Installing a vertical dpc
Summary: Why and when a dpc is installed vertically
A vertical dpc or damp proof course stops water moving through masonry from one surface to another in exactly the same way as a horizontal dpc stops water rising up through the walls, a vertical dpc stops it moving sideways.
This is especially important at the point in a property where the walls have to be "returned" to meet each other when inserting an opening such as a door or window. At these points the cavity has to be closed and a vertical dpc is inserted to stop water travelling from the outside skin, to the inside skin. You can see from the diagram on the left how one wall is turned at right angles to meet the other. This is called closing the cavity. A vertical DPC is installed here because it would be easy for any external moisture to soak through one skin and into the other. This would cause damp on the inside of the building.
A further problem develops when closing a cavity and that it brining the cold external wall in contact with the warmer internal wall. The cold from outside is soon transferred, through the masonry, to the inside wall. Once "cold spots" form on the inside wall it invites the moisture laden air from inside to condense on the colder sections of the wall. This is one of the reasons that condensation is very often found in the corners of window and door recesses.
This problem is now easily overcome with the introduction of a thermal bridge insulating DPC which can be seen on the right and found in the toolstore to the right of this page. The DPC has a strip of polystyrene stuck to it and when this is inserted the heat cannot travel easily through the masonry.
A vertical DPC is also installed where two walls of a building abut and there is a danger of moisture being transferred from one building to the other. You can see from the image left how the DPC is placed at the point where the cavity is to be closed and then the brickwork or blockwork is returned to it. This traps it at the point where the walls meet. The DPC shown in this image is not a thermal bridging DPC.
All project content written and produced by Mike Edwards
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