What is Rising Damp – A Complete Guide
damphub.co.uk 02 May, 2024
Rising damp occurs when water from the ground moves up through the walls of a building. This happens because bricks and concrete can soak up water like sponges.
Imagine you dip one end of a tissue paper in water. The water slowly moves up the paper. Rising damp works the same way in walls!
If a house does not have a proper barrier under its walls, rainwater from the ground can slowly rise inside the bricks. This can make the walls wet, cause paint to peel, and even grow mould.
Have you ever seen dark, wet patches at the bottom of walls inside old houses?
That is rising damp! It makes homes feel cold and can cause damage over time.
What Does Rising Damp Look Like? Signs of Rising Damp
Rising damp creates wet patches and damage on the lower part of walls inside buildings. It usually starts from the ground and moves upward.
1. Damp & Stained Walls
In an old house, you see dark, wet patches on the bottom part of the walls, even though it hasn’t rained inside. The dampness feels cold and looks discolored.
2. Peeling Paint or Wallpaper
Imagine painting your bedroom wall, but after a few months, the paint starts bubbling and peeling off near the floor. This could be due to rising damp.
3. White Powder (Salt Deposits) on Walls
In a basement or an old home, you may notice a white, chalky substance forming on the wall. This happens because water brings up salt from the ground.
5. Musty Smell & Mold Growth
Walking into a house, you notice a damp, musty smell coming from the walls. In some places, black or green mold starts growing near the bottom of the walls.
What Causes Rising Damp?
Rising damp occurs due to capillary action, where moisture from the ground moves upward through the pores of building materials (like bricks, mortar, and plaster). This happens when there is no proper barrier to stop water from traveling up the walls.
1. Capillary Action in Porous Materials
- Building materials, especially bricks and mortar, contain tiny pores (capillaries).
- When these materials come in contact with wet soil, they pull water upward just like a sponge absorbs water.
If you place a dry brick in a shallow pan of water, you will see the water slowly rising into the brick. This is how rising damp occurs in walls.
2. Lack of or Failed Damp-Proof Course (DPC)
- A Damp-Proof Course (DPC) is a waterproof layer (often made of plastic, bitumen, or slate) installed at the base of walls to block moisture.
- If a building does not have a DPC (common in pre-1950s homes) or the DPC is damaged or bridged, water can rise through the walls.
In an old Victorian house with a cracked DPC, moisture bypasses the barrier and seeps into the walls, leading to damp patches inside.
3. High Ground Levels Around the Property
- If the soil level outside is higher than the internal floor level, moisture can bypass the DPC and enter the walls.
- This commonly happens when a driveway, patio, or garden bed is built too high against the house.
A homeowner adds a new paved path outside, raising the ground level higher than the damp-proof course. Over time, water begins rising into the walls inside the house.
4. Poor Drainage or Water Accumulation Near Walls
- Blocked or poorly designed drainage causes rainwater to pool around the foundation, increasing water absorption into walls.
- Leaking pipes or gutters can also contribute to excess moisture around the base of a building.
A home with clogged gutters has water constantly dripping near the foundation. This increases moisture in the soil, worsening rising damp inside.
5. Salt Contamination and Hygroscopic Salts
- Groundwater contains dissolved salts (e.g., nitrates and chlorides). As moisture evaporates from the walls, these salts crystallize, causing damage.
- Some salts are hygroscopic, meaning they attract moisture from the air, keeping the wall damp even after the water source is removed.
An old wall with rising damp shows white, powdery salt deposits. Even when dry weather comes, the wall remains damp because the salts keep pulling moisture from the air.
What Are The Effects of Rising Damp
1) Structural Damage to Buildings
Weakening of Walls and Plaster
A house with rising damp has crumbling plaster on the lower walls. When touched, the plaster feels soft and flaky due to prolonged moisture exposure.
Damage to Paint and Wallpaper
In the living room, the paint near the floor starts to bubble, crack, and peel off, making the walls look untidy.
Rotting Wooden Skirting Boards and Floors
A wooden skirting board near a damp wall begins to warp and decay. If left unchecked, the moisture spreads, weakening the wooden flooring and causing it to become soft or collapse over time.
2) Health Issues Due to Mold and Damp Air
Mold Growth and Musty Odor
A child’s bedroom has rising damp, leading to black mold patches near the floor. The room smells musty, making it uncomfortable to sleep in.
Respiratory Problems and Allergies
A family living in a damp home suffers from constant coughing, sneezing, and asthma attacks due to mold spores in the air.
Increased Humidity Leading to Dust Mites
High humidity from rising damp creates the perfect environment for dust mites, which can trigger allergies and skin irritation.
3) Aesthetic and Property Value Damage
Unattractive Appearance
A homebuyer visits a property with rising damp and notices stained, peeling walls. The home looks neglected, making them less interested in purchasing.
Reduced Property Value
A house with rising damp gets a low valuation from an inspector, causing the owner to lose thousands of dollars in resale value.
Expensive Repair Costs
A homeowner ignores rising damp for years. Later, they have to spend $5,000+ on professional damp-proofing, wall repairs, and replacing damaged floors.
How to Fix Rising Damp
1) Installing or Repairing a Damp-Proof Course (DPC)
A Damp-Proof Course (DPC) is a barrier placed at the base of walls to stop moisture from rising. If a building lacks a DPC or the existing one is damaged, it must be repaired or replaced.
2) Lowering External Ground Levels
If the ground outside is higher than the damp-proof course, moisture can bypass it and rise into the walls. Lowering the soil or paving helps prevent this.
A house has a raised garden bed touching its exterior wall, allowing water to soak into the bricks. By lowering the soil level, the homeowner prevents further damp issues.
How To Fix:
- Remove excess soil or paving that is above the DPC level.
- Ensure at least 150mm (6 inches) of clearance between the DPC and ground level.
3. Improving Drainage
Poor drainage around a building can lead to water accumulation, increasing moisture levels in walls. Fixing drainage prevents rising damp from getting worse.
How To Fix:
- Repair leaking gutters and pipes that cause water to pool near walls.
- Install French drains (gravel-filled trenches) to redirect water away from the house.
- Ensure proper ground slope so rainwater drains away instead of collecting near walls.
A house with clogged gutters allows rainwater to drip near the foundation, soaking the bricks. After cleaning and repairing the gutter system, the damp problem improves.
4. Using Specialist Damp-Proof Coatings and Plaster
Even after fixing the root cause, walls may still have residual moisture and salt deposits. Damp-proof coatings and plaster help protect against further damage.
How To Fix:
- Damp-resistant plaster prevents moisture from spreading on interior walls.
- Salt-resistant coatings stop salts from forming white, powdery marks (efflorescence).
- Damp-proof paint seals walls to reduce further moisture absorption.
After treating rising damp, a homeowner applies damp-resistant plaster and waterproof paint to prevent future salt stains and peeling paint.
How to Prevent Rising Damp?
Regularly Check Walls for Early Signs of Damp
Why?
Catching damp problems early prevents serious damage and costly repairs.
What to Look For?
- Dark, wet patches near the bottom of walls.
- Peeling paint or bubbling wallpaper.
- White, powdery salt deposits (efflorescence).
- Musty smell or mold growth.
Prevention Tip: Inspect both inside and outside walls at least twice a year, especially after heavy rains.
Maintain Gutters and Drainage Systems
Why?
Blocked gutters or poor drainage cause rainwater to collect near walls, increasing moisture levels and leading to rising damp.
How to Maintain Gutters?
- Clean gutters and downpipes regularly to prevent water overflow.
- Fix leaking or broken gutters so water doesn’t drip near walls.
- Ensure water drains away from the house (not towards it).
Prevention Tip: Check and clean gutters at least twice a year (before and after the rainy season).
3. Avoid Raising Soil or Paving Above the DPC Level
Why?
If the ground level outside is too high, it can bridge the damp-proof course (DPC), allowing moisture to bypass it and enter the walls.
How to Prevent This?
- Ensure at least 150mm (6 inches) of clearance between the DPC and ground level.
- Avoid building raised flower beds, patios, or driveways against exterior walls.
- If necessary, lower the soil or paving to keep the DPC exposed.
A homeowner builds a new paved patio that is level with the house’s floor. Over time, water seeps into the walls, causing rising damp. To fix it, they lower the patio height to expose the DPC, preventing further damp issues.
Prevention Tip: Always check the ground level before laying paving, garden beds, or driveways next to walls.
When to Get Professional Help for Rising Damp
While minor damp issues can sometimes be managed with DIY solutions, professional help is needed when the problem is severe, persistent, or affecting the structure of the building. Here’s when you should call an expert:
When You See Extensive Damage
Signs:
- Large damp patches covering walls.
- Peeling paint or wallpaper over a wide area.
- Crumbly, soft plaster falling off.
When You See Extensive Damage
Signs:
- Large damp patches covering walls.
- Peeling paint or wallpaper over a wide area.
- Crumbly, soft plaster falling off.
2. If There’s Mold or a Musty Smell That Won’t Go Away
Signs:
- Black or green mold growing on walls or skirting boards.
- A strong musty smell even after cleaning or airing out the room.
- Family members experience coughing, sneezing, or allergies.
3. When Your Damp-Proof Course (DPC) Might Be Failing
Signs:
- A house built before the 1950s without a modern DPC.
- The DPC is cracked, bridged, or missing in certain sections.
- Rising damp symptoms appear despite previous damp-proofing.
4. When DIY Fixes Aren’t Working
Signs:
- You tried ventilating, repainting, or dehumidifiers, but the damp keeps returning.
- DIY damp-proof paint works temporarily but doesn’t fix the root cause.
- You fixed drainage and checked the DPC, but the issue persists.
5. Before Buying or Selling a House
Why?
- If a home shows signs of damp, it’s best to get a damp survey before purchasing.
- Rising damp lowers property value, so sellers should fix it before listing.
Who to Call for Help?
🔹 Damp Surveyor: To assess the severity and recommend solutions.
🔹 Damp-Proofing Specialist: To install or repair a DPC and treat damp issues.
🔹 Plumber or Drainage Expert: If poor drainage or leaks are contributing to the damp.
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