What are the 6 estimating methods?
- Single rate: Functional unit of accommodation.
- Single rate: Floor area.
- Multiple rate: Elemental cost per (GFA) m2
- Multiple rate: Elemental unit rate
- Multiple rate: Approximate quantities
- Multiple rate: BQ
How do you estimate using the functional unit of accommodation? 2 points
Nr of units x Cost range = Cost
Adjust rate for finishes, location etc.
How do you reverse budget using the functional unit of accommodation?
Budget / Cost per unit = Nr of units
How do you estimate using the floor area method?
GIFA x Cost range = Cost
GIFA - measured at each floor level
What are the advantages and disadvantages of using the floor area method of estimating? 9 points
Advantages
1. Quick.
2. Simple.
3. Ideal for early budgeting purposes.
4. Directly relates to accommodation.
5. Allows for comparisons of different designs.
6. Allow comparisons between buildings that differ in size and shape.
Disadvantages
7. Doesn’t allow for extra ceiling height eg. warehouses. Allowances must be made.
8. Very loose estimation because quantity of key elements do not necessarily increase or decrease per m2 eg. number of walls and doors.
9. Specification adjustments not feasible as quality differentials are element specific.
How do you estimate using the elemental cost per (GFA) m2?
Calculate the proportion of the total cost for each element on a similar building then apply to measure for the new building.
How do you estimate using the elemental unit rate?
Approximate quantity of each element x Unit rate = Cost of each element
Name 6 sources of cost data.
- Own historical data - preferred.
- National historical data.
- Price books.
- Specialist subcontractor quotes.
- Magazines.
- Web sites eg. larger cost consultants.
Priorities when selecting cost data? 3 points
- Similar buildings.
- Recently tendered buildings.
- Using several comparable sources.
What adjustments to source rates must be made? 3 points
- Inflation.
- Location.
- Quality.
What assumptions and exclusions should be included in cost estimates? 9 points
EXCLUSIONS
1. External works / preliminaries.
2. VAT
3. Professional fees.
4. Fittings and furnishings.
5. Land cost.
6. Interest charges.
ASSUMPTIONS
7. Overheads and profit added at 5%
8. Preliminaries added at 10%
9. Contingencies added at 5%
What affects the degree of accuracy of an estimate? 3 points
- Quality of information supplied / available.
- Quality of sources of cost data.
- Skill of the surveyor.
What are the three adjustment calculations?
Time adjustment = Proposed index / Historical index
Location adjustment = Proposed index / Historical index
Cost x Time x Location = New total
How much contingency should you allow for in an estimation? 2 points
5% on new builds and 10% on refurbishment.
How do you estimate using the approximate quantities method?
Measurements concentrated to a few items as needed, per element. eg cavity wall - same area for external brick facing, cavity, insulation, internal block skin.
