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Updated: Jun 12

Nothing makes a potential build client more comfortable than using the square metre rule to determine the cost of their drawings. Unfortunately, sometimes they trust this metric more than a builder's cost estimate.

In this month’s Insiders Series, we go full math to show how all square metres are not created equal and how redundant the cost per metre metric is for pricing your concepts. Also, we’ll show how keeping the shape of your build design simple can help keep costs down.

When a Quantity Surveyor does a measured estimate, costs are based on the perimeter of your build, along with gross floor areas, neither of which are the same from build to build. Amounts of materials required like guttering, cladding, foundations, windows, external walls, floor covering, ceiling coverings and roof cladding are all affected by the perimeter lengths of your home and also the number of corners. These corners, both external and internal, affect the cost - and don’t get us started on curves.

Diagram 1 above (10 x 10)

This square home has a 100m2 floor area and a perimeter length of 40 lineal metres. With 0 internal corners and 4 external corners, you couldn’t get more basic. But let's take a look at diagram 2.

Diagram 2 above (2 x 50 shape)

Doesn’t look too different right - but wait! Yes, the floor area is still 100m2, but we now have 202 lineal metres of perimeter. So our cladding, foundations, guttering and painting all just went up.

Diagram 3 above (H design)

Now let's take a look at diagram 3 - the shape has become more complex. We now have 12 facades, as opposed to the original four. We have 4 internal corners and 8 external corners, yet with the same 100m2 floor area. And the lineal metre length of the perimeter is 56m. So more time in planning and materials to manage those corners.

Diagram 4 above (staircase design)

Diagram 4 is the ultimate in crazy facade design, but it helps explain the point. Still with 100m2 of floor area, however we have 16 facades to manage, 6 internal corners and 10 external corners.

When we break down the many shape variations for a floor area, we understand how the costs can vary and potentially get larger. You can have your premium floor coverings, stone bench tops and raking ceilings, if you do just one thing - keep the shape simple!!

If you're looking for a true costing of your concepts, please get in touch. We offer a robust Measured Estimate service, carried out by our in-house Quantity Surveyor.

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