FLAT GRID OR WAFFLE SYSTEM
Sinhagad College of Architecture
This Presentation is compiled by:
What is Flat Grid Slab / Waffle Slab System ?
• A waffle slab is a type of building material that has two-directional
reinforcement on the outside of the material, giving it the shape of the
pockets on a waffle.
• This type of reinforcement is common on concrete, wood and metal
construction. A waffle slab gives a substance significantly more
structural stability without using a lot of additional material.
• This makes a waffle slab perfect for large flat areas like foundations or
• The top of a waffle slab is generally smooth, like a traditional building
surface, but the underside has a shape reminiscent of a waffle.
• Straight lines run the entire width and length of the slab, generally
raised several inches from the surface.
• These ridges form the namesake square pockets of the entire length
and width of the slab
Where this system is used ?
• Waffle slab can be used as both ceiling and floor slab. They are used in the areas where less number of columns are
provided, i.e. it is basically used in th areas which has huge spans.
• Waffle slab is not used in typical construction projects. They are used for specialized projects that involve clean rooms,
spaces requiring seclusion from low frequency vibration or those needing low floor deflections.
• The concrete waffle slab is often used for industrial and commercial buildings while wood and metal waffle slabs are
used in many other construction sites.
• This form of construction is used in airports, parking garages, commercial and industrial buildings, bridges, residences
and other structures requiring extra stability.
• The main purpose of employing this technology is for its strong foundation characteristics of crack and sagging
resistance. Waffle slab also holds a greater amount of load compared with conventional concrete slabs.
Features of the Waffle Slab
The features of the Waffle slab are as follows :
• They are used on flat sites
• They are wholly above ground
• No beam excavation is required
• No controlled or rolled fill is used
• Cardboard slab panel/void formers are used
• Slab panels are on 1 metre grids (approximately)
• Trench mesh or individual bars can be used
• Slab thickness is 85 - 100 mm
• Internal beams are 110 – 200 mm wide
• There is minimal concrete volume
• No beam down drag from clay (above ground slab) occurs
• Shrinkage of slab is lower than stiffened rafts and footing slabs
• They use 30% less concrete than a stiffened raft
• They use 20% less steel than a stiffened raft.
Design & Production of the Waffle Slab
• Waffle slabs can be casted by placing he pods on he formwork itself or they
can be available pre-casted.
• Concrete waffle slabs can be purchased and shipped to the construction site as
prefabricated or precast sections, or they can be poured on-site.
• If prefabricated products are not in the budget, consider purchasing casts for
the concrete waffle slabs.
• The pre-casted pods are then placed directly on the site and then provided
with reinforcement and filled with concrete.
• There are three basic designs for concrete slabs that improve the strength-to-
weight ratio. For each design, the top surface is flat while the underside is
modulated with either a corrugated, ribbed or waffle design.
• Corrugated slabs are created when concrete is poured into a wavy metal
form. This shape prevents the slab from sagging.
• Ribbed slabs add strength in one direction, while the concrete waffle slab
design adds strength in perpendicular directions. Concrete slabs can be
reinforced with rebar for additional strength.
Services Provided in Waffle Slab
Spanish architects, Alarcon & Associates, have modified
the conventional waffle slab to fill it with holes so that
services can be run within the depth of the slab, reducing
the floor to floor height and getting some of that extra
cost back. This new system they invented is called the
Due to the holes in the waffle system following services
can be provided:
• Insulation Materials
Electricity and Telecomunication :
• Wiring installations can flow in pipes embedded
in the floor, or inside a registrable tile system .
• They can also circulate through the suspended
ceiling, being fully accessible by just lifting it.
Maintainance and Cleaning:
• It is registrable, and performing plenum ventilation, easy
cleaning of the ducts without requiring demolition or
specific equipment is possible.
• In addition, , immediate access to installations, enables
repairs and reconfigurations withot requiring the
interruption of the normal activity of the building.
The formwork required for waffle slabs are as follows:
• Vertical support stand
• Horizontal support beams
Different Types of Pods
• Wall connectors
• Metal/Steel bars
• Cube junctions
• Hole plates
Waffle Pods Providers (India)
The main element required to provide waffle slab is
There are many Waffle pod producers all over India,
and some of their names are as follows:-
• Supreme Fibre Glass Pvt. Ltd. (Mumbai)
• Envo plast (Kolkata)
• Teknik Kalip (Mumbai,Banglore)
• Utracon (Gujarat)
• Geo plast (Chennai)
• Maruti Plastics (Mumbai)
Types of slab
4. Radiant Floor ducts
5. Insulation/Ducts Seat
6. Installations Tray
7. Holedeck slab
9. AC Ducts
1. AC Ducts
2. Holedeck slab
3. Installation tray
5. Installation drop tower
6. Air impeller
Square Pod System
Triangular Pod System
at Junction of Sloping
Slab and Waffle slab.
at Junction of Wall
and Waffle slab.
at Junction of Beam
and Waffle slab.
Example of the Slab
Reflected Ceiling View of the slab
Plan of tendon placement layout
3d view of the Ceiling
3d view of tendon placement
Load deflection in the provided
Providing a horizontal
Placing the Pods
Fixing pods to the
Advantages & Dis-advantages
• Waffle slabs are able to carry heavier loads
and span longer distances than flat slabs as
these systems are light in weight.
• Suitable for spans of 7m – 16m ; longer spans
may be possible with posttensioning.
• It is also economical as the amount of
concrete and steel is reduced as compared
to flush slabs. Saving 15% concrete and 10%
steel as compared to traditional T beams.
• These systems are light in weight and hence
considerable saving is ensured in the
framework as light framework is required.
• Coffered underside is usually left exposed for
• Construction requires strict supervision and
• The casting forms or moulds required for pre-
cast units are very costly and hence only
economical when large scale production of
similar units are desired.
• Headroom is reduced , hence increased
• Due to waffle ceiling , it creates problem in
lighting facilities and hanging pipes or ducts.
Iconic Landmarks using Waffle Slabs
Development Centre, Spain
It was the first building to use the
Holedeck pods for waffle sytem.
Chattrapati Shivaji Terminal,India
It is recognized for its innovative
column design which also consists
It is the world’s largest wooden
structure which is made up of waffle