A structure is only as good as its foundation, right? Right!
Get the foundation right and the structure can do as intended for years on end.
Selecting the right subbase comes down to knowing one thing: the purpose of the surface. Select the base to fit the surface purpose. An engineer should always specify a suitable subbase; however, this article will look at the cost of commonly specified subbases.
You must always allow for the materials to compact, so be sure to multiply your quantities by the correct bulk density factor. If you find that you’re always running a little short, double check the bulk density factor with your supplier because they do vary from product to product.
To compare apples with apples we are going to compare the cost to install of each material per square metre at standard depths. The following variables have been removed from the rates, but must be included when you price a real project: waste, access, formwork, preparation, delivery/float, supervision, overheads, profit margin, GST.
Small to medium format pavers are suitable to lay on flexible surfaces, while large format paver and tiles require a concrete surface. Split surfaced pavers are suitable for both flexible and concrete because they need to be laid on mortar, while thinner tiles should be glued onto a smooth concrete subbase.
Road base and recycled road base are permeable to an extent but once compacted thoroughly, water penetration is slowed drastically. For increased permeability choose a porous reinforced surface such as Gravel Cell from Atlantis or No-fines Concrete. Be aware that No-fines Concrete cannot be pumped, so if access is difficult the costs could blow out drastically.
Recap:
Be sure to calculate your required quantities of material using the correct bulking factor.
Wherever possible engage an engineer to specify the subbase material and depth. Don’t forget to add all those variables to your estimate, they add up!
NOTE: These prices are to be used as a guide only! They do not include overheads, profit margin or make allowance for site conditions.
Happy estimating!
Anna Turner
Professional Estimator