The cost of building a house can be affected by the nature of the site. It is wise to investigate the suitability of the site before selecting a block of land.
When choosing a block
When selecting a block of land that will meet your requirements, you might:
- choose a block of land on your own;
- employ a qualified professional to help you select a block of land after discussing your design requirements; or
- select a house and land package through a builder.
Consideration should be given to:
- the location (including budget, closeness to schools, shops, transport, and other facilities);
- access to services, such as electricity, water, gas, sewer and telephone (and the cost and time it would take to connect to these utilities);
- where the sun rises and sets and climatic conditions;
- the plans for the area, especially if the block is part of a development; and
- the nature and condition of the site (sitework costs and whether work will affect other land).
Nature of the site
On sites with low lying land or uniform land containing soils that are partly or entirely clay, silt or peat, it may be necessary to remove unsuitable foundation soils and import fill, or carry out special work to establish a sound foundation.
The cost of concrete footings and slabs can increase due to the need for additional concrete and reinforcement when unstable site soil conditions are discovered. An unstable foundation does not provide adequate support to the building structure and allows differential settlement to occur resulting in cracked house slabs and walls.
The planting of certain trees and shrubs in the vicinity of the house can severely effect the moisture content of the ground. This change, together with the tree roots, may cause cracking in the slab or the masonry of the house.
Land features (or site conditions) can affect the price of building and the layout or design of the house that may be built. Site conditions will have an impact on the cost of building as it affects the amount of preparation (or site works) required to lay the foundations for the house.
Site conditions include:
- the type of soil;
- how the soil is distributed across the block;
- how high is the water table; and
- any trees or rock contained in the soil.
Some of these factors can be assessed before you build.
Do I need a site investigation?
Site investigations should be carried out before entering into a building contract. The investigation may be carried out by a builder, architect, engineer or an independent consultant, to provide an accurate appraisal of the structural requirements and the eventual site work costs.
When entering into a building contract there is likely to be a ‘provisional sum’ for site works. A ’provisional sum’ is a sum of money set aside in a contract to provide for work of which the scope and cost cannot be clearly foreseen. Where the home building work contract is valued between 7,500 and $500,000, the provisional sum cannot be less than the least amount that it would reasonably cost to perform the work. The builder should only estimate the costs after carrying out a reasonable inspection of the site as penalties apply for understatement of costs (section 12 of the Home Building Contracts Act 1991).
When purchasing a block of land, be aware of the approximate site costs to include in your building budget.
Work affecting other land
Any site works or building which impacts adversely on an adjacent property requires the consent of adjoining owners.
Work adversely affecting other land is:
- changing the natural site drainage in a way that reduces the effectiveness of drainage or affects buildings or structures on adjoining land;
- reducing the stability or load bearing capacity of adjoining land or a building or structure on the land.
The Work affecting other land fact sheet details the requirements for obtaining adjoining owners’ consent.
Building and Energy may assist with queries or disputes regarding site works. Call 1300 489 099. The CSIRO produces a publication `Foundation Maintenance and Footing Performance: A Homeowner’s Guide’ available online from the CSIRO website at www.publish.csiro.au or call 1300 788 000. The building and health officers of the relevant local government may provide information about development restrictions.