How to improve drainage on side of house?

blackraven

Hi everyone,

Thanks for the help so far. Onto my latest project. I am looking for advice and ideas or recommendations on what is best for our house in this annoying situation.

I have noticed the concrete path at the back of our house is too high. We moved in 12 months ago and since the house was cleaned for sale I can see algae/damp appearing on the rear brick wall. House is double cavity brick on concrete slab. The damp proof course is at the level of the concrete or only a few cm above it (ie: the first line of mortar above the concrete in the pictures). You will see there are no weep holes - unsure why. There is no expansion foam or similar between the wall and the concrete. There is also insufficient fall in the concrete away from the house to my eyes. The concrete itself has moved and cracked in places. The area is west facing and a small patio-type area so doesn't get an enormous amount of sun, compounding the issue.

I will also add the gutters need replacing - that project is underway. Nevertheless, the damp is not just from leaking gutters. Often people inquire about other sources of moisture but I don't believe there are any.

One complicating factor is that the house's plumbing is very shallow. I'm not even 100% confident I could put in an effective strip drain at the height of the current concrete path. If I lowered the concrete path by 15cm then any drains would almost certainly have to travel uphill to the nearest stormwater pipes. 

At the moment, I am thinking the options are 

1) Cut concrete and place strip drain against the wall of the house, draining to nearest stormwater pipe (if the water won't be running uphill.) This doesn't solve the cracked concrete which we can live with.

2) If drain not possible, cut a strip out of the concrete (maybe 20cm wide), dig out dirt, replace with easy draining material eg sand, decorative pebbles on top. I hear this is better than concrete for preventing termites and could in theory prevent water pooling against the bricks or landing on the concrete and splashing against the bricks. 

3) Demo and replace the damaged part of the concrete path (and pavers), lowering it by 10-15cm. Fall the concrete away from the house. Won't be possible to place any catch drains so run-off will probably go to the fence and the neighbours backyard. May even need to replace the rear colorbond fence or at least somehow reinforce the now vacant section beneath the lower edge?

4) Install a 1m clear awning above the clothesline. Water will then mainly fall on the pavers away from the concrete and that may be enough to prevent most of the moisture reaching the bricks. Doesn't fix the underlying problem though. 

Appreciate any thoughts and other ideas. I thought of a waterproof coating for the bricks but I understand this would mainly prevent the bricks from dying out. 

MitchellMc

Hi @blackraven,

Given the location of the concrete path, the damp conditions, lack of sun, and the leaking gutters, it’s not unusual to see algae buildup along the rear brick wall. However, the primary concern is whether the moisture is causing damage to the building. If the damp proof course (DPC) is above the concrete or just slightly above it, water should not be able to creep into the walls.

Your ideas are on the right track. If the concrete is causing water to pool and run directly against the wall, then more drastic measures like removing or lowering the concrete may be necessary to improve drainage. However, if the water is falling away from the house, it might be sufficient to clean the area regularly and monitor the internal walls for signs of moisture ingress. High-pressure washing every six months could help maintain the area and prevent further algae buildup.

If you opt for installing a strip drain, make sure it’s correctly placed to ensure water drains effectively to the stormwater system, but be mindful of your plumbing depth. The second option of replacing the concrete with permeable materials like sand and decorative pebbles might also work, especially if it helps with drainage and prevents water from splashing against the bricks.

In any case, it’s essential to check the condition of the damp proof course and monitor any internal moisture issues. If the damp persists or worsens, you may need to revisit the drainage and concrete path solution, but for now, cleaning and monitoring might be enough. However, you might like to enlist the services of a drainage professional to give their thoughts before attempting to pull the concrete up.

Please let me know if you have any questions.

Mitchell