180
200mm thick wall 240/240/240
The normal range of blocks is as follows:
Length 1 metre
Widths 200mm for 100mm concrete core
250mm for 150mm concrete core
300mm for 200mm concrete core
Other widths can be manufactured to fulfil a bulk special order.
Walls consisting of Insulform blocks, reinforced concrete, 3mm external plaster finish
(Insulclad) and 9.5mm (Gib Board) internal linings weigh:
270 kg/sq metre for 100mm concrete core
390 kg/sq metre for 150mm concrete core
510 kg/sq metre for 200mm concrete core
If the external plaster finish is solid plaster in accordance with N.Z.S.4251:1998 then these
weights must be increased by 45kg/m².
7.7. Insulation Value
A 100mm concrete core Insulform block wall system with external plaster and internal
plasterboard linings has a thermal resistance of at least 2.9 square metres °C/W.
A 150mm concrete core Insulform block wall system with external plaster and internal
plasterboard linings has a thermal resistance of at least 3.0 square metres °C/W.
7.8. Structural Strength – Non Specific Design
The building scope shall be as defined by clause 1.1.2 of N.Z.S 3604;1999
Construction is to be in accordance with N.Z.S.3604:1999 except as varied
? All external walls shall be Insulform walls. Or timber framed (2nd storey).
? Internal walls may be Insulform or timber framed walls built in accordance
with N.Z.S. 3604:1999.
? Foundation walls must be 250mm thick (minimum) Insulform walls built in
accordance with the Insulform Manual.
? Floor to ceiling heights can be up to 2.5m.
? These details shall apply to the following buildings:
- Single storey buildings based on 100mm thick or thicker concrete
- Two storey buildings where the lower storey is of 100mm thick
concrete Insulform walls and the upper storey including the floor is
light timber framed construction conforming to N.Z.S. 3604:1999.
? If 100MM thick or thicker concrete core Insulform block walls are to be used
for the lower and upper walls of two storey construction with a timber floor or
concrete floor, a specific design is required for bracing, lintels, foundations
and concrete floored. Refer to Engineer’s Design Information of Page 30.
7.8.2. Bracing Requirements
These are determined as follows:
? Wind – Tables 5.3 to 5.7 of N.Z.S. 3604:1999
? Earthquakes – Tables 5.8 to 5.10 of N.Z.S. 3604:1999
7.8.3. Bracing Resistance (Ratings)
Bracing ratings shall be those for reinforced concrete walls of N.Z.S.3604:1999,
except that, 100mm thick concrete core Insulform block walls have a rating of 120
bracing units per metre if the top of the storey in question finishes with a ceiling
diaphragm, built in accordance with Paragraph 13.5 of N.Z.S.3604. A value of
200 bracing units per metre can be used for lower storey walls, having a first floor
particle board diaphragm built in accordance with Paragraph 7.3 of N.Z.S.3604.
These strengths are governed by the ceiling diaphragm or the floor diaphragm
respectively, as the concrete wall formed is stronger
The minimum length of wall for the above to apply is 0.5m.
Insulform walls must be evenly distributed around the perimeter of the building
otherwise a specific design will be necessary.
Internal Timber framed walls can be used to provide bracing resistance to
Insulform walls. The bracing resistance provided by these shall be determined by
NZS3604:1999 or the latest version of theGib “Ezybrace Systems” manual.
Floor diaphragm connections to Insulform walls shall be as detailed in Figure 9.5
N.Z.S.4229:1999 except that the stringer or a square timber pack shall be bolted
directly to the concrete by cutting away the EPS.
Ceiling and roof diaphragm connections shall be as detailed in Figs 9.2 and 9.4 of
N.Z.S.4229:1999, except that connections shall be bolted directly to the concrete
by cutting away the EPS, load bearing members at the top of the wall shall be
located directly against the concrete.
8. ENGINEER DESIGN INFORMATION
8.1. Structural Strength – Specific Design
The strength of structures can be determined by designing to the NZS 3101: Part 1 and
Part 2: 2006 “New Zealand Standard – Concrete Structures Standard”.
The design of walls, beams and columns shall be carried out to the above standard
except that he strength reduction factor, ? , for shear and torsion shall be 0.65 to allow for
the effects of the bridges.
Enclosed are tables for the following that can be of assistance with a specified design.
- Insulform face loaded capacity Design Aid 1
- Insulform lintel and beam capacity Design Aid 2
- Insulform shear wall capacity Design Aid 3 and 4
- Insulform wall interaction diagram Design Aid 5 and 6
8.2. Structural Limitations
All loads must be transferred directly to the concrete, not the polystyrene.
Bolt fixings and all other fixings must be designed to allow for any extra eccentricity due to
the polystyrene spacing a load away from the concrete where the fixings is not bolted
directly to the concrete.
The blocks need to be braced against the wind and site working loads during erection as
pour heights up to 3m are achievable.
Small square or circular openings may be placed at mid depth of beams provided the
reinforcement still has adequate cover and the holes are at least 200mm apart. These
shall be no more than 32mm sq or 26mm diameter. Penetrations in wall may have the
same size, spacing and cover as beams but shall be at least 300mm away from any wall
edge. Larger holes may be permitted by Design Engineer subject to specific design.
8.3. Further Information
Reference should be made to the relevant section of the insulform manual for more
detailed information such as plaster specification, standard drawing details etc.
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