Avoiding Common Errors In Setting-Out Operation -Osaz' Enobakhare

The whole idea behind setting out is to ensure that the building or structure is positioned on the ground or the surface it is to be built upon in accordance to the original site plan/drawings. It naturally involves four processes which include; the planning aspect; largely involving the building drawings (i.e. site plan and floor plans accompanied by short technical and general notes). 

This activity precedes the actual marking out of the positions of the building elements on the ground as represented in the plan/drawings using various tools and equipment e.g. the compass, theodolite, measuring tapes, lines, spirit level plum, square, etc. 

While marking out, control of level is simultaneously carried out. Taking levels across the entire building area is quite tasking because of the often non-uniform nature of land surfaces. If the levels are not properly taken, it would affect the integrity of the horizontal bearing of the entire structure and may further impede on the ground dimensions and sometimes its verticality. 

Control of verticality is the last step in this all important activity. The verticality of the base structure is very important because it will invariably determine the straightness of the vertical stretch of the building or structure. 

If the foundation is not erected or constructed properly in relation to horizontal and vertical bearings, the super-structure may be poorly projected upward –making it appear slant in an awkward way when viewed from outside and when you tour the interiors of affected buildings, the dimensional inconsistencies become even more obvious.

Buildings affected by these fundamental errors are not rare, hence understanding the causes of such errors and making conscious efforts towards eliminating them during construction is very imperative. The causes of these errors are; The false assumption that our eyes are always straight hence will give us straight horizontal or vertical projections and then relying heavily on it to mark or set out straight lines or points on the ground.  

Although the eye is the most useful sense organ for carrying out setting out operation, there is no existing proof that the human eye can always give a correctly straight projection at all times. Hence it is not very reliable for such functions; therefore avoid the temptation to use it in isolation to your instruments.

Poor reading of instruments used is another error often made during setting out operations. If you read the markings of the measuring tapes wrongly at some point, you will end up transferring that error to the other parts of the building area and if you make multiple errors in this regard, you would have incurred a multiplicity of errors, thereby making a mess of the whole process. Although there are acceptable margins of error, usually between ±0.01 to ±0.25mm for perimeter length and width, deviation from the stated margin could well affect the ground dimensions of the building. Likewise the inability to properly read or take horizontal levels as well as ascertain verticality using the instruments designed for such purposes could lead to terrible departure from the original design.

L-R: Engr. Osaz' & David Adegbite (Site Worker) paying attention to details on 
a construction site in Ijebu-Ode, Ogun during setting-out operation, 2016

Disregard for building regulations stipulating the minimum standards for offsets, sizes and spatial arrangement of spaces within the building and its exteriors are common errors made. For instance, to develop a residential building in most parts of Nigeria, the existing regulations states that a minimum offset/airspace of 3 metres must be allowed between the face of the building and the plot perimeter on all sides and that a minimum offset of 6 metres or more must be allowed in relation to the adjoining public infrastructure especially an access road. So if such regulations were ignored during the site planning, it may attract demolition leading to wastage.

Improper squaring is another common error. In order to avoid this error, always check for squareness of the area that is being set-out by first projecting it as if it were a rectangle and then taking diagonal measurements which should always tally with what obtains on the plan. Check for consistencies as you move from one point to another along the horizontal plane. Once you observe any inconsistency, you can easily trace the source of the error and correct it before moving on.

Poor arrangement and positioning of pegs, lines and instruments used can also promote error in the setting out process. If the distances between pegs arranged in a straight line are beyond 6m, there is likelihood that some of the pegs may either fall out of place or the lines attached to them may sag off the mark. Also, if lines are connected to pegs in an irregular manner, it may lead to avoidable errors and if adequate clearance is not provided during the operation to accommodate legroom in the case of a manual excavation, it may also give rise to post setting-out errors.

Between Cost to Design and Design to Cost: Making the Right Choice For Your Project -Osaz' Enobakhare

Before embarking on a project, for example a housing project, considerations must be given to several factors ranging from the project cost (or finance) to the duration (or time) and then the quality of the final product. 

First you have an idea in mind, and then you contact a designer/contractor. As the designer/contractor begins to develop your imaginations into a realistic concept, cost becomes an issue. In making a decision on the cost model to adopt, it is very important to be properly guided so as not to attract frustrations along the line which may eventually lead to pre-mature abandoning of the project or even poor handling of the work. 

The two major cost models relative to the project design are; Cost to design (CTD) and Design to Cost (DTC). Cost to design simply means putting up a concrete design first and then estimating the total construction cost from the design usually without formally tying it to any budget while Design to cost entails stating your budget for the project first, then ensuring that the project is designed to be completed within that budget. For easy comprehension, view CTD as ‘cost my design’ and DTC as ‘design to my budget’.

The choice of what model best fit your project depends largely on your earning power and it’s a decision you must make. However it has been observed that most project owners across the country (perhaps out of sheer ignorance) opt for the cost-to-design model and this has been identified as a major cause of in-completion of several building projects especially embarked upon by private individuals.

The popular orientation that revealing your budget to the designer/contractor at the pre-contract stage may affect the integrity of the final estimates is not very correct. In fact, research in value engineering has shown that it is often better to adopt the DTC method so as to transfer more project risks to the contractor especially a nominated contractor in a negotiated contract. 

A nominated contractor is a contractor that you have engaged based on enduring trust or performance in past works often without inviting estimates from other contractors. Lately, a lot more landlords/project owners across the world are keying into the benefits of the design-to-cost model which apart from transfer of greater project risks to the contractor, also includes overall cost reductions, better planning, reduced contractor-client friction during the project life cycle, an opportunity to compare several design options relative to the cost goal as well as improved outcomes.

For instance using the recommended DTC model, a project owner can approach a designer/contractor with say 4 Million Naira to construct a simple bungalow and achieve his/her desires within it in the following simple steps;

-          First, you discuss the development idea/concept with the designer/contractor,

-          Thereafter you reveal your initial budget, say 3.5 Million Naira and retain the balance,

-          Then request that the designer/contractor provide two or three design options that can be achieved within your budget and based on your specifications (e.g. It should consist of 3 beds -all rooms en-suite, French-style windows, an ante-room, slanting height, a court yard etc). 

  However it is strongly recommended that you employ the service of a designer/contractor with good knowledge of both design, estimation and construction from the start as it is in common knowledge that most independent designers/architects aren’t good estimators or alternatively you co-engage a Quantity Surveyor to achieve your cost goal (You will have to pay for this service say around 5% of the total project cost).

-          Once the preliminary site investigation is completed and the building designs and cost estimates are ready, you then choose the most appealing design. Do not hesitate to pre-inform the estimator/contractor to simplify the cost estimates by breaking it into two main sections one showing the Material cost/schedule and the other, the labour cost/schedule (which will include the contractor’s profit so that it can be negotiated separately). You have to study the estimates carefully and compare for consistency with the design.

-          Because some features would have been deliberately excluded in the design in order to make it fit into the cost plan, you may have to add some much desired features (like special finishes, fittings and fixtures, etc) within your initial retention budget (in this case, the 500,000 NGN left). But don’t use all of it; keep a fraction for contingencies, and 

-           You are good to go.

However in the Cost-to-Design model, the project owner/landlord is highly disadvantaged in that the designer/contractor may come up with fabulous designs that may be far beyond your budget because there have been little or no consideration of the cost implication of the design at the initial stage.

This is the most common case in practice. When this happens, subsequently the project owner lured to this expensive design begins to run helter-skelter to source for additional funds to complete the project and this is not usually a funny experience

But on the flip side, the CTD model has the advantages of allowing both the designer and the landlord to enjoy some degree of design freedom and input flexibility respectively as well as gives the owner the opportunity to compare numerous estimates from invited bidders before embarking on the project. Think carefully and make the right choice of cost model to adopt for your next building project.

How to Install Rubber Dog-Bone Interlocking Pavers on Floors - Osaz' Enobakhare

Interlocking pavers made from concrete i.e. a combination of crushed natural stones, sharp sand and cement are the most common in use across Nigeria. They come in various shapes and sizes, although in specific colors (especially brick-red, brown and natural); fitting or locking perfectly into each other when installed to give a firm longitudinal bearing and surface brilliance throughout the entire area of application. These interlocking stones are often used in external flooring in buildings, walkways and on roads. 

However they continue to suffer from issues ranging from poor strength to low staying power especially due to poor production and faulty installation as well as their inability to sufficiently withstand weathering, tension forces and frequent trampling which they were originally designed to accommodate. This is not abnormal because pure concrete only perform well against compression and will fail under tension if not sufficiently reinforced. In other to make up for these shortcomings, there have been increasing calls for the introduction of reinforcement in concrete paving stones; a call which seem to fall into deaf ears.

Now with the invention of a new variant of pavers made from either pure or recycled rubber a few years ago, the option scale has widened. This 50mm thick rubber dog bone interlocking pavers (also referred to as I-Pavers or Bow-tie pavers) is increasingly gaining popularity amongst builders, home owners and developers across the globe owing to its toughness, low-impact surface condition, non-slip property and durability (up to 50 years) even though it is not good against fire. 

Despite all these admirable qualities, it is still cheaper than the concrete or brick type, a lot easier to produce, install and maintain and comes in a wider range of exciting colours, designs and patterns. Its low-impact surface quality make it the delight of children when used in their play grounds because even when they fall to the ground while playing, they won’t sustain as much injuries as with the concrete or brick type pavers. 

Together with its effective noise control potentials, it is very suitable for use on camp grounds, sport grounds, studios, schools, relaxation centres, resorts, restaurants, supermarkets, bus stops, hallways, walk-ways, road pavements, car parks, estate roads and residential homes. Although there is no known manufacturer of this product in Nigeria, this line of business is highly profitable elsewhere hence should be encouraged back here to reduce importation and create more jobs. 

The production processes are beyond the scope of this article but the preferred mode of installation is meticulously described thus;

Prior to installation, a shallow or topsoil excavation should be performed on the ground/earth upon which the pavers will be laid up to 150mm depth after adequate site preparation.

Note: Where the sub-soil shows high quantity of clay, shallow excavation up to a reasonable depth (say 200mm beyond the top-soil excavation) should be carried out to remove the clay-saturated soil and replace it with highly draining soil like mined sharp sand. This is the best practice for installing all types of interlocking paver including the traditional (concrete) interlocking stones. The reason is that due to the plastic nature of clay, it tends to retain water/moisture which should have drained quickly and naturally into the earth; expanding and contracting abnormally with change in weather conditions at different times of the year, forcing uneven settlement and surface cracks which impedes on the stability of the pavers and displaces them in various directions.

On grounds with high water table (i.e. swampy or water-logged areas), a damp proof material should be laid flat in between the sand bed and above the water table/level. In such cases the interlocking pavers should be sloped slightly during construction such that it empties all surface water into a nearby drainage, since the damp-proof barrier will prevent water from soaking away beneath the surface.  

         Above the natural ground level, smooth or sharp sand should be used to fill the earth and make up levels and to receive the pavers directly. Do not use earth filling (or red sand) here. This surface fill should be properly treated with eco-friendly herbicides. No cement is required to install rubber dog bone pavers.

    Once the sand filling is completed, it should be well compacted till it is relatively stiff and firm. Using a preferred style (e.g. slanting/angular, perfectly vertical or perfectly horizontal patterns), the tiller pushes and locks the pavers into the soil and into each other respectively in an organized manner up to half the depth of the pavers with the use of a soft mallet (for manual installation).  A stopper (e.g. a thin fibre frame) should be installed at the open ends of the paved area to prevent the systematic collapse of the entire set-up by weathering.

-          In the end you have an exquisitely finished paving that can stand the test of time.