Is your garden or paving causing damp in walls?

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Dampness within walls can be a serious problem for a home leading to costly repairs and health problems. Damp walls can lead to mould, bad smells, discolouration, flaking, cracking and even structural issues.

Although many assume damp walls are caused by leaky roofs or plumbing, it is also important to consider other sources.

Poorly designed gardens and paving can actually contribute significantly to the build up of moisture within walls. This is particularly the case in homes that are of older construction and have poor, landscape, drainage.

In this article we will explore various ways gardens and paving can contribute to damp walls. I will explain how to diagnose if the garden is causing dampness and how to solve the issue. 

Regardless of if you have knowledge of garden drainage or construction this should provide you all the information you need.  

If your garden or paving is causing damp walls a swift resolution is essential to maintain a healthy living environment. 

Common causes of dampness in walls
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• Exposure to extreme weather
• Clogged gutters
• Leaking roofs
• Leaking pipes
• Failed damp proofing
• Cracked brickwork & render
• Poor ventilation
• Drying clothes indoors
• Damaged window frames
• Rising damp
• Poor garden drainage 

How to tell if it is your garden or paving is causing damp in walls

​It is not always easy to know exactly what any one cause of damp walls is. Very commonly it is a combination of factors which contribute to a dampness problem.

There are however tell tale signs of if your garden or paving is causing a problem. Normally damp walls caused by garden landscaping effects the lower ground floor walls.

Flaky paintwork, render and brickwork are a sign of garden induced dampness.  
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Does your local area have a high water table or does your garden have poor drainage?

This can easily be determined by monitoring how wet your garden soil is, especially during the summer months. 

​Even with a robust damp proof layer, (DPC) saturated ground under a property can lead to rising condensation and humid conditions. Poor garden drainage can also help exacerbate general dampness around your home. 

Garden surface levels

Very often, ground surface levels and contours around your home can contribute to water pooling around your property.

This is not only restricted to the boundaries of your own properly but can also be influenced by surrounding plots. 

​It is common to see excess storm water run down from adjacent properties upon a higher level. This is particularly so if they have installed extensive hard or impervious surfacing. 
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Occasionally the natural lie of the land means water naturally runs down towards your home.

In such cases you will need to capture and divert water in drainage channels and grated channel drains. You will need to landscape your garden with a flush and level surface which gently falls away from your home.

​This should be the case with all surfaces including lawns, flowerbeds and patios. 

Clay soil

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Clay soil has very fine particles which can become extremely compacted and dense when wet.

These particles are capable of absorbing large amounts of water and can become completely saturated in times of heavy rain. This can further be exacerbated by local hydrology factors such as flood zones or a high water table.

Building foundations in wet clay subsoil can remain damp all year round. Concrete foundations can become completely saturated leading to damp conditions under the structure.

Even though the DPC layer prevents damp rising such conditions can lead to excess humidity and condensation. This can contribute to causing damp in walls especially if combined with other contributing factors.

​Consequently it is best to prevent too much water absorbing into clay soil around your home.  
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Paving surface levels

One of the biggest culprits of damp walls with moisture coming from outside is paving levels. This is especially so if your garden naturally slopes downwards towards your home.

In times of heavy rain, surface water rushes towards the building saturating external walls. Over the years, many contractors have left a ‘shingle trap’ or ‘gravel strip’ along the house to improve drainage.

​Although this does allow surface water to drain away it creates a saturated pocket along the building.

​After a few years silt and dirt builds up and clogs gaps between the gravel. 
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This can lead to continuous saturation even during the summer months.  For this reason such shingle traps are not an advisable solution for draining water away from around the home.

If they absolutely have to be implemented they should be waterproofed with waterproof render and bitumen paint.

The best option however, is to install grated channel drains to guide excess storm water away from the home.

When planning any new paving the surface levels should fall away from the home. For more in-depth information on patio drainage read our article on the subject here. 
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The DPC (damp proof course)

The DPC or damp proof course is a waterproof layer around 150mm above the surrounding ground level.

This layer is designed to stop moisture rising up through the ground and into the structural masonry of a building. The DPC typically takes the form of a plastic membrane which is laid within the mortar layer of brickwork.

In older buildings, thin layers of slate were used as a waterproof layer easily identified by a much thicker mortar joint.

​The damp proof layer can also be identified by a thin layer of plastic just visible within the mortar. 
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On buildings with external render and pebble dash the render starts above the DPC like in the image above.

Building regulations require paving and other external surfacing to sit at least 150mm (or two bricks below the damp proof.)

​This is to prevent surface water or splash back from absorbing above the DPC level. Consequently you may wish to check your garden or paving does not come up too high upon your DPC. 

How to solve dampness in walls from patios.  

Impermeable paving

​​In recent times there has been a push to implement more permeable surfacing around developments.

Permeable surfaces allow water to pass through the surface into the ground below. Permeable paving and surfacing does reduce accelerated storm water runoff into the drainage network.

This prevents pollutants being washed into natural watercourses and wetlands being an ecological choice. However, permeable surfacing will increase the moisture content of the ground which is not ideal either.

​The best solution for this is impermeable surfacing which channels water far from the property into a miniature wetland. This could be a bio-swale at the bottom of the garden or a seasonal flooding wetland habitat. 
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Changing surface levels or falls

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​The most potent remedy to get water and moisture away from your walls is by manipulating surface levels.

Ideally your surface levels should fall away from your property so water runs away. If your garden naturally slopes towards your property you may wish to implement a 'back fall'.

A 'back fall' is a section of surfacing near a building which falls contrary to the primary level. This allows water to collect and run away parallel to the external wall.

The surface run-off can then be collected and channelled away to a drainage chamber and drainage point like in the image below. 
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Drainage gullies

​Drainage gulley’s are simple depressions created within surfaces to channel water away to a specific location.

These can come in a variety of forms and made from varying materials. A common example would be granite sets laid into a depression to collect and channel water.

Drainage gulley’s can also be created with concrete, paving or tarmac. Occasionally strong edgings are used to create linear channels and filled with free draining gravel. 
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Channel drains

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Channel drains are linear sections of drain which join together to create a channel drain. The most typical example of these is Acco chambers with a metal grate or grill cover.

These allow pedestrians to walk over making them perfect for paving and patios. Channel drains are capable of draining surfaces quickly of large quantities of surface water.

These can be plumbed or piped into drainage features such as soak-aways and drainage systems. For more information on channel drain installation visit our article here. 
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How to solve dampness in walls coming from gardens

Improving your gardens drainage

​Generally improving your gardens drainage is extremely beneficial if you have damp in ground level walls.

Even though most modern buildings have damp proof courses moist ground can still contribute to damp walls. Boggy ground around your home can create excess condensation and air humidity.

Poor garden drainage can also increase the probability of surface water accumulating in times of heavy rainfall. This can lead to excess splash back onto external walls. 
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Changing surface levels

A garden surface levels are crucial in where rain water ends up. If you have undulating ground, rain water will become trapped within low areas.

This can lead to excess saturation, compaction and boggy areas. Gardens which naturally slope downwards towards your property will dam around your external walls.

​For his reason it is a good idea to visually assess your surrounding levels. Do this from every far corner of your property as your eye can determine levels much better at distance. 
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This will give the eye some special context in regard to the surrounding surface levels around the home.

Once your analysis is complete, think about how you can design levels to direct water away from the home.

Re-grade your ground so it has more flush and consistent levels falling away from the home. If a sites topography makes this difficult,trap and collect water within drainage channels. 

Storm water can then be directed to a drainage pond, soakaway or other drainage feature. 

Drainage channels

Drainage channels act as underground, free draining, course-ways for groundwater to be drained from surrounding ground.

Not only can drainage channels collect surface run-off they can alleviate hydraulic pressure within the ground. This makes them very effective at draining boggy areas including lawns and flower beds.

​Where ground slopes towards a building, drainage channels can be utilised to block approaching surface water by collecting it. 
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The water can then be directed away into a drainage feature. Drainage channels generally consist of a linear trench with a perforated pipe encased within free draining gravel.

Free draining gravel enables water to seep out from the surrounding, saturated ground. The perforated pipe acts as a central flush for collected water which can be directed away.

Drainage channels can help to drain excess water from around your home helping to mitigate dampness within walls. 

For more information on drainage channel installation read our article here. 

Garden soak-aways

​Garden soak-aways are submerged vessels which hold large volumes of collected water.

They provide a drainage destination and holding facility for water drained from surrounding ground. Drainage soak-ways allow large volumes of water to be reabsorbed slowly by the underlying subsoil.

In the past, garden soak-aways consisted of large trenches filled with broken masonry such as bricks. This masonry reduced volume capacity leading to fast filling and breeching in times of heavy rain.

​The large voids also led to excessive silting resulting in reduced capacity and eventual failure. Today it is more common to install drainage soak-away crate systems. 
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These strong, plastic, structures clip together to create very large voids for drainage water to flow into.

If you are attempting to drain the soil around your home, soak-aways can provide an effective drainage destination.

​Drainage channels can draw water out of surrounding ground and direct it straight into your soak-away system. For more information on installing garden drainage soak-aways visit our step by step guide here. 

Improving soil structure

One of the most common culprits of bad garden drainage is poor soil quality. If your topsoil layer does not allow water to percolate freely, your topsoil will become boggy.

Damp and boggy topsoil can easily become stagnant and compacted leading to even more impervious ground.

The result is more ground saturation and standing water around walls and buildings. In some occasions this can contribute to damp in walls and under the home. 
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Therefore, improving your soils structure so it is more free draining is crucial for improving drainage. Typically the best way to achieve this is to incorporate plenty of organic matter and grit.

This is especially so with soil types with dense and fine particles like clay. The best way to do this is loosen the soil using a tiller during warm and sunny weather.

Materials such as horticultural grid, sharp sand, leaf mould and compost can be added during tilling.

​Such a process will boost soil life helping to create plenty of tiny air pockets where water can percolate. 

Ecological drainage

Ecological drainage involves draining away excess water in an environmentally friendly way.

Instead of channelling storm water into manmade pipes or storage vessels water flows into wetlands. This not only helps to drain water away it also creates habitats for wildlife.

Water can be drained from surfaces and boggy ground can be channelled into bioswales, wildlife ponds and seasonally flooded wetlands. 
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This enables water to be reabsorbed slowly back into the landscape in a more natural way. Aquatic plants and microscopic organisms help to oxygenate and clean the water naturally.

This reduces pollution within natural watercourses and eases pressure on the local drainage network.

​Ecological drainage installations such as swales and ponds can be landscaped to create attractive features and focal points.

​Not only can they look good they can also increase biodiversity and wildlife value around your home. 
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​Thank you for reading our article on, is your garden or paving causing damp in walls? Below we have linked to some of our other drainage articles you may find relevant. ​ 

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