Design economics i l.jpg
This presentation is the property of its rightful owner.
Sponsored Links
1 / 18

Design Economics I PowerPoint PPT Presentation


  • 63 Views
  • Uploaded on
  • Presentation posted in: General

Design Economics I. Decisions made in this stage in the project have major implication which is also fundamental to good cost management. A decision can be very expensive to correct at a later stage.

Download Presentation

Design Economics I

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


Design economics i l.jpg

Design Economics I

  • Decisions made in this stage in the project have major implication which is also fundamental to good cost management.

  • A decision can be very expensive to correct at a later stage.

  • The available information may be basic. The cost adviser is to establish the most cost effective solution such building shapes, heights, configurations etc for particular situation.

ss5


Design economics i2 l.jpg

Design Economics I

  • Smith (1998, p54) suggests that the project manager has to balance the following factors:-

    • functional

    • technical

    • aesthetic

    • financial

    • environmental

  • or it is simply balancing (i) time (ii) and (iii) quality.

  • An undue bias towards any one of these three will create an imbalance and lead to failure to achieve the client requirements.

ss5


Design economics i3 l.jpg

Design Economics I

  • Time

  • Design length

  • Start date

  • Hand-over

  • Completion

  • Performance

  • Appearance

  • Quality

  • Function

  • Durability

  • Maintenance

Clients Requirement

  • Cost

  • Budget

  • Estimate

  • Tender

  • Final account

  • Cost-in-use

Relationship between time, cost and quality (Ashworth, 1994, p 103)

ss5


Design economics i4 l.jpg

Design Economics I

  • Smith (1998, p56) simplifies the design considerations of these factors as follows:

    • Time usually increases with demands for higher quality

    • Increase in time generally results in higher costs

    • cost increases with greater quality

  • The Project manager (and cost adviser) must understand the sensitivity of the relationship when discussing the factors:

    • the architect will traditionally favour better quality and higher cost,

    • the builder may favour a lower cost and a timing of progress that optimises his resources.

ss5


Design economics i5 l.jpg

Design Economics I

  • The cost adviser’s role is to “protect” the client’s building budget, making sure that designs do not, when costed exceed the clients predetermined financial limits.

  • However quality and time should not be excluded for the sole sake of cost.

ss5


Design economics i6 l.jpg

Design Economics I

  • Types of design decisions that will influence cost

    • total height

    • storey height

    • circulation areas

    • plan shape (cost geometry)

    • size

    • configuration of buildings

    • cellular or open plan

    • mechanisation / prefabrication

    • redundant performance

    • buildability

ss5


Design economics i7 l.jpg

Design Economics I

TOTAL HEIGHT

  • Ashworth (1994, p111) summaries the reasons why tall buildings are more expensive than low rise of comparable size:

    • the need to provide cranage for construction purposes

    • the need to provide expensive services such as lifts throughout the building

    • the higher cost of related elements such as the footings, staircases, etc

    • the increase in fire regulation requirements

    • the increase in requirements for circulation areas (ie lifts)

    • there is less competition for high rise work therefore builder’s prices are higher.

    • There are additional structural costs due to windloading factors (see Figure 1.2)

ss5


Design economics i8 l.jpg

Design Economics I

TOTAL HEIGHT

  • Ashworth (1994, p111) also pointed out that because of the above factors “tall structures are preferred only where the land is either expensive or in scarce supply”.

ss5


Design economics i9 l.jpg

Design Economics I

STOREY HEIGHT

  • Largely determined by the needs of the user of the building.

  • The reason for a greater storey height might include

    • accommodating types of plants and machinery,

    • for prestige reasons (ie a hotel room), or

    • tradition (ie churches).

  • These buildings also share the same problems as tall buildings (ie greater areas of circulation, vertical transportation costs are greater, etc).

ss5


Design economics i10 l.jpg

Design Economics I

STOREY HEIGHT

  • These buildings will also cost more per square metre because there is more wall required to enclose the same amount of space

  • In multi storey building construction (noting the timsing factor on additional floor height), it is important to minimise the height of any vertical zone (ie floor to floor height, ceiling to underside of slab height, etc).

ss5


Design economics i11 l.jpg

Design Economics I

STOREY HEIGHT

  • There are several effects that reduction in storey height will have on the components of a building:

    • it will make the footings less expensive

    • it will allow shorter columns of smaller section

    • it will require less treads and risers

    • it will require less external wall area

    • it will reduce the amount of internal walls and finishes required

    • service distribution lines, pipes, etc., will all be reduced.

ss5


Design economics i12 l.jpg

Design Economics I

CIRCULATION AREAS

Smith (1998, p60 - 61)

  • Circulation areas can account for between 10% and 50% of the gross floor areas of a building depending upon efficiency of layout and function.

  • The amount of circulation space required affects the following factors:

    • Standards of usage (prestigious buildings require more circulation, ie banks)

    • vertical circulation - higher quality building require more lifts and therefor more circulation space.

    • Horizontal circulation - affected by usage of the building, ie schools where large volumes of occupants need to be moved quickly from points around a building, or hospitals where beds need to be move around.

ss5


Design economics i13 l.jpg

Design Economics I

PLAN SHAPE (COST GEOMETRY)

(Smith, 1998, p61)

  • The plan shape of a building has an important effect on its costs.

  • The more a building retreats from a square (the circle is the most efficient enclosure of space, but the cost of building circular work makes it too expensive) the more expensive the external envelope (ie external walls and windows) will become in relation to the remaining building costs. The simpler the shape of the building the lower will be its unit cost.

  • Longer, narrower, complicated and/or irregular outlines will increase the perimeter/floor area ratio which will be accompanied by higher cost.

ss5


Design economics i14 l.jpg

Design Economics I

PLAN SHAPE (COST GEOMETRY)

(Smith, 1998, p61)

  • The plan shape of a building has an important effect on its costs.

  • The more a building retreats from a square (the circle is the most efficient enclosure of space, but the cost of building circular work makes it too expensive) the more expensive the external envelope (ie external walls and windows) will become in relation to the remaining building costs. The simpler the shape of the building the lower will be its unit cost.

  • Longer, narrower, complicated and/or irregular outlines will increase the perimeter/floor area ratio which will be accompanied by higher cost.

ss5


Design economics i15 l.jpg

Design Economics I

PLAN SHAPE (COST GEOMETRY)

  • an irregular outline will also result in increased costs for other reasons; setting out site works and drainage works are all likely to be more complicated and more expensive.

  • Plan shapes also affect other elements e.g. internal partitions, wall finishes etc.

ss5


Design economics i16 l.jpg

Design Economics I

PLAN SHAPE (COST GEOMETRY)

The two methods used for assessing the

plan shape of a building:

  • The wall to floor ratio (or perimeter to floor area ratio)

    • this measures the efficiency of enclosing space. A lower ratio implies that less wall is required to enclose the same floor area. As walls are extremely expensive, this reduction in wall area would represent a saving in the building cost.

    • Computed by diving the face area of external surfaces of the building by the fully enclosed covered area (FECA)

ss5


Design economics i17 l.jpg

Design Economics I

PLAN SHAPE (COST GEOMETRY)

The two methods used for assessing the

plan shape of a building:

  • the perimeter over plan ratio (pop ratio)

    • this measures the compactness of the plan shape. A circle is the most efficient way to enclose the most space but it is not cost effective to build curved walls.

    • It computed by relating the perimeter of a buildings at a building at typical floor level to that of a circle enclosing the same area and expressing the result as a percentage.

ss5


Design economics i18 l.jpg

Design Economics I

PLAN SHAPE (COST GEOMETRY)

The two methods used for assessing the

plan shape of a building:

  • the perimeter over plan ratio (pop ratio)

    • the formula for POP ratio is :

      POP = 2A x 100

      P

      Where:

      A: the FECA of a typical floor level

      P: the perimeter enclosing that area, measured internally

      Note:POP ratio for a circle = 100%

      POP ratio for a square = 89%

ss5


  • Login