Issue
Stormwater drainage. This looked to be a 50s/60s property. It is situated on a mildly sloping section for the most part, which gets considerably steeper at the back of the house. At one time, a flat area had been carved out behind, close to the house, and a concrete swimming pool installed. When regulations for fencing and pool safety were introduced back in the 80s/90s, the pool at this property was non-compliant, and cost prohibitive to make compliant. When the current owners purchased the property, the pool was derelict. They had a very young family, and the whole situation at the back of the house was completely unsafe for kids that age (Or any age by the sound of it). A solution had to be found – quick and on a budget.
Landscapers were employed to re-shape the rear using a digger. The pool was dismantled and interred under a concrete pad with a wooden deck extending to the house for the last 1.5 metres, and a substantial terrace was formed above – properly fenced off. It all looked rather attractive, but insufficient, if any, attention had been paid to drainage. Right from the beginning, water was getting under the house and being led to the downstairs garage at the front. The owners had built a sort of dam just outside the retaining wall from the garage area to the rear sub-floor which had to be manually drained in wet weather.
On the surface, it looked fairly easy – just form drainage along the rear of the south facing property, and lead it to an existing drain which took the water to a kerb side drain to the west of the property. Job done!
Solution
We began by excavating the stormwater drain leading to the west. It was completely blocked, the rear deck/concrete had been completed at a higher level than originally, presumably to bury and ‘dispose’ of the pool remains etc.
The landscapers had formed a wooden cavity to accommodate the existing drain, but the connection had been damaged allowing material to get in. Ok, we fixed this problem and had Aquablast Ltd clear the pipes with their water jet. Then we found that the concrete and decked back yard had been formed to drain to the east. Subtle but definite. Water was directed toward the back of the house and under the deck.
We were told that the surface under the deck sloped away from the house, and a channel had been formed to lead water away from the house (So the homeowners were told). We took up some planks to get under it with a level. What we found was that there was no drain, and the deck joists reached ground level in some places. Water could not get away and was instead directed under the house. We investigated the crawl space under the house and found ponding water. This was in summer, and the weather was dry. This was far more of an issue than we thought.
Now we were suspicious and started paying attention to the whole landscaped area where the pool had been, and found a field drain under a seating area which led under a concrete planter to the east side of the house. Only… it didn’t go through the planter but discharged into it!! There was no release at all, and so this drainage had the opposite effect and trapped water in the back yard where it simply overflowed the concrete deck and under the wooden deck, and thus directly under the house.
The deck was wrapped around the house and halfway along the eastern side where it ended next to a landing by the side door. From there, down to the front of the house where there was a drain taking water from the roof to a kerb side discharge to the south (The property is on a corner intersection). Of course, a garage had been built over the top of this drain which was also completely blocked. It was a dig up. We sought advice from the homeowners who wanted the problem fixed after having lived with it for years.
We proceeded to remove all the wooden decking as we needed full access. The first line of defence was formed by emplacing a channel and grate drainage system between the concrete patio and the wooden deck to intercept any stormwater that fell on the patio (Recall, it was sloping toward the house) and connected it to a new silt sump at the corner of the house large enough to cope with any flow rate likely.
We cut trenches into the concrete down to below the level of the house footings in the backyard. Both under the deck, and at the back of the concrete where the field drain was. This time we routed it through the planter and not into it. Geocloth wrapped 100mm perforated pipe was laid leading to the new silt sump and the trenches backfilled with drainage chip to the surface.
The trenches were filled with drainage chip and, where necessary, we reinstated lawn. All the decks were re-laid successfully, and the result was very tidy.
Observations
The inclination is to be fairly forgiving of mistakes by fellow tradies – we don’t know the circumstances at the time of the initial work, and they weren’t drainlayers. Indeed, the result was attractive. But in fact, the drainage had been completely botched and created a problem that was costly for the homeowners to rectify. We were frustrated and disappointed by what we found.
Outcome
Drainage has been put in place where previously water had been forced under the property. The house will be dry underneath, the downstairs garage spaces will be dry for the foreseeable future and the homeowners can make full use of these areas for the first time. A considerable improvement in amenity value. Hopefully sufficient compensation for the aggravation and cost incurred.