Meeting Building Regulations: Key Construction Aspects

When your outbuilding project needs to follow Building Regulations, you'll need to make sure it meets specific standards. Let's explore the crucial details for your foundations, walls, and flooring.

Foundations for Your Outbuilding

Your outbuilding's foundations play a vital role in safely distributing its weight into the ground. Most often constructed from concrete, their exact design will be tailored to your specific project and the existing ground conditions.

Types and Purpose

When it comes to foundation types, you'll typically find two main approaches:

• Deep-fill foundations: These designs fill most of the excavated trench with concrete.

• Shallow-fill foundations: These provide just the minimum required thickness of concrete to effectively transfer the building's load.

If the ground conditions on your site aren't suitable for either of these "trench fill" methods, don't worry – other foundation solutions are available. For expert guidance, we strongly recommend reaching out to a structural engineer or your local building control office.

Factors Influencing Foundation Design

When planning your foundations, you'll need to think about several key aspects:

• Type of Soil: The type of soil on your site significantly impacts foundation design. Crucially, you need to understand how much weight the ground can support. Different soil types have varying load-bearing capacities. For instance, clay soils are particularly sensitive, expanding or shrinking noticeably with changes in moisture levels – consider periods of prolonged wet or dry weather. To prevent any movement or instability, foundations in clay-rich areas typically need to extend deeper, often exceeding 0.75m.

• Adjacent Structures: How close your outbuilding is to existing structures can also affect how you design the foundations.

• Trees: Trees pose a unique challenge. Their root systems actively absorb moisture from the ground, leading to soil shrinkage. This is especially problematic with clay soils, as the resulting ground movement can potentially damage your foundations. You'll need to consider the tree's species, its anticipated mature size, and its distance from your proposed building to assess the potential impact. It's also vital to remember that if you remove or significantly cut back existing trees, the soil can swell as moisture is no longer extracted, which might, in turn, harm nearby buildings.

• Drains and Sewers: When a foundation bears weight, that load spreads downwards and outwards at roughly a 45-degree angle. If any drains or sewers are located within this spread, they could be compromised. To prevent this, your foundation excavations should typically reach at least the same depth as the very bottom of the deepest part of any drain, sewer, or its trench.

• Size and Construction of New Building: The overall size and construction method of your new outbuilding directly influence the foundation design. A larger structure or one with multiple storeys will exert greater weight, so you'll need to design the foundation's depth and width to match the soil's load-bearing capacity and the thickness of your walls.

• Ground Condition: Always ensure your foundations are laid on undisturbed ground. This means the soil should not have been previously built upon or backfilled, for example, over old drain trenches or areas used to level the site.

• Landfill Sites: If your property is located on a former landfill site, you might need more extensive foundation solutions, such as piling, because the depth of undisturbed ground can be considerable. In such complex situations, a structural engineer can provide expert advice, possibly recommending options like 'raft' foundations.

A critical safety note: you must always exercise extreme caution when working in trenches. There's a significant risk of collapse, which could lead to serious injury. Your health and safety are paramount.

Walls Below Ground Level (Substructure)

Once your foundations are in place, you'll move on to the substructure – these are the walls built below ground level. The specific type will depend on whether you've opted for deep-fill or shallow-fill foundations. Its main job is to provide strong, reliable support for your superstructure (the walls above ground). The materials you use for your substructure, such as bricks, blocks, and mortar, must be exceptionally robust, resistant to frost, and able to withstand any sulphates found in the ground.

Flooring for Outbuildings

Your outbuilding's flooring needs to serve a dual purpose. Firstly, it must offer robust structural support for everything inside the room – that includes its contents, anyone using the space, and the weight of the floor itself. Secondly, if you're constructing a ground floor, it's essential that it effectively resists moisture rising from the ground and minimises heat loss through proper thermal insulation.

Types of Ground Floors

When considering ground floor construction, you generally have three primary options:

• A solid, ground-bearing concrete floor

• A suspended timber floor

• A suspended concrete floor

Flooring for Specific Uses

• Garages: For your garage floor, a common construction includes a layer of hardcore, followed by sand blinding, a damp-proof membrane (DPM – which prevents moisture from rising), and finally, a concrete slab. It's a sensible approach to embed reinforced mesh within the concrete; this helps to significantly reduce the risk of cracking under the weight of vehicles. Generally, you won't need to insulate a garage floor.

• Storage Buildings, Annexes, and Summer Houses: For these types of structures, you can use any of the three general ground floor types we've just discussed (solid concrete, suspended timber, or suspended concrete). The precise specifications for your floor will be determined by how you plan to use the building and whether you intend to heat it.