Terrain, surveys and valuations

Ground stability

It is important to know your section is solid. For example, a subdivision built over an old dump site could be slowly sinking, or it could have toxic waste below the surface.

The services of an engineer are likely to be needed if there is concern about the stability or compactness of the earth. A geo-technical engineer will be called in, usually by the architect or designer, to do some testing. If there are difficulties with stability or compactness, special design of the foundations will be required, with input from an engineer.

If you are buying in a new subdivision, the developer will probably have an engineer’s report you can ask to see. Any earthworks in urban areas have to be done to standards, with engineer certification of earthworks over a certain depth or height identifying the finished ground is suitable for residential development.

There may be limitations on the types of materials that can be used. If there is a lot of infill it may not be possible to use heavy materials, such as concrete block or brick, to build the house. This is important as most of us assume the ground will be suitable for any type of construction.

For older areas, the LIM or council files may give you information about the ground stability and likely bearing capacity at the site. Or there may be encumbrances placed on the certificate of title identifying any uncertified or un-engineered fill in the site.

Tip: If you are unable to find any information, you can check for things like uneven ground, leaning trees, old slips and evidence of fill. This could indicate ground instability. Also talk to the neighbours and check old photographs, if any exist, to note any movement or history relating to the section.

If there is any reason to think the ground might not be stable, or provide adequate bearing, or needs special drainage, call in the services of a suitably qualified engineer. You can find a list of chartered professional engineers in the Yellow Pages.

You can also request a Hazard Report from Quotable Value Ltd. A Hazard Report gives an assessment of earthquake frequency, fault rupture, amplification, liquefaction and landslide risk specific to the site. It is not to be used instead of a site inspection or engineering report, but does provide information about what lies underneath a property. You can request the report online www.qv.co.nz or phone 0800 164 444. Regional councils may also have relevant property information.

Environmental zones

Wind, earthquake load and other environmental factors will determine your home’s design and maintenance requirements.

Every property is classified into wind, earthquake, snow load and corrosion zones.

These zones determine how strong any building on the property needs to be, what materials should be used, and how it should be maintained.

Why do zones matter?

When you build, renovate or maintain your home, knowing something about the zones your house or section is in will help you or your designer choose the best materials.

It will also help you design your home to take advantage of the site’s natural assets and ensure it is strong enough to withstand the elements.

Using more durable materials may mean less maintenance is required or the materials will not need to be replaced as soon. The zone of the property may also affect how often you need to carry out normal maintenance.

For example, a house built on the seafront will need washing more regularly than a house built in the middle of the island because of the effects of sea spray.

How do you know what zones you’re in?

The various calculations required to identify the zones your house or section is in will usually be worked out by the designer or engineer after a site visit. The local council may also be able to identify some of these issues for you.

The following zones are from New Zealand Standard 3604:1999 Timber Framed Buildings. This standard is an acceptable solution to the Building Code and guides much of the construction of timber-framed buildings in New Zealand. You can purchase a copy of this standard from the Standards New Zealand website.

Wind

Wind forces, like earthquakes, create horizontal forces on buildings. Any building needs to be sufficiently strong to withstand these forces.

There are five things to consider when looking at the effects of wind on your site:

• Wind region.
• Lee zone.
• Ground roughness.
• Site exposure.
• Topographic class.

Topographic class and ground roughness

Land formations change wind flow.

Wind speed increases as it passes over or between hills and through valleys. This is the wind-tunnel effect you feel in cities with lots of tall buildings.

Wind speed slows as it goes over rough terrain, caused by a drag effect. The shape of the hills and valleys (the topography) and the amount of shelter upwind will also have an effect on the wind speed over your site. At least 500m of rougher ground is needed to affect the wind profile of your site.

Site exposure

The amount of protection from other buildings or natural obstructions affects whether your site is classed as “exposed” or “sheltered”. Most suburban developments on flat or gently sloping sites would be considered “sheltered”.

Bracing requirements

Your home's bracing design will limit the amount of sway during frequent wind storms and earthquakes. It will also stop the house collapsing due to more severe earthquakes or wind storms.

NZS 3604 can help you to determine your wind region, whether you are in a lee zone or if you need to consider rough terrain and wind drag.

The calculations for this determine the house bracing demand. The overall bracing demand for your site for wind will be classified as low, medium, high, very high or “specific design”. A house in a low-wind zone will require less bracing than a house built in a very high-wind zone.

In some cases an engineer will need to work out bracing requirements if the wind zone is higher than very high – this is called specific design.

Earthquake

The earthquake zone your site is in will affect its bracing demand. As with wind, bracing demand is the horizontal forces the building, or parts of the building, can resist.

The cladding materials on the roof and walls of your house also affect bracing demand, as does the height of your house.

For information about environmental zones visit BRANZ's Level.org.nz website.

Survey information

You need to make sure your section is surveyed correctly so you don’t encroach on your neighbour’s property and your house is correctly set out in relation to the boundary pegs.

It can be useful to get a copy of the cadastral plans and an aerial photo of the property. Your council can provide these, for a fee. While these can provide you with background information about the section, they are not guaranteed to be accurate and may not provide the amount of detail needed to accurately define the boundaries. To order a plan or photos, you need the legal description of the property, e.g. Lot 1 DP 12345 (DP stands for deposited plan). A rates demand or valuation notice will have this information.

If there is any doubt about the exact dimensions of the section, use the services of a registered surveyor to identify the precise boundaries. For example, the pegs might not be able to be found, especially with older properties. In some cases, the property may never have been surveyed so it won’t have a deposited plan (DP).

Getting it re-surveyed will help you avoid expensive encroachment disputes and ill will between you and your neighbours.

To engage a surveyor, you can make an appointment to see them in their office or at the section. The surveyor has access to maps, survey plans, and the district plan. If possible, you should take with you:

• The certificate of title.
• The current valuation for rating purposes.
• Aerial photos.
• Engineering drawings.
• A sketch of your proposal.

Look in the Yellow Pages or on the NZ Institute of Surveyors website to find a surveyor.

Getting a valuation

A valuation will allow you to see if the price reflects the market value of the section. You may need it if you are borrowing from a bank. A private valuation done by a registered valuer is most likely to give you the true value of your property at the time when you apply for a mortgage.

Note: There may already be valuation done for the vendor; we say it's wise to get your own.

You can find a registered valuer by searching on the New Zealand Property Institute website. A registered valuer is one who has met the standards and requirements of the Valuers Registration Board (VRB), and has a current practising certificate from the VRB.

A Rating Valuation (which you will find on the rates bill for a property, or by searching www.qv.co.nz) can also give you some idea of the market value of a property.