Does Your Garden Room / Garden Office Suffers From Rising Damp?

If you have noticed that your much valued garden room or garden office has been smelling a little musty, or that jacket that you left hanging on the back of your chair overnight has a definite whiff of something malodorous, you may have to face up to the fact that you could have a problem with damp.

Damp can be an issue for any type of building and it is a common problem in garden rooms and garden offices in the UK, this is often not noticed during the warmer months of spring and summer and it can be quite an unpleasant shock for new owners of these buildings as they enter their first extended period of seasonally inclement weather. Of course, depending upon what is causing it, damp can actually affect any building at any time of the year and it is vital that, once you realise that you may have a problem with damp, you get it dealt with at your earliest opportunity. Early diagnosis and intervention could not only save you a great deal of expense and upheaval, it could, more importantly, avoid any potentially serious health issues for you and your family.

Garden rooms and garden offices generally suffer with one or more types of damp, these include damp resulting from leaks, damp caused by condensation, penetrating damp and rising damp. This article is the second in a series of four in which we investigate these four most common kinds of damp, our first article in this series looked at the issues of damp caused by condensation, please click here if you would like to view this article. This second article will cover rising damp and we will look at the cause of rising damp, how to spot it and how it should be dealt with once it has been diagnosed.

The problem of Rising Damp in Garden Rooms and Garden Offices?

Rising damp is the least common of the different types of damp we will cover in our series of four articles, it is also the most controversial as there are many who consider that this type of damp does not exist at all, they consider it to be a myth. The main reason for this ongoing controversy is the fact that rising damp is often incorrectly diagnosed, this means that the wrong treatment is applied, the problem is not dealt with and the damp problem remains. As with all types of damp, it is vital that you arrange to have the issue diagnosed and dealt with as soon as you realise that you may have a problem. In order to avoid a potential misdiagnosis, it is also extremely important that you use a fully qualified professional who has industry recognised qualifications

Why does Rising Damp Happen in Garden Rooms and Garden Offices?

Garden rooms and garden offices are often built with blocks, brick or stone walls and it is these buildings that are at risk of rising damp issues, brick and stone are porous materials, which means that they can allow the ingress of water, the more porous the material, the more it can soak up moisture – like a sponge!

What is groundwater? When it rains the rainfall is absorbed into the soil and soaks deeper into the ground, this is called infiltration. The rain trickles into the rocks beneath the soil where it becomes groundwater, when this water reaches saturation level it is known as the water table.

Rising damp happens when groundwater moves upwards through the walls by capillary action, basically this means that the water is sucked up through the pores of the blocks, bricks or masonry, the more porous the material, the higher the water can travel, often reaching levels of over a metre before evaporating out of the wall.

What are the tell-tale signs of Rising Damp in Garden Rooms and Garden Offices?

Rising damp can occur in both external and internal walls of a garden room or garden office, unfortunately, it is not always easy to detect as it can lurk in masonry behind the plaster before it begins to show any noticeable signs. One of the first signs of any damp issue is often the smell, does your garden room or garden office smell damp, particularly when you first open the door and step in? If you do smell a damp odour then we recommend that you investigate further as damp, if left untreated, can cause potentially serious issues for the health of anyone using your garden room or garden office, the structure of your building and, last but not least, your pocket.

Signs to watch out for:

  • Smell of damp
  • Tide marks caused by salts left behind after the groundwater has evaporated out of the wall
  • Peeling wallpaper
  • Blistered paint
  • Damp areas on walls
  • Stained wall coverings
  • Stained plaster
  • Crumbling mortar
  • Signs of rot in floor boards, joists and skirting boards

Common causes of Rising Damp in Garden Rooms and Garden Offices

We know that rising damp happens when water is drawn up via capillary action into porous building materials, such as bricks, blocks or stone, and over time this causes damp problems within the building. Rising damp would not be able to occur if a barrier were in place to prevent this capillary action, fortunately, most buildings do indeed have such a barrier, it is called a damp proof course, or DPC.  

A damp proof course will obviously need to consist of a water resistant and non-absorbent material in order to provide an impervious barrier against water ingress via capillary action, common materials include slate, bitumen, plastic and chemical, hessian was occasionally used in construction of older properties, although we fail to see how this could have been considered impervious!

Many period properties were constructed without a damp proof course, so if the building that you use as your garden room or garden office was built before the advent of the DPC you may find that you will have issues with rising damp. Rising damp can be found in period properties that have a damp proof course, this may be due to it breaking down and failing over time.

Another cause of rising damp in both external and internal walls is when the damp proof course has been bridged, this allows the moisture to travel up and bypass the damp proof course via whatever has caused the bridge.

Examples of damp proof course bridging include:

  1. Mortar droppings or other debris in wall cavity
  • Incorrect cavity wall insulation
  • External render or internal plaster overlapping the damp proof course
  • Concrete floors laid higher than the damp proof course
  • External ground levels higher than the damp proof course
  • Flower beds higher than the damp proof course abutting external walls
  • Garden walls abutting external walls

How is Rising Damp Diagnosed in Garden Rooms and Garden Offices?

As previously mentioned, rising damp is often misdiagnosed, giving rise to the myth that it does not exist at all. It is mainly for this reason that we highly recommend that you contact an experienced and fully qualified professional to carry out a comprehensive survey in order to diagnose your damp problem and give their recommendations for any treatment that may be required. This survey is likely to be carried out using a wide range of equipment, including electronic moisture detection, electronic probes, thermal imaging, borescope cameras and so on; mortar sample analysis from within walls and salts analysis will also be an important part of the survey in order to reach an accurate diagnosis.

How is Rising Damp Treated in Garden Rooms and Garden Offices?

There are various methods of treating rising damp in a garden room or garden office once it has been diagnosed, you should be aware however, that whichever product you decide to use, the affected walls can still take up to a year to dry out.

Types of Treatment for Rising Damp:

Chemical Damp Proof Course

Injection of a chemical damp proof course is a highly effective and economical method of treating rising damp; this can be purchased on a DIY basis as individual cartridges of cream or in kit form, however, using a reputable, professional company will ensure the work is carried out correctly and you will receive a guarantee. The chemical cream is injected into holes drilled at regular intervals in the mortar course, once injected the cream turns into liquid and soaks into the blocks, bricks or masonry, forming a new water resistant, chemical damp proof course as it cures. Dealing with chemicals can be hazardous and it is crucial that you follow the instructions to the letter, we recommend that you contact your supplier or the manufacturer if you have any queries or concerns.

Replacement damp proof membrane

If you are averse to using chemicals then the installation of a replacement damp proof membrane is an alternative option. This is a much more labour intensive method as each block, brick or stone on the mortar course will require removal before the replacement damp proof membrane can be installed.

Whichever method of treatment you decide upon, you will need to remove all contaminated external render and internal plaster right back to the blocks, bricks or stone up to a height of 1.5m, replastering should be carried out using a salt neutralising plaster. Should you have external ground levels that are higher than the damp proof course, meaning that part of your external wall is below ground, you will need to apply a completely impermeable waterproof membrane to the internal wall to prevent damp re-occurring.

Rising damp can cause damage to a garden room or garden office long before the owner becomes aware of it, this means that you may have to replace rotten timber, such as floor boards, joists and skirtings. You will need to redecorate once the internal plaster has dried out and that goes for any external rendering too.

Chemical materials can be hazardous to your health and they should always be handled with extreme care, we recommend that you employ the services of a professional.

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