What is Damp Proof Membrane (DPM) in Construction?

For DIY-ers or people new to construction, it can sometimes feel like everything is said in shorthand. C-studs, MF5s, B1 foams, PVCs – until you know what you’re doing, it can all feel a bit unknowable.

We’re here to break down some of the details of construction, one abbreviation at a time, starting with DPM. It’s something you might hear a lot when it comes to property builds or damp issues, and it’s a great example of something that’s so simple yet so important.

What Does DPM Stand for?

In the world of construction, DPM stands for damp-proof membrane.

As the name suggests, a damp-proof membrane, commonly just called DPM, is a layer used in construction to stop damp from seeping into a building from the earth below, a phenomenon known as rising damp.

DPM can come in different forms. It’s usually a thin polythene plastic sheet, but can also be supplied as liquid DPM, which is painted or sprayed onto a surface.

How is DPM Used in Construction?

A damp-proof membrane is added to properties to protect them from rising damp, which can creep through porous materials like cement and masonry. As a result, a DPM is usually applied just above the foundation level, protecting the building itself from damp.

A DPM sheet is usually applied to new builds, covering the foundation layer before more work commences. When applied accurately – often by overlapping sheets and attaching with DPM jointing tape to ensure full protection – a DPM sheet will often protect a building for the lifetime of its use. As anyone aware of climate change knows, plastic takes an incredibly long time to break down.

Liquid DPM is applied at the same stage as sheet DPM, with the difference being that it is rolled or sprayed onto the foundation layer rather than being placed on top like a sheet. Again, when applied professionally and correctly, liquid DPM can protect the building for a lifetime of use.

Damp-proof membranes can also be used for remedial work. If a building has tide marks against the walls, this can be a sign of rising damp and that existing damp-proofing has failed. In these cases, a liquid DPM is often sprayed into holes in the wall to provide fresh damp-proofing coverage.

Note that DPM is used differently from DPC, or damp-proof course, which is a similar product with different use cases.

Why is Damp Proof Membrane Important?

A damp-proof membrane sheet is such a simple, inexpensive piece of kit, and yet no property build is complete without one.

Damp-proofing is a vital part of any construction as the only protection against rising damp. Without it, moisture from the earth would permeate up through concrete, masonry, wood and so on, causing all manner of issues, including:

• Tide marks on walls
• Damaged paint and sideboards
• Salt deposits on walls
• Rotting wood
• Persistent damp

So long as DPM is installed correctly, alongside supporting products such as DPC, properties should be completely protected from rising damp. Some specialised DPMs can also protect against gases such as radon. 

Hopefully, this little guide helps explain everything you need to understand about damp-proof membranes! If you’d like to learn more, check out our guide to choosing the correct DPM thickness.

Get everything you need for effective damp proofing at Fastbuild, from DPM sheets to jointing tape and DPC products. Order before 4pm for next working day delivery and keep your project moving without delays.