There are several compelling reasons why most developers avoid “tricky” sites. Groundwork expenses that may be prohibitive, coupled with extended periods of uncertainty, might quickly transform a good idea into a high-risk venture. However, a ‘problem plot’ may occasionally turn out to be a blessing in disguise for self-builders brave enough to embrace technical difficulties.
What Does a Tricky Plot Look Like?
The three most common reasons for an increase in groundworks are sloping sites, the presence of trees, and ‘poor’ ground.
According to ADA Fastfix, “even modest slopes might be difficult.” The drainage and access will need to be planned carefully, and surface water flowing down the hill must be channeled around the building. The greater the slope, the more costly the site, with expensive retaining walls typically necessary on gradients of more than 1:25 to keep back the earth.
Another option is to dig down into the hill and create a level base. Another choice is to build on top of the hill, which will require excavation. Alternatively, you may opt to expand the structure outward by adding supporting walls beneath the raised area. Both methods are likely to cost around £5,000 in groundwork fees.
Instead of laying the support boards vertically against the slope and building a flat surface, you might utilize a series of steps to create a split-level design. This will cut down on excavation, but it might still raise your total construction cost by 10%. Sloping sites, on the other hand, may be used to give more area by building down below ground level for a low cost.
The ground can be susceptible to shift for a variety of reasons, some of which are listed below.
Volume change: Shrinkable clays are affected by seasonal volume fluctuations. However, these seldom extend beyond a meter below the surface. Trees and shrubs in close proximity, with periods of drought and heavy rainfall exacerbate the problem.
Frost heave: Springy or soggy ground indicates a high water table, during which soil may expand when frozen. Surface groundwater, on the other hand, seldom freezes deeper than half a meter.
Made up ground: Brownfield sites may contain all manner of horrors, such as foundations, drains, and wells from previous development. Toxic chemicals or methane gas may be lurking in old industrial sites or dumps, so it’s vital to check local government registries of contaminated land. However, in some circumstances, the answer may be rather straightforward, such as requiring sulfur-resistant cement.
Unstable ground: The ground under your property may have been damaged by previous excavation or mining, making new foundations susceptible to periodic, unanticipated subsidence.
The following are some of the most common methods for trekking across difficult terrain:
If you’re working on a surface that offers poor bearing capacity, such as soft sandy clays, the most effective solution is to dig down a bit farther. If a typical trench foundation is deep enough, its base should rest on solid ground free of seasonal changes, while beam and block floors may comfortably span over the surface.
In clay areas, though, the ground on the foundation’s perimeter will still be subject to periodic expansion and shrinkage as it becomes saturated and then dries. The sides of the trenches may be lined with a flexible slip membrane to allow the clay beside to independently shrink or swell, thus resisting lateral pressure.