Composite Rate Build Up for Roof and Ceilings – Approximate Quantities in Elemental Estimate Layout

Composite Rate Build up – Roof

The Elemental Estimate layout and grouping of items will be used in this example. When building up composite rates for Approximate Quantities, you have to follow some basic principles. We are going to illustrate a composite rate build-up for the Roof:

Roof construction: 6 x Double-pitched Truss Type 1, size 7020 x 1100mm high at maximum 1200mm centres, 114 x 38mm wall plates, 38x76mm diagonal bracing, longitudinal binders, roof covering 0.5mm thick IBR embossed galvanised profiled troughed steel sheeting fixed to 75x50mm timber purlins at 1200mm centres, including Super Sisalation Residential Grade 410 waterproof insulation laid taut over timber purlins at 1200mm centres and fixed concurrent with roof covering including galvanised steel straining wires at 275mm centres over purlins. Horizontal plasterboard ceilings 6.4mm thick x 1200mm wide boards with and including H-type pressed steel jointing strips and 38x50mm sawn softwood brandering at 400mm centres, plus paint to ceilings.

Step 1

First, you have to determine the Group unit of measurement. When you are measuring the Roof in Elemental or Approximate Quantities estimating, the group unit of measurement is the square metre (m2) on flat area or sloping surface. We will use the flat area.

Step 2

The second step is listing all associated Bill items that can be mapped to the Roof by area. These are:

• IBR roof covering  – (m2) Rate – R155.00
• Super Sisalation waterproof insulation – (m2) Rate – R25.00
• Plasterboard ceilings including softwood brandering – (m2) Rate – R35.00
• Painting to ceilings – (m2) Rate – R40.00

Step 3

The next step is listing all associated Bill items that can be linked to the Roof. These are items which cannot be mapped to the area.

Timber Roof Construction:

Timber roof construction has members which are measured in metres and number. In order to convert the members of roof construction to cost per square metre, we should associate them to the flat area between two trusses. The trusses are spaced at 1200mm centres, and the base length of the truss is 7020mm. The flat area between trusses is 7.020 x 1.200m

• Truss 7020 x 1100mm high – (No.) Rate – R900
• 114 x 38mm wall plate – (m) Rate – R22.00
• L-shaped angle brackets nailed to truss  and wall plate – (No.) Rate – R2.00
• Purlin clips (Hurricane type) nailed to rafter and purlin – (No.) Rate – R2.00
• Galvanised hoop iron roof tie 1500mm, built into brickwork and wrapped around wall plate – (No.) Rate – R2.00
• 38x76mm Diagonal bracing – (m) Rate – R22.00
• 38×50 Longitudinal binders – (m) Rate – R20.00
• 75x50mm Purlins – (m) Rate – R19.00

Step 4

Rate Build Up for mappable items (areas). Since your Group unit is the square metre (m2), you should convert the Bill item rates to Cost per Square Metre:

The composite rate for items which can be mapped to the Flat Roof Area is R295 per square metre.

Step 5

Rate Build Up for Timber Roof Construction:

Timber roof construction requires a Rate Build Up for items which cannot be mapped to Roof Area. The flat area between trusses is 7.020 x 1.200m.To convert the Bill item rates to Cost per Square Metre, we have to use principles that are used in building up composite rates for Windows. In this case, the flat area between trusses (7.020×1.200)m should be treated as a single entity (Think of a single window). This allows us to link associated items to this single entity, for example, we can link items in Step 3 to this entity. We will then find the total cost of items in this entity, and then convert the cost to cost per square metre:

The composite rate for ROOF CONSTRUCTION is R1399.82 per Flat Area (7020×1200). Now we have to convert this rate to Cost Per Square Metre:

Step 6

Convert Composite Rate to Cost Per Square Metre

You can convert this rate to Cost Per Square Metre for the Elemental Estimate:

Flat Area between two trusses 7020 x 1200,

Area = 7.020 x 1.200 = 8.424m2

Therefore, cost is R1399.82 per 8.424m2

Elemental Rate = R166.17 per m2

Step 7

Add up the rates to get the Total Rate:  295 + 166.17 = R461.17 per square metre.

Total Composite Rate for Approximate Quantities = R461.17 per m2

Elemental Layout and Grouping

Items which go into the element ROOF and components Construction, Coverings and Insulation are stated in the description:

Items which go into the element CEILINGS AND SOFFITS  and components Nailed Up Ceilings and Cornices are stated in the description: