17/07/2021
Drainage issues - the no. 1 cause of cracking problems in homes.
Clients find it hard to believe that something that appears as solid as a house can be vulnerable to the effects of water. This factor alone though contributes to virtually all the cases I’ve seen in nearly 30 years specialising in this very niche area of house repair. The simplest way to think about water problems is to imagine a typical house on a sloping block founded on clayey soils. If you excavated all the backfill against the upstream wall to expose the concrete footing then left it that way, you wouldn’t be surprised to see puddles forming along the trench after rain periods would you? As this water is normally hidden from view in the backfill reinstated after the bricks were laid during construction, most people assume it isn’t there, but it often is. The white powdery deposits commonly seen on the inside face of this block work from under the house is typically due to this trapped water passing through the masonry to the inside. The issues that result from this ‘dammed up’ water are many-fold; the moisture eventually soaks downwards and under the footings downstream of these locations including causing settlement of vulnerable pier pad footings as the clay foundations are softened. These trapped stores of water against the house attract nearby tree roots which set up camp there happy with the regular top up that each rain event provides. Only problem is, when an abnormal drought occurs these same roots become desperate for water and extend their reach to moist areas nearby which are generally further under the house, leading to settlement of affected footings in time and more extreme moisture fluctuations from then on. Trees and bushes are often blamed for causing house cracking but often they are a sign of a moisture problem rather than the problem themselves.
Agg. Drains (or french/‘aggy’ drains) are an unfortunately regular contributor to drainage problems and their detailing is typically flawed, even ones specified by experienced engineers. The Australian Plumbing Standard doesn’t help with the detail often just copied by those in the design area. The main issue centres around the more common perforated pipe style drains that are normally laid on a bed of gravel in a constant depth trench. If you put yourself in the mind of a water droplet, it’s only purpose is to follow the force of gravity and try to travel down. As water enters these drains it drops straight to the base of the trench and either soaks into the likely porous material directly (and eventually out the base or side of the drain) or else waits until forced further along by the next rain event. In other words, there is no active entrapment of the water so it is free to do ‘what it wants’. Consider then what happens when the perforated drain enters a PVC pit (as is typically found at the end of drains). If the pipe is cut into the pit part way up the side as is typical, then any water in the trench can’t get into the pit but instead flows around the outside. If the rain continues and the depth in the trench fills to the depth of the pit pe*******on then, and only then, will the pit collect any water. Once the rain slows and the flow depth recedes once more, the water in the trench is again prevented from entering the pit and simply loiters in the trench (leading to eventually soaking into the area the drain was installed to protect) or infiltrates the surrounding area of the pit, likely leading to additional issues in that area.
Our patented “CracKontrol” drain system however takes the water on a very different and more considered path. It has features that prevent seepage from passing under the drain, collects the surface and subsurface water and feeds it securely into the stormwater system. As well as this, a provision to provide an underpinning option to the adjacent footing (our drains are normally installed directly against the upstream house footing) is easily incorporated so should the foundation settle excessively (this has never happened to date, mind) our ‘deep pinning’ bars can be installed retrospectively in minutes.
There are many other benefits of our Drainage System including complete removal of stray moisture from the underfloor area leading to prevention of mold (allowing more practical household storage possibilities) and control of condensation problems in rooms above. Clients have commented that even after as little as 2 weeks since our drain has been installed, the smell of the air in older houses is transformed as the dank, musty smell they assumed was unavoidable in older houses, effectively disappeared.
It is critical when assessing a house experiencing footing movement that the priority is to pinpoint the cause of the problem rather than focus on the symptoms (the cracks). I often assess houses from the outside conditions without even considering the internal cracking – it’s essentially irrelevant. Concerning then that many businesses in this specialist field focus completely on the cracking and completely ignore the cause of the movement. Any solution that does not attempt to rigorously find the cause is effectively ‘treating the skin blemish’ rather than the underlying ‘cancer’, which no-one would understandably encourage in our health specialists. The unfortunate consequence can be that the underlying issue is left untreated (as I have discovered too many times when called in to repair failed underpinning work by other businesses) and the continuing issue either causes the superficial repair to re-fail and/or the differential settlement to spread to other areas.
I can’t stress enough that underpinning can be extremely complicated and should never be pre-occupied with the cracking in isolation - it takes years of experience understanding the effect of water and the depth to which undetected drainage problems can affect to fully understand why a house is behaving the way it is – the cracks are your home’s ‘cry for help’ but it’s underlying ‘disease’ should always be the focus.
Below: a typical pit detail with the agg. Drain entering part-way up the side.
Update 10/10/21:
Another concerning assessment recently where a self-proclaimed dampness specialist in Hobart installed a drain around the entire perimeter of a house and effectively made the situation worse - the drain traps seepage to a depth of 150mm and has caused the owners continuous health issues due to the resultant mold effects. This is serious negligence and these contractors need to be regulated.
