The primary dimensions of a strip foundation for concrete cavity wall construction and timber-framed cavity wall construction are comparable. The length and breadth of the strip are proportional to the entire width of the wall. The depth of the strip is equal to the height of the wall plus the thickness of the exterior sheathing or siding.
The secondary dimensions of the strip are determined by the location of the door openings and windows, which will affect what materials can be used for interior and exterior walls. If material is to be used for both walls, then the opening for one room should be at least as large as the strip is long. If not, the strip can be made wider to allow for expansion and contraction without cracking the wall.
The depth of the strip must be deep enough so that the top of the strip is at least as high as the ceiling of the room it supports. If the floor of the room is lower than the strip, add flooring material to bring the floor up to the same level as the strip. This prevents objects from being thrown against the wall when someone opens the door or pulls on the handle of a window.
The strip should be wide enough so that objects such as furniture cannot fall through it. Allow 1-2 inches between pieces of furniture for easy access.
Foundations for a single-story building strip will normally be 450mm wide and at least 200mm deep, while foundations for two-story buildings will be 600mm wide and 200mm deep. The weight of the building will cause the earth beneath it to collapse around these holes which are then filled with more earth to make way for another floor or room. The deeper the hole, the better its capacity to resist damage from an earthquake.
The depth of a foundation depends on many factors such as soil type, amount of moisture present in the ground, whether there are any gas lines nearby etc. In general, the deeper you go the better since more serious earthquakes tend to happen near the surface.
In terms of feet, the depth of a foundation is based on how much land you have available for it to rest on. If you can build it, they will come.
Single-story buildings up to 5 stories high usually have foundations that are between 150mm and 300mm deep. On larger projects, those levels may be divided into smaller rooms or floors.
At its deepest point, a foundation for a two-story building should be 400mm or 1.5 feet deep. More than two stories creates its own problems that require different solutions.
Strip foundations are made out of a continuous strip of material, commonly concrete, that is constructed centrally underneath load-bearing walls. The foundation wall serves as the base for the floor above. As such, it must be thick enough to support any loads placed on the floor above.
The foundation strip is usually about one-eighth of an inch thick. It is poured before the wall is completed so there is no need for the builder to work at height. The foundation strip can be formed into various shapes to meet the requirements of the project. For example, if the floor above will contain openings (such as windows or doors) the foundation strip should be shaped to match these features.