What is the difference between a raft concrete slab and a waffle slab?
Raft concrete slab
This is the simplest and most common slab construction. It consists of a 100mm or thicker steel reinforced concrete slab integrated with steel reinforced concrete beams founded into the bearing soil for strength and support. The raft concrete slab provides great flexibility and strength on most soil classes and site conditions.
Waffle pod concrete slab
This is often used on sites with very reactive soil classes or shallow rock. It is constructed above ground on a level surface. Polystyrene pods are placed in a grid formation, typically 1m x 1m, separated by 110mm wide internal steel reinforced concrete stiffening beams to support a 85mm steel reinforced concrete slab. The waffle pod concrete slab provides improved insulation qualities.
Which concrete slab should I use?
Both concrete slabs are engineer designed and therefore structurally sound. They both provide clean, level finishes to accommodate the installation of blockwork or clad framing as well as a suitable base for most floor coverings. Both will likely develop thin cracks over their life.
To determine which concrete slab is best for your site you should consider site conditions, slope, soil classification and complexity of house design. The right choice will take into account not only the slab cost, but the incidental costs associated with any excavation of the site and any requirements for retaining structures or soil fill to level the site before and after slab construction. These considerations are not only critical in preparing the site for the slab construction; they will also impact on your enjoyment of the site once your home has been constructed.