The waffle is an uncommon type of building solution in Kenya and East Africa. It is not clear why this is the case but it is possible that information on its use on the broader construction landscape is not widely available. However, as you’ll shortly see, the waffle is a resilient and cost-effective method of building, suitable for both foundations and typical floor slab systems.
What is a waffle system and how is it constructed?
Waffle systems can be composed of either waffle slabs or waffle foundation systems. In both cases, the load-bearing system is made up of a two-way spanning joist grid with reinforcement laid orthogonally in the spaces between the waffles. These waffle pods can be made of plastic, EPS, or any other suitable material, usually proprietary. Concrete is then poured into the space system between the waffle pods and vibrated as usual. The effect is the waffle system with spaced grids or ribs underneath and a flat slab on the top. The entire system can also be pre-cast and installed on-site, which is a much faster alternative.
The procedure for building an in-situ waffle slab system is as below:
- Pour the columns that will support the waffle slab (applicable where the first floor or any other floor other than the ground floor is to be constructed using waffle.) Solid column heads or band beams can be incorporated into the waffle support system to reduce the effect of punching shear at the column sections.
- Install the formwork and support shuttering that will support the waffle slab.
- Lay the waffle pods and spacers according to the desired depth of the slab and structural drawings.
- Lay the reinforcement, for example, main beam reinforcements placed in-between the waffle grids. Secondary reinforcement can be included, and mesh reinforcement to eliminate cracking can also be placed on top of the waffle grid.
- Pour the concrete once everything is in place and vibrate it. Setting and curing times for the concrete depending on the desired grade of concrete.
- Remove the formwork and waffle pods once the concrete is cured.
Practical advantages of waffle systems
Waffle systems, either for slabs or foundations, are useful for the transmission of bending and shear loads across large spans. While the necessity for this might not be immediately apparent for small residential dwellings with usual slab spans of 12 meters or less, the benefits are impressive for structures with large spans above 12 m. Waffle slabs have high strength, i.e. resistance to bending and shear across large spans, and thus are useful for commercial and industrial establishments such as warehouses, airports, cinema halls, and cafeterias where large column-to-column spans are necessary.
Structures constructed with waffle systems have a higher aesthetic appeal, can have increased storey heights, and eliminate the need for hanging ceilings since utility services such as HVAC and lighting conduits can be installed within the waffle system. Besides, the plastic, EPS, or any other proprietary waffle pod system can be easily removed if coated with a grease substitute before concrete pouring, and reused in other waffle construction.
The proprietary wafflemat foundation is especially useful where raft or spread foundations are necessary, such as in areas with low or uneven bearing capacity. The wafflemat acts as a single monolithic unit, improving the integrity of the foundation and negating the effects of negative uplift forces that would otherwise damage the foundation and superstructure. In the same reasoning, the depth of foundation can be significantly reduced even for large structures, which ultimately reduces the earthworks and general foundation costs, and improves drainage.
Is the waffle system for you?
While the practicality of the waffle system is mostly limited to structures with large spans where free space in-between columns is a necessity, their use isn’t limited to these large structures. Residential homeowners constructing smaller dwellings may not see the overall cost benefits, as these lie in the need to increase slab spans while reducing their overall depth. Commercial developers such as hospitals and malls will, however, benefit immensely from the practicalities of waffle systems.
