Going underground – foundation movement and what it could mean15/03/21
There are many aspects of a building construction that can’t be seen when the project is finished. This includes things like the plumbing and electrics, or underground drainage. All these components need to be installed to strict criteria such as the building regulations, British Standards and other regulatory bodies to ensure they are fit for purpose and will stand the test of time. None more so than the foundations, which are a critical part of the construction process.
Problems with foundations can be revealed in a variety of worrying ways and if you think you have an issue with them, it’s best to employ one of our professional Building Surveyors. They can offer expert advice on what might be causing the issue and the remedial measures needed to remediate.
Probably the most obvious sign of a foundations problem is when cracks appear in the walls. The walls are supported by the foundations and any movement below ground might manifest itself in the locality of the failure.
There are many contributing factors that can cause foundations to fail and give rise to problems. Examples include a weak concrete mix, where the wrong mix ratio of sand, cement and aggregate has been used, insufficient size for their width and depth or the wrong type of foundations for the type and size of property, including certain types of ground conditions that require a specific type of foundation. Another contributing factor is when foundations are affected by settlement.
Settlement can be in two forms, differential or uniform. Differential settlement occurs at differing rates between different portions of a building. It also 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. Usually this is visible when the building becomes distorted, floors can slope, walls and glass may crack, and doors and windows might not work properly. In worst case scenarios, uneven foundation settlement may force buildings to shift out of plumb.
Uniform settlement is when foundation settlement occurs at the same rate throughout all portions of a building. If all parts of a building rest on the same kind of soil, then uniform settlement is the most probable type to take place.
Problems sometimes occur on DIY projects, such as extensions because there has been no structural input from a structural engineer or the local authority Building Control Inspector has not been involved, to pass the foundations and sign them off.
One cause of foundation settlement is when foundations have been laid on shrinkable clay soils. Clay soils are made up of about 40% water, but any trees or vegetation, or indeed rainfall, can change this amount throughout the seasons. Any shrinkage or swelling can be enough for the supportive strength of the ground to be lost and weaken foundations. Clay shrinkage can be monitored by specialist equipment, but if it is left alone, it can cause longstanding problems. As a result of settlement, any cracks or gaps in the foundation or wall can become further weakened by the weather cycle, as frost damage can cause the water to expand more, widening the cracks.
Water penetration in general is bad news for foundations. A leaking drain or gutter downpipe can cause untold damage to foundations. If a blocked drainage grid or pipe leads to the overflow of water, the erosion over time will cause issues with the foundations and brickwork in the vicinity. It’s surprising the amount of damage even a small trickle of water can do over a long period. This can occur, for example, if the drainpipe or grid is hidden behind bushes or fencing. The first indication of anything amiss could be the appearance of cracking to the wall above, as the foundation shifts.
Natural causes of foundation damage
Another cause of foundation damage and movement could be due to trees in the area. Even if a tree is metres away from a building, its roots could be causing problems underground. This can be either be due to clay shrinkage, as thirsty roots drain water from the ground, or where foundations are lifted by ground heave, as a result of clay swell, where trees have been removed from the site. The problem doesn’t go away even if the trees do. Big trees can also cause a great deal of damage from the roots, which can disturb drains, and prise against foundations and walls. This is a gradual process and, like other damage, may only be acknowledged in its latter stages.
Underpin as remedy
The likely remedy for most foundation issues is underpinning, which will need to be carried out by specialist contractors, who should be members of the Association of Specialist Underpinning Contractors (ASUC). Generally, this will involve the area around the affected foundation being excavated.
The underpinning of foundations involves increasing the depth of existing foundations in order to transfer the building load to a more supportive soil type.
Although there are a number of different techniques available for underpinning foundations, the most common method is traditional mass concrete underpinning. This is a simple technique that involves excavating a segment of ground below the existing building foundation in controlled stages, to a depth where suitable soil conditions exist. The excavation is then filled with concrete and allowed to cure before the next 'pin' is excavated.
Get in touch with our professional Building Surveying team if you think you have problems with the foundations at your home or commercial premises.