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A guide to cost efficient house design

A large amount of owner builders are often caught off-guard in terms of the budget of a building project and being conscious of this fact early on during the design process can save you a lot of headache during the building process. Following is a few pointers to keep in mind when designing and budgeting for your proposed home:

 

Size

Obviously making a home smaller makes it less expensive, but instead of making all the rooms in the existing design 10% smaller, why not rethink the design entirely. Think carefully about redundancy – do you really need a separate dining & living room or can it be combined as one room? By combining same uses into the same space eliminates interior walls and at the same time less space is required compared to smaller rooms confined by interior walls.

If you do not know how a room is going to be used you usually design it much too big. Think about your furniture and how you are going to arrange it – when designing your floor plan, always make use of realistically sized furniture symbols to define the room sizes accurately.

 

Levels

The next thing to consider is whether you would like to build a single-storey or double-storey home. Factors that will influence your decision might be amongst others: Stand size / shape, soil conditions, views and of course cost. In very favourable soil conditions, (and if the stand permits it) it is usually up to 15% less expensive to build a single-storey house as foundation construction costs can be kept to a minimum. However, the cost of building a double-storey is not necessarily more expensive than a single-storey as the cost of the 1st floor slab might cancel out a big percentage of the cost of the foundations and treating of the ground and ground floor slab especially if the ground conditions are of poor quality.

 

Building Shape

The shape of the floor plan can have a significant impact on the building cost of a proposed project. If you are on a very tight budget, there can be a substantial saving in keeping away from long rectangular or complex shapes with a lot of direction changes. Where possible, try to keep the shapes as square (boxy) as possible and eliminate unnecessary internal walls and direction changes in walls. Remember: Attractive homes are very often based on relatively simple box forms, properly proportioned, composed, and detailed.

The diagram below is an efficiency comparison between various floor plan shapes. Other than the circle which is the most efficient shape, note that the closer a ‘box shape’ is to a perfect square the fewer the perimeter wall material required to construct a house with the same area. All four designs below are the same floor area of 64 square meters, but the perimeter walls when straightened differs by over 15 meters between the circular & irregular shape! Also note that every corner added to the perimeter makes the plan and roof construction more complex and less cost effective.

House plan shape cost comparison

 

Efficient use of Building Materials

Try to keep material wastage to a minimum in your design. Design your house as much as possible on the established modules of building materials.
A simple example: Gypsum ceiling sheets are manufactured in sheets of 900x2700mm, hence wouldn’t it make sense to try to design your rooms in a grid with 900mm increments and then use 300x300mm tiles to keep wastage to a minimum?

This applies to many other building materials which can be a lot more expensive. Always try to keep material wastage in the back of your mind when designing your floor plan.

 

Openings

Every opening in the building envelope add to the costs considerably. Whether it’s a window, door or even just an open arch, all openings are labor intensive and windows and doors are expensive items. Also large windows might require very expensive special safety glass and costs will quickly get out of hand.

 

Roof Material

The different roof material considerations might be one of the following in approximate order of descending cost: Waterproofed concrete slab, Thatch, Clay roof tiles, Sheet metal, Concrete roof tiles. Other roofing materials like Natural slate tiles or Copper sheeting are available as well but less commonly used and expensive.

In general, a double Roman concrete roof tiled roof at 26 degree pitch might be one of the most cost efficient roofs. Using sheet metal roofing might add between 20-80% to the cost and a concrete slab or thatch roofing might be as much as three times the cost.

 

Roof Shape

When designing your home also keep the shape of the roof in the back of your mind. If you are looking at building a double pitch roof, having a lot of unnecessary valleys and ridges as opposed to a very simple roof can work out as much as double the cost for the same area of roof. Thatch roofing, being a lot more of a free-form in its construction, a lot more complex designs can be designed without it being significantly more expensive than as is applicable to a rigid tiled roof. A concrete slab roof might be expensive, but there would be almost no limit to the shapes that can be created in the floor plan, without an effect of the cost. With concrete roofs the size is directly proportional to the cost.

 

Services

These two items might be the most overlooked cost items for 1st time home builders. The installation and labour cost of plumbing & electrical services without the fittings could be as much as 15% of the total building project cost depending of the complexity of the design and number of points for fittings supplied.

When designing the bathrooms & kitchen try to place them together as close to the sewer connection point as possible but don’t let this control your overall design.

 

Finishing

The choice of finishes in your home would noticeably be the dominating factor in the total project cost. Put the money in finishes and fixtures where it will be most appreciated. For Example: Put the expensive granite counter-tops in the kitchen and perhaps the master bath, but not in the laundry room.

If you are a really cost conscious 1st time builder or perhaps a developer, this is where the most savings could be made, but be careful to take it beyond the point where it starts to compromise re-selling value of the home.