How To Build a Garden Building Base

Firstly, to ensure both ease of assembly and the longevity of your garden building, it is essential that it has a firm and level base constructed from a durable material. Construction without such a base may not only invalidate any product guarantee that comes with your garden building but also lead to problems such as doors dropping out of square and water leakage. 

When choosing the location for a garden building base, make sure not to place it too close to walls or fences as your garden building may have an overhanging roof. Similarly, be careful when placing the base near overhanging branches or large bushes especially if they are likely to grow and come into contact with the building in the future. If this is the case, cut these branches in advance and, once your building is assembled, make sure to check nearby foliage regularly as any damage to the roofing felt may make your garden building vulnerable to bad weather conditions. Finally, don't forget to allow sufficient access to the outside walls so that you can apply regular wood treatments. 

We recommend using a reputable local builder to construct a base for your garden building where possible but if you feel comfortable with the task yourself, it is relatively straightforward to do. 

It is strongly advised that you build your base slightly larger than the dimensions of your garden building by approximately 30-40 mm (1.2-1.6 inches) on each side. 

There are three main methods described below: 

1. Concrete Base Method 
2. Paving Slab Method 
3. Timber Bearers Method 

The first step is common to all methods: 

Mark out the area where you plan to build your base with pegs and string and clear any vegetation within. You can ensure that your marked area is square by measuring diagonally between the top-left and bottom-right pegs and making sure that distance is equal to the distance between the top-right and bottom-left pegs. Alternatively, you can make use of a try square to ensure that all angles are at 90 degrees. 


Concrete Base Method 

(This method is strongly recommended for larger garden buildings or log cabins.) 

Excavate the ground in the marked area to an approximate depth of 150 mm (6 inches). Lay approximately 75 mm (3 inches) of firmly compacted hardcore, scalping or brick rubble to act as a sound foundation and level with compacted sand if appropriate with the aid of a rake. You can now remove the pegs and string. 

The next step is to cut and fit four timber rails or steel shutters to create a frame for the concrete that will rest atop the foundation you just laid. Ensure that the base with its new shuttering is completely level and square with the aid of a tape measure, spirit level and try square. 

Now lay approximately 75 mm (3 inches) of concrete. Concrete can be produced with bags of dry mixed concrete with small amounts of water added gradually or by making a mixture of "all-in" ballast, cement and water. If going for the latter option, mix five parts "all-in" ballast to one part cement. "All-in" ballast is usually sold in 40 kg bags at most building merchants and DIY stores and you will need approximately 
1.25 kg per cubic foot of concrete. Take care not to let the mix become too wet however as this will weaken the resulting concrete. 

Spread the concrete evenly in the shuttering, making sure to push it into corners and edges. A good technique is to lay the concrete a layer at a time, compacting each as you go until the shuttering frame is full. Use a wooden or plastic float to make the concrete flush with the top of the framework. 

Cover the concrete with sheets and allow it to dry naturally. Concrete must not dry too quickly so it may be necessary to spray it with water in warm and dry weather conditions to prolong the drying process. 

Once dry, your base is complete and ready for you to begin assembly of your garden shed. 


Paving Slab Method 

Excavate the ground in the marked area to an approximate depth of 64 mm (2.5 inches) and remove the pegs and string. Lay approximately 40 mm (1.5 inches) of a mix of one part cement to eight parts building sand. Level this dry sand and cement mix with a rake and use a spirit level to check it. 

Starting from a corner, lay paving slabs tapped down with a rubber mallet ensuring that the top of the slabs is slightly higher than the surrounding ground for rain water drainage. Again, use a spirit level when checking that the slabs are square, level and firmly butted together. 

After brushing off any excess sand and cement mix, your base is now ready for your garden shed. 


Timber Bearers Method 

Excavate the ground in the marked area to an approximate depth of 50 mm (2 inches) and remove the pegs and string. Lay approximately 40 mm 
(1.5 inches) of gravel or soil, levelling it with a rake and checking with a spirit level. 

Equally space concrete or pressure-treated (sometimes referred to as 
"tanalised") timber bearers at intervals of approximately 400-600 mm 
(15.7-23.6 inches) across the gravel or soil. Ensure that the bearers are perpendicular to any floor joists that come with your garden shed. 
Use a spirit level to ensure that the bearers are level and use a rubber mallet to tap them down if necessary. 

The number of floor bearers you need depends entirely on the size of your shed but here are some examples to give you a rough idea: 

* 6x4 shed = 4 x 1150 mm (4 feet) long bearers 
* 7x5 shed = 4 x 1450 mm (5 feet) long bearers 
* 8x6 shed = 5 x 1750 mm (6 feet) long bearers 
* 10x8 shed = 6 x 2350 mm (8 feet) long bearers 

Your base is now ready for your garden building. 


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