Stumps are used to hold up the floor frame, which in turn supports your chosen flooring surface and frames. If your floor is supported by many columns or stumps, then you have a raised (or stump) sub-floor. It is very important that there are enough stumps to support the weight of the home, and that they are spaced in such a way as to provide maximum strength. The layout of the stumps must be designed by an engineer to ensure correct sizing and spacing.
Adjustable galvanised steel columns are commonly used, particularly on soil that is subject to a lot of movement. These have the distinct advantage of being able to be adjusted onsite, which makes a very big difference in terms of the maintenance required further down the track.
The advantages of using a raised sub-floor include:
* necessity for sloping sites where a slab cannot be used;
* rural areas where the costs of transporting cement is too expensive;
* ease of building (particularly for owner-builders);
* adjustable to counter-act any movement in soil;
* easy access under the home;
* aesthetics ie. for a Queenslander-styled home.
The disadvantages of using a raised sub-floor include:
* labour cost, as the floor system is more labour-intensive;
* some estate covenants will not allow raised homes;
* raising a home adds additional costs for items such as stairs and balustrade.