Building deck in extreme bushfire area

[AV Elec]

Hi all,

Firstly, great forum - I have learn't a lot looking around. If you have any audio visual installation questions, just ask me :2tsup:

I am looking to build a deck at the rear of my house 6mX5m. Some of the posts are 4.5m high, and it is in a VERY high bushfire prone area.

I have yet to complete the calculations from the RFS, but it could very well be zoned "flame zone" due to the elevation and closeness to vegetation.

Now this seems to be a bit out of my league. I would be fine to build a low deck in normal situations, but this is a bit more than that. It may be that I cannot even use timber due to the fire risk! I don't mind using steel, but I understand that it has to be engineered. How does steel compare to timber in terms of cost?

I think I might need to get the design drawn up by an expert, and get a builder to assist me with posts, bearers, and then I do the joists and decking boards.

If I was to do a lot of the legwork, how much would I expect to pay for the designing? I can get it drawn up by a CAD drawer for free if it made a difference in the price, however this CAD drawer doesn't have any structeral qualifocations.

[Wood Borer]

AV,

Decking is not only dangerous because it can burn but it is also dangerous with what it can conceal during a fire by this I mean embers.

If even the smallest ember gets under your decking it can easily start a fire in all those leaves and cobwebs and other combustables.

Before, during and after a fire, you will need to gain easy access under your decking so you can detect and extinguish every little ember. A steel decking could make this task difficult if not impossible. You may wish to install sprinklers under your decking which would overcome this problem. You can't rely on electric pumps unless you have a generator because your power will more than likely be out during the fire.

We have a timber decking and when we were threatened this time last year, I had the axe and the chainsaw ready to quickly demolish the decking. Fortunately it didn't quite come to that but if the decking had been steel, it would have made cutting up the decking near impossible.

Good luck with your design, I am sure there will be a simple solution to the problem.

[AV Elec]

Directly under the decking is mostly rock, at 2.5-4.5 metres. Keeping that area clean is easy.

If a fire comes through this valley, I will be packing the car and will be outa here:o. By that time it would be more than too late to do anything. Just hope the insurance is AOK.

[Wood Borer]

Steel shouldn't be a problem then apart from buckling with the heat.

Like you said, insurance should look after any damage in the awful case of a fire.

[glock40sw]

G'day.
Go here http://www.timber.net.au/documents

1/2 way down the page is all the relevant data for timber in busfire prone areas.

[AV Elec]

G'day.
Go here http://www.timber.net.au/documents

1/2 way down the page is all the relevant data for timber in busfire prone areas.

You are a wealth of knowledge :2tsup::2tsup::2tsup:

[dazzler]

What does the zoning buillding controls say about the use of combustable material.

We are in a bush fire area and cannot have any combustables attached to the dwelling so timber decking is out of the question. What were you going to put on your deck :?

[Barry_White]

If you want to build it in steel go to Onesteel and they would be able to give you a design. They have a computer generated design system for doing flooring systems.

[AV Elec]

I wanted to put merbau on the deck, but quite likely this might not happen. The alternative is non slip tiles. If it comes in that we are in the "flame zone" (above level 3 extreme) then it is likely I cannot use combustable materials. There is no AS for flame zone- it is pretty much on a case by case basis. They also mention that in a flame zone I might be required to upspec the bushfire resistance of the house :o. I can see many $$$.

Yeah hopefully onesteel, stratco, strammit, etc should be able to give me a computer designed system. I'm thinking out loud here, but they quite possibly could make up a custom kit similar to kit homes for me to put together with distructions.

If I can't use timber deck, I will probably tile the floor. The added advantage with this is I could make a room underneath if the deck is sealed.

At this stage I don't care what it is made of. I just want a cost effective deck I can build, then get on it with the family and have a few cold ales. I am up high and face the national park. It will be great:U.

[kkperth]

I am in the same situation re bushfires as the bush is 6m from the back of the house. The back of the house is also 900mm above the surrounding ground and as such I need some area built up to match the back door. Original thought was a nice wooden deck but after a bushfire that destroyed 2 homes got within about 1km two weeks ago I am rethinking this idea.

Any thought on alternatives?

[AV Elec]

Any thought on alternatives?

The one steel system is called Duragal. http://www.onesteel.com/images/db_images/productspecs/DFS%20Brochure.pdf 90X90x2mm piers can go up to 4.5m high. For my roof piers I would probably need to go up a size.

As Barry White mentioned, one steel will draw up the design to suit. You still need an engineer to confirm the site conditions though.

Stratco's product is Tuffloor http://www.stratco.com.au/pdfs/Tuffloor_InstallGuide.pdf
I assume they will also draw it up for you.

Are there any other products to consider?

[Barry_White]

The one steel system is called Duragal. http://www.onesteel.com/images/db_images/productspecs/DFS%20Brochure.pdf 90X90x2mm piers can go up to 4.5m high. For my roof piers I would probably need to go up a size.

As Barry White mentioned, one steel will draw up the design to suit. You still need an engineer to confirm the site conditions though.

Stratco's product is Tuffloor http://www.stratco.com.au/pdfs/Tuffloor_InstallGuide.pdf
I assume they will also draw it up for you.

Are there any other products to consider?

Lysaght also do a floor system but I think the Onesteel system would be better because it is all RHS steel whereas the Stratco and the Lysaght systems have a component of cold rolled form section in them.

Another way for Bushfire areas would be structural steel with Lysaght Bondek with a concrete slab poured on it. And if you wanted a deck appearance you could fix joists down to the concrete and then put your decking down on the joists. Probably end up being pretty XXXXX'y

[AV Elec]

HAHA BONDEK...

I had to install some stuff under a slab in a highrise which had bondek. I knew about the clips you slip into the grooves underneath, but I couldn't remember the name. I literally rang about 25 people, drove around Sydney on a big wild goose chase before I found out I had to get them from Chullora Lysaght... wasted 2 days:o. I now have a whole box of different bondek clips...

OK I think I have this deck sorted out, except for one thing.

If I used compressed fibreboard and tiled it, what do people think are the issues with having the spa sunken in the deck. When not in use I plan on putting a hard cover over the spa to increase the floor space.

There is an old slab 2.5 metres below which I am thinking of building a bessa brick plynth to sit the spa on. That should be OK, I am really concerned with the moisture that the spa creates.

Perhaps I should completely line the underside of the steel framing? It started out as a deck, now it's looking more like an extension...

[wayneo75]

as the bush is 6m from the back of the house.

Any thought on alternatives?

First alternative is to increase the separation distance from the bush! 6m from a bush fire, the house will melt from the radiant heat, not to mention what the flames will do!

[silentC]

Mine is Duragal with Merbau decking. Design is easy with the span tables. You can't use Duragal within a couple of km of the coast though (not sure where in Sydney you are).

I'm in a bush fire zone but we got a medium rating. Merbau is fine in my situation as it's on the list of low-flammability timbers provided by RFS. If you're in the extreme zone, which it sounds like you are, then you probably can't use timber at all.

We have to provide a 40 metre asset protection zone around the house - no dense vegetation, no connected tree canopies etc. You'll possibly have to do a bushfire assessment when you submit the DA and that will guide you on what materials you can use.

[Loki429]

We are in a bush fire area and cannot have any combustables attached to the dwelling so timber decking is out of the question. What were you going to put on your deck :?

I raised that question with our local Council (useless) and with the RFS. Although I couldn't get a definitive answer on exactly what "attached to the dwelling" means I was lead to believe that it was referring to not having and of the house floor members (bearers, joists) extending beyond the wall and forming the structure for the deck.
I did get my design through council, the rfs, structural engineer and a private certifier with a ledger attached to the wall.

Have a search through the forum as there was a thread about a year ago that discussed this.

[Loki429]

AV Elec

Have a good look around the RFS website. There are many useful resources there including workbooks for determining the bushfire threat, categorising your property, even working out the classification of the bush and scrub type.
When we built our house (3 years ago) we had to get a private "bushfire consultant" to prepare a report for submission to council for building approval. When I put the plans in for the deck I added a copy of this report which would have helped speed our approval through council and the RFS.

cheers,
Loki

[AV Elec]

Thanks for the advice everyone. The next step is for me to get the design drawn up and engineered. Once this is done, I will post updates:2tsup:

[Ivan in Oz]

Once this is done, I will post updates:2tsup:


With Pictures:?:?:?
Hope so:2tsup:

[AV Elec]

Too many projects, limited amount of funds:C
It will happen, but I might have to use the tax return mid year...

[DvdHntr]

Check out AS3959 - "Building in bushfire prone areas"


I actually think that timber is not much worse than light gauge steels like Duragal and the like. They are so thin that the fire will cause them to yield and the deck will collapse.

[thebuildingsurv]

AS 3959 is what you need to be referring to as dvdhntr says.

Merbau satifies the non-combustable requirement and you could use blackbut for the posts, bearer and joists. Talk to your local council they may be able to help and give you some info (although some dont appreciate time wasters that drill them for free info then use a private building surveyor anyway) You will need to have your decking spaced at 5mm and keep the subfloor open. It aint such a big deal.

You can also get paint coatings which satisfy the requirements i think its called flame guard and has relevant testing data to give to your approval authority.

You should also consider chopping down some trees.

[glock40sw]

You should also consider chopping down some trees.


Yeah....That's what I like to hear...Nothing says "I care" more that the sound of a Chainsaw in the early mornin.