We get a lot of enquiries from members of the public who have purchased an existing shed or building from another person, and re-erected it on their property.
Council then becomes involved and ask them to seek development approval retrospectively for the works.
This retrospective work is difficult to undertake and costly, and also may involve remedial works on the structure to ensure that it complies with current standards and appropriate loads.
We always recommend that people looking to relocate existing buildings obtain council development approval prior to undertaking the works to avoid this retrospective work and costly surprises down the track.
If you are considering purchasing and relocating a shed or other buildings, contact Magryn first to avoid any unexpected costs or surprises from your local Council.
The severe beach erosion of the last few days on the Central Coast of NSW was well publicised, with graphic photos and videos of houses teetering on the edge of cliffs, with combined high tides and large swell crashing into the beach below, stripping away the soil under the houses as the owners look on in fear of their multi-million dollar properties falling into the ocean.
Image courtesy of The Guardian
Could this Coastal Erosion happen to us in South Australia?
Yes, but not to the same extent.
Sydney and the NSW coast in general fronts onto a high energy beach, which is often pounded directly by ocean swell. Much of the coastal development in South Australia is in the two main gulfs, Spencer and St Vincents, and the wave action in these is not as extreme as on an open ocean beach. Other development along the coast is often in semi-enclosed bays.
Also, Sydney and some areas of the NSW coast are more heavily populated, bringing more pressure to bear on building very close to the beach.
The coastline of Adelaide is in St Vincents Gulf and hence is more protected than an ocean beach, but has also generally been well armoured with rock revetment seawalls along much of its length, protecting it from on-going erosion.
Coastal Erosion control in South Australia
However, there are many spots around our coast which are a concern in regards coastal erosion impacting or threatening to destroy development. This is often shacks or groups of shacks built very close to the beach, but can also include infrastructure such as pipelines or roads.
These images show the pre-treatment beach erosion, then after the installation of an erosion control rock revetment wall. The batter above the wall can now be re-vegetated.
The before and after photos above are typical of rock seawall protection Magryn can design and arrange installation for to protect properties against the erosion threat which may damage or destroy buildings adjacent the beach.
Please don’t hesitate to call us should you be concerned about the safety of your assets.
Magryn often deals with coastal erosion control to protect these assets, and we have designed works to counteract this threat.
The article discussed that the lack of rainfall around Australia generally is causing the soil under and around many houses to dry and shrink, leading to cracking of the houses. The article is mostly informative and correct, but it doesn’t actually give you much information on when you should start to worry.
Any cracking is a concern, but the rapidity with which it appears and develops is a larger cause for worry. Some cracking is slight and only shows minor seasonal change (getting wider over summer and then closing up over winter). It tends to remain generally constant over the years. Other cracking however may be rapid and severe, going from no cracking to cracks 10mm and wider in the order of 3 months. This may indicate a severe and worsening problem with the underfloor plumbing, or another cause. This type of rapid appearance of cracking should be investigated urgently.
With any cracking, investigation to find the cause and remedial works undertaken in a timely manner are likely to result in a cheaper overall cost, rather than putting the problem off by ignoring the issue for several years.
It’s cheaper to fix a smaller problem…
It is always cheaper to resolve a smaller problem earlier rather than wait until the problem is larger, requiring more extensive and expensive works to remediate it.
has suddenly appeared
is worsening slowly over time
is causing you to worry or stress
Magryn strongly recommends that you seek professional advice from a suitably qualified and experienced engineer.
Retaining wall engineering involves the assessment and design to create a wall to retain a height of material. In some situations, an engineering design is legally required to satisfy local council requirements.
Retaining walls come in all sizes from 0.2m to 10m high and many different styles. There are moss rock walls, steel post/concrete sleeper walls, stacked block walls, steel-reinforced concrete-filled block walls and many more.
And of course, retaining walls come with many different prices. They are generally expensive, and the longer and taller they are, the more costly the total price.
But what type of retaining wall is best for you?
What are the main types of retaining walls?
Post and Sleeper Retaining Wall
The most common type of wall used in residential cases is the post and sleeper wall. This can either be:
Timber post and sleeper, with the posts set in a concrete fill bored pier. These are not recommended as the timber rots or is eaten by termites, reducing the lifespan of the wall. If you get 15 years out of a wall like this, you are doing well.
A steel post/concrete sleeper wall with the posts set in concrete-filled bored piers. These walls should last at least 40 to 50 years and are a similar price to the timber version above.
walls can have metal sheet fences installed over.
The timber sleepers come in many different colours and textures and don’t have to be concrete grey and flat.
tend to be the cheapest type of retaining wall and are very versatile.
As the wall is supported by a concrete pier in the ground, these walls may not be suitable for sites with shallow rock, as the cost of boring into rock is high. If rock is suspected or known to be shallow in the area, it is best to take some soil logs to determine upfront if this type of wall is the best option or not.
type of wall is suitable for wall heights of 200mm to 5m. Obviously, the
greater the level change, the greater the cost of the wall.
This type of wall is suited to placing a retaining wall across an easement, where it may be necessary to excavate and replace a pipe sometime in the future. In this case, the sleepers in one bay can be removed, giving easier access to the pipe under that area. The general requirements are for the in-ground concrete piers to be at least 1m away from the pipe.
Moss Rock Retaining Wall
type of wall is basically a battered earth slope with large rocks stacked over
it, in an engineered layout.
This type of wall does not extend far below ground level and hence is suitable for sites with shallow rock, but it has a very wide footprint due to the batter slope and the size of the rocks. This width is typically as wide as the wall is high, or wider.
These walls have a very natural look compared to other types of retaining walls.
Steel reinforced, concrete fill block walls
These retaining walls are made from concrete besser block (or similar) and contain steel reinforcement. Cavities in the blocks are concrete filled. They are narrow (about 200mm wide generally) and can be several metres high.
must be founded on either:
a concrete strip beam with reinforced concrete piers under,
a concrete slab footing.
concrete slab footing makes these walls suitable for sites with shallow rock.
However, the concrete slab will extend out some distance in front of the wall.
If the wall is to be installed on a site which is to be filled, the slab footing can extend back under the fill, which makes the wall more efficient and the slab footing narrower.
the walls are blockwork, they are often finished by render and/or paint to
improve their appearance.
walls tend to be more expensive than post and sleeper walls, as they require
a concreter for the slab footing
a bricklayer for the blockwork
Stacked Block Walls
are walls constructed of special proprietary engineered blocks, such as
keystone or AB blocks.
are suitable for lower height garden walls (up to 1m, depending on the type of
block) and they are:
founded on a rubble base
consist of stacked blocks, which may be unfilled, filled with screenings or concrete
may be hand-
assembled by owners.
Walls higher than 800mm (depending on the block type) may be engineered by including geotechnical tie backs to tie the wall to the soil mass behind.
Engineering Requirements for Walls
the different types of retaining walls discussed above require structural
engineering design to ensure they are suitable for their intended application.
engineer should be engaged to design your wall for your particular situation.
We would be happy to assist with your selection of retaining wall type and the design of it to ensure your wall is cost-efficient and long-lasting.
is the process of lifting or supporting the footing of a building or structure,
so as to provide a more stable foundation.
is commonly used to stabilise houses when they experience severe cracking.
are several different types and methods of underpinning. Two of the most common
Traditional concrete underpinning, which involves piering or excavating under a footing to install a concrete support for the footing.
Chemical underpinning, using an expanding urethane foam or similar to create piers in the soil under a footing, to provide lift to it.
methods are quite different and are best used in different situations, the
choice dependent on the cause of the cracking.
Traditional concrete underpins
Traditional concrete underpins used to be dug by hand and were typically 1m cubes of concrete placed under a footing beam. The footing beam could then be jacked up, using the concrete underpin as a stable base.
the cracking in some houses is related to seasonal moisture variation in the
soil which can extend down to over 3m in depth. This seasonal moisture
variation is the drying/shrinkage of the clay soils over summer and the
wetting/expanding of the clay soils over winter. Hence, due to the depth of
soil moisture variation, the 1m cube concrete block also experiences some lift
and settlement over the seasons. Hence, a 1m cube underpin may not be a stable
It is better practice to install a concrete underpin as a concrete-filled bored pier to a depth of at least 4m, founding the pier in soils which are stable over the seasons. Please note that this depth may vary due to other considerations, such as the permanent water table depth, soil conditions or shallow rock, proximity of trees, etc.
The footing under the building may then be jacked off the underpin if jacking is viable.
location of underpins will affect the decision to use traditional concrete
underpins or another method, as it is preferable to use a machine such as a
small excavator to auger or dig the underpin. It may not always be possible or
practical to position an excavator where required to dig the underpin – you
don’t want an excavator in your hallway!
Jacking over underpins
Underpins are often installed as a stable base so that the footings of the building can be jacked up and re-levelled. This can only be done using traditional concrete underpins.
there are many limitations to this jacking, which include:
concrete strength of the footing. If this is too soft, the footing concrete may
crush rather than lift.
the footing is bluestone rather than concrete, it may not be recommended to
jack as it is not structurally continuous, or strong
footing may crack if lifted too far, which in turn may cause additional
cracking to the building over
suction on the footing may prevent lift.
Chemical underpinning is undertaken by injecting an expanding urethane foam (or similar) into the soil at selected locations under the footing. This creates a pier of foam in the soil to lift and support the footing over. This type of underpinning incorporates jacking.
Chemical underpinning has some advantages and some disadvantages when compared to traditional concrete underpins. These are discussed below.
The advantages of Chemical Under-pinning are:
It can be done relatively quickly – only one day is required for a normal house, whereas a week may be required using traditional concrete underpins.
The method provides a large degree of control over the lift undertaken to the footing.
The injection can be undertaken at numerous points close together.
The injection can be undertaken under internal walls more easily than the installation of traditional concrete underpins.
The disadvantages of chemical underpinning are:
The chemical is injected using a wand or tube inserted into the soil under the footing. This limits the founding depth of the pier and the resultant pier is likely to be founded in soil which may show seasonal lift and settlement. This is undesirable (see above).
The system requires the use of a very high-pressure pump.
Which underpinning method to choose? Chemical or Traditional?
decision whether to use traditional concrete underpins or chemical underpins
should depend on the reason for the movement and cracking occurring, and
location of the cracking.
the movement is due to seasonal wetting and drying of soils around the exterior
of a house, traditional concrete underpins are better as they are founded at a
If the movement is in the centre of a house and is not related to seasonal wetting and drying of the soils, chemical underpins may be a better option.
Magryn recommends both types of underpinning, with the choice depending on the details and requirements of the individual project.
We recommend that you engage a structural engineer to review any project which may require underpinning, to ensure that:
You receive an unbiased and professional opinion on the need for underpinning.
You receive a report documenting the scope of underpinning you require. You can then take this scope to several underpinners to obtain easily comparable quotes. The report should detail the number and location of underpins required, as well as the details of these underpins (depth, size, reinforcement, etc).
Magryn would be pleased to assist you by providing an underpin report and design for your house. We can even recommend quality, reliable contractors to undertake the work. Our preferred underpinner is Complete Underpinning (contact Grant on 0423 305 078)
Give us a call on 8295 8677 and discuss your problem and requirements with us.
relative cost of chemical underpinning vs traditional concrete underpins is
variable and depends on many factors, but the order of magnitude of both
options is similar. The exact relative costs are best explored with individual
recommends both types of underpinning, with the choice depending on the details
and requirements of the individual project. We recommend that you engage a
structural engineer to review any project which may require underpinning, to
receive an unbiased and professional opinion on the need for underpinning.
receive a report documenting the scope of underpinning you require. You can
then take this scope to several underpinners to obtain easily comparable
quotes. The report should detail the number and location of underpins required,
as well as the details of these underpins (depth, size, reinforcement, etc).
Magryn would be pleased to assist you by providing an underpin report and design for your house. We can even recommend quality, reliable contractors to undertake the work.
Give us a call on 8295 8677 and discuss your problem and requirements with us.