A good garden office is made up of several layers, and a very important layer in this make up are the building membranes, which help control moisture within the building.
A breather membrane is a key layer in the construction, it allows the building to breathe.
Modern breather membranes are a high performance, fabric like material which wraps around the building, but some suppliers still use the older paper style products, which are sheets of Kraft paper with bitumen substance in-between. The premise is the same for both products – the external structure of the garden office is covered in the breathable membrane, with any joints well lapped and sealed.
The breather membrane sits behind the external cladding, and its job is to prevent moisture entering the main structure of the garden office, whilst allowing moisture generated within the office to escape from the building.
The breather membrane is a very important element in the construction of a garden office, and it is wise to check with your supplier that it is present in the build up of your chosen design.
A garden office is temporarily weather tight once the breather membrane has been installed, and its common for garden office suppliers to get the breather membrane on, quickly after the main structure is installed, so as to protect it from our inclement weather!
Vapour membranes work in conjunction with insulation. Not every garden office will feature a separate vapour membrane because the insulation chosen has a impermeable coating, which creates the vapour barrier or they use a insulated plasterboard which has a vapour barrier.
However its created, the vapour membrane helps control condensation, and this is a big fear of many garden office buyers, so check with your supplier how they address the matter.
In most cases all walls in a garden office are external walls. The worry is that warm vapour created within the garden office, will get trapped behind the insulation as it escapes and cools through the walls, creating condensation. You don’t want unnecessary moisture in your walls because it can cause rot – which is not a good thing in a timber building!
Vapour membranes are fitted on the warm side of the insulation i.e. the inside of the room, and often take the form of a plastic sheeting which is well lapped and sealed. Rigid insulation’s which are popular in garden office construction have a aluminum foil facing, which if joints are sealed with aluminum tape creates a vapour barrier. Other suppliers use foil backed plasterboard, again with the joints tightly sealed.
Whatever system is used the vapour membrane should be continuous, so there are no gaps for moisture to get through.
Damp Proof Membranes
If you are building your garden office off a traditional concrete slab foundation, it should feature a damp proof membrane (DPM), this is a high density plastic sheeting and is laid before the concrete slab is poured. The DPM stops moisture from traveling up from the ground, through the concrete slab into the framework of the garden office.
Damp Proof Course
If the structure of the garden office i.e. the floor joists or if the walls are sitting directly on the concrete slab, they should be laid on top of a damp proof course (DPC) to prevent moisture traveling up from the concrete into the timber framework.
A DPC is a reinforced, heavy duty plastic strip which sits under the timbers, it should have a continuous coverage with any joints lapped.
When reading the specification lists of the different garden offices, look out for the inclusion of building membranes, if they’re not listed ask your supplier about them.