What Site Reports are Required?

Each council has an overlay mapping system which shows environmental factors affecting sites. These can include bushfire, flood, slippage, heritage, noise corridor, protection, acid sulfate soil and other overlays. Each overlay generally requires a specialist report. 

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Before ordering site reports, a Preliminary Design (floorplan, elevations, site plan) is sent out which are referenced in the reports. The results of these reports are then added to the final Working Drawings. The result of the reports can affect design aspects such as cladding, windows, footings, site location, and overall design.

 

At this stage a treatment system should be designed, as the design of the home can affect the cost and type of system dramatically.  

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What are the Design Stages for Building Approval?

There are four main stages of design:

i) Preliminary Designs: these are basic floorplans, elevations and site plans and are used to obtain site reports and estimates.

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ii) Site Reports: It is essential that all relevant site reports are obtained before completing the next stage. 

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iii) Working Drawings: which include floorplan, site plan, elevations, door/window schedules, roofing layout, cabinetry/plumbing layout, floor coverings, electrical layout and sectional views.

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iv) Engineering Stage: these are produced by specialist consultants and include energy assessment, structural engineering and foundation engineering. There may be other specialist reports required. The engineer will issue a certification for the designs, which are checked by the certifier onsite. 

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All Working Drawings and engineering documents (and certifications) are required for building approval. 

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Some financial lenders will not approve finance without the Working Drawings and all engineering documents. 

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Owners should be wary of 'cheap designs' as they are usually Preliminary Designs only with owners being charged exorbitant fees for the remaining full set of designs required. 

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What Are PC and PS Items?

PC (Provisional Cost) items are set allowances for items that the owner has not selected. PC amounts are usually used by custom design companies, where an allowance is made for Inclusions that the owner can select from the supplier of their choice eg. $300 for a toilet. If the owner spends more or less than this amount, a variation is made for the difference.

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PC allowances should not be made for trade work or materials costs eg. rendering, framing etc. 

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PS (Provisional Sums) are made for works that cannot be confirmed until the works are completed. However, a reasonable allowance must be made eg. a builder may allow a PS of $3000 for tree clearing as the site cannot be accessed until the trees are cleared. 

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An experienced builder and a detailed set of plans should reduce the need for provisional sums altogether. 

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Can A Pre-Built Modular Home be Put on Any Block?

Many modular home companies sell pre-built modular homes. This saves a lot of time for the owner. However, there are some important factors to consider, which are often overlooked. Different blocks have different requirements. These include fire ratings, wind ratings, floor heights for flooding etc. A lot of modular home builders will build the homes to the absolute basic requirements - often N2 wind rating, with no bushfire provisions and bracing is usually based on a standard 700-900mm height off the ground. Many modular homes are sold 'ex-factory', which means the owner is responsible for organising not only the delivery, but the certifications and approvals. Buying a cheap modular home that doesn't comply with the requirements of the block can be a very expensive mistake. 

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Before purchasing any pre-build modular home, owners should always obtain an overlay report and relevant site tests and reports, and compare the results with the engineering of the pre-built modular home. 

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Soil Types

The first report to obtain, even before purchasing a block, is a soil classification report. The results of the report can impact the overall design of the home. Soil types are determined by the clay content of the soil which affective the reactivity of the soil, making the ground shrink and swell.

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Trees on the block also affect the results of a soil report. Trees absorb moisture, causing the ground to shrink and causing cracking. Trees and their roots should be removed prior to obtaining a soil report. 
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Soil types are:​

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A - little reactivity. This is perfect soil types, but rarely found.

S - slightly reactive. This is very good soil type for building.

M - moderately reactive. This is the typical result for residential estates.

H - highly reactive. For slabs, additional engineering is required. Typically, raised homes are considered. 

E - extremely reactive. Typically black soil on farming land. Large footings and adjustable heads are typically used. 

P - problematic. This can be a result of trees, land slippage, underground water or other issues.

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Raised or Slab?

The decision to build on slab or a raised home depends on several factors:

 

i) Cost: Generally, a slab is the most cost-effective option. However, with the increasing costs of concrete and labour, both options are becoming comparable.

 

ii) Location: Delivering concrete to rural sites may be too costly, making a raised home more cost-effective. 

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iii) Soil Type: unstable or reactive soils can crack slabs which cause damage throughout the home. On very reactive sites, adjustable heads are used on top of the stumps so the home can be levelled when movement does occur. 

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iv) Site Slope: If the site is sloping, blockwork and drainage needs to be factored into the costs. Typically, blockwork retaining, in-filling and compaction is very costly and can settle over time, causing cracking. Generally, if there is more than 1m of cut/fill, owner's should consider a raised home. 

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Note: slabs can be raft slabs or waffle pods. Although cheaper, waffle pods have been problematic for decades. Owners should research waffle pods before finalising their design. 

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What Documents Should Go With a Build Contract?

There are many, many, many cases where build costs escalate and owners are issued seemingly endless variations. How does this happen with a Fixed Price Contract? Basically, the contract price is fixed. However, the specifications and inclusions are not of the standard the owners thought they would be, or the engineering was not completed and now there are additional 'unforeseen' works required.​

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A contract should contain four parts:

i) the build contract;

ii) a detailed set of Working Drawings (plans)

iii) the engineering documents, including structural and foundation designs;

iv) specifications, listing every item with Make and Model, or an allowance. 

  

Owners should confirm the details by stating 'as per display home' or 'as per engineering' eg. Hamptons Fan HDC342, as per display home alfresco'. 

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Who Should Design the Home: Builder vs Designer

Generally, builders understand the costs of building a home, and understand basic engineering requirements. However, builders typically design boring homes and don't use current building methods. 

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On the other hand, architects and drafters are notorious for designing homes that look amazing, but end up costing well over the owner's budget. 

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There is also the issue with ownership and IP. If the builder designs the plans, and then quotes a price that is unreasonably high, owners may not be able to use the plans with another builder. This can also be the case if an architect designs the home. 

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The balance is to use a designer who is also experienced in building and ensure the plans can be used by any builder (usually on license by the designer). ​​​​​​​​​

                                               

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Design Elements to Avoid When Designing a Home

There are some elements in design that look amazing, but end up costing a fortune, or have serious issues in the long term. Some of these include:

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i) box gutters: when rooflines slope down into a wall or parapet, a large internal gutter is used. These are notorious for overflowing and leaking, and when they do, the water runs down the inside of the walls and ceilings of the home causing large-scale damage. Many builders will not build a home that has box gutters.

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ii) rooftop alfresco areas: instead of a roof, an outdoor area is built. These are common in apartment buildings and 2 story beachfront homes. Typically the roof is waterproofed and tiled. Over time, the waterproofing membrane breaks down, or the tiles are damaged, and water finds its way into the home. The damage is usually extensive and very expensive to repair. 

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iii) glass walls: they look great and a lot of renderings incorporate glass walls. However, there are two major downfalls:

* they are very expensive and the structural around them usually required oversized members;

* with current energy requirements, large areas of glass can be very difficult to pass energy assessments. 

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iv) cheap items from hardware stores or online. Cheap items from hardware stores and online stores are notorious for causing extensive issues. These include:

* tiles cracking and absorbing water​

* plumbing fixtures failing and leaking water inside walls

* plumbing and electrical items not to Australian Standards, with non-standard connections

* stone benchtops that are not sealed and crack or pit easily

... and the list goes on. 

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Only quality items from reputable businesses who offer guarantees and warranties should be used. 

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Design Steel Frame or Timber Frame

This has been one of the most argued points in the building industry for decades. There are Pros and Cons for each:

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Steel framing:

* stronger than timber. Greater spans can be achieved

* lighter than timber and typically easier to assemble

* termite proof

* straight and true, and does not warp, twist, rot or crack 

* steel is unforgiving and mistakes in the fabrication can be expensive and cause delays

* needs to be galvanised when close to the beach 

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Timber framing:

* can be delivered quicker, particularly if in stick form

* easier and quicker to design and engineer

* susceptible to termites, rot and mould

* installation is usually rough and uneven 

* limited spans - steel members are required for large spans 

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In recent years, steel framing and timber framing have become comparable in pricing, with steel pricing being cheaper on some designs. In general, steel framing is becoming the accepted option.