Constructing a Timber Base
Not everyone wants the permanency of a concrete slab to use as a base for a garden building.
A timber platform, properly constructed, will provide a suitable environment your garden building to sit on !
This style of platform is also useful when the underlying ground is sloping - it is far easier to provision "stilts" rather than levelling the ground by digging out soil, constructing a retaining wall and then dealing with the drainage issue.
Issues to consider :
- Will the elevation of a timber platform compromise any planning issues regarding height restrictions ?
- Size of joists - Stating the obvious, but the thicker the joist, the less supports are required. For the most part, we would use either a 100x47mm (4x2) or 150x47mm (6x2) As a rule of thumb, a 100x47 joist needs supporting every 1.5m where as a 150x47 can be extended to 2.0m
- Are you planning to add underfloor insulation ?
- No - OK, replicate the base bearer layout provided in the installation guide.
- Yes - Good plan ! In that case the easiest method is to construct your timber base with the joists perpendicular to the base bearer layout. This will allow you to cust the insulation to sit between the bearer joists and on top of the base joists.
Components Required
Support Posts
We like to use these concrete decking support posts. Available in various lengths to accommodate a sloping site, once concreted into the ground, they can be left safe in the knowledge thery won't rot or disintegrate over time.
Post Mix
Although more expensive than buying raw ingredients, PostMix is so convenient and quick to use. We would recommend using this product to secure the concrete support posts. We are showing a Blue Circle product, but there other brands available !
Treated Timber
Most timber merchants will be able to supply either the 100x47 or 150x47 joists in various lengths to suit. Good practice is to treat the ends of the joists that have been cut so that the treatment is not compromised.
Quality Screws
To hold the joists together a good quality wood screw is required. Timberlok produce an excellent fixing for this purpose and there are plenty of other similar products. It isworth spending a few pounds on these to ensure longevity.
Construction
From within your installation guide, you will find a diagram of the base bearer layout. This will show the minimum base size required for your cabin.
Use this as a template for your timber base OR, if planning to insulate under floor, design your base perpendicular to these, using this plan as an example, here is how your timber base joists would work.
Use this as a template for your timber base OR, if planning to insulate under floor, design your base perpendicular to these, using this plan as an example, here is how your timber base joists would work.
Construct the base using a minimum of 2 screws per join. Suggest three if using 150 joists.
Now work out where you need to support the frame.
Let's assume the frame in our example is made using 150x47 joists, in which case, the concrete supports would need to be positioned as follows, indicated by the yellow discs :
Here are a couple of pics of a completed base, all ready for the cabin construction.
Author - Martin Corby
Posted - 12 May 2023