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We don’t normally think of ground floors as needing waterproofing. Damp proofing is all that’s required right?
Well normally, yes; but sometimes even ground floors need waterproofing rather than just damp proofing.
- If the external ground level is at the internal finished floor level around a lot of the building then you need waterproofing design advice.
- That waterproofing design advice might be that damp proofing is enough
- Where ever possible raise the building or lower the landscaping so that the internal finished floor level is at least 150mm above external ground level.
Ground floors can suffer from water ingress. Get the right advice to protect your interests and the buildings you work on.
You can watch a 4 min video here.
Hello and welcome to waterproofing wisdom my name is Ben I am the Technical Director of CLW in this Episode I wanted to talk about waterproofing the ground floor, which seems like an odd thing to say but if I show you this section detail this, I think is becoming much more common in I guess residential buildings in the UK.
The red line here is intended to indicate a damp proof membrane under insulation and a screed and this red line is intended to be a cavity tray and, in some ways, nothing unusual about that and you get that sort of detail with a door in it as a level threshold which is standard practice, particularly with disabled access requirements.
But if I then remove the white patch and you see the section through the whole building what you can see is that the whole building is actually below ground level only very slightly but it is and a damp proof membrane is exactly that it’s a damp proof membrane and not a waterproofing membrane this is how most buildings used to be built.
You would anticipate a step up into the building and an increasingly common I think is for the building to be set down so the finished floor level is roughly the same as the external ground level I think that causes issues and I wanted to show you an example.
This is from a job that I worked on a long time ago but these are the details here I’ve added in red just to accentuate here’s the damp proof membrane under the floor slab and up there is the cavity tray external ground level here finished floor level here, in some ways not a big deal but that was the full perimeter of the building it was always like that the whole way around the building.
The problem with that I think in this situation was a very high water table, and very poorly drained soil and so I’ve put this blue shading there to indicate the presence of water and with the presence of water there, if we assume that the damp proof membrane is keeping water out then you would expect some sort of hydrostatic force to be acting on the damp proof membrane and water is trying to get in there’s potential for flotation forces as well.
That’s the scenario if we look at the same project during construction you can see in the background here that there are puddles it’s poorly drained soil the puddles are slightly more obvious back here but poorly drained soil and external ground level the same as internal finished floor level throughout.
That led to this where there was a lot of moisture under the vinyl and the adhesive got wet and didn’t like that situation with very high moisture content in the floor and you can see here the internal floor level was very similar to the external ground level and so because of that I wonder if even some ground floor structures need waterproofing design advice.
Where the water table or where the external ground level is the same as the internal finished floor level because that is essentially earth retaining and even if that design advice is simply to assess the risk and say no further action is needed and the architect can carry on and design with the DPM as they normally would.
So be it but assessing the hydrogeology and flood risk all of that content should be something that a waterproofing designer could bring to the party and that could be a very helpful requirement so I think even ground floors can require structural waterproofing.
I think that the people who should be assessing that risk and designing if necessary is a structural waterproofing designer and I think within that like I mentioned you’d want to be thinking through flood risk and the risk of surface water flooding or other forms of flooding and considering the hydrogeology.
Thank you for watching this is waterproofing wisdom.
If you’ve got any queries about basements or waterproofing or even ground floor waterproofing give me a call.