Watch TuffBlock Frequently Asked Questions Video



Frequently asked questions:

0:00 What is a floating foundation system?
0:31 How much weight can each TuffBlock support?
0:43 Are TuffBlocks UV resistant?
0:58 Can I use TuffBlocks on sloping ground?
1:14 Do I need council approval?
1:34 How do posts/joists sit in the TuffBlock and do they require fixing?
Can TuffBlocks be used on wet surfaces?
2:22 Can I use TuffBlocks on sand?
2:35 Will TuffBlocks sink into the ground?
3:08 Can I use TuffBlocks in high wind areas?
3:27 How many TuffBlocks will I need for my project?
3:57 What if I have ground movement in my area?

Please note.
The following information relates to both the TuffBlock and Evo-Crete Handi Block products. BuildTuff.com.au offers this information as a general guide only. You should rely only on relevant building codes and standard industry established construction methods in any construction project.

Do we need council approval?

As building guidelines change from shire to shire we always recommend checking your local guidelines before commencing construction, we always suggest you get the thumbs up before starting your project. Unfortunately there is no single or “golden rule” answer. That being said, most councils have an exemption for structures that are less than a certain size e.g. 10m2, therefore if your structure area is less than specified you don’t need to seek any approvals.

How many TuffBlocks will I need for my project?

This obviously depends on the type and size of the project you are building. As a general rule if you are supporting joists directly on TuffBlocks, you will need to support joists with a TuffBlock at 1.5m intervals. Joists will need to be spaced at a distance appropriate to the finishing material (e.g. it is recommended that some decking timber be spaced at 450mm centres, it is always best to check with your timber/material supplier for material specific recommendations). As an example, a low level deck 3m x 3m would require 21 TuffBlocks for the above configuration – that is 3 x TuffBlocks per 3m joist, 7 x joists spaced 450mm apart.

If you intend on using bearers on top of TuffBlocks, joists on top of bearers, and then decking or finishing material/sheeting – less TuffBlocks will be required. As an example, a low level 3m x 3m deck would require bearers to be supported say every 1.5m, bearers would be spaced every 1.5m to support the joists, so 3 x TuffBlocks per bearer, 3 x bearers = 9 x TuffBlocks. The above measurements are a basic guide only, refer to the TuffBlock installation guide and your material supplier to ensure correct spacing is maintained for structural integrity.

Are TuffBlocks cheaper than using Steel Post Supports and in Concrete?

In most cases, yes. Especially when you consider the time and effort taken to dig multiple holes and then mix the concrete to fill them back in, not to mention the cost of buying the steel post supports and bags of concrete in the first place. Generally a steel post support and two Bags of concrete will set you back around AU$35-45. So even if you use a few more TuffBlocks you are still well ahead of the old conventional footing method.

How high can I build using TuffBlocks as the foundation?

TuffBlocks have been engineered for structures up to 1m above ground. Having said this many people have built structures higher than this using the composite foundation method (TuffBlocks in combination with concrete-in-ground footings). We recommend that you consult with a qualified builder or engineering regarding your special design and environment.

I live in a Far North Queensland which can be a high wind / cyclonic area, can I use TuffBlocks?

Of course (as always check with your local building authority). Some TuffBlock users will use TuffBlocks in combination with concrete-in-ground footings to ‘tie-down’ their project (e.g. in each corner).

Will my project be stable or shift once it is finished?

No, the collective weight of the construction materials used, and the unique ‘u-channel’ locking design of TuffBlocks means that your project will be extremely difficult to budge if you are not actively trying to move it. Once all materials are fastened together your project will be just as stable as concrete-in-ground foundations (you will just save time and money by using TuffBlocks!).

What if I have ground movement in my area – clay/sandy soils?

The TuffBlock product is based on the floating foundation system, designed to ensure the structure is able to move slightly if the ground was to move. This is what makes the floating foundation system so safe; the structure is able to move slightly and independently of other structures as natural ground movement occurs. The TuffBlock construction method therefore avoids stresses that would otherwise see an extension from an existing structure fail. The system was originally designed for regions where the annual freezing and thawing of the ground meant that either: 1) the ground was too hard to dig, or 2) with the constant shrinking, expansion, and movement of the ground many fixed structures failed due to inability to cope with the movement they sustained.

Will TuffBlocks sink into the ground?

The short answer is no. If you consider that a TuffBlock construction has similar or greater downward surface area than a standard concrete-in-ground footing then sinking will not be an issue, or at least no more of an issue than it would have been if you used the old method in the same soil. TuffBlocks should be installed on stable compact earth – this is not to say that you need to compact the ground, if however the top surface is extremely loose just take a layer or two away with a shovel and your TuffBlock will be a nice and stable base for your project.

The Floating Foundation System while relatively new to Australia since we introduced it back in 2011, has been a tried and trusted building system in North America since the late 1980's with literally tens of millions of decks and other structures built using this system. Ground sinking is absolutely something that needs to be considered, however this is also the case for a traditional "dig a hole and pour concrete" installation. So if your ground is particularly unstable you need to consider this regardless of what installation method you choose. The great thing about TuffBlock is that it's far simpler to install more TuffBlocks than it is to dig deeper, wider and more holes and fill them with more concrete. In fact the Floating Foundation System was developed for grounds that were heavily affected by Freeze and Thaw ground movements. If your grounds are particularly unstable the Floating Foundation System such as TuffBlock is possibly a far better solution for you as it keeps the structure independent from any surrounding fixed structure allowing it to move and settle independently. Furthermore you can very easily install far more TuffBlocks to greatly increase the amount of support for the structure.

Can I use TuffBlocks on sloping ground?

Yes. Simply level the ground under each TuffBlock and then level the structure above using extension posts supported in the pocket of the TuffBlock below (refer to the installation guide for more detail). Alternatively, if the impenetrable surface is sloping at a severe angle it may be worth considering using an alternative support/footing/foundation.

Can I use TuffBlocks for a project spanning across different surface substrates?

Yes. Use them on concrete, soil, gravel and everything in between so long as it meets the “stable ground” criteria. What is stable ground you might ask? Basically put them on any substrate which would be an acceptable base for concrete-in-ground footings, is the ground is not compact just clear away a few layers until you find compact earth.

How much weight can each TuffBlocks support?

An individual TuffBlock is capable of supporting up to 770kg. The TuffBlock has been break tested to over 5,000kgs.

Will my timber posts rot or be prone to attack by termites if supported by TuffBlocks?

No. As TuffBlocks support the structure well above the soil line and the blocks themselves wick moisture away from the timber there is no reason for the timber to rot or for termites to attack the posts.

Are TuffBlocks UV resistant?

UV stabilisers have been included in the manufacturing process which means TuffBlock is manufactured to the highest standard of any plastic product for use outdoors. However, like any plastic product we recommend TuffBlock is not installed where it is exposed to direct sunlight as this will reduce its service life below 25 years.

Can I use TuffBlocks on Sand?

Like anything you will need to prepare the site well and ensure there is no issues with erosion or wash away (no different to if you used concrete footings). Although it is very site specific, if you are worried about erosion then we recommend reinforcing the base material. That said sand is a great substrate as long as erosion isn’t an issue.

What about Frost Heave?

This is exactly where the Floating Foundation System was developed for areas in the north (USA) where freeze and thaw ground movement is a major issue for traditional "dig a hole and pour concrete" structures. So TuffBlock is a perfect solution for their application.

How do you anchor the TuffBlocks down?

When the structure is required to be anchored (eg. high wind areas) you do not anchor the individual TuffBlocks. If necessary, you may anchor down the structure itself with a single point in the middle or at each corner. Methods include; concreting down steel chain into a hole, or the use of earth anchors hammered down into the ground. 

For example, temporary housing developments in the mining towns use 12mm galvanised chain, attach it to the structure on each corner and then place it into a hole before filling with concrete. In most situations an earth anchor will suffice.

How do posts/joists attach to it and stay up straight?

Generally the posts/joists/bearers simply sit in the TuffBlock without requiring fixing to the product. It is very easy, however to fix the block to the timber if required. As for the post staying upright, this is a function of the deck build itself. Your structure should be adequately designed and reinforced to ensure the posts are structurally sound and cross-braced.

Can TuffBlock's be used on soil that gets wet? What surface preparation is needed?

TuffBlock should be installed on stable undisturbed grade surface with well draining sub grade material. If your soil is consistently wet and gets flooded you would need to ensure you prepare the ground by introducing drainage which could be done via gravel or additional drainage to remove the flooding. If the ground is particularly unstable we would recommend increasing the number of TuffBlocks supporting the structure.

Other Information


You may need approval depending on size, structure, height and your local council or authority.

Contact your local council to confirm requirements regulations and permitted sizes vary by region. If in a bushfire prone area you may need to factor in specific requirements to meet regulations.

For more information about building a deck in your region including which project do not require approval, contact the Australian Building Codes Board.

Site Considerations

Plan and understand your project and seek professional advice if needed

BuildTuff strongly suggests you make your own enquiries through appropriate bodies and professionals before any work is carried out.

Some questions you may need to address are:

  • Is the site going to need protection from wood boring insects?
  • Has the deck got potential for water pooling or constant exposure to water?
  • Is there a need to install drainage due to potential soil erosion?
  • Are there any trees growing near the project whose roots could upset foundations or branches create a hazard?
  • Are you building on solid ground ie not reactive soil?
  • Will you need electricity, gas, water or other services to your project in the foreseeable future?
  • Are there any height considerations ie Fencing, balustrade and handrail needed to comply with codes?
  • Do you need an engineer to specify and detail construction drawings and methodology?
  • Are there Bushfire regulations I need to follow?

Bushfire Prone Areas

If you are building a decking structure in a bushfire prone area it is important to comply with building codes and the Australian Standards AS 3959.
The standard covers construction in Bushfire prone areas and applies to new and retrofitted structures. Prior to construction, it is important to establish the bushfire attack level (BAL) of a home. Once BAL is established refer to the relevant section of the Australian Standards AS 3959 for a guide to the the steps that should be taken during construction or retrofitting of your project. Compliance with Australian Standard AS 3959 Construction of Buildings in Bushfire Prone Areas is part of the BCA requirements for Class 1 Buildings. Click here for more info.

Bushfire Attack Levels (BAL)

These are broken down into 6 categories; BAL Low, BAL 12.5, BAL 19, BAL 29, BAL 40, and BAL Flame Zone. These levels are based on;

  • The region where you live.
  • The vegetation type around your property.
  • The distance from your home to individual vegetation types.
  • Slope on the property.
Simply click this bushfire attack level calculator link to establish the level for your construction.

Some steps for you to consider in planning, construction and ongoing maintenance.

Utilise dense timbers in construction of both sub floor and decking boards. The following timber species have been tested and found to meet the required parameters without having to be subjected to fire retardant treatment: Blackbutt, Merbau, Red Ironbark, River Red Gum, Silvertop Ash, Spotted Gum andTurpentine. Composite materials are also available with a BAL up to 40.

  • Make sure that gaps between each board measures between 0 - 5mm. Any more may result in vulnerability to ember attack.
  • Enclose the subfloor of the area using mesh or bushfire resisting timbers
  • Remove leaves and twigs from the roof and gutters.
  • Utilise non combustable decorative stones and more fire resistant plant species as landscaping around the structure. Avoid flammable shrubs like eucalypts and media like woodchips as these just become fuel for a fire
  • Keep your verandah well maintained by sealing timber with a non-combustible seal.
  • Fill in small gaps around the deck structure where an ember might be able to lodge - larger openings can be fitted with ember guards (such as perforated mesh with 2mm openings).
  • Contact your local fire authority for more information.

    Planning and Construction

    It should be noted that BuildTuff offers this information as a general guide only.

    You should rely only on relevant building codes and standard industry established construction methods in any construction project. Summarised below are the general steps you may undertake in the construction process:

    1. Estimate materials required and place order
    2. Prepare site and locate footings/post holes using string line, line level, pegs and footing stirrups.
    3. Erect deck supports – posts/poles/piers.
    4. Locate Bearers on supports and fix in place as appropriate
    5. Locate joists on bearers
    6. Apply a weed control measure under the deck
    7. Paint/stain (first coat), all deck framework
    8. Cut to fit and install guard rail supports if necessary then cut and fix decking
    9. Install railing, balusters, fascias, other trimwork as required.
    10. Finish with paint/stain as desired.