2 Aug 2012

Beat the Damp by Improving Drainage under Your Home

Posted by bcsands

Sometimes it’s not noticed until an El Nina cycle brings lots of rain, and that’s when you find you have a problem with water under your home. When you do discover it, improving drainage under your home is vital to the integrity of the whole structure. Rising damp often affects new homes, but established homes can also suddenly develop this problem.

What is Causing Damp under Your Home?

Not all the reasons are easily fixed, and several can be completely out of your control, so let’s have a look at some of the more common causes:-

  • Blocked gutters pouring water down walls instead of downpipes.
  • Water draining from one or more blocks of land outside your property.
  • Soil settlement soon after construction if the foundations were not properly compacted.
  • Soil settlement due to movement or inundation years after the house was built.
  • Natural soil erosion on a sloping block can allow mud to settle in the foundations of a house.

Prevention is always better than cure, so here are some do’s and don’ts to help prevent damp foundations:

  • Do clean your gutters regularly to prevent rain water flowing where it shouldn’t.
  • Do build up settled areas where water could build up and penetrate the house foundations
  • Don’t create barriers that prevent water flow – for example, by building flower beds against the walls of the house
  • Don’t allow reticulation sprinklers to hit the walls of the house.


What to do to Beat the Damp

If you have the problem you need to take immediate action to fix it. Sometimes there is not much you can do to fix water drainage from outside your property, but there are things you can do to minimise the damage to your home.

When you have found where the water comes from, you can work on diverting it from the house. This can be done by installing ag-pipe (agricultural pipe) at the highest point and allowing the water to flow to an approved drainage area such as a street drain. You will need to check with your local council before you end your drain there. You should then check that you will not be interfering with electricity, gas or sewage lines on your land. Finally you need to ensure that your drainage system will not impact on anyone else’s property.

  • Dig one or more channels where water needs to be diverted from and to, ensuring that they flow downhill all the way. If you are starting from the house, dig deep enough so that the ag-pipe will lie below the bottom of the concrete pad or stumps.
  • Fill the bottom of each channel with at a thin layer of aggregate, stamping it down to level it. Check the downhill flow again.
  • Place the ag-pipe in the trench and pour water down it to ensure it really does flow downhill all the way.
  • Backfill the trenches with more aggregate and place a protective filtering material on top before replacing the soil and/or grass over the top


Removing water from under a house is a big job, there’s no doubt about it, but when done you will have not only beat the damp and improved the drainage under your home, you will have peace of mind, a dry house and you will also have added to the value of the property.

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