A house's foundation is critical to its stability. It supports the entire weight of the building and distributes it evenly through to the ground beneath. Therefore, any issues with the foundation can be a major problem and certainly something you’d want to be aware of before purchasing a property.
Types of house foundations in New Zealand
New Zealand houses are normally built on one of two foundation types – suspended timber floor or concrete slab foundations. Sometimes a home can have a combination of both.
Suspended timber floor foundations
A suspended timber floor foundation normally has wooden floorboards or sheets attached to joists. The joists sit on perpendicular beams, which are in turn supported by bearers. Beneath the bearers are piles that go down into the earth. Sometimes, there is a concrete perimeter foundation that sits beneath the outer walls of the building. Usually, there is enough space beneath a suspended timber floor for someone to get underneath and look at the foundations. These kinds of foundations are good for sloping sections, where the piles can be engineered to differing heights to keep the house level.
Concrete slab foundations
As the name implies, a concrete slab foundation is a big concrete pad that the house sits on top of. The slab is poured onto the ground, which is prepared with a layer of gravel and then a sheet of plastic which stops damp from rising through the concrete. The outer edges of the slab are poured with a lip that penetrates lower into the ground to form footings that hold it in place. These kinds of foundations are best suited to flat sections.
Foundation warning signs
If you know what to look for, it’s possible to spot the signs that there are problems with a home’s foundation by looking at other parts of the house. These include:
- Uneven or sloping floors
- Uneven or cracked tiles and grout
- Stretched vinyl flooring
- Warped wallpaper
- Windows and doors that jam or don’t fit correctly
- Cracks or gaps between the walls and floors or ceilings
- Cracks in the concrete base of the house
- Exposed, cracking, or crumbling piles beneath the outer wall
- Soil movement around the bottom the house
Checking underneath the house
If it is safe to do so, you can check beneath a suspended timber floor for signs of foundation damage. Never go underneath a house if you are concerned it is not structurally sound.
First, you will want to check the piles are in good condition. If they are made of wood, they should not have any visible rot or borer damage. If they are concrete, they should not show signs of cracking or crumbling. Regardless of what the piles are made of, they should be firmly embedded in the ground, standing straight, spaced evenly, and not undermined by slips or ground excavation. None of the piles should be missing or substituted with alternative structures.
Next, you should check that the piles are connected to the bearers properly, and the bearers to the joists. The piles should also have bracing to prevent them shifting in an earthquake. Villas that have not been re-piled, or were re-piled prior to 1980, may not have had extra support added. If possible, check the bracing is properly secured, and that any concrete perimeter walls are not cracking or crumbling.
Get an expert to check
With something as important as the stability of a home, don’t leave it up to chance. It’s recommended that you get a professional building inspector to check the foundations of any property you intend to buy. While major damage might be easy to identify, an experienced inspector may notice more subtle warning signs. A comprehensive Innohome building inspection can put your mind at ease that your potential new home is structurally sound.