Garden office construction takes its lead from house construction and the walls of a garden office are just scaled down version of those found in a house. There are several types of wall construction used in garden offices but by far the most common are traditional studwork timber frames and structural insulated panels (SIP’s), let’s take a closer look at the options:
With this type of construction the walls are made up of a skeleton of timber studs fixed to horizontal plates at the top and bottom, to strengthen the framework horizontal braces known as noggins can be fitted between the studs. The space between the studwork holds the insulation. On the outer side of the studwork timber sheathing is fixed, this is normally exterior grade plywood and sometimes OSB – some garden office suppliers omit this layer but it does strengthen the frame considerably and stops the frame twisting. The next layer is a breathable membrane, this works like a one way valve letting moisture escape from the building but not letting moisture into the building, it is important that this layer is present in the wall makeup. Next up is the cladding, some suppliers fix this directly over the breather membrane but it is good practice to fix it on counter battens, this creates an air space behind the cladding and any moisture that passes through the cladding runs down this channel and not into the wall structure. On the inside of the studwork is a vapour membrane, the joints of which need to be firmly taped to prevent condensation occurring, over this the internal lining is fixed.
Structural insulated panels (SIP’s) have become very popular in garden office construction as they have excellent thermal properties and are quick to install. SIP’s remove the need for any structural framework as the SIP’s panels are load bearing. SIP’s are engineered products made up of two layers of OSB (Orientated Strand Board) with a rigid insulation laminated (glued) in between. Garden offices built with SIP’s are thermally efficient because the insulation wraps around the whole building with no timbers creating ‘cold spots’, which are areas with no insulation which can occur in traditional timber frame systems. The exterior of the SIP’s is sheathed in a breather membrane which prevents moisture entering the building but lets it escape from within, over this the cladding is fixed, usually on counter battens to create an airspace between the cladding and the breather membrane. Internally many garden office suppliers use battens to create a service void for electrics and plumbing between the inside of the SIP and the internal wall finish.
Some suppliers have designed modular garden offices which have a timber framework that can be in filled with different panels – solid and glazed. The solid panels are made up of a sandwich of colour coated steel and rigid insulation. This type of construction creates a relatively narrow wall thickness.
Post & Beam
One of the oldest forms of timber construction is the post and beam method and a few garden office suppliers have adopted this system as it lends itself to modular garden office construction. The post and beam consists of two upright posts joined by a horizontal beam, for optimum strength this should have a traditional joint such as a mortise and tenon. Post and beam frames create bays which can be filled in with insulated panels, windows and doors. The insulated panels will have a similar makeup of insulation, membranes and cladding as described above.
Although not common there are a few garden office suppliers who build in block. Built like a house walls consist of two layers of block with insulation in between. The exterior can be rendered or battens can be fixed into the block and timber cladding added. Internally the walls are lined with plasterboard and skimmed with plaster.
Oak garden offices are very popular and they have a unique character. Substantial oak timbers often 150mm x 150mm are jointed using traditional methods to create the main frame of the garden office, the wall is then filled in with panels made up like the traditional timber frame described above.
Some garden offices on the market are made from interlocking timbers which form both the wall framework and the exterior cladding. At around 50mm thick a thin wall structure is created but although timber itself has good thermal properties this type of construction does not have the thermal performance of the other wall construction methods described here.
Although many people like to call garden offices posh sheds you can be assured that whichever construction method you choose your garden offices construction takes its lead from the house building rather than shed construction.
In the next part of this guide we look at the different cladding options for garden offices.