Property Repair Systems

How to Fit a Vertical DPC

This project is sponsored by Property Repair Systems

Summary: We explain what a vertical DPC is, as well as guiding you through which products you need to lay a damp proof membrane around your windows.

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What is a Verticle DPC?

A vertical DPC is similar to a horizontal DPC (or Damp Proof Course) in that it stops damp travelling through your masonry. Whilst a horizontal DPC stops damp rising up from the ground through your walls, a vertical DPC is used to stop water travelling sideways through walls and surfaces that may come in contact with each other. In builders speak we say that walls of this type are being "returned".

Vertical damp proof courses are usually installed around windows or doors when they are being installed in a cavity wall. When new windows and doors are installed in a cavity wall, he cavity needs to be closed around the frame to secure the window or door properly as shown in the image below.

A vertical DPC membrane between closing cavity walls

A vertical DPC membrane between closing cavity walls

Closing the cavity forms the door or window reveals once this closure has then been plastered over.

The cavity closing around the window or door means that the external and internal walls come into contact with one another. The vertical DPC is inserted between the walls around the window to stop water travelling in from outside through the external wall from reaching the internal wall.

Vertical DPCs are usually damp proof membranes, but laying a normal damp proof membrane intended for horizontal DPC use isn’t actually sufficient for use as a damp proof course around windows, it is usually recommended to use an insulated DPC (these can be purchased from most DIY stores or builders merchants).

Vertical Damp proof courses stop water passing through the wall

Hold the vertical damp proof course in position until the cavity is closed

Heat Loss from Cavity Closing Around Windows and Doors

The cavity closing around your windows or door means that your warm internal wall is brought into contact with your cold external wall. Without any treatment or insulation this means that you lose internal heat more easily from this wall area as the heat from the warmer inner wall is transfered through to the colder outer wall.

Additionally the outer wall can also help to keep the inner wall at a colder temperature as it passes cold from outside to inside through the touching surfaces. This will in turn make your heating work harder to heat your home and maintain that heat costing you money and wasting energy.

These cold areas are known as cold spots. Not only do these areas make the internal air around your windows and doors feel cold, these cold spots can also attract moisture from your internal air – this becomes condensation on the wall area around your window which can give rise to black mould.

In addition to the fact that these cold spots around your windows and doors are costing you money in terms of energy, they can also be bad for your health because of issues like mould. This is why fitting a vertical DPC around your windows and doors is a must.

Insulated vertical DPCs have a layer of polystyrene attached to them (see the picture on the above - "An insulated vertical DPC") which acts as an insulating barrier in the damp proof course around the window, preventing water from entering your internal wall and heat from leaving it.

Insulated vertical DPC in position

Insulated vertical fixed in position

An insulated vertical DPC

An insulated vertical DPC

Installing Vertical DPC's Where Two Walls Meet

Vertical DPC's are often also installed where the walls of two buildings meet each other and there is a risk of damp passing between them. As you can see in the picture below, the damp membrane is inserted vertically between the two walls where they meet, and then the additional brickwork is built up around the membrane.

Note that this damp membrane is not an insulated vertical DPC membrane.

Vertical DPC damp membrane inserted between two walls

A vertical DPC damp membrane can be inserted between two walls to limit the movement of damp from one wall to another

If you need any help with laying your vertical DPC damp proof membrane around your windows or doors or any other cavity damp problems you can contact Property Repair Systems for more information. We have worked with them on a number of projects over the years and they are specialists in this subject.

You can also find out more information on Damp Proofing on the Damp Proofing Association’s website.

If you are experiencing issues with cold spots on your walls then more information on this can be found in our Cold and Damp Spots project page.

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