Damp Proof Membrane: What It Is and How It Works

Houses of all ages contain moisture. It’s present in the materials used in home construction and the air within and around a building, which could lead to dampness. However, one of the innovative materials used in modern houses is damp proof membrane (DPM).

We'll explore everything you should know about a damp proof membrane. So, if you’re looking to improve or maintain your home, keep reading to find helpful info for keeping moisture at bay.

What’s a Damp Proof Membrane?

A damp proof membrane (DPM) is a water-tight material that inhibits moisture. It’s installed beneath concrete flooring, walls, and other structures, such as sloping roofs with low water permeability courses.

A DPM may also be used with a damp proof course (DPC) to ensure complete protection from penetrating and rising damp.

Purpose of a Damp Proof Membrane

A damp proof membrane (DPM) ensures that damp doesn’t rise from the ground by capillary action. It also prevents moisture from penetrating insulation materials like wool and cellulose, thereby safeguarding their insulating properties.

Effectiveness of Damp Proof Membranes

Damp proof membranes are made from high density polyethylene (HDPE), a semi-rigid material that provides protection from moisture. This makes the DPM strong, durable, and suitable for areas that require air and vapour barriers.

These membranes may also be made from bitumen or aluminium, which possess low water permeability.

How Damp Proof Membranes Work

Damp proof membranes used on walls possess studded profiles on the surface that are similar to the design of an egg box. This formation creates an air cavity, allowing the evaporation of water without damaging the wall.

Those used on floors are in the form of sheets. They’re installed below the concrete, following the approved British building regulations to prevent building materials from absorbing moisture.

By blocking moisture from rising from the ground, damp proof membranes ensure that houses constructed on waterlogged soil are dry and habitable.

Damp Proof Membrane Uses

There are many use cases for damp proof membranes, and we’ll discuss them in detail in this section.

Walls

You can use a damp proof membrane for walls, but you should get a professional to determine what’s causing the damp issue in the building. The inspection report will determine the appropriate solution to the problem.

External Walls

Although external walls are more vulnerable to absorbing moisture, you can’t use a damp proof membrane on them. Instead, other measures such as applying waterproof coating, constructing a cavity wall and installing a damp proof course are utilised.

Internal Walls

The use of a damp proof membrane is ideal for internal walls as it prevents the ingress of moisture from the surrounding. However, care should be taken to ensure that all joints and overlaps are properly sealed.

Brick Walls

A damp proof course (DPC) is more suitable for brick walls as it’s installed in the block course, whereas a DPM is installed over a surface that requires waterproofing. The DPC is applied at the plinth level all the way to the length of the wall.

Floors

A damp proof membrane can be installed on both new and existing floors. It ensures the durability of the flooring materials and protects the structure from mildew and mould attack.

Concrete Floors

Concrete floors require a damp proof membrane because of the porous nature of concrete. It allows moisture to pass through to the finishing layer, resulting in damp issues on carpets and floor coverings.

Laminate Flooring

You can install a damp proof membrane beneath laminate flooring if the house is older or you suspect that there's damp in the subfloor. It enhances the longevity of the final floor and reduces swelling of the material due to moisture.

Sheds

Because a shed is constantly exposed to the elements, a damp proof membrane is necessary to prevent the buildup of moisture. It's important to consult a professional as they'll assist in investigating potential ingress points or moisture sources around the shed that may reduce the efficacy of damp proofing.

Shed Base

When building a shed base, you should lay a sheet of damp proof membrane before setting the concrete or slab on the base material. This is because the shed base is in direct contact with soil and can absorb moisture over time, which will damage the wooden frame.

Shed Walls

Although shed walls are a major concern for dampness, you should consider other effective alternatives besides a damp proof membrane. That's because it's designed for floors and beneath structures.

Under Sheds

You should use a damp proof membrane under a shed as it provides an extra layer of protection against rising damp. However, you should ensure that the wood is properly treated to prevent rot.

Under Summerhouses

Before constructing a summerhouse, you should lay a damp proof membrane on its footprint to prevent penetrating and rising damp. You can also include measures like adequate ventilation and insulation to reduce the risk of condensation.

Under Concrete Slabs

Using a damp proof membrane under concrete slabs prevents moisture from seeping in and degrading the material over time. It also slows down the curing process, resulting in stronger concrete slabs.

Weed Control

Since a damp proof membrane doesn’t allow water to pass through, it can suppress the growth of weeds. But you have to hold down the material with a wooden frame or a rod to prevent wind from going underneath it.

Different Types of Damp Proof Membranes

There are various types of damp proof membranes. However, the type you’ll use depends on the moisture level of the surroundings and the building regulations.

Liquid Damp Proof Membrane

A liquid damp proof membrane is a substance that's applied over a floor covering to protect it from rising damp or residual moisture from construction activities. It's ideal in buildings where there's a damaged structural damp proof membrane.

Damp Proof Membrane Paint

Damp proof membrane paint is a liquid DPM that blocks the action of penetrating damp on floors, ceilings, and internal walls.

Epoxy Damp Proof Membrane

Epoxy damp proof membrane is a coating that suppresses residual moisture in cement and concrete floors to speed up the process of installing floor coverings. It's also ideal for damp proofing walls and floors where rising damp is visible due to a missing or damaged sheet membrane.

Damp Proof Membrane Sheet

A damp proof membrane sheet is a plastic material installed under a concrete floor to prevent rising damp.

Damp Proof Membrane Roll

A damp proof membrane roll is a roll of large plastic sheets that form a continuous moisture barrier on a concrete slab.

Plastic Damp Proof Membrane

Plastic damp proof membrane is a flexible, high density polyethylene that you can cut and fix to walls and floors to stop rising and penetrating damp from affecting the interior of a building.

Damp Proof Mesh Membrane Kit

A damp proof mesh membrane kit typically contains a meshed membrane, plaster plugs, a roll of tape, and a drill bit.

Clear Damp Proof Membrane

A clear damp proof membrane is a high-quality plastic for damp proofing above-ground structures when the wall finish is a block wall, timber battens or metal tracks.

Proof Membrane Thickness

Damp proof membrane thickness is measured in micrometres (µm) or millimetres (mm). The acceptable thickness is a minimum of 300 micrometres.

Self-Adhesive Damp Proof Membrane

A self-adhesive damp proof membrane is a bitumen-based membrane with an adhesive backing that makes it easy to be applied to surfaces. It's suitable for retaining walls, underground structures, and reservoirs.

Different Brands of Damp Proof Membranes

There are various brands of damp proof membranes on the market. Here are some of the popular brands and whether they're effective or not.

Visqueen Damp Proof Membrane

Visqueen is a leading brand in the UK waterproofing industry. Its damp proof membrane is made from recycled polyethene, making it eco-friendly. It's also resistant to wear and can prevent acids and chemicals from affecting a building's structure, which makes it an excellent choice.

Drybase Liquid Damp Proof Membrane

Drybase Liquid damp proof membrane is a product of Safeguard Europe Limited. It blocks damp and gasses like carbon dioxide and radon from invading a building. Overall, the brand is versatile and easy to use.

Newton Damp Proof Membrane

John Newton is known for the production of high-quality waterproofing membranes, and its DPM is puncture resistant and durable.

Mapei Damp Proof Membrane

Mapei damp proof membrane is a single-coat product that controls constructional or residual moisture on cement subfloors. But it's not suitable if you intend to install wood floor coverings.

Permaseal Damp Proof Membrane

Permaseal offers a wide range of damp proof membranes for walls and floors. They're high-quality, highly effective and permanently eliminate dampness.

Radon Damp Proof Membrane

Radon damp proof membrane provides protection from damp and radon gas, which makes it quite economical.

Sika Damp Proof Membrane

Sika damp proof membrane doubles as a waterproof membrane and can be used for exterior and interior damp proofing.

Travis Perkins Damp Proof Membrane

Travis Perkins offers various sizes and thicknesses of damp proof membrane with 10 years warranty on selected items.

B&Q Damp Proof Membrane

B&Q sells various damp proof membranes from superior brands. They're made from recycled materials and meet the British standards.

Black Jack Damp Proof Membrane

Black Jack damp proof membrane is highly effective, odourless and best for walls, foundations and aboveground structures.

Damp Proof Membrane Costs

Several factors determine the cost of a damp proof membrane. They include your location, the brand, and the area you want to cover. However, the price ranges between £22 to £350.

Costs for Different Types of Damp Proof Membranes

Type of DPMPrice range
Liquid DPM£22 – £180 (5 litres)
DPM sheet£26 – £80 (100 square metres)
Mesh membrane£35 – £194
Self-adhesive DPM£60 – £350

What's the Cheapest Damp Proof Membrane?

The cheapest damp proof membrane is liquid DPM; one litre should cover about 3 square metres. Liquid DPM is versatile as it can be used for various applications.

What's the Most Expensive Damp Proof Membrane?

Self-adhesive damp proof membrane is the most expensive because it's convenient and saves time during installation.

Damp Proof Membrane Installation Price

A professional may charge between £150 to £300 to install a damp proof membrane. Overall, the average cost of damp proofing a house in the UK is between £300 to £3,000.

Other Factors Affecting the Price

Several factors may affect the cost of installing a damp proof membrane. They’re explained below:

  • The size of the affected area: If you’re damp proofing a few walls or a few square metres of the floor, it may not cost a lot of money compared to damp proofing an entire building.
  • The extent of damage: Moisture may cause structural problems such as cracked ceilings and damaged plaster and paint. In this case, you’ll have to make major repairs.
  • The type of damp proof membrane: Depending on the damage, you may choose to use a liquid or plastic sheet DPM. The price of each type depends on your location. For instance, prices in London are on the high side compared to other locations in the UK.

How to Install a Damp Proof Membrane

Installing a damp proof membrane involves rolling out the sheet, cutting the exact size required for each area, and sealing up all joints. For existing floors, you can apply a DPM coating using a brush or trowel.

The Damp Proof Membrane Installation Process

You should follow these steps to install a damp proof membrane:

  1. Prepare the surface: remove loose debris, weak wall render, and evidence of rot on the wall. Also, remove the skirting boards on the floor and dry the entire area.
  2. Cut the required membrane size: decide how you want to fit the membrane, whether vertically or horizontally, then cut it with scissors.
  3. Seal all joints: overlap any joins in the membrane, then seal with an adhesive or mesh tape.
  4. Fit the membrane: using a drill bit and fixing plugs, fit the membrane to the wall. If it’s for the floor, lay a moisture-resistant chipboard on the membrane and refit the skirting boards.
  5. Apply finishing: appropriate finishings for walls include careful plastering and rendering.

How Long Does it Take to Install a Damp Proof Membrane?

It takes between 6 to 24 hours to apply a liquid DPM, depending on the weather condition. Also, if you’re applying a two-coat liquid membrane, you’ll have to wait for the first coat to dry before applying the next. Installing DPM sheets on walls may take up to 1 week, depending on the damage.

Tools Needed to Fit a Damp Proof Membrane

To fit a damp proof membrane sheet, you’ll need the following:

  • Fixing plugs
  • Drill bit
  • Waterproof tape

A liquid DPM requires:

  • Gloves
  • Paintbrush
  • Pile roller

Can You Install a Damp Proof Membrane Yourself, or Do You Need a Professional?

You can instal a damp proof membrane yourself, but it’s always best to contact a professional. They have the required tools and experience to tackle damp.

What Are Damp Proof Membrane Plugs?

Damp proof membrane plugs are fixings used to hold the membrane securely to the wall to prevent moisture from penetrating.

Advantages of a Damp Proof Membrane

  • Protects against condensation and rising damp
  • Compatible with various construction materials like concrete, metal, and timber
  • Comes in various forms like sheets and liquid, providing flexibility in its applications
  • Prevents moisture from penetrating insulation materials, thereby improving their efficiency

Disadvantages of a Damp Proof Membrane

  • The overall cost of installing a DPM is expensive
  • A minor puncture may tamper with the integrity of the material
  • Incorrect installation may be an effort in futility

Are Damp Proof Membranes Completely Waterproof?

A damp proof membrane is 100% waterproof, preventing water and moisture from penetrating.

Difference Between Damp Proof Membrane and Waterproof Membrane

A damp proof membrane prevents moisture from the soil and the surrounding area of the property, while a waterproof membrane blocks water from penetrating the walls and floor.

What Causes Damp in Properties?

Damp is caused by the excess accumulation of moisture due to condensation, the level of water around the building, and the products used during construction, such as mortar, plaster, and concrete.

How to Prevent Damp in Properties

Here’s how to prevent damp in properties:

  • Active ventilation
  • Check pipes, gutters and drains for leaks
  • Check for missing roof tiles
  • Inspect window frames and exterior for peeling paint

Laws and Regulations for Damp Proof Membranes

Installing damp proof membranes on existing properties or new constructions requires building regulations. The regulations vary for walls and floors, and you can find them in the Approved Document C.

British Standard for a Damp Proof Membrane

The recommended British Standard for damp proof membrane thickness is 1,200 gauge (300μm). Anything less than this violates the building regulations and will result in expensive repairs.

Difference Between a Damp Proof Membrane and a Damp Proof Course

A damp proof membrane is used under the floor and in internal walls to stop moisture from rising into the building. A damp proof course, on the other hand, is installed at basement levels to prevent the flow of moisture through floors and walls. 

Conclusion

From mildew to corrosion and poor insulation performance, damp causes many problems in buildings. But a damp proof membrane ensures that the interior of a building is dry and comfortable all year long.

If you suspect your property isn’t damp proofed, then it’s a good time to install a reliable DPM. Contacting a professional is ideal to avoid accidents that may ruin the whole essence of damp proofing.

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