Building Measurement and Estimation: Key Concepts for Construction Costing
1. Ordinary Measurement
Ordinary measurement is the process of measuring completed or proposed construction work in suitable units for preparing estimates, bills of quantities and payments.
Measurement is generally taken item-wise for different types of construction work.
The measurement represents the actual quantity of work to be executed or completed.
The dimensions are generally recorded in the order of length × breadth × height/depth/thickness.
Linear works are measured in metres.
Surface works are measured in square metres.
Volume-based works are measured in cubic metres.
Steel reinforcement is generally measured by weight.
Individual items such as sanitary fittings and electrical points may be measured by number.
Measurements form the basis for calculating the cost of construction.
Proper measurement is essential for preparing estimates, bills and contractor payments.
The lecture specifies that measurement should be made for the finished item and that its description should account for materials, transport, labour, fabrication, tools, plant and overheads required to complete the work.
Sketch: Draw a simple measurement sheet showing an item with columns for length, breadth, height/depth, quantity and unit.
2. Quantity Surveying
Quantity surveying is the systematic process of calculating and managing the quantities and costs of materials, labour and construction work required for a project.
It involves measurement and calculation of different construction items.
Quantities are calculated from architectural and structural drawings.
It includes quantities of earthwork, concrete, brickwork, plastering, flooring, painting and other works.
It helps in preparing the estimate of a project.
It forms the basis for preparing the Bill of Quantities (BOQ).
It helps contractors determine the cost of construction.
It assists in preparing tenders and quotations.
It helps in checking work executed at site.
It assists in determining payments to contractors.
Accurate quantity surveying helps in controlling construction expenditure.
The purpose of estimating is also connected with tendering, contractor payments and resource planning.
Sketch: Draw a simple sequence: Drawings → Measurement → Quantities → BOQ → Rate → Cost.
3. Plinth Area
Plinth area is the covered built-up area measured at the floor level of a building.
It is measured at the floor level of a storey.
It can also be measured at the basement floor level.
It is generally measured using the external dimensions of the building.
Internal and external wall areas are included.
Open courtyards and open spaces are generally excluded.
It is also commonly referred to as built-up area in the lecture.
Plinth area is generally greater than carpet area.
It is important for preparing approximate cost estimates.
For a multi-storeyed building, the plinth area of each storey is determined separately.
Plinth area = carpet area + wall areas + applicable openings/other included areas.
The lecture states that plinth area is generally about 10–20% higher than carpet area and is obtained using the outer-to-outer dimensions of the building.
Sketch: Draw a floor plan showing the outer wall boundary as plinth area and inner usable rooms as carpet area.
4. Circulation Area
Circulation area is the area provided for movement of people within and around a building.
It facilitates movement between different spaces.
It forms an important part of building planning.
It may include corridors and passages.
It may include verandahs.
Staircases are part of vertical circulation.
Lift areas are associated with vertical circulation.
Balconies may also be considered as circulation-related areas depending on their function.
Circulation can be classified into horizontal and vertical circulation.
Horizontal circulation includes corridors, passages and similar movement spaces.
Vertical circulation includes staircases and lifts.
The area lecture specifically defines circulation area as the floor area of verandahs, passages, corridors, balconies, staircases and lifts used for movement of persons.
Sketch: Draw a simple floor plan highlighting a corridor, staircase, lift lobby and verandah as circulation spaces.
5. Site Plan
A site plan is a drawing showing the proposed building and its relationship with the surrounding site.
It shows the site boundary.
It indicates the position of the proposed building.
Building setbacks can be shown.
Access roads and entrances can be indicated.
North direction is generally shown.
Existing site features may be represented.
Landscaping and open areas can be indicated.
Parking and circulation can be shown.
Important site dimensions are provided.
It helps the estimator understand the site conditions and the location of the proposed work.
Site conditions directly influence construction cost because construction methods, labour, weather, ground conditions and machinery requirements can vary from site to site.
Sketch: Draw a rectangular site boundary with north arrow, road, building footprint, setbacks, entrance and parking.
6. Line Plan
A line plan is a simple preliminary drawing showing the basic arrangement of spaces in a building.
It represents the basic layout of the building.
Rooms are shown in their approximate positions.
Walls are generally represented using simple lines.
Room relationships are clearly indicated.
Circulation spaces can be identified.
Doors and openings may be indicated.
Dimensions may be provided at a basic level.
It helps in understanding the planning arrangement.
It is useful during the preliminary design stage.
It can form a basis for developing more detailed drawings.
Sketch: Draw a simple rectangular plan divided into living room, bedroom, kitchen, toilet and corridor, using simple lines.
7. Index Plan
An index plan is a small-scale drawing used to indicate the location and general arrangement of a project.
It provides an overall understanding of the project location.
It is generally drawn at a smaller scale than detailed drawings.
It may show major roads and surrounding features.
It indicates the location of the site.
It helps in identifying the project in relation to its surroundings.
It may include important landmarks.
It can indicate the orientation of the site.
It is useful for reference and identification.
It provides a quick overview rather than construction details.
It is generally used along with more detailed drawings.
Sketch: Draw a small-scale map showing site, surrounding road network, north direction and important nearby landmarks.
8. Detailed Plan
A detailed plan is a properly dimensioned architectural drawing that provides information required for understanding and executing the building work.
It shows the detailed arrangement of spaces.
Walls are represented with their actual thickness.
Doors and windows are indicated.
Room dimensions are provided.
Wall thicknesses are shown.
Staircases and other building elements are detailed.
Fixtures and important components may be indicated.
It provides information required for estimation.
It is used along with sections and elevations.
It provides a more accurate basis for calculating quantities.
For estimation, the estimator must be able to read building plans, notes and specifications and identify discrepancies before preparing the estimate.
Sketch: Draw a properly dimensioned floor plan showing walls, doors, windows, rooms, staircase and dimensions.
9. Centre Line Plan
A centre line plan is a drawing in which the centre lines of walls are used as the basis for calculating quantities.
Centre lines represent the middle axis of walls.
The method is particularly useful for walls having similar cross-sections.
Total centre line length is calculated.
Quantity is obtained by multiplying centre line length by breadth and depth/height.
It reduces repetitive calculations.
It is especially useful for regular plans.
Junctions of cross walls require special attention.
Half the breadth may need to be deducted at wall junctions.
It is quicker than the long-wall short-wall method in suitable buildings.
It provides accurate quantities when junctions are properly considered.
The lecture specifically states that the centre-line method is suitable for walls of similar cross-sections and requires careful treatment of cross-wall junctions.
Sketch: Draw a rectangular building plan with a centre line running through the middle of each wall.
10. Rates
A rate is the cost assigned to a unit quantity of a particular construction item.
Rate is required to convert quantities into monetary cost.
It may be expressed per cubic metre, square metre, running metre, kilogram or number depending on the item.
The rate includes the relevant material cost.
Labour cost is considered.
Equipment and machinery costs may be included.
Transportation costs may be considered.
Overheads are considered where applicable.
Contractor’s profit may be included in the final rate.
Rates depend on location and prevailing market conditions.
Accurate rates are essential for reliable estimates.
The lecture identifies material, labour, equipment, overhead and profit as major components of construction cost.
Sketch: Quantity × Rate = Amount/Cost.
11. Types of Area Calculations
The important area calculations used in estimation are plot area, plinth area, built-up area, covered area, carpet area and circulation area.
Plot area: Total area enclosed within the site/plot boundary.
Plinth area: Covered area measured at floor level using the building dimensions.
Built-up area: Area covered by the building on different floors, including applicable building components.
Covered area: Ground area covered by the building above the plinth level.
Carpet area: Actual usable area of rooms that can be carpeted.
Floor area: Plinth area after deducting the area occupied by walls.
Circulation area: Area used for movement such as corridors, passages, stairs and lifts.
Super built-up area: Built-up/plinth area with applicable common/exterior areas added.
These areas are important for planning and estimating.
They should not be confused because each represents a different measurement basis.
Sketch: Draw three nested plans labelled Carpet Area → Built-up/Plinth Area → Super Built-up Area.
12. Carpet Area
Carpet area is the usable floor area within a building that can actually be occupied or carpeted.
It represents the usable area of rooms.
It is measured within the structure.
Wall thickness is not included in the carpet area.
Circulation areas are deducted according to the lecture definition.
Sanitary accommodation is deducted according to the stated method.
Kitchen, pantry and stores may be deducted according to the lecture definition.
Carpet area is smaller than plinth area.
For residential buildings, the lecture gives an approximate range of 50–65% of plinth area.
For office buildings, the lecture gives an approximate range of 60–75% of plinth area.
It is useful for understanding the actual usable space of a building.
Sketch: Draw a floor plan with the usable room areas shaded inside the wall boundaries and label them Carpet Area.
13. Built-up Area
Built-up area is the area covered by a building within the premises and may include various building components depending on the applicable definition.
It includes covered building areas.
It may include areas on different floors.
It may include applicable cantilevered portions.
It may include basement areas.
It may include stilt/podium areas.
Utility and service areas may be included.
Mezzanine floors may be included where applicable.
Built-up area is generally greater than carpet area.
It is used in planning and cost estimation.
The lecture refers to the UBBL Amendments 2020 definition for built-up area.
Sketch: Draw a floor plan showing Carpet Area + Wall Area = Built-up Area.
14. Plinth Area Estimate
A plinth area estimate is an approximate method of estimating the cost of a building.
The plinth area of the building is first calculated.
External dimensions are generally used.
Open courtyards are excluded.
For multi-storeyed buildings, each storey’s plinth area is determined separately.
A suitable plinth area rate is obtained.
The rate is based on similar buildings in the locality.
The plinth area is multiplied by the plinth area rate.
The result gives the approximate building cost.
Additional components may then be added as applicable.
It is useful during preliminary planning and feasibility studies.
Formula: Building cost = Plinth area × Plinth area rate
The lecture gives an example of 100 m² at ₹2,000/m², giving a basic building cost of ₹2,00,000.
Sketch: Plinth area × Plinth area rate → Approximate building cost.
A.R./A.M. estimate: prepared for annual repair and maintenance.
15. Long Wall–Short Wall Method of Measurement
The long wall–short wall method is a method used to calculate quantities of construction work.
The wall along the longer dimension of the room is considered the long wall.
The wall perpendicular to it is the short wall.
Centre-to-centre dimensions are first determined.
Long wall length is calculated out-to-out.
Short wall length is calculated in-to-in.
Long wall length = centre-to-centre length + one wall breadth.
Short wall length = centre-to-centre length − one wall breadth.
These lengths are multiplied by breadth and depth/height to obtain quantity.
Long wall length generally decreases as the construction moves through footing stages towards superstructure.
Short wall length generally increases correspondingly.
The lecture gives the formulas: long wall out-to-out = C/C length + one breadth and short wall in-to-in = C/C length − one breadth.
Sketch: Draw a rectangular room with the two longer sides labelled Long Wall and the two shorter sides labelled Short Wall, showing centre-to-centre and out-to-out/in-to-in dimensions.
16. Long Wall–Short Wall Method: Example
Consider a room of 5 m × 4 m with a wall thickness of 0.3 m.
Centre-to-centre length of long wall = 5 m.
Long wall length out-to-out = 5 + 0.3 = 5.3 m if 5 m represents centre-to-centre dimension.
Centre-to-centre length of short wall = 4 m.
Short wall length in-to-in = 4 − 0.3 = 3.7 m.
For two long walls: 5.3 × 2 = 10.6 m.
For two short walls: 3.7 × 2 = 7.4 m.
These lengths are multiplied by the respective breadth and depth of each construction layer.
Different footing widths require separate calculations.
The same procedure is repeated for excavation, foundation concrete, footings, plinth and superstructure.
This produces the quantity required for the detailed estimate.
Sketch: Draw a 5 m × 4 m room plan with 0.3 m wall thickness and label long wall out-to-out and short wall in-to-in.
17. Centre Line Method of Measurement
The centre-line method calculates quantities using the total centre-line length of walls.
It is suitable where walls have similar cross-sections.
Centre lines of all walls are determined.
Total centre-line length is calculated.
The centre-line length is multiplied by the breadth of the item.
It is then multiplied by its depth or height.
The same centre-line basis can be used for different stages of construction.
It is quicker than the long-wall short-wall method for suitable plans.
Junctions between cross walls and main walls require special attention.
Half the breadth is deducted at applicable junctions.
Accurate calculation of junctions is essential for obtaining correct quantities.
Formula: Quantity = Total centre line length × Breadth × Depth/Height
Sketch: Draw a rectangular plan with centre lines through all walls, including a cross wall and its junctions.
18. Centre Line Method: Rules at Junctions
Junctions are the most important part of the centre-line method.
For a simple rectangular building without cross walls, the method is straightforward.
Total centre-line length is calculated.
At corners where walls meet, no separate addition or subtraction is generally required.
Cross walls joining main walls require special consideration.
For each junction, half the breadth of the respective main wall may be deducted.
A partition wall having two junctions may require deduction of one breadth.
Different types of walls should be calculated separately.
Main/outer walls of one type are taken together.
Inner cross walls of another type are calculated separately.
Proper treatment of junctions prevents overestimation or underestimation.
The lecture specifically explains that for different wall types, each type is dealt with separately and deductions are made for junctions where required.
20. Units of Measurement for Different Items
Different construction items are measured using different units according to their nature.
Number (no.): Sanitary fittings, electrical points and appliances.
Running metre (m): Cornice, fencing, handrails and pipe lengths.
Square metre (m²): Plastering, painting, flooring, tiling and glass.
Square metre (m²): Half-brick work, honeycomb brickwork and brick-on-edge work.
Cubic metre (m³): Earthwork, earth filling and concrete.
Cubic metre (m³): Masonry work.
Kilogram (kg): Steel reinforcement.
Kilonewton/tonne: Steel may also be expressed in these units depending on the measurement system.
Doors and windows are measured according to the applicable specification and nature of work.
Correct units are essential for preparing accurate quantities and payments.
Sketch: Write no. → m → m² → m³ → kg/tonne and give one construction example under each.
21. Rules for Measurement
The following rules are important while preparing estimates.
Measurement should be made for the finished item of work.
The description should include materials, transport, labour, fabrication, tools and plant where applicable.
Overheads and incidental charges should be considered.
Dimensions are recorded in the order length × breadth × height/depth/thickness.
Linear measurements are taken to the nearest 0.01 m.
Areas are measured to the nearest 0.01 m².
Cubic contents are calculated to the nearest 0.01 m³.
Woodwork for door and window frames may be measured to 0.0001 m accuracy.
Kilogram measurements are taken to 0.01 kg accuracy.
Similar work under different conditions should be measured separately.
The lecture also states that the bill of quantities should properly describe materials, proportions, workmanship and the work to be executed.
22. Need and Importance of Estimate
An estimate is required before and during construction for financial and planning purposes.
It gives an approximate idea of project cost.
It helps determine project feasibility.
It helps determine whether available funds are sufficient.
It helps estimate requirements of controlled materials such as cement and steel.
It is used for preparing tenders.
It helps in checking contractor’s work.
It helps determine payments to contractors.
Quantities obtained from detailed estimates help allocate resources.
It assists in planning and scheduling construction activities.
It helps control expenditure during execution.
23. Role of an Estimator
The estimator is responsible for preparing reliable estimates of building project costs.
The estimator prepares project cost estimates.
Accuracy of estimates is important to the success of the contractor.
Experience in the construction industry is important.
The estimator must understand construction methods.
The estimator must be able to read drawings.
Specifications must be properly understood.
Discrepancies between drawings and specifications should be identified.
The estimator should keep updated with new construction technologies and materials.
Knowledge of market trends and current costs is required.
The estimator should use appropriate reference books, tables, software and cost data.
Sketch: Drawings + Specifications + Site Knowledge + Cost Data → Estimator → Estimate.
24. Factors Affecting Overall Construction Cost
The cost of construction varies according to site and project conditions.
Type of construction affects the cost.
Construction technique affects the cost.
Machinery requirements vary with the type of project.
Formwork requirements can affect cost.
Labour quality varies between locations.
Labour productivity affects construction cost.
Weather conditions influence labour output.
Ground conditions affect excavation and foundation work.
Transportation conditions affect material costs.
Availability of materials and local labour also influences the estimate.
The lecture specifically identifies construction method, machinery, formwork, labour, weather and ground conditions as important cost factors.
25. Preliminary / Approximate Estimate
A preliminary estimate is prepared during the early stages of a project to determine its approximate cost and feasibility.
It is also called an approximate or rough cost estimate.
It is prepared using limited project information.
It helps determine whether a project is financially feasible.
It is based on practical knowledge and similar completed works.
It can be prepared using the plinth area method.
It can be prepared using the cubical content method.
It can be prepared using the unit-base method.
Approximate quantities may also be used.
It is useful for administrative approval and preliminary planning.
A contingency allowance may be provided; the lecture notes 5–10% for approximate estimates.
26. Cube Rate / Cubical Content Method
The cube rate method is an approximate estimating method based on the volume of a building.
It is useful particularly for multi-storeyed buildings.
The cubical content of the building is calculated.
Length, breadth and height/depth are considered.
External dimensions are generally used.
Height is measured according to the lecture’s stated floor-to-floor/top-of-roof method.
Cubical content = Length × Breadth × Height.
The volume is multiplied by the local cubic rate.
It is generally more accurate than the plinth area method.
It is useful for preliminary cost estimation.
Additional costs such as services, contingencies and other provisions may be added as applicable.
Formula: Building cost = Cubical content × Cubical rate
Sketch: Draw a simple cuboid building and label Length × Breadth × Height = Volume.
27. Unit Base Method
The unit-base method estimates cost according to the number of functional units in a building.
It is an approximate estimating method.
The cost per functional unit is determined.
The number of units is then multiplied by the unit rate.
For hospitals, the unit may be the number of beds.
For schools/hostels, the unit may be the number of students.
For schools, cost may also be based on classrooms.
For theatres, cost may be based on seats.
For residential buildings, cost may be based on tenements.
It provides a quick preliminary estimate.
Its accuracy depends on the reliability of the unit rate.
Formula: Total cost = Number of units × Cost per unit
For example, the lecture gives a 50-bed hospital at ₹60,000 per bed, resulting in ₹30,00,000.
28. Approximate Quantity Method
The approximate quantity method is another method used for preparing rough estimates.
The structure is divided into two major parts.
The first part is the foundation including plinth.
The second part is the superstructure.
Total wall lengths are determined.
Approximate quantities of foundation items are calculated per running metre.
Approximate quantities of brickwork are calculated.
Roof quantities can be considered.
Flooring quantities can be considered.
The method is based on practical knowledge and similar construction.
It is useful for preliminary estimation.
29. Detailed Estimate / Item Rate Estimate
A detailed estimate is prepared when adequate information about the building is available.
Detailed drawings and specifications are required.
Individual items of work are identified.
Quantities are calculated item by item.
Suitable units are assigned to each item.
Rates are applied to the quantities.
The amount for each item is calculated.
All item amounts are added to obtain the estimated cost.
Services and miscellaneous works are included where applicable.
It provides a more accurate project cost than a preliminary estimate.
It forms an important basis for tendering and cost control.
The lecture’s detailed-estimate sequence includes earthwork, foundation/plinth work, DPC, superstructure, RCC, doors/windows, flooring, plastering, terracing, painting, water supply, sanitation, electrification and miscellaneous works.
Sketch: Drawings → Item identification → Quantity calculation → Rate analysis → Amount → Abstract estimate.
30. Revised Estimate
A revised estimate is prepared when the originally sanctioned estimate is expected to change substantially.
It is prepared when the original sanctioned estimate is likely to be exceeded by more than the specified limit.
The lecture states more than 5% in one stated condition.
It also refers to expenditure exceeding administrative sanction by more than 10%.
It may be required when there are material deviations from the original proposal.
Changes in design may require revision.
It compares the original and revised quantities.
A comparative statement is prepared.
Reasons for variations are recorded.
The revised estimate gives the updated expected cost.
It helps obtain the necessary approval for changed costs.
31. Supplementary Estimate
A supplementary estimate is prepared for additional work not included in the original estimate.
It is a fresh detailed estimate.
It covers additional work.
The additional work arises during project development or execution.
It is prepared in addition to the original estimate.
Additional quantities are calculated.
Appropriate rates are applied.
The cost of additional work is determined.
The original estimate amount is retained for reference.
The supplementary amount is added to determine the total.
The abstract should show the original estimate and the total including supplementary work.
32. Supplementary and Revised Estimate
A supplementary and revised estimate combines changes to the original work with additional requirements.
It is prepared when there are significant changes to the original proposal.
It may be required when work is partially abandoned.
It may be required when the design is materially changed.
It may be prepared if the original estimate becomes excessive.
The remaining work is reassessed.
New quantities are calculated.
Changes are compared with the original estimate.
Additional works are included.
The revised cost is determined.
Proper approval is required for the revised proposal.
33. Annual Repair / Maintenance Estimate
An annual repair or maintenance estimate is prepared to keep a building or other work in proper and safe condition.
It is prepared periodically.
It covers routine maintenance requirements.
For buildings, it may include whitewashing.
It may include painting.
It may include minor repairs.
It helps maintain the building in proper condition.
For roads, it can include patch repairs.
Repairs to bridges and culverts may also be included.
It helps avoid deterioration through regular maintenance.
It provides an estimated annual expenditure for maintenance.
34. Detailed Estimate: Order of Items
This is very important for exams and numerical questions because it helps arrange items in the correct sequence.
Earthwork.
Brickwork or RCC work in foundation and plinth.
Damp-proof course.
Brickwork in superstructure.
RCC work in superstructure, including centering and steel reinforcement.
Woodwork for doors, windows and ventilators.
Structural steel and grill work.
Paving and floor finishes.
Internal, external and ceiling plastering.
Terracing, weathering course and waterproofing.
Painting and colour washing.
Water supply and sanitation.
Electrification.
Miscellaneous works such as overhead tank, sump, elevation finishes, platforms, septic tank, compound wall and gate.
This sequence is given in the types of estimates lecture.
Sketch: Earthwork → Foundation → DPC → Superstructure → RCC → Doors/Windows → Flooring → Plaster → Terracing → Painting → Services → Miscellaneous.
35. Most Important Formulas for AP-329 Revision
Plinth area = Outer length × Outer breadth
Plinth area cost = Plinth area × Plinth area rate
Cubical content = Length × Breadth × Height
Cube rate cost = Cubical content × Cubical rate
Unit base cost = Number of units × Cost per unit
Quantity of an item = Length × Breadth × Depth/Height
Long wall length = Centre-to-centre length + one wall breadth
Short wall length = Centre-to-centre length − one wall breadth
Centre line quantity = Total centre line length × Breadth × Depth/Height
Total cost = Sum of individual item costs + applicable additional provisions
36. Important One-Line Differences to Remember
Plinth area: Covered area measured at floor level using outer dimensions.
Carpet area: Usable area of rooms that can actually be carpeted.
Built-up area: Covered building area including applicable walls and building components.
Floor area: Plinth area after deducting wall area.
Circulation area: Area used for movement of people.
Long wall method: Long walls are measured out-to-out.
Short wall method: Short walls are measured in-to-in.
Centre line method: Total centre-line length is multiplied by breadth and depth/height.
Preliminary estimate: Approximate cost prepared at an early stage.
Detailed estimate: Item-wise quantity and rate-based estimate.
Revised estimate: Prepared when the sanctioned cost/design/quantities require substantial revision.
Supplementary estimate: Prepared for additional work not included in the original estimate.
Difference Between Long Wall–Short Wall and Centre Line Method
Basis: Long Wall–Short Wall: Long and short walls are measured separately. | Centre Line: Total centre-line length of walls is measured.
Long wall: Long Wall–Short Wall: Measured out-to-out. | Centre Line: Measured along the centre line.
Short wall: Long Wall–Short Wall: Measured in-to-in. | Centre Line: Included in the total centre-line length.
Formula: Long Wall–Short Wall: Long wall = C/C + one breadth; Short wall = C/C − one breadth. | Centre Line: Quantity = Total C/L × Breadth × Depth/Height.
Calculation: Long Wall–Short Wall: Each wall is calculated separately. | Centre Line: Similar walls can be calculated together.
Footing: Long Wall–Short Wall: Length changes at different footing levels. | Centre Line: Length generally remains the same for similar wall sections.
Junctions: Long Wall–Short Wall: Walls are calculated separately. | Centre Line: Junctions require deductions, generally half breadth at each junction.
Suitability: Long Wall–Short Wall: Suitable where wall dimensions/sections vary. | Centre Line: Suitable for walls having similar cross-sections.
Speed: Long Wall–Short Wall: Comparatively slower. | Centre Line: Comparatively quicker.
Main advantage: Long Wall–Short Wall: Easy to understand and apply. | Centre Line: Saves time and reduces repetitive calculations.
Main limitation: Long Wall–Short Wall: More calculations are required. | Centre Line: Incorrect junction deductions can cause errors.
Memory tip: Long Wall–Short Wall = OUT + IN. | Centre Line = CENTRE × BREADTH × DEPTH.