How to install Damp Proof Membranes (DPM)

General

Damp can be a silent destroyer of buildings. From weakened structural integrity to the appearance of mould and mildew, uncontrolled moisture can lead to significant and costly damage. One of the most effective defences against moisture ingress is the use of a Damp Proof Membrane (DPM). In this blog, we’ll take a look at how to install a DPM, what they’re made of, how they work, and why damp prevention is vital for any building project.

Whether you’re a contractor, builder or property developer, understanding the principles and application of DPMs will help you stay compliant with Building Regulations and deliver dry, durable structures.

What is a damp proof membrane?

Before diving into the installation, it’s essential to understand what a Damp Proof Membrane is. A DPM is a type of moisture barrier typically installed in floors or walls to prevent moisture from passing into a structure from the ground or the surrounding environment.

A damp proof membrane works by forming a continuous physical barrier between moisture-prone areas (such as the subsoil or surrounding masonry) and interior elements like concrete slabs, flooring, or wall structures. It’s usually installed at or below floor level, either laid underneath concrete or integrated with other damp-proofing products like a Damp Proof Course (DPC).

What is a damp proof membrane made of?

The material of a DPM varies depending on the product, but you’ll often find that they are made of high-quality polyethylene (PE), a plastic polymer known for its strength, flexibility, and resistance to moisture. Some of the key materials used include:

Low-Density Polyethylene (LDPE): A widely used option due to its durability and water resistance. It’s a thermoplastic polymer made from the monomer ethylene. It’s essentially pure polyethylene with a low crystallinity, which makes it soft and pliable. Its polymer chains are highly branched, which results in a less dense and more flexible structure compared to HDPE.
High-Density Polyethylene (HDPE): Offers greater puncture resistance and tensile strength than LDPE. HDPE is also a thermoplastic polymer made from ethylene, but with minimal branching of its polymer chains. This gives it a more linear structure with higher crystallinity and density, meaning a stiffer, stronger plastic than LDPE.
Bitumen-based sheets: Sometimes used in more complex or demanding waterproofing situations, especially in vertical applications. These are typically composed of bitumen (a sticky, viscous form of petroleum), which is blended with polymers (like SBS — styrene-butadiene-styrene, or APP — atactic polypropylene) to improve its flexibility and durability. The bitumen compound is usually reinforced with a core material such as fibreglass or polyester fabric to add strength
Reinforced membranes: These are usually flexible waterproofing sheets made from a base polymer (such as PVC, EPDM rubber, TPO, or modified bitumen) with an embedded reinforcement layer. The reinforcement is typically a mesh, scrim, or mat made of fibreglass, polyester, or sometimes metal, which helps resist tearing and stretching.

Manufacturers often make these membranes with additional properties, such as UV resistance, flexibility in cold temperatures, or compatibility with specific adhesives or primers.

Regardless of the material type, always check the product specification to make sure the membrane is suitable for your project.

How to install a damp proof membrane

Now that we understand the basics, let’s look at how to install a damp proof membrane. Although the precise method can vary depending on the type of project, the general process follows the same steps. Let’s have a look:

1. Site preparation

Before installing the membrane, the ground must be prepared appropriately. The substrate should be clean, level, and free of sharp objects or debris that could potentially damage the membrane. A well-prepared base is important because it ensures the membrane lies flat, which prevents wrinkles, folds, or punctures that could allow moisture to pass through or compromise the seal at overlaps and joints. Here are a few overview points:

Make sure the sub-base is well compacted to provide a stable, even surface. You could use a mechanical compactor or roller, then check with a straightedge or spirit level.
Remove any stones, rubble, or protrusions that could puncture the membrane, using a sturdy landscaping rake to clear loose debris, or a spade for those larger rocks and roots.

2. Laying the membrane

With the base prepared, the membrane can be laid out across the floor area. Unroll it smoothly and without creases, making sure it covers the entire surface.

Sheets of membrane should be overlapped (your product instructions should highlight the overlapping measurements)
All overlaps must be sealed using a suitable DPM tape or adhesive to keep them watertight.
Around structural features or awkward corners, the membrane should be carefully trimmed to fit using a sharp utility knife or heavy-duty scissors to avoid tearing it.
Avoid stretching or tearing the membrane

Where multiple sheets are required, they should be laid to fall in the direction of water flow to encourage drainage away from the structure.

3. Membrane detailing

Detailing is one of the most critical steps in getting the most effective results. Any errors here can lead to water ingress. The membrane should be taken up to any adjoining walls to create a continuous barrier that links with the DPC.

The upstand of the membrane on vertical surfaces should be at least 100mm above finished floor level, which can be checked with a tape measure or a spirit level with a ruler.
Where service entries, such as pipes or ducts, penetrate the membrane, these areas must be sealed using compatible detailing products such as collars or tape.
Use corner details and pre-formed components where provided by the manufacturer for consistent, reliable seals.

Attention to these details helps to prevent weak points and future issues with rising or lateral damp.

4. Pouring concrete

Now the membrane is fully in place and detailed, the concrete can be poured directly over it. It’s still important to take care throughout the process not to damage or shift the membrane.

Avoid walking on the membrane unnecessarily
In windy or uneven areas, secure the membrane at the edges or weigh it down temporarily until the concrete is poured. You could use bricks, sandbags, or timber battens to do this.
Make sure the membrane remains flat and in contact with the substrate by smoothing it out by hand or with a soft broom, and don’t forget to check for trapped air or folds as you go.

A consistent pour helps to press the membrane firmly into place, embedding it beneath the structure for long-term moisture control.

5. Finishing and inspection

Once the slab has cured, it’s time to check it. Take a look at the membrane and look for any potential punctures, poor seals, or misaligned overlaps.

Check around service penetrations and upstands for secure, continuous seals
Ensure that the membrane joins correctly with the DPC and other damp proofing elements
If any damage or failure is found, repair using manufacturer-approved products before continuing

How does a damp proof membrane work?

Essentially, the membrane acts as a barrier, preventing water and moisture from moving upwards or sideways into the structure.

Through capillary action, groundwater and water vapour can cause moisture to move through porous building materials like concrete. This is where Damp Proof Membranes come in. When installed correctly, they block this pathway, making sure the internal structure remains dry and free from any damp issues.

These membranes are made from waterproof materials (usually plastics or bitumen) that have a continuous, impermeable structure, meaning water molecules can’t pass through them, effectively stopping moisture from travelling through capillary action. Because they don’t absorb water themselves, the membranes remain dry and prevent damp from reaching the building’s internal structure.

When used alongside other damp proofing products like cavity trays, damp-proof courses and tanking membranes, a DPM forms part of an integrated system that manages moisture across floors, walls and basements.

Working with a Damp Proof Course (DPC)

It’s also essential to understand how DPMs interact with DPCs. While a Damp Proof Membrane is usually laid horizontally beneath floors, a Damp Proof Course is generally installed horizontally within walls, just above ground level, to stop rising damp.

It’s best practice to lap into or join your DPM with the DPC so it creates a continuous moisture barrier. If this isn’t done, then it could leave gaps in the protection. When planning your complete damp proofing strategy:

Align the DPM with the DPC wherever possible
Make sure overlaps are well sealed

The importance of tackling damp

Tackling damp at its source is essential, and doing so early with the right damp proofing products can help towards a longer lifespan for the structure and healthier indoor environments.

Common causes of damp

Understanding where damp comes from is the first step to preventing it. In the UK, with frequent rainfall and high humidity, damp problems impact many homes, and in 2023-24, around 1.3 million households were living in damp homes, according to the English Housing Survey. This leads to issues like mould growth, structural damage, and poor indoor air quality. Some of the most common causes of damp include:

Rising damp: Moisture from the ground travels upward through porous materials, such as bricks and mortar, by capillary action. This moisture can cause plaster to deteriorate, encourage mould growth and lead to structural damage over time. Properties built on clay soils, near high water tables, or without adequate damp-proof courses are more prone to rising damp, especially if the foundations are shallow or damaged.
Penetrating damp: Water entering the building through external walls, roofs, or faulty detailing due to poor weatherproofing or damage.
Condensation: This happens when warm, moist internal air meets cooler surfaces, especially in poorly ventilated spaces. For example, drying washing indoors, cooking without extractor fans, and bathrooms with inadequate ventilation.
Poor drainage: Poor site drainage or water management systems can cause surface or sub-surface water to build up around foundations. It happens when rainwater or groundwater isn’t directed away from the building effectively, resulting in water pooling around foundations. Signs include soggy or muddy areas near the building, blocked or overflowing gutters and downpipes, soil sloping toward rather than away from the structure, and clogged or damaged drainage channels. These conditions increase the risk of damp and structural damage.
Defective construction detailing: Improperly installed or missing DPMs and DPCs allow moisture pathways into the building fabric.

Issues that arise from damp

When left unchecked, damp affects more than aesthetics. It can also compromise a building's structural integrity. Aside from the structure itself, damp can also cause health issues to those living in damp houses. Of the 1.3 million damp households mentioned previously, over 600,000 had at least one member with a health condition, according to the English Housing Survey.

Some of the main problems include:

Structural decay: Moisture can lead to the corrosion of embedded metal elements, rotting of timber joists, and breakdown of masonry over time
Health hazards: Persistent damp causes mould growth and other issues, such as dust mites
Thermal inefficiency: Wet materials conduct heat more readily than dry ones, meaning insulation becomes less effective, increasing heating costs.
Damage to finishes: Plaster, paint, wallpaper, and floor coverings can become discoloured, bubble, or peel due to moisture.
Reduced property value: Properties with damp, or suspected damp, can actually be harder to sell. Because of the repair work needed, there are often price reductions to compensate.

Browse damp proofing products today!

If you’re in the market for DPMs & DPCs for your project, then take a look at our range of waterproofing & damp proofing products. We stock products designed for use in these situations, such as Visqueen EcoMembrane (DPM), Visqueen High Bond DPC, and many more. If you have any questions about our products or want to learn more about how they can support your project, then contact us today.

By Katie Taylor