Concrete slab vs posts with a sub-floor
Choosing the correct footings for your home is an important decision as it makes up a very significant part of the overall construction costs.
There are many factors to be considered ranging from personal preference to conditional regulations.
If your land is a very steep sloping block, then footings might be limited to a post and sub-floor option rather than a concrete slab. However, having a slightly sloping or flat block can give you the option of either posts and sub-floor or a concrete slab.
A major consideration when using a concrete slab on a sloping block will be the amount of works required which will reflect in the overall cost. The land will require levelling out which generally involves cutting and back filling, retaining walls to support the cut and specialised waterproofing and drainage to prevent damp from rising. Depending upon the soil type, the slab may also require underpinning which involves deeper footings in the ground to support the concrete.
Posts and a sub-floor are generally the more cost-effective option when construction is on a sloping block. This type of footing will eliminate the need for cutting and filling, retaining and waterproofing. The footings may require deep beddings; however, this will be far more economical than an entire slab. There are now options available that eliminate the need for concrete altogether. This is an anchor footing system that is rammed into the earth. It is mounted with a base plate that the post is then bolted to.
Wind loadings, flood zones and high fire areas will also play a role in which footings will be best suited. A flood zone will generally regulate that you must use a post and sub-floor system. A high cyclone region will require additional bracing, a wider post thickness for an elevated system and more tie downs and bracing for a slab. A high fire zone will need under floor protection and generally require a fire-resistant sheeting for an elevated system.
When deciding upon posts or slab simply for aesthetics and for a flat to gentle sloped block, the cost difference is minimal. You outlay more for the kit materials when on a flooring system as we supply the posts, a steel sub-floor, internal floor sheeting and deck timber, however the amount of concrete is less so although the kit without a flooring system is a lot of less upfront costs, the concrete slab outlay is far higher.
So when selecting which footings to use, do your homework and consider all the factors as this is the foundation of your new home so you need to get it right.