Everything You Need to Know About Garden Room Under Floor Membranes

The popularity of garden rooms in the UK is showing no sign of abating, in fact, with the pandemic taking longer to end than many had expected and worries about how commuting affects the climate, garden rooms have become even more popular.

You have decided to take the leap and purchase your own garden room, or build it yourself of course. You have carried out all the necessary research, this is crucial before embarking upon a major project such as this, so you shouldn’t have any unpleasant surprises lurking at any point during your build, hopefully! One part of garden room construction that is sometimes overlooked, most often by those who are building on a DIY basis but also, shockingly, by a number of garden room suppliers, are the waterproof or damp proof membranes and the breather membrane, garden rooms are also often fitted with a vapour control layer, also known as a vapour membrane. In this series of three articles, We will be exploring these membranes in detail, in this first article we will examine the different types of membranes used under the floor in the construction of buildings, we will look at how and why they are used, particularly in relation to garden rooms.

What are Garden Room Under Floor Membranes?

A garden room under floor membrane, also known as a damp proof membrane, is a sheet or liquid applied material that forms an impermeable barrier to protect against moisture entering the building via the foundation through capillary action. Of course, good drainage is an essential element of preventing the ingress of moisture into your garden room, however, the installation of an underfloor membrane serves a role that is equally as important in preventing damp, rotting timbers and ineffective or ruined insulation.

Foundation Waterproofing Membranes

The foundation is the solid base upon which your garden room is built, there are several types of foundation but this article will refer to the most commonly used foundation in the UK, namely the concrete foundation, also known as the concrete base or concrete slab.

The foundation waterproofing membrane does exactly what its name suggests, it protects your garden room from the ingress of moisture, thus preventing issues with damp, mildew and mould. Depending upon the type used, a foundation waterproofing membrane can be fitted beneath your concrete base or on top of it, many garden room owners even opt for both. It is essential that the material used as a foundation waterproofing membrane is strong and durable in order to prevent damage which could allow moisture through, care should be taken during installation to avoid accidental damage and joints should be carefully sealed.

Foundation waterproofing membranes are available in sheet form, as a heavy duty composite or PVC membrane, these types of membrane require precise jointing to avoid any leakage. Another type of sheet form foundation waterproofing membrane is a bituminous membrane, this type of membrane requires the use of blow torches and hot, tar based adhesive for installation.

Foundation waterproofing membrane is also available in a liquid form, of which there are several versions available. The liquid is brushed or sprayed onto the surface of your foundation and allowed to dry, this process should be repeated until the required thickness of membrane is reached. This method of installing a foundation waterproofing membrane is popular as there are no joints.

Retro-Fitting of Foundation Waterproofing Membrane

It is sadly quite common for garden room owners to find that they have an issue with damp in their floors, you may have noticed a musty smell or have staining or warping of your floor covering. This can often mean that the foundation waterproof membrane has failed and moisture has risen through to your flooring, of course some garden rooms will have been built without a foundation waterproofing membrane at all so it would have been only a matter of time before problems with damp flooring arose.

Once damp has penetrated your concrete foundation it is imperative that it is dealt with as quickly as possible, this is not an issue that is going to resolve itself. Fortunately, it is a problem that can be dealt with without having to demolish your garden room and start all over again.

The first remedy is to completely remove all of your flooring, such as parquet, laminate, tiles or carpet, followed by your underfloor insulation – this will probably have been rendered ineffective by now anyway, then dig up your concrete floor. This will sound like an awful upheaval, not to mention expensive and time consuming, but it is probably the most effective way of ensuring that your problems with damp are dealt with. Once the old concrete floor has been removed, a new foundation waterproofing membrane can be installed, ensuring that the edges are lapped up and any joints are carefully sealed, following this, a new concrete foundation can be laid.

The second option is nowhere near as drastic, you simply remove all the affected flooring and insulation and install a foundation waterproofing membrane, also known as a damp proof membrane or DPM. An epoxy liquid membrane is an effective product for a situation such as this, it can be applied directly to a damp floor and it is low odour and solvent free. Before applying an epoxy liquid membrane, it is important to ensure that the concrete surface is clear of any dust, debris and standing water. The epoxy liquid membrane can then be applied using a roller and a brush, a minimum of two coats is generally recommended – but no more than three. You should usually allow at least 12 hours between coats – but no more than 48 hours.

So, there you have it, we trust this has taken the mystery and confusion about which type of membrane you should use under your garden room floor, there are a lot of products to choose from so we recommend that you always make sure you do your research before making a purchase.

We suggest that you seek advice in order to ascertain the most suitable product for your needs, it should be noted that the application of some types of foundation waterproofing membranes can be hazardous to your health and should only be handled by professionals.

Our second article in this series covers the membranes used in the walls of a garden room, to view this article please click here. Our third article explores the membranes used in garden room roofs and it can be accessed by clicking here.

Special thanks Robin Croft for providing the image