Foundations for a Garden Studio
Foundations are required to transmit the load of the building safely to the ground. Therefore, all buildings should have adequate foundations, which will vary from one project to another depending on the circumstances of each case. For most Studios that dont need to comply with Building Regulations, we use a small pile system and we can use the same system or a raft system for Studios that need to comply with Bulding Regs, but this will require a visit and report from our Structural Engineer and we can arrange this for you.
Factors to be taken into account of when designing a foundation:
Type of soil
The type of soil that the foundation will sit on is important for two reasons:
- it should be able to bear the weight (load) of the foundation and the extension – different soils have different load bearing capabilities
- the way it reacts to variations in moisture content (such as in prolonged rainy or dry seasons) can lead to the soil expanding or contracting. This is a particular issue with some clay soils. These changes mainly occur up to a certain depth (typically about 0.75m) therefore foundations should be made deeper so they are not affected by ground movement (although see “Trees” below).
It is important to ensure that the excavation for the new foundation does not undermine adjacent structures. In general it is good practice to excavate at least to the same depth as the bottom of the foundation to the adjacent building. If the excavation runs alongside an existing footing then care will be needed.
Trees will draw moisture from the ground around them and beyond through their root system. As moisture is drawn from the ground it will have a tendency to shrink. How much the ground will shrink will depend on the following factors:
- Type of soil – Clay soils shrink more than other types of soil. Therefore excessive movement of the ground could cause damage to the foundation and the structure it supports.
- Size and type of tree – How large a tree or shrub will grow (its mature height), and the tree type will determine how much moisture it generally draws from the ground.
The presence of trees in clay soil areas can mean foundations need to be significantly deeper than might be first expected, although if the trees are far enough away, there may be no impact. Note: If existing trees are removed or significantly reduced in size, all or some of the moisture in the root system will be released over time into the soil and, if the soil is clay for example, could cause swelling of the soil and damage to nearby foundations and structure(s) supported.
Drains and sewers
As the weight (load) from the foundation of a building is transferred to the soil it spreads downwards outside the footprint of the foundation at a typical angle of 45 degrees. If a drain or sewer is within the area coveredby that 45 degrees area there is a risk that it could be affected by the load from the foundation and possibly crack. Therefore,the foundation excavation should normally be at least to the same depth as the bottom (invert) of the deepest part of the drain, sewer or its trench.
Speak to us today to areange a site visit appointment on 01954 488306