Building a House in a Bushfire Zone

One of the first questions I ask, either to the land sales agent or the client (or even of myself when I am standing on a block of land) is: Is this block of land affected by potential Bush Fire Attack?

I did this the other day when I was standing with a client in a newly established subdivision out in Moggill, which is a suburb of Brisbane about 20 kilometers west of the city. It was the nice block of land. It was large, and it had a great aspect, but I checked it out with the Brisbane City Council and prior to the subdivision that parcel of land was designated within a BAL 19 Rating for Bushfire Hazard.

As it turned out we spoke to the developer and the new land subdivision had been re-zoned to include a new bushfire zoning overlay and my client’s block was no longer in a BAL rated zone. That was because a large corridor of trees had been cleared as part of the development. However, the block next door was still BAL Rated at 12.5. So that was great for my client but not so good for the people buying the blocks that were clearly exposed to the bush.

So what does all this mean for you?

Building a House in a Bushfire ZoneIf you are thinking of buying a block of land and it doesn’t matter whether it is in a close city environment or in the hinterland, you have to ask the question: Is the building site affected by a Bushfire Attack Level? And don’t fool yourself about an existing property close to the city. I was looking at a knockdown and rebuild project in Camp Hill which backs onto the White Hill Forest Reserve and you guessed it, the land was in a Brisbane City Council Bushfire Hazard Overlay Zone. That’s only 8km from the Brisbane CBD. There are suburbs in the Inner West and North West of Brisbane that are even closer to the city which can also affected.

You must know what the questions are. Stand on your block and look around: Are you exposed in any way to any natural bush nearby? This will be appealing, and it is. But bear in mind that the Queensland Government and the Local Council will have applied some zoning rules that might impact your block.

So you don’t need to know all the intimate details. You just need to know to ask the question. If your building site is affected by a BAL rating, then you need to know what the rating is. The BAL Zone Rating is what will affect the construction methodology and therefore the cost of building your home.

A Bushfire Attack Level (BAL) is a means of measuring the severity of a building’s potential exposure to ember attack, radiant heat, and direct flame contact. It’s measured in increments of radiant heat (expressed in kilowatts/m2).

A BAL is a basis for establishing the requirements for construction (under the Australian Standard AS 3959-2009 Construction of Buildings in Bushfire Prone Areas), to improve protection of building elements from bushfire attack.

The greater the distance from the fire the lower the heat flux and therefore the construction standard is lower.

Once assessed, your property will be defined by one of six BAL ratings:

  • BAL Low: There is insufficient risk to warrant specific construction requirements
  • BAL 12.5: Ember attack. (BAL 12.5 Construction Requirements)
  • BAL 19: Increasing levels of ember attack and burning debris ignited by windborne embers, together with increasing heat flux. (BAL 19 Construction Requirements)
  • BAL 29: Increasing levels of ember attack and burning debris ignited by windborne embers, together with increasing heat flux. (BAL 29 Construction Requirements)
  • BAL 40: Increasing levels of ember attack and burning debris ignited by windborne embers, together with increasing heat flux and with the increased likelihood of exposure to flames. (BAL 40 Construction Requirements)
  • BAL FZ: Direct exposure to flames from the fire, in addition to heat flux and ember attack. (BAL FZ Construction Requirements)

Building a House in a Bushfire Zone

Where your building is greater than 100 Metres from any classified vegetation the BAL rating will more than likely be BAL–LOW and will not require any special construction requirements.  Where there is a risk or potential that ember attack could affect your home then you will likely fall into one of the BAL Rating Zones.

It would take too long for me to describe the various building and construction requirements for each BAL level. Suffice to say that the average sized home in a BAL 12.5 Zone can generally manage the costs within a sound budget. But in a BAL FZ, you will need a custom designed and built solution that will likely have a budget to take your breath away.

If you are about to buy a block anywhere in Brisbane or South East Queensland and you are not sure if it is BAL rated, drop me an email and I would be happy to check it out for you. Better to find out sooner than later.

Having an Independent Building Consultant in Your Corner

Having an Independent Building Consultant in Your Corner

Knowledge is your key to success in the building industry. As an independent building consultant who has been working with builders and building designers to deliver on the needs of customers for over 15 years I still cannot stress the importance of getting good independent information and to get that information as early as possible.

Yes, our main business is making sure you get the right builder at the right price. But before all that our job is to help you understand and navigate through some of the intricate decisions that you may face.

Now don’t get me wrong. Your project, like many, could be very simple and straightforward. Most are. The point is most of my clients don’t find out the bad news until it is too late.

Before you buy your land, before you choose your builder; do your homework. I urge you to call me at any time with any questions about your project. Obligation free. Why? Because one good piece of information could save you from so much financial pain and stress.

I get asked so many different types of questions here at HBB and there are so many because there are so many different challenges to overcome and decisions that must be made. Each of those decisions will have an impact on the outcome of your home building experience.

For Example, here are some of the questions I have been asked in the last few weeks:

Andrew, I have discovered that the block I have bought is affected by a Bushfire Hazard Overlay. Can you tell me what that means and what it will mean to the design of my home? Will it affect the cost of construction?

Andrew, I have noticed in the inclusions from my builder that they do not allow for a termite protection system but rather insist that the “slab is exposed” and that it is my responsibility to ensure the slab remains exposed. What does that mean? Can I ask the builder to use a reputable termite control product?

Andrew, there is an access easement to my block which services two other blocks in the subdivision. I want to buy the block but I am worried about the stormwater connection and manhole that sit on the block and are part of the easement. Can you help me?

Andrew, I have a large block of land that slopes to the rear. I want to subdivide it. What are the challenges that I am going to face?

Andrew, what are the differences between a waffle pod concrete slab and a raft engineered concrete slab? I am worried about the foundations of my home. Can you explain please?

Andrew, I am considering buying a block of land and demolishing the house. How do I know if the house has asbestos in it and what do I need to keep in mind if it does?

Now over time I hope to be able to write some good articles about these issues and lots more but in the mean time the thing you must do is this: If you have a question: Ask? If not to me at HBB then to someone you know who has the background and experience in designing and building.

Your success is dependent on many factors. Some are just common-sense things like:

  • Don’t be afraid to ask a builder, building designer or architect (or anyone) questions that you don’t know the answer to.
  • Never assume that everyone is an expert in everything.
  • Always ask about the consequences in time, money and scope. In other words, “If I do this over here, what happens over there in relation to time, money and scope.?”
  • Pay attention to detail, always. Never be complacent.

When you enter into a contract with a building designer and / or a builder you are in a commercial partnership. That means success is a place where you arrive at together. So, do what you can to get as much education and knowledge as possible. You don’t need to be the “client from hell”. But you do need to be confident and firm and not be afraid to ask the right questions in the right way. If we can help you with any of that, then feel free to call me.

Soil Tests, Geotechnical Reports and Soil Reactivity

Soil Tests, Geotechnical Reports and Soil Reactivity

When building a home, you’ll hear about soil tests, Geotechnical Reports and soil reactivity. It all boils down to this: if you are building a home, you must have a soil test.

It’s one of the things spoken about often at House Builders Brisbane. You will also hear it discussed by pretty much every home building company in Australia. If you are going to build a home, no matter what type, you need to have an independent soil test undertaken by a qualified geotechnical engineer.

So, what will this produce?

In its simplest form, it’s called a Geotechnical Report and this is what is produced by the qualified engineer.

Soil is a naturally reactive substance and different soils react in different ways under different conditions. Structural engineers and house builders know this and so the process of determining what type of soil you have and how reactive it is, comes from the Geotechnical Report.

This process should always be done as early as possible – even before you purchase the land. Because it will identify any extreme elements that could severely affect the cost of building your home. In addition to the soil reactivity information the Geotechnical Report will also highlight any hidden chemical or physical conditions on the building site that could affect your costs or pose a long-term threat to your house building project.

Ok, so what is soil reactivity?

Soil reactivity refers to how much the soil on the building site is likely to expand, contract, shift and settle (normally as a direct result of changing moisture content). This is a real issue, its why the report and the engineering specifications that derive from it are mandatory for all construction. The structural engineer will consider the reactivity of the soil and weight this against what you are planning to build and will provide detailed structural foundations as a result.

Reactive soil can cause a lot of damage to a house, especially if the home that was built was done so with the wrong type of engineered foundations. House cracking is a major concern when reactive soil is identified in the Geotechnical Report. Check out the picture in this article as an example.

What are the soil classifications?

Soil reactivity is generally graded in terms of the following classifications:

Class A
Stable, non-reactive. Most sand and rock sites. Little or no ground movement likely as a result of moisture changes.

Class S
Slightly reactive clay sites. May experience slight ground movement as a result of moisture changes.

Class M
Moderately reactive clay or silt sites. May experience moderate ground movement as a result of moisture changes.

Class H
Highly reactive clay sites. May experience a high amount of ground movement as a result of moisture changes.

Class E
Extremely reactive sites. May experience extreme amounts of ground movement as a result of moisture changes.

Class P
Problem sites. The ability of the soil to evenly bear a load is very poor. Sites may be classified as ‘Class P’ as a result of mine subsidence, landslip, collapse activity or coastal erosion. Ground movement as a result of moisture changes may be very severe.

Class A, S and M are generally considered ok and if there are no other concerning issues then you should not be concerned.

Class H and E will need investigation and analysis by the structural engineer relative to what you are planning to build.

If you are building on a Class P site you will need to consult a structural engineer very quickly. The costs and risks must be considered early in the feasibility of the project.

What does the Structural Engineer do with the Report?

The Geotechnical Report that lands with the structural engineer indicates the physical properties of the soil on your site, the stability of natural slopes, the chemical composition of the soil and various other details. From all of this information the structural engineer will work with your builder and building designer to design the type of footings or concrete slab subfloor that can be built on your site. Once final engineering plans are produced then the structural engineer will eventually come to the site and inspect the actual foundations prior to the pouring of concrete and sign off on them.

If you need a soil test provided at any stage of your land acquisition then feel free to drop us a line and we would gladly provide you with a recommendation to one of our high-quality providers at our volume prices.