The land surveyor is not a building surveyor who evaluates building conditions. Instead, he measures buildings to prepare building survey drawings such as floor plans, elevation views, roof plan, cross sections and structural dimensional details.
Building survey drawings, also known as ‘measured drawings’, are needed for:
- Accurate details of existing features to facilitate design
- Conservation buildings where reliable building plans are not available
- Buildings with renovated features to be regularised for statutory compliance
- Resolution of disputes
- Statutory certification by a Registered Surveyor
There are also other less common situations requiring measured drawings such as:
- Accurate documentation of organic details such as motifs, figurines
- Documentation of a preserved monument
- Dimensionally accurate details of existing structures such as steel bridges, beams and columns, roof trusses.
For dimensional correctness and certain statutory compliances, measured drawings are to be prepared and certified by Registered Surveyors.
Measured drawings often do not stand alone. For submissions, they usually include the boundaries which only Registered Surveyors can establish and certify. If a topographical survey plan is required, the building and boundaries would also be outlined in it.
Floor plans prepared by Registered Surveyors are also required for computation and certification of Strata Areas and Gross Floor Areas (GFA) of existing buildings. These also include floor plans with delineated areas for tenancy and sales agreements.
The need for a Registered Surveyor is his expertise in survey measurements including:
- Specialist skills in measurement
- Relating the measurements to national datums such as SVY21 Datum and Singapore Height Datum
- Being licensed experts in boundaries and related issues
The authorities’ requirement for certification by Registered Surveyors is to protect the interest of the public (i.e. property owners, developers).
The surveyor employs a mix of tools to measure the buildings according to the needs and situations. The following provides an overview of these tools:
- Measuring tapes:
The measuring tape is a traditional tool that, if used on its own, has become inadequate for the prevailing complexities and expectations. Being able to measure only linearly is not suitable for non-square configurations and curves. As the measuring tapes are not calibrated, the inaccuracies increase over distances. It should be used minimally, and only for short distances such as wall thicknesses. If used for a whole building, a total station should be used to verify gross dimensions to minimise cumulative errors.
The distometer uses the laser to measure distances. Although it is more accurate and can measure longer distances than the tape, it is also a linear distance measuring instrument. It can be useful for measuring longer distances such as a cross checks across a large room that had been measured with the tape. However it cannot measure very short distances such as thicknesses of wall. If used for a whole building, a total station should be used to verify gross dimensions to minimise cumulative errors.
- Total Station:
The total station is the standard instrument for a land surveyor. It measures both angles and distances with high precision. Using laser, it can measure a point or feature without physically contact – thus making it a versatile yet precise tool for measuring both interior and exterior of a building – including the high out-of-reach points. Walls that are not at right angles are also measured accurately.
The total station is essential for boundary and party wall surveys which are referred to in the measured drawings. Hence, it is indeed the basic tool for accurate measured drawing surveys.
- Laser Scanner:
The laser scanner collects billions of points of a building – literally making a 3D copy of the subject. Details can then be extracted from these 3D points.
The laser scanner has unique advantages:
- Captures minute details
- Fast, minimal field time required on-site – minimum inconvenience to clients
- Accurate documentation of organic shapes
These minimise the need for revisits to site for further details.
If the scanned data to be referenced to the SVY21 datum, the total station is necessary to supplement the scanner. The surveyor’s level is also required for the platform or floor levels.
What can go wrong?
Not all plans are made the same way or of similar qualities. Inaccuracy often only rears its ugly head only during the construction and result in delays and remedial redesigns, and in more serious cases, requiring resubmission to authorities.
A building totally measured using the measuring tape will likely have severe cumulative errors. The floor levels and roof profiles cannot be properly measured. If any part of the building is not right angled, distortions will be the likely consequence. It is also not possible to incorporate the boundaries reliably. Essentially, it is not possible to produce a reliable building drawing with the tape alone.
Documenting organic details such as motifs is always a challenge. Sketching, tape measure or tracing off photographs will result in dimensionally distorted drawings. These are severe limitations in documentation of conserved monuments. The most appropriate instrument to use is the laser scanner.
Measuring the roofs of conserved buildings in congested areas is not easy as they are often not visible from available ground positions. The ridges are often adopted by the authorities to compute the required setback distances for new annex buildings. Accurate heights and profiles of the roofs are also essential for exact interface with the new structures. Survey data for the roof should not be left to estimates or adopting data from non-survey plans. Surveyors use photogrammetry, drones, raised platforms, measuring from other buildings or develop new methods to acquire accurate data.
Unreliable building or measured drawings, apart from not complying with statutory requirements, can also result in project delays, remedial designs, additional construction costs, resubmission to authorities and contractual disputes and litigations. These can be avoided by getting the right people for the job.
If you have any further queries about building survey drawings, you can contact us here and we will be happy to assist you.