By Matthew Baring-Gould, Kingscliff-based drainage plumber. Servicing Tweed Heads for 4 years. 5.0 stars across 173 Google reviews. Licensed NSW 383340C and QLD 15036450. ABN 74 605 392 348.
Gold Coast property with water coming under the garage into a void under the house with the stump footings. A previous retaining wall and drainage attempt had not solved the problem. We excavated against the front wall down below the footings, waterproofed the full garage front and three metres into the cavity with three coats, installed a 150mm EvoMax channel grate across the two garages, and laid a French drain underneath the channel grate to catch sub-surface water coming under the driveway. Discharged to the left-hand side of the property.
What the customer called us for
Owner had already paid for a retaining wall and drainage behind it, and water was still coming in. Called us for a second opinion and a proper fix.
What we found when we got there
Water was coming in under the driveway and into the void under the house. The earlier retaining wall was not catching it, and the surface drainage alone was never going to. The fix needed to work on both surfaces: a visible surface drain across the garages for rain, and a hidden French drain underneath it for the groundwater coming through the driveway slab.
Why we did it this way
This is one of our favourite drainage designs. The channel grate catches the obvious surface water and is what you see. The hidden French drain under the grate catches the sub-surface groundwater coming under the driveway and is where most of the actual water is coming from on a job like this. Three coats of waterproofing on the wall is the belt-and-braces layer for anything that still makes it through. Three systems working together, each covering a different water path.
What we did on site
- Excavated against the front wall of the garage down below the footings.
- Dug three metres into the cavity under the house.
- Applied three coats of waterproofing across the full garage front and the cavity.
- Laid two socked aggie lines as a French drain below the surface drain line, wrapped in geofabric.
- Installed a 150mm EvoMax channel grate across both garages above the French drain.
- Connected both the channel grate and the French drain to the left-hand side discharge.
- Backfilled with specified drainage gravel over the French drain.
- Reinstated the surface around the channel grate.
The result
Garage and cavity now protected by three systems in series: waterproofing on the wall, EvoMax channel grate across the garages, and a hidden French drain below the grate. Water discharged cleanly to the left-hand side of the property.
If you have the same issue
If you have already paid once for drainage and water is still coming in, the first fix probably solved one of the water paths and not the others. A combined channel grate plus hidden French drain plus waterproofed wall is the full solution on a driveway-and-garage water ingress problem. Call Matty on 0447 188 394 or request a quote.
Customer names and addresses have been withheld. Individual results vary. Drain Masters Plumbing is licensed in NSW (383340C) and QLD (15036450).
Frequently asked
What is an EvoMax channel grate?
It is a modular linear drainage system. The 150mm wide version we installed here handles vehicle loading over the garage and gives a clean architectural finish at the garage door line while catching surface water.
Why put a French drain under a channel grate?
The channel grate catches water you can see (rain on the driveway). The French drain underneath catches water you cannot see (groundwater soaking in under the driveway slab). On a job where the original attempt did not fix it, that sub-surface flow is almost always the thing that was missed.
Why three coats of waterproofing?
Each coat builds up thickness, cures separately, and covers any pinholes in the previous coat. Spec on this product is three coats for anything below ground level where there is going to be water pressure against the wall. One coat does not meet the spec.
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