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How to fix dampness arising from a rear wall built against the earth


We are in the process of purchasing a house, however the surveyor's report highlighted a problem of the rear extension of the house. The external ground level to the rear of the rear extension is about 1.5m above the internal floor level. There is a risk therefore of water penetration and high moisture level readings were obtained at the base of the rear wall (3.3m).

The surveyor suggested to lower the rear ground level to 150mm below the internal floor level and build a retaining wall about 1m from the rear wall.

Is there any better way to treat/prevent the dampness problem?


4 Answers from MyBuilder Extension Builders

Best Answer

Hi you could get a specialist damp company in to tank the extension but all you are doing is holding back the damp which may appear somewhere else at a later date my advice would be to do what your surveyor suggested and dig around the extension and maybe add a french drain to take the water away obviously what you do depends on if you own the ground around the extension regards nick


Answered 21st Sep 2019

The choice depends on how much you are willing to spend,and on what you want to use any room below ground level for.the cheapest option is to build a wall in front of the existing wall and run a damp proof membrane up it .then build another wall on from to sandwich the membrane,however this might not be as effective as tanking the current wall with a hight quality system,and taking it right across the floor.which in effect creates a bucket .But keeps the water out.rhe final solution I can offer which again I have been involved with is to dig out the material outside against the wall and tank the wall on the outside with a water proof render and back fill with pea gravel.the more expensive methods do work and can be guaranteed to work if done correctly.


Answered 21st Sep 2019

render the internal wall with sbr waterproofer
and install french drain outside if necessary tank and install moister collectors
its probably cheaper at 1.5 meters high to just bank away from the wall
dig out and shape the bank to allow air outside to dry the wall
hope this helps


Answered 25th Sep 2019

Step back garden away from building with either sleepers or retaining wall.
Add an ako channel or french drain along wall depending on drain access.


Answered 10th Oct 2019

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