Membranes used in a garden offices build-up
A quality garden office is made up of several layers of material. A significant layer in this makeup are the building membranes, which help control moisture within the building.
A breather membrane is a critical layer in the construction. It allows the building to breathe.
The garden office is wrapped in a breather membrane before the external cladding is added. This is one of the most important layers in the build-up.
Modern breather membranes are a high performance, fabric-like material which wraps around the exterior of the building. Some companies still use the older paper style, breather membrane 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 enveloped 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 from entering the main structure of the garden office. While allowing moisture generated within the office to escape from the building.
The breather membrane is an essential 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 weathertight once the breather membrane has been installed. It is common for garden office suppliers to get the breather membrane on, quickly after the main structure is installed. 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 an impermeable coating, which creates the vapour barrier. Or they use an 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 an aluminium foil facing, which if joints are sealed with aluminium 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 travelling 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 travelling 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.