Contents

1. Foundations

2. Order and system

3. Ground work 3.1 Excavation 3.2 Disposal 3.3 Earthwork support 3.4 Surface treatments 3.5 Disposal of water

4. Concrete

5. Brickwork/Blockwork 5.1 Lengths and girths

6. Damp-proof courses

7. Concrete ground floors

8. Self-test project

9. Answers 9.1 Answer to Self-Assessment Question 9.2 Self-test project commentary

© The College of Estate Management 2013

Paper 1407V6-0

Measurement of substructures

Measurement of substructures Paper 1407 Page 3

1 Foundations

As always, it is important to adopt a logical order for measuring the work. In this case the most natural order is that in which the work is executed and therefore the first section of the taking-off usually deals with ‘foundations’, sometimes referred to as ‘work below damp-proof course’.

2 Order and system

It is as well to think for a few moments about the items to be measured. Whether you make a written list or not will depend upon your ability and experience, but at this stage you are recommended to prepare a take-off list prior to commencing take-off which will provide a useful checklist. A taking-off list is prepared using the drawings for that particular project and could look like this:

Strip turf Remove topsoil Excavate trench Concrete Brickwork Cavity DPC Filling Adjusting topsoil outside.

Before starting to measure you should study the drawings available, specification and borehole records. In practice the following need to be clearly marked on the drawings:

Existing ground levels Finished ground levels/floor levels Depths of foundations Groundwater level (plus date as this varies seasonally) Any known existing foundations or services.

After preparing the taking-off list it is good practice to calculate the over-site area of the building and the centreline of any trench foundations that are required.

Measurement of substructures Paper 1407 Page 4

SELF-ASSESSMENT QUESTION

To test yourself, try to calculate the over-site area of the building shown dotted below and the centreline of the trench foundation (this is the same as the centreline of the wall).

Here the wall is 250mm thick and the spread of the foundation is 300mm, i.e. an overall foundation trench width of 850mm.

Note: The indent to the plan shape is called a want. The total depth of excavation is 1,200mm.

(Answer under Section 9.1)

Measurement of substructures Paper 1407 Page 5

3 Ground work

3.1 Excavation

Where construction is to be carried out on a site not previously developed it is usual to assume a layer of topsoil covers the site. This should be excavated and is normally preserved on site for later use. A depth of 150mm is normal but it could be considerably more and reference to any borehole records would be made to establish an average for your project. Site levelling is then measured down to the underside of the hardcore bed below any ground slabs. This is either in m² or m³ depending on your standard method. The area required to be stripped should be measured to the outside face of any excavations or the spread. Precise areas are measured, not large rectangles, despite what may actually be excavated in practice.

If there are existing ground slabs or pavings on the site then these will need to be broken up. This is measured as ‘extra over’ the item of excavation, describing the composition of the paving and the thickness. If any foundations are left in the ground then these are measured in cubic metres and can again be extra over any excavation.

The trench excavation is normally measured in cubic metres, along the centreline of the trench, multiplied by the width and then the depth. It is important to note if there are any width categories that need to be identified for compliance with your standard method of measurement (SMM) and how the different depths are classified. Figure 1 shows what is required for the RICS New Rules of Measurement: Detailed Measurement for Building Works (NRM2). Identifying commencing levels if trenches are excavated from a level below the existing ground level is required for NRM2, as this can make the choice of plant used or method of working more expensive.

Working space may be required to allow the worker in the trench room to fix formwork or apply a finish such as tanking to the foundations. Under NRM2 this is not measured and neither is the earthwork support – these items are contractor risk items. The contractor can then make his own assessment on the amount of working space and earthwork support required, depending on the construction work and depths involved. Other SMMs may require a working volume to be calculated and added to the trench or other foundation excavation and a separate item to be measured for the backfilling.

The term ‘excavate trenches’ includes for digging and getting excavated material up to the original ground level, hence the need to state the starting level and to give the depth of excavation in stages; the rules are drafted on the basis of mechanical excavation. The subsequent handling and disposal of the excavated material must be measured separately.

Where excavation is next to existing services this is measured by the metre and is extra over a previous excavation item. If, for example, a gas service crosses a trench excavation then this is numbered and again measured extra over the trench excavation.

3.2 Disposal

Every item of excavation must have its volume included in a corresponding backfilling or disposal item.

Measurement of substructures Paper 1407 Page 6

This balancing can be achieved in two ways: either

1. each item of excavation is regularly followed by an item of similar volume for backfilling around foundations, which is subsequently adjusted for the volume displaced by concrete and brickwork below ground level; or

2. the excavation items are followed by a disposal of surplus spoil item and this later adjusted for the volume of backfilling.

The method used will depend on which is the quicker and easier according to the particular foundation design. For example, see Figure 1. Here, the volume of backfill with excavated material is vertically hatched and is relatively easy to calculate. Therefore, it is better initially to dispose of all the excavated material off site and then later deduct for the volume required to be used as backfilling.

In Figure 1 either of the two methods previously described could be used. In many situations the backfill to the side of the wall under a ground-bearing slab will be in hardcore, and Method 2 is more applicable.

Where the full depth of the trench is filled with concrete, as in Figure 2, it should be described as disposal of excavated material from site in the first instance and no further adjustment is then necessary.

Do not overlook the fact that if topsoil has been stripped off or there has been reduced level digging as a first item, there may be a need to return some on top of the backfilling around the perimeter of the building. This is not in any adjustment of trench item and will generally involve a separate deduction of depositing topsoil on site and an addition of backfilling with topsoil from site.

FIGURE 1

FIGURE 2

Measurement of substructures Paper 1407 Page 7

EXAMPLE 1

3.3 Earthwork support

Temporary support for the sides of excavation, of whatever nature may be necessary for the particular position and circumstances, is referred to as Earthwork Support. You should check the rules in your SMM governing this item as they will be seen to cover a whole range of possibilities, the simple first and the greater risk situations later.

It should be noted that under NRM2 earthwork support is not measured unless specified by the engineer and not at the discretion of the contractor. This is measured in square metres, with the maximum depth stated. Again, if you are using a different SMM, check to see what is applicable.

It is important to describe the location of the earthwork support as this will affect the loadings placed on the support and hence its cost. If the ground is unstable, next to a roadway or an adjacent building, this should be clearly stated. Other situations affecting the cost of providing the support would be if the face requiring support were to be curved or if the excavations went down into the water table (groundwater).

20.000.60

0.85

Excavating trenches commencing 150mm below ground level, depth less than 2m

&

Filling obtained from excavated material, final thickness greater than 500mm

Stage 1 Initial measure of trench

20.000.60

0.23

Concrete, 1:3:6, 20mm aggregate in foundations poured against face of excavation

&

Deduct Filling obtained from excavated material, final thickness greater than 500mm

&

Add Dispose excavated material off site

Stage 2 Measure of concrete strip. And adjustment for the volume of filling displaced by the concrete

20.000.25

0.62

Deduct Filling obtained from excavated material, final thickness greater than 500mm

&

Add Dispose excavated material off site

Stage 3 Adjusting for the volume displaced by brickwork. This item cannot normally be ‘anded on’ as each skin of the wall may well have been measured

Note: the depth is not the height all the way up to the dpc as measured for the brick- or blockwork.

Depth Trench 0.850Less concrete 0.230 0.620

Measurement of substructures Paper 1407 Page 8

3.4 Surface treatments

Under NRM2, no item is to be measured for compacting the bottom of excavation. Again, you should check your SMM to see what is applicable.

3.5 Disposal of water

Whenever it is proposed to dig into the ground it is prudent to make provision against water of any form getting into those excavations as conditions rapidly become unworkable if not immediately checked. NRM2 only requires the disposal of groundwater to be included as an item so that the estimators can include their assessment of the cost of keeping the excavations free of water.

4 Concrete

The rules dealing with the measurement of concrete are normally divided into the following sections:

In situ concrete Formwork Reinforcement Designed joints Worked finishes Accessories.

If the foundations are stepped the additional concrete in the steps should be cubed and added to the general concrete in the foundations. It will also be necessary to measure formwork to the vertical face of the steps. (See Example 2.)

The concrete should be described as either mass concrete or reinforced and the type of mix included. The description would also try to identify the function the concrete is performing, for example: beam, column, foundation. Concrete is measured in cubic metres but the size of the member and its location will affect the subsequent pricing.

Measurement of substructures Paper 1407 Page 9

EXAMPLE 2

(mean girth as previously used in Example 1)

FIGURE 3

20.00 0.60 Conc (1:3:6 (20mm agg))

in fdns poured against face of excav

0.23 2/ 0.30 0.60 (Steps) 0.15 2/ 0.60 Fwk to sides fdn

ne 1.00m hi

Measurement of substructures Paper 1407 Page 10

5 Brickwork/Blockwork

The rules relating to brickwork and blockwork should be particularly noted and understood as they affect even the simplest work. These rules are included in Section 14 of NRM2. Again, check your own SMM rules as you work through this section.

The measurement of brickwork is a self-contained section and under the group system of measurement one does not initially take notice of any adjustment for door or window openings. Blank openings, which are in the nature of small openings without doors or windows, would also be disregarded and measured later after ‘Doors’. However, discretion has to be used, particularly with the more modern type of construction where often whole walls are ‘window openings’, and in such a case it would be pointless to measure a non-existent wall. A careful consideration of the particular problem is necessary and having considered the particular details the most suitable approach is decided upon.

This attitude should be cultivated even with the simple tasks that are set, whether the building is a box-like structure or a spine or cross wall type.

Once the approach has been decided, one should keep everything else out of one’s mind; one should concentrate on visualising the nature and extent of all walls, where they have their foundations or bases, where their tops and ends are, what the various thicknesses are and whether there are any projections.

It is also necessary to consider the nature of the bricks and mortar, for quite often there are two kinds of brickwork apart from special bricks for facing purposes which will be discussed later.

One usually measures the external walls of a traditional building first. This is followed by the internal, load-bearing walls. Walls which divide or partition larger spaces into smaller spaces are then considered and measured. Although not normally an SMM requirement it is advisable in the case of the substructure that brickwork be separately classified under the heading of foundations.

Any projections on or above a wall are measured immediately after the length of wall on which they occur and a chimney stack (if present) is measured after the uppermost height of the wall to which it is attached. Most chimney stacks have the topmost metre in height built in a denser mortar to safeguard the exposed, and therefore vulnerable, brickwork against premature dilapidation.

Measurement of substructures Paper 1407 Page 11

5.1 Lengths and girths

The first calculation, or ‘waste calculation’, is to determine the mean girth of the wall (i.e. the length along the centreline of the wall) in the following manner:

This is a very important and fundamental calculation, one that is always occurring and therefore should be completely and unhesitatingly understood before proceeding any further. It is often called 4 times, 2 times the distance moved.

It will be readily appreciated that the sum of twice the length plus the breadth will give the internal girth of the walls. To make allowance for the increased length of the mean girth of the walls for the corners, four times the thickness of the walls is added to the internal girth. If the external girth had been calculated this allowance for the corners would have been deducted. The reasoning for these adjustments is as follows:

Care should be taken when cavity walls are used and each skin is of a different material or thickness.

EXAMPLE 3

Length 8.000Width 4.000 12.000 × 2 24.000Angles 4/2/½ × 215 0.860Mean girth 24.860

Measurement of substructures Paper 1407 Page 12

The next point which you must understand is how to make adjustment for a building having a re-entrant angle or one having a projection. For example:

The corners still require the addition of only four times the wall thickness as each extra internal angle cancels out one of the extra external angles. If you are not perfectly clear on this point you should draw two sketches to scale, showing the mean length dotted as in previous examples, and deduce the reasoning for yourself and check by actual measurements of wall by wall.

In each case the mean girth is:

Length 6.500Max width 5.000 11.500 × 2 23.000Corners 4/215 0.860 23.860

Measurement of substructures Paper 1407 Page 13

6 Damp-proof courses

The measurement of damp-proof courses is a part of substructure brickwork. It would almost certainly be the demarcation line between foundations and load-bearing superstructure. These should be measured in metres if less than 300mm wide and in square metres if over 300mm wide, as required by item 14.16 of NRM2.

EXAMPLE 4 Please take your time to work through Example 4, understanding why all the dimensions and descriptions have been arrived at.

Consider the measurement for a foundation up to dpc for the following sketches.

Measurement of substructures Paper 1407 Page 14

FOUNDATIONS 1

Taking-off List Lifting turf for preservation Excavating topsoil for preservation Depositing topsoil in heaps Excavate foundation trench Backfill Concrete in foundations Brickwork in foundations Form cavity Fill cavity and concrete Adjust backfill for concrete and brickwork Topsoil filling around perimeter

A description of the soil or a borehole report should be given, e.g. The Contractor is to assume that the strata is 100mm of vegetable soil on top of light sandy loam (no water was found)

Surface strip

Wall 4.000 × 5.000

2/.255 .510 .510

Spread

750 255 2/495

247 × 2 .495 .495

5.005 6.005

Calculations set out in parallel can be adopted where the details are similar for both of the build-ups

Rounded off to nearest 10mm

5.016.01

Lifting turf for preserving in 1,000 × 300mm pieces, roll, wheel average 20m & stack on site for reuse

5.5.1

The turf is removed for the area of the building plus the ‘spread’ of concrete around the outside

0.601.20

Deduct ditto (Want

Leave a reasonable space between items. Explain by annotation or signposting why the deduction is made

Measurement of substructures Paper 1407 Page 15

FOUNDATIONS 2

Topsoil 100Less turf 25 75

5.01 6.01

Site preparation, remove topsoil for preserving average 75mm deep

This description could be anded-on to the first item

0.60

1.20 Deduct ditto (Want

5.016.01

0.08

Add Preserve topsoil wheel average 20 m & deposit in temporary spoil heap

It is good practice to emphasise the change back to positive quantities

0.601.20

0.08

Deduct ditto (Want

Trench 5.000 4.000 2/ 9.000 18.000Corners 4/255 1.020 Centreline 19.020

G.L. 100.000Datum 98.800 1.200Topsoil, etc. .100depth 1.100

As this girth is an internal one it is necessary to make adjustment for the corners (5 ext – 1 int = 4 net)

Measurement of substructures Paper 1407 Page 16

FOUNDATIONS 3

19.020.75

1.10

Foundation excavation, trench commencing 100mm below ground level, maximum depth not exceeding 2.00m

5.6.2.1

&

Filling obtained from excavated material, final thickness greater than 500mm

5.11.2

19.0204/2/½/.750 3.000 22.020

Measurement of substructures Paper 1407 Page 17

FOUNDATIONS 4

19.020.75

0.15

Concrete (1:6 – 40 mm aggregate) horizontal work in foundations poured against earth

11.2.1.2.1

G.L. 100.000 Dpc .150 100.150Datum 98.800 Concrete .150 98.950

Height of bwk 1.200

2/ 19.02

1.20

Half brick vertical wall in sand-lime bricks in gauged mortar (1:1:6)

14.1.1.1

The average length of the two skins is correct here but could not be used if they were of differing materials or thickness

19.02 1.20

Forming cavity 50mm wide in brickwork with galvanised twisted ties to BS 1243, spaced 5/m²

14.14.1.1

1.200 Less .150Height to ground level 1.050

2/ 19.02

Horizontal dpc to BS 743 in widths not exceeding 300mm, 100mm laps, in cement mortar (1:3)

Damp-proof courses are normally measured here

Measurement of substructures Paper 1407 Page 18

FOUNDATIONS 5

19.020.05

1.05

Concrete (1:12) vertical work < 300mm thick in filling to hollow wall

11.5.1.1

19.020.75

0.15

19.020.26

0.95

Deduct Filling to excavation a.b.

Depth trench 1.100Less conc. 0.150 .950

&

These are the volumes of concrete strip and wall below topsoil displacing backfilling

Add Disposing excavated material off site

As the disposal is deemed to be at the Contractor’s discretion there is no need to state any distance in the disposal item

Int. girth 18.0004/2/.255 2.0404/.247 .990 21.030

21.030.25

0.10

Filling obtained from preserved topsoil from on-site spoil heap, wheel average 20m & deposit, spread & level in making up levels N/E 250mm thick

Assume that backfilling to original ground level is of topsoil as turf would be beyond reuse

Spoil heap was ‘temporary’ in earlier description

Measurement of substructures Paper 1407 Page 19

7 Concrete ground floors

A distinction must be made between the different classifications of concrete and they are to be billed in separate sections.

The ground-floor items comprise filling to make up levels, hardcore bed and concrete bed; the finishings are usually taken later in the Finishings section. The filling may be either excavated material or imported hardcore and in both cases it is measured cube, stating whether the average thickness is less or more than 500mm. It is normally specified to be deposited and compacted in layers. You should refer to your own SMM to see if this is applicable to you.

If there is an opening in the bed, formwork must be measured to the edge of the concrete. It should be noted that rebates, grooves and the like are produced by the formwork and are not labours on the concrete.

8 Self-test project

The following take-off sheets have been prepared using NRM2.

You are required to check them for conformity with the principles within that document.

Mark any errors or revised descriptions and then go to Section 9.2 and compare with the commentary.

On completion, if you do not understand any item, seek help from within your workplace or from CEM.

The same exercise can be undertaken using your local SMM if you do not normally use NRM2, and please ask if you are unsure about any item.

Measurement of substructures Paper 1407 Page 20

Self-Test Project USING NRM2

6.210 3.642spread 2/.30 0.600 0.600 6.810 4.242

total dig 1.956less veg. soil 0.200

1.756

6.8104.242

Site preparation, remove topsoil for preservation ave. 200mm deep

&

Retaining excavated material on site, topsoil in temp. spoil heap not exceeding 50m

6.8104.242 1.756

Bulk excavation, exc. to red. levels comm. 200mm below extg. g.l. not exc. 2m deep

&

Filling material obtained from site to exc.

&

Dispose exc mat off site

2/6.810 12.6202/4.242 8.484

21.104less 4/0.600 2.400

18.704

18.070.60 1.20

Foundation exc. trench comm. 1.7m below g.l. not exc 2m deep

&

Filling to exc.

1

Measurement of substructures Paper 1407 Page 21

18.70 0.60

Plain conc. (1:3:6 – 40mm agg) in foundations 200mm thick

&

Deduct Dispose ex mat off site

&

Add Backfilling as before

2

Measurement of substructures Paper 1407 Page 22

9 Answers

9.1 Answer to Self-Assessment Question

The waste calculations can be written over the description and dimension column to save space.

Length Width 12.000 6.000

Add 2/wall 0.500 0.500

Add 2/spread 0.600 0.600 13.100 7.100

13.10 7.10

Site preparation, remove topsoil for pres. on site av. 150mm deep

&

Retaining excavated material on site, in temporary spoil heap n.e. 50m from excavation × 0.15 = m³

It is also acceptable to put a waste calculation immediately prior to an item it is referring to.

4.50 2.50

Deduct Both Last two items

Length 12.000 6.000 2/ 18.000 36.000Add for the corners 4/0.25

1.000

37.000

37.000.85

1.05

Foundation excavation, trench depth ≤ 2m

&

Backfilling with excavated material obtained from site

exc. depth 1.200Less t.soil 0.150 1.050

Measurement of substructures Paper 1407 Page 23

9.2 Self-test project commentary

You need to be able to visualise what you are measuring.

The original take-off follows. The errors have been numbered and then explained.

200mm veg soil

1.756m reduced level

1.200m trench

600 mm

Self-Test Project USING NRM2

6.210 3.642spread 2/.30 0.600 0.600 6.810 4.242

total dig 1.956less veg. soil 0.200

1.756

1

6.8104.242

Site preparation, remove topsoil for preservation ave. 200mm deep

&

Retaining excavated material on site, topsoil in temp. spoil heap on site not exceeding 50m

2

56

6.8104.242 1.756

Bulk excavation, exc. to red. levels comm. 200mm below extg. g.l. not exc. 2m deep

&

Filling to exc.

&

Dispose exc mat off site

3

4

4

2/6.810 12.6202/4.242 8.484

21.104less 4/0.600 2.400

18.704

7 8 9

11 18.07

0.60 1.20

Foundation excavation, exc. trench comm. 1.7m below g.l. not exc. 2m deep

&

Filling to exc.

10

12

1

Measurement of substructures Paper 1407 Page 24

Items to be considered

1. Dimensions to 2 decimal places only and rounded to nearest 10mm.

2. Topsoil disposal is cubic metres.

3. Commencing level is only stated if more than 250mm below ground level.

4. Only one disposal item taken either backfill or removal and then adjustments made later.

5. See (1).

6. Error in dimension 1.756 to be 1.76.

7. Calculation error should be 13.620.

8. Ditto = 22.104.

9. Ditto = 19.704.

10. Commencing level should be 1.756.

11. 18.07 should be 19.70.

12. Compaction is square metres and cannot be ‘&–on’. 19.70 × 0.60.

13. Need to state if less than or greater than 300mm thick.

14. 18.70 should be 19.70.

15. Should be cubic metres. Cube × 0.20 for all three items.

1415

18.70 0.60

Plain conc. (1:3:6 – 40mm agg) in foundations 200mm thick

&

Deduct Dispose ex mat off site

&

Add Backfilling as before

13 16 16

2