Damp proof membranes (DPMs) stop moisture from travelling through floors, walls, and foundations. Choosing the right type matters because the wrong membrane leads to damp problems, wasted money, and failed projects.
This guide compares every major DPM type so you can pick the one that actually works for your situation.
What Is a Damp Proof Membrane and Why Does It Matter?
A damp proof membrane is a waterproof barrier that blocks moisture movement. You install it in floors, under concrete slabs, or within wall constructions.
Without proper damp proofing, ground moisture rises through porous materials like concrete and brick. This causes:
- Wet floors and walls
- Mould growth
- Damaged finishes
- Health problems
- Structural deterioration
The right DPM creates a reliable barrier between wet ground and your building’s interior.
Main Types of Damp Proof Membranes
Different projects need different membranes. Here’s what’s available.
Polyethylene (Polythene) Sheet Membranes
The most common DPM type in the UK. These come as large rolls of plastic sheeting.
Thickness options:
- 300 micron (0.3mm): Light duty, minimal protection
- 500 micron (0.5mm): Residential floors
- 1000 micron (1mm): Heavy duty, commercial use
- 1200 micron (1.2mm): Maximum protection
Where to use them:
- Under concrete floor slabs
- Beneath screed
- As a wall cavity barrier
- Ground floor conversions
Advantages:
- Cheap (£20-40 per roll)
- Easy to source
- Simple to install
- Good for most residential projects
Disadvantages:
- Tears easily during installation
- Punctures from sharp aggregate
- Difficult to repair once damaged
- No vapour control in some grades
Polythene membranes work well when installed carefully. The key is overlapping joints by at least 150mm and taping them properly.
Bitumen Based Membranes
Traditional DPM material, still used in specific applications. Made from modified bitumen with fabric reinforcement.
Common types:
- Self-adhesive sheets
- Torch-on membranes
- Cold-applied liquid bitumen
Where to use them:
- Retrofit damp proofing in walls
- Tanking basements
- Below ground structures
- Flat roof applications
Advantages:
- Excellent adhesion to surfaces
- Very puncture resistant
- Long proven track record
- Self-healing properties in some grades
Disadvantages:
- More expensive (£4-8 per square metre)
- Requires skilled installation
- Heat needed for torch-on types
- Strong odour during application
- Slower installation process
Bitumen membranes excel in basement tanking where you need absolute reliability.
Liquid Applied Membranes
Paint-on or spray-on systems that create seamless barriers.
Available types:
- Polyurethane based
- Acrylic polymers
- Epoxy systems
- Rubber latex compounds
Where to use them:
- Complex floor shapes
- Existing floor surfaces
- Wet rooms and bathrooms
- Detailed waterproofing areas
- Refurbishment projects
Advantages:
- No joints or seams
- Conforms to any shape
- Easy to detail around pipes
- Quick application
- Good for retrofit work
Disadvantages:
- Expensive (£8-15 per square metre)
- Requires two or three coats
- Needs proper surface preparation
- Drying time between coats
- Skill needed for even coverage
These work brilliantly in awkward spaces where sheet materials fail.
Self-Adhesive Membranes
Modern DPM solution with sticky backing for direct application.
Construction:
- Polymer modified bitumen core
- Protective film on adhesive side
- Reinforced fabric layer
Where to use them:
- Internal wall tanking
- Floor overlays
- Detailed waterproofing
- Renovation projects
Advantages:
- No heat or flame needed
- Clean installation
- Strong bond to substrates
- Immediate protection
- Works on damp surfaces (some types)
Disadvantages:
- Premium pricing (£6-12 per square metre)
- Surface must be clean and prepared
- Temperature sensitive during installation
- Limited to vertical and horizontal surfaces
Perfect for internal wall damp proofing where you cannot use heat.
Gas Resistant Membranes
Specialist DPMs that block ground gases like radon and methane.
Key features:
- Multi-layer construction
- Gas barrier layer (often aluminium)
- High puncture resistance
- Tested to specific gas permeability standards
Where to use them:
- Radon affected areas
- Brownfield sites
- Former landfill sites
- Areas with methane risk
- Commercial and industrial buildings
Advantages:
- Protects against harmful gases
- Often combines gas and water protection
- Building regulations compliant
- Proven performance data
Disadvantages:
- Most expensive option (£8-20 per square metre)
- Strict installation requirements
- Needs certified installers in some cases
- Must maintain integrity throughout
These are mandatory in certain locations. Check if your site sits in a radon affected area at UKradon.org.
Reinforced Membranes
Heavy duty membranes with fabric or mesh reinforcement.
Construction types:
- Woven fabric reinforced polythene
- Grid reinforced polymers
- Geotextile backed sheets
Where to use them:
- Heavy traffic areas during construction
- Large commercial slabs
- Industrial floors
- Where puncture risk is high
Advantages:
- Extremely tear resistant
- Can walk on during construction
- Withstands sharp aggregate
- Long term durability
Disadvantages:
- Higher cost than standard polythene
- Heavier to handle
- More difficult to cut and shape
- Overkill for light residential use
Use these when your slab will see rough treatment during construction.
Damp Proof Membrane Comparison
| Membrane Type | Typical Cost | Installation Difficulty | Durability | Best Use |
|---|---|---|---|---|
| Polythene Sheet | £20-40/roll | Easy | Good | Standard residential floors |
| Bitumen Based | £4-8/m² | Moderate to Hard | Excellent | Basements and tanking |
| Liquid Applied | £8-15/m² | Moderate | Very Good | Complex shapes, retrofit |
| Self-Adhesive | £6-12/m² | Moderate | Very Good | Internal walls, clean projects |
| Gas Resistant | £8-20/m² | Hard | Excellent | Radon areas, brownfield sites |
| Reinforced | £50-80/roll | Easy to Moderate | Excellent | Heavy duty commercial |
How to Choose the Right Damp Proof Membrane Type
Match the membrane to your specific situation. Ask these questions:
What are you protecting?
Floor slab: Standard polythene (minimum 1200 gauge) or reinforced for commercial projects.
Wall cavity: Bitumen based or specialist cavity DPM.
Basement: Bitumen tanking system or thick polythene with proper detailing.
Wet room: Liquid applied membrane for seamless coverage.
What’s the ground condition?
Dry sandy soil: Basic polythene sufficient.
High water table: Heavy duty polythene or bitumen system.
Contaminated ground: Gas resistant membrane mandatory.
Aggressive ground conditions: Bitumen with chemical resistance.
What’s your budget?
Standard polythene costs least but needs careful installation. Spending more on reinforced or bitumen membranes reduces installation failure risk.
Calculate the total cost including:
- Material price
- Labour for proper installation
- Repair costs if it fails
- Delay costs from getting it wrong
Cheap membranes installed badly cost more than good membranes installed properly.
Who’s installing it?
DIY project: Stick with polythene sheets. They’re forgiving.
Professional builder: Any type appropriate to the job.
Specialist contractor: Bitumen, gas resistant, or complex liquid systems.
Match the membrane complexity to installer skill level.
Installation Requirements for Each Type
Polythene Sheet Installation
- Prepare a smooth, clean base free from sharp stones
- Lay sheets with 150mm minimum overlap at joints
- Tape all overlaps with approved DPM tape
- Turn membrane up walls by at least 150mm
- Seal to wall DPC if present
- Protect membrane before pouring concrete
Common mistakes:
- Insufficient overlap causing gaps
- No tape on joints
- Punctures from walking on it
- Sharp aggregate damage
- Poor detailing at edges
Bitumen Membrane Installation
- Clean and prime the substrate
- Apply adhesive or heat the torch-on membrane
- Roll out and press firmly into place
- Overlap by 100mm minimum
- Seal all laps properly
- Detail carefully at penetrations
Bitumen needs dry conditions and skilled hands. Don’t attempt torch-on work without proper training.
Liquid Membrane Application
- Clean the surface thoroughly
- Prime if required by manufacturer
- Apply first coat evenly
- Allow to cure (usually 4-24 hours)
- Apply second coat perpendicular to first
- Third coat if specified
- Inspect for pinholes and bare patches
Use the correct thickness. Too thin fails, too thick wastes money.
Self-Adhesive Membrane Installation
- Ensure surface is clean, dry, and dust free
- Remove backing film gradually
- Press firmly from centre outwards
- Use roller to ensure good bond
- Overlap edges by 75-100mm
- Seal laps with pressure
Temperature matters. Most need 5°C minimum for proper adhesion.
British Standards and Building Regulations
All DPMs must meet British Standards:
BS 8102:2009 covers protection of below ground structures against water and ground moisture. This is the key standard for basement and ground floor waterproofing.
BS 6515 specifies requirements for polythene DPM sheets used in building construction.
Building Regulations Approved Document C (Site preparation and resistance to contaminates and moisture) requires effective damp proofing in floors and walls.
For radon protection, follow BRE guidance and use tested gas resistant membranes where required.
Check full requirements at gov.uk planning portal before starting work.
Common Problems and How to Avoid Them
Punctures and Tears
Cause: Sharp stones, dropped tools, rough treatment.
Solution:
- Use blinding layer of sand under membrane
- Choose reinforced membrane for rough sites
- Install protective layer immediately after membrane
- Keep the site clean
Failed Joints
Cause: Poor overlapping, no tape, movement.
Solution:
- Overlap 150mm minimum
- Use proper DPM tape, not general purpose
- Avoid stretching the membrane
- Detail carefully at corners
Incomplete Coverage
Cause: Rushed installation, poor planning.
Solution:
- Plan the layout before starting
- Order 10% extra material
- Turn membrane up walls adequately
- Seal to existing DPCs
Water Bypassing Membrane
Cause: Poor detailing at edges, no wall connection.
Solution:
- Connect floor membrane to wall DPC
- Seal all penetrations
- Create continuous barrier
- Don’t leave gaps at walls
Real World Performance: What Actually Works
After 30 years in construction, here’s what performs:
Best all-rounder: 1200 gauge polythene, properly installed with taped joints. Handles 95% of residential projects.
Best for basements: Type A bitumen tanking system with proper structural waterproofing design.
Best for retrofit: Liquid applied membranes. They adapt to existing conditions and seal everything.
Best for problem sites: Gas resistant membranes on brownfield land. They’re expensive but mandatory.
Best value: Standard polythene with reinforced membrane in high traffic areas during construction.
The membrane type matters less than installation quality. A cheap membrane installed perfectly outperforms an expensive one installed badly.
Cost Analysis: Initial vs Long Term
Initial Costs Per 100m² Floor
- Standard polythene: £100-150 materials
- Reinforced polythene: £200-300 materials
- Bitumen system: £400-800 materials
- Liquid applied: £800-1500 materials
- Gas resistant: £800-2000 materials
Add labour costs:
- DIY: Your time only
- Professional: £300-800 for polythene installation
- Specialist: £1000-3000 for complex systems
Long Term Costs
A failed DPM means:
- Lifting the floor: £2000-5000
- New screed: £1000-3000
- New floor finish: £1000-5000+
- Replastering damp walls: £500-2000
- Mould remediation: £500-2000
- Lost time: Weeks of disruption
Spending an extra £500 on proper membrane and installation saves thousands later.
Summary
Choose your damp proof membrane based on these factors:
For standard ground floors: Use 1200 gauge polythene with proper overlaps and taping. It’s proven, cheap, and effective.
For basements: Specify bitumen tanking or specialist waterproofing systems designed by a structural waterproofing specialist.
For retrofit work: Liquid applied membranes work best on existing surfaces and complex shapes.
For contaminated sites: Gas resistant membranes are mandatory. Don’t compromise.
For commercial projects: Reinforced membranes handle site traffic and provide long term performance.
The best membrane is the one installed correctly. Poor installation ruins any DPM type. Take time to prepare the base, overlap joints properly, and seal everything.
Damp problems rarely fix themselves. Invest in the right membrane now and install it properly. Your building will stay dry for decades.
Frequently Asked Questions
Can I use any thickness of polythene as a damp proof membrane?
No. Building regulations and British Standards specify minimum requirements. Use at least 300 micron (1200 gauge) polythene for floors. Thinner plastic from builders merchants won’t provide adequate protection. The extra cost for proper specification DPM is minimal compared to failure costs. Always buy material marked as complying with BS 6515.
Do I need a separate vapour barrier if I install a damp proof membrane?
It depends on your floor construction. A DPM stops liquid water. A vapour control layer (VCL) stops water vapour. Some modern membranes combine both functions. Check the manufacturer’s specifications. For heated screeds and some insulation types, you need a separate VCL above the insulation. The DPM goes under the concrete slab, the VCL goes above the insulation.
How do I join two pieces of damp proof membrane together?
Overlap the sheets by minimum 150mm. Use proper DPM jointing tape, not ordinary duct tape or masking tape. Press the tape down firmly with no air bubbles. Some installers use double-sided tape underneath as well. For critical applications like basements, consider heat welding the joints or using solvent welded seams. Never leave untaped overlaps.
Can I walk on a damp proof membrane during construction?
You can walk carefully on reinforced membranes designed for foot traffic. Standard polythene tears easily under boots, especially with sharp stones underneath. Lay protective boards or use a reinforced membrane if people must walk on it. The best approach is to pour concrete or lay screed immediately after installing the membrane. Every day exposed increases puncture risk.
What happens if my damp proof membrane gets damaged during installation?
Repair it immediately before continuing. For polythene, patch tears with a piece of membrane and DPM tape, ensuring good overlap. For bitumen, use repair tape or additional membrane. For liquid membranes, apply extra coats over damaged areas. Large damage means replacing that section entirely. Check the whole membrane carefully before covering it. One small hole ruins the entire installation.