Structural Inspections
A home's structural components are most potential homebuyer's largest concern when buying or building a home in today due to the massive potential cost if a repair is needed. A home inspection before a large financial commitment is the best way to go to mitigate this risk. But what really does one look for when evaluating the structure of a home?
What are the structural components of a home?
A structural analysis starts with the ground on which a home is built. It then moves to the foundations (footings), foundation walls, supporting walls (load-bearing walls) and finally the roof and its interconnections. Homes are designed with weights and forces in mind and certain engineering standards are put in place in the design of a home to prevent a failure of the components.
​
The most obvious of these forces is compression (squeezing) and this is in most cases moves with the force of gravity downwards. The loads that are taken into account are characterised as dead-loads (weight of the structure e.g. roof, walls) and live-loads ( weight of movable things within a structure). The load of your roof is distributed through the load-bearing walls into the foundation wall and down into the foundation and soil below. Most South African homes are built with brick and mortar with concrete foundations (footings). Cement is great at dealing with a compressive force but not that great with tension/tensile forces. That is why steel is added to a structure/cement as steel is great with tensile forces.
​
Tension/tensile (stretching) forces are less obvious in the structure of a home but the best example of this can be found in a regular pitched roof. A roof rests on the load-bearing walls but in order to stop the roof spreading and falling flat, a large horizontal piece of structural timber is placed at fixed intervals (rafter-tie). I most cases the aforementioned timber forms part of a pre-engineered truss structure in South Africa.​​
​
Lateral/racking forces are those that commonly move in a horizontal direction and come into consideration when the wind or seismic forces impact a load-bearing wall or the roof.
​
​​​
The Soil
The type of soil in which a home is built determines the type of components needed to make a sound structure. The load bearing values of soil differ dramatically with clay/silty soil (1,500 psf) on the one end of the spectrum and bedrock (12,000 psf)on the other. Residential builds are seldomly tested for soil-bearing unless there are known issues with the land (landfills/organic deposits/expansive soils(clay)).
​
Homes built on clay are a large challenge in South Africa. The reason for this is that clay has the ability to absorb and loose large amounts of moisture depending on the season creating uplift and lateral forces if mitigants are not put in place during the build process. Engineers may recommend piers to be built which are concrete columns that are built into the ground to a level where more stable soil or the bedrock is present. In the alternative, a raft foundation may be built or methods will be put in place to control the moisture content of the soil.
​
A home inspector will start a structural inspection of your home looking at all visual indicators around the home that may result in structural issues - please note that we will not open, dig or dismantle any structure. The impact of water on a structure is often overlooked by a homeowner. Water has the most damaging effect on a home and its structural components over time. Simply grading the land so water flows away from the foundations could save a fortune in future potential repairs. Another thing worth noting is trees in close proximity to the structure of the home - trees through their root structure have the potential to damage foundations as well as sewer systems.
Foundations and renovations
Differential settlement occurs if there is difference in soils, loads, or structural systems between parts of a building. In this case, different parts of the building structure could settle by substantially different amounts. Indicators of differential settlement are doors and openings that are out of square, non-level foundation walls as measured by a laser meter, cracks in the foundation wall, floors and other walls.
It may be caused by a number of factors but in the case of the renovation of a structure the first point of investigation is the foundation.
Sizing of the shallow foundations is done based on the allowable bearing capacity.
Area of Foundation = Column Load (SLS) / Allowable Bearing Capacity
The column load at the serviceability limit state (SLS) will be divided by the allowable bearing capacity of the soil to obtain the area of the footings. This is the initiation of the foundation design. In this manner, pressure is maintained under the foundation at the same level. When the pressure under all the foundations is similar, there is a high possibility of having a similar settlement of footings if the condition of the ground remains the same for all the footings. However, if pressure is mistakenly or intentionally changed under the footings there will be different settlements in foundations.
Settlement and cracks
All homes when built will settle/compress the ground on which they are built. Some homes however, will experience differential settlement. Most settlement will occur in the few years after a home is built. It is very unusual to have differential settlement after this date and we have found that water,subsequent renovations or poor building practices to be the culprit.
​
Shrinkage occurs when the surface of concrete dries and water evaporates from the spaces between particles. As this water dissipates, the particles move closer together, resulting in shrinkage of the concrete. Every home will have these cracks and they are not a cause for concern.
Types of cracks:
Vertical cracks
A vertical foundation crack could be due to serious settlement if it is significantly large or shows signs of ongoing movement. If the cause is shrinkage, it is of less concern than if the cracks are a result of settlement.
Diagonal cracks
Diagonal cracks that grow in width, especially ones that are wider at the bottom than at the top, indicate settlement. Diagonal cracks over windows indicate a weak header/lintel. Diagonal cracks in a poured concrete foundation that are fairly uniform in width or are hairline-type are caused by shrinkage and, though they may allow water entry, do not constitute a structural defect.
Cracks along the mortar line
Some home inspectors think that if the crack follows the mortar joint, rather than going through the brick or block, the crack isn't a problem. This is false. Walls crack at their weakest point. If the mortar is stronger than the brick, the wall will crack through the brick.
Horizontal cracks
Horizontal cracks are not indicators of settlement. These cracks are due in most cases to lateral forces and may be an indicator of a structural defect in another component of the home.
Bowing
Sometimes walls may bow out and the ridge line of a roof may sag and this is due to structural issues in the roof structure.
​​
Below is a picture of a crack caused by improper building. A structural I-beam was placed in a home without a spreader below which resulted in the masonry cracking under compression.​​​​​​​​​​​​​​​​​​​
​
The Roof
Trusses form part of the structure of a roof and are normally made of timber in South Africa but in some cases steel is used. Trusses are designed in a triangular form which limits movement and rotation. The slope of the roof can be adjusted for its covering and aesthetic appeal. It is good practice to get an engineering certificate on any new build and in some jurisdictions it is required before an occupancy certificate is issued.
​
Trusses should never be cut or notched in principal as this undermines the strength of the roof. Rafters should always be attached to load-bearing walls with straps to mitigate against wind uplift.
​
If you are interested in this service please check our pricing and contact us today. We are certified structure and foundation inspectors and look forward to your call.
