Learn How to Look: The Subtle Art of Site Evaluation (Part 2)—— May 24, 2021
Following on our last discussion with respect to how access to a site as well as how security considerations can influence our property purchase decision, we will now look at some other factors that are equally important when prospecting a potential site.
The first of these factors is the nature and availability of infrastructure around the site whilst the second deals with the impact of groundwater on the subject site as well as the soil characteristics prevalent in the locale.
CONTIGUOUS INFRASTRUCTURE IN DEVELOPMENT PROJECTS
This factor is something that very few people put into consideration when going to look at a site but which is nevertheless critical when trying to arrive at an estimate of the possible development time horizon especially if the property in question is in an area which is not yet fully developed.
What are the elements that make up what we call contiguous infrastructure?
In more developed societies, development infrastructure would be referred to as utilities and would consist of Electricity, Water Supply, Gas and the Sewer System. Unfortunately, In Nigeria there is a general lack of infrastructure and we are not yet at a stage where the connection points to the Gas, Sewer lines and in most cases public water mains are of any relevance. Therefore we would have to limit our discussion to proximity of Electricity connection points to the potential site location.
Electricity: What to look out for when inspecting a prospective location
Basically on your first trip to the site, you should watch out to see if there are electricity poles leading to the site and which serve the purpose of carrying cables that terminate around the site’s vicinity.
We should however make it clear that even with the presence of such electricity cables; there is still the need for more clarity as to their relevance to your prospective site. In this wise, if the property one is going to inspect is located in a large estate or community, perhaps being marketed by a developer, it should be borne in mind that such a large Estate would require its own transformer and the challenge would then be to ascertain that such a transformer already exists on the estate. However, if the transformer has not yet been installed and the developer is promising that it would soon be, one should check that the electricity cables terminating at or near the site are high voltage cables rather than low voltage which would be more appropriate for single dwellings in an already built-up neighborhood.
Distinguish between high and low voltage cables
To distinguish between high voltage and low voltage cables, you should be aware that high voltage cables are usually three in number, are strung parallel to each other and are normally placed above the poles upon which they are strung. Low voltage cables are on the other hand four in number, stacked vertically above one another and strung at the top side of the pole carrying them.
Should there be an absence of high voltage cables in the vicinity of such an estate, then you should immediately have it in mind that the development horizon for the project would most likely be longer than what is being propounded by the developer or in the alternative the Estate would be experiencing large voltage swings due to excessive demand beyond the capacity of the low voltage cables.
Where no electricity cables of any sort can be seen at the site or on the route to same, then you may safely conclude that purchasing the plot being inspected is most likely a speculative venture and it may therefore still take quite some time before the location becomes habitable.
SOIL CONDITIONS & SITE DRAINAGE
Doubtless, another critical factor that should be given serious consideration when prospecting a potential site is the type of soil that is predominant in the area; its inherent ability to support building loads and what type of building foundations have generally been employed or can be employed in the neighbourhood.
In this regard and with respect to the Lagos metropolis, the simplistic yardstick used by the average layman appears to be that foundation types for properties on the island tend to generally require piled or raft foundations and are more expensive to construct whilst foundation types required on the mainland are generally cheaper to construct. This classification or mental paradigm is however quite simplistic and does not hold true when subjected to empirical scrutiny or considered in the light of practical experience.
What in actual fact is indeed critical are the following factors;
- The presence of groundwater in and around the site location.
- The inherent characteristics of the soil itself.
The Water Table and proximity of Water bodies
In large parts of the mainland such as Ebute-metta, Yaba and Surulere, soil conditions can be as poor as or even worse than what is found on most parts of the Island such as Lekki, Victoria Island and Ikoyi.
Large parts of Ebute-metta and Ikoyi in fact share similar soil properties and require almost identical foundation types in many cases since they were both formed by alluvial deposits along the Lagoon coastline. Even in areas on the mainland that have generally stable and apparently sound soil types, large pockets of weak soil abound in mainland neighbourhoods such as Ikeja, Anthony, Maryland, Opebi, Oregun and others.
The critical factor underlying the weak soil types found in all these areas thus turns out to be not so much whether they lie on the mainland or on the Island but rather their proximity to large water bodies such as Streams and marshlands, or are to be found in low lying areas water saturated areas like valleys or gullies.
The presence of weak soil types in areas close to water bodies and where consequently the water table is likely to be quite high arises from the fact that in most non-monolithic soil types, the action of water on the soil particles and overall soil cohesion tends to reduce soil bearing capacity greatly, even as much as by fifty percent of the normal soil strength except where such soils are granular in nature and exhibit minimal compressibility under loading.
In the light of the foregoing therefore, when evaluating the site of a property being considered for purchase the intending buyer needs to ascertain how close the land or built up property is to a large water body such as the Ocean, the Lagoon, natural water channels, drainage canals, Rivers, Streams etc or whether or not they are located in low lying areas such as valleys, gulleys or any location where water from higher elevations naturally tend to collect.
If the site is close to large water bodies, is submerged or in an area with a high water table or perhaps subject to seasonal flooding, then one should immediately be aware that there would be a strong possibility of special foundation type for the building and one should then decide whether one has the resources to embark on such a venture and where one decided to proceed then the advice of professionals would certainly be required.
It should be clearly understood that we are not in any way saying that the presence of water on a prospective site should be a deterrent to its purchase as after all structures of various types are indeed built on water all over the world, whilst for example the sites for our Arcadia Mews and Clover Courts Estates amongst others were totally submerged when acquired. What we are saying is that the presence of water should ordinarily serve as a red flag to the ordinary person prospecting to purchase a piece of land or built up property.
There are indeed visual and environmental clues that can indicate whether a submerged piece of land consists mainly of compressible or non-compressible soil materials. There also exist field techniques for achieving the displacement of organic materials during sand filling or reclamation if the compressible soil layers are not too thick. However, such clues and techniques are well beyond the scope of a discourse such as this and one would run the risk of inadvertently misleading the uninitiated if we were to delve into them.
The best advice we can give in this regard therefore is for one to seek the advice of experienced professionals if faced with situations where the presence of groundwater may pose a challenge to a potential building project.
In determining the soil characteristics of any prospective location, it should be noted that the best approach in this wise is to undertake a full soil investigation carried out by a qualified professional. This is indeed now a key requirement for planning approval in Lagos state for structures that go beyond the ground and first floors.
As the decision to purchase a particular piece of land usually needs to be made well before the issue of a soil investigation comes into focus, we will proceed to attempt indicating below key criteria to consider prior to making the decision whether to go ahead with the proposed land purchase or not.
Where the property is an already built up one though, we would still strongly advise the engagement of a knowledgeable professional such as an Estate Surveyor, Architect or Structural Engineer to inspect the property and provide necessary advice to guide the purchase.
Soil Nature: What to look out for when inspecting a prospective property
General nature of the soil in the neighbourhood
By careful observation, try to determine the general nature of the soil in the neighbourhood. Is it Sandy, Silty, Clayey, Marshy or Rocky? Each soil type has implications for the kind of foundation the building would require with rocky soil generally being the most favourable soil type and marshy soil being the least favourable due to the presence of water. Sandy (granular) soil is indicative that the site is unlikely to be waterlogged when it rains as surface water would quickly percolate. However this is no measure of bearing capacity which is best determined by means of a soil investigation as earlier stated.
Assess the soil whilst walking
Whilst walking over the soil, how does it feel underneath your feet? Does it feel generally firm or does it yield as you step on it even if slightly? Soft yielding soil may be an indication of water underneath or a telltale sign of decomposing vegetation or peat material under the top layers of soil that are more readily visible to the eye.
Observe the colour of the soil as this is also an indicator of soil characteristics for the experienced. Sandy soil is generally light coloured and indicates high silica content in the soil.
Reddish soil points to abundance of iron oxides and is characteristic of laterite but may be loose and easily susceptible to erosion or extremely firm and tending to being rocky in nature.
Where there are shades of yellow and tan in soil, this indicates the presence of ground moisture or periodic water saturation which is characteristic of clayey soil and has water retention properties. Clay tends to expand and contract with variations in moisture content of the soil across the seasons and could be detrimental to some foundation types.
Brown or Black soils indicate organic materials in the soil with Humus – the final stage of the breakdown of organic materials – presenting as black.
The high presence of organic materials in soil calls for caution as these are inimical to soil strength and stability due to continuing decomposition. Each soil type tends to require a different approach to building foundation design and one is thus advised to rely on the advice of experts in this regard.
Soil colours also reflect the presence of groundwater in various degrees. Bright colours such as strong reds indicate well drained soils or soils that do not experience prolonged water saturation. Where soil exhibits yellow colours, this derives from yellowish iron oxides in the soil and is indicative that the soil is not well drained or experiences periodic water saturation. Blue-grey to blackish colours indicate poorly drained soils or soils exposed to prolonged saturation for most of the year and the foregoing could serve as guides in deciding whether or not to proceed with any location being inspected.
Proximity of water
As earlier mentioned, the presence of groundwater greatly affects the load bearing properties of most soils, therefore ascertaining the presence or otherwise of proximate water bodies and their likely effect on building foundations in the neighbourhood is imperative prior to making a commitment to purchase or not purchase a particular property.
When inspecting a prospective site therefore, it is advisable such site visit be done within or around the rainy season as much as possible, so one can see firsthand the soil conditions when it rains and how well or otherwise the site and its environs are drained. If the visit is being done in the dry season, take careful note of the existence or otherwise of Water reed plants in the locale as their presence gives away the fact that the area is a wetland irrespective of whether or not the site is dry at the time of visit.
If one is going to inspect a building in a built up neighbourhood, take a close look at the buildings on the access road to the specific site and try to ascertain if they have water marks which would be an indication of seasonal flooding. The observation of signs of rising damp or flaking and peeling of plaster coats and paints at the base of a building indicate a high water table and the high likelihood of periodic flooding.
The foregoing concludes our discussion with respect to site selection considerations and represents a snapshot of features an average layman can look out for when inspecting a prospective property location and which can guide him or her to an extent in making the purchase decision.
The approach outlined in this discourse is also essential the blueprint we use at Beachway Homes in making our site selection decisions though of course the depth of knowledge in applying them would obviously differ. Having said this and considering the average resources one needs to commit to a property purchase or building project whilst this discourse can serve as a guide, it certainly should not be used as a substitute for sound and well-informed professional advice.
We nevertheless do hope you find it useful enough as we continue in our various blog posts to endeavour to elucidate in simple terms the various complex considerations required to make sound property investment decisions.