Fullness on plan A concept closely relates to that of size as discussed under the previous section but distinguishing for the usage factor. It is obvious that the rate per square metre for a block of bachelor flats will differ a great deal from the rate for a block of three bedroom flats.
Let us look at the following buildings.
Assuming that an internal division wall will cost us R4,500.00 and a bathroom will cost R25,000.00 complete. We can then calculate the influence of these elements as follows.
Block A
Cost of division walls
= 3
@
4,500 =
R 13,500.00
Cost of bathrooms
= 4
@
25,000 =
R 100,000.00
=
R 113,500.00
Cost /m²
=
113500 ÷ 200
R 567.50
Block B
Cost of division walls
= 1
@
4,500 =
R 4,500.00
Cost of bathrooms
= 2
@
25,000 =
R 50,000.00
=
R 54,500.00
Cost /m²
=
54500 ÷ 200
R 272.50
Although other more complex relationships come to operate with such a comparison we can generally state that an increase in the fullness of a design will also increase the cost per square metre .
Perimeter/ Floor area We have already seen that the plan shape directly conditions the enclosing walls. The Perimeter/Floor area Ratio allows us to compare different plans to establish the more economical proposal.
The lower the ratio, the more economical will be the proposal. Circular buildings have the best ratio but savings are more than offset by the higher cost of circular work.
Let us once again look at a practical example:
Assuming that both houses have an identical floor to ceiling height of 3.00m then the:
Perimeter/floor area ratio for:
House A = AREA OF ENCLOSING WALLS ÷ TOTAL FLOOR AREA = 50m x 3m ÷ 100m² = 1.50
House B = AREA OF ENCLOSING WALLS ÷ TOTAL FLOOR AREA = 40m x 3m ÷ 100m² = 1.20
It should be borne in mind that the perimeter cost can be in the order of 20% to 30% of total cost and an external wall is normally almost twice as expensive as an internal wall.
Once again we should keep other design criteria in mind but the Perimeter/floor area ratio does allow the more experienced client to state the optimum ratio (from analysis of similar houses erected in the past) as part of the design criteria during his brief to the Architect.
Circulation space The minimisation of circulation space by the economic layout of the house provides a definite cost benefit. Entrance halls passages corridors, stairways and ducts can be regarded as dead space which cannot be used but involve considerable cost in air-conditioning, lighting, cleaning and decorating.
In doing a tradeoff analysis between cost and circulation space, one has to consider the functional and aesthetic inputs as previously discussed, but substantial savings can be made by sound subjective judgment.
A fair ratio for circulation to total space can be obtained from previous projects and included in the criteria given during the design brief.
Click on the link to read about Other influences on cost