A Guide To Underpinning Building Regulations

Underpinning is structural work done by the engineers to improve the foundation of the building. It is one of the most crucial projects for the construction and renovation of buildings. This helps stabilise the house structure, which has suffered foundation deterioration. It is important to understand the depth of the existing foundations. You can plan to build a building above or below ground level. You can read this guide for details about underpinning building regulations.

Do I Need Building Consent?

You will need to obtain consent under building regulations to underpin the foundations of your house. This usually requires structural design submission prepared by an underpinning engineer following some on-site investigations conducted by either a structural engineer or a survey. The structural plan must also include the process to be carried out during construction. Compliance with these regulations is essential to securing the structural stability and safety of the building.

How To Acquire Approval For Underpinning Building Regulations?

Before starting any underpinning work, you must check with a building control body to check the regulations, submit a plan, and apply for approval. The control body may need to assess the foundation or execute site inspections. Once the work is accomplished, the Building Codes Board(BCB) will also provide you with a completion certificate confirming that the underpinning has been carried out in alignment with building regulations.

Building control bodies can be of two types: the building control department of the local authority or a private, approved inspector who will notify the local authority.

You can also hire stumping contractors or underpinning engineers to help you with the approval process.

Types Of Building Regulation Applications For Underpinning

There are three types of building regulation applications related to underpinning:

• Full Plans Application: This is the most extensive option for underpinning projects and is required if you are having underpinning work carried out. You can submit a detailed work plan to allow inspectors to check if they meet building regulations.


• Building Notice Application: This is suitable for smaller projects. It is normally used for domestic properties. This application is submitted without plans, allowing you to begin work shortly compared to the full plans application.


• Regularization: This is a backdated application used to get approval for underpinning work that has already been started or completed without consent. It can only be applied for by a local authority, the BCB.

Types Of Underpinning Methods

Underpinning is essential for your building in various ways. The following are the different underpinning methods:

• Mass concrete underpinning method: As it has been followed for centuries, the mass concrete underpinning method is the traditional one. This method includes extending the old foundation until it reaches a stable layer. Due to its low cost for shallow depth underpinning, and heavy foundation loads, this is the most common method. It involves excavating sections below the foundations, one at a time, and backfilling each with concrete before passing on to the next.


• Beam and pier underpinning method: This method is more technically advanced. It is found feasible for most of the ground conditions. A reinforced concrete beam transfers the load to mass concrete bases or piers. The size and depth of the beam are based on the ground conditions and applied loads.


• Mini-piled underpinning: This is the most suitable method for sites with variable ground conditions, restrictive access, or environmental pollution. This method is used where the loads from the foundation need to be transferred to a layer located at a distance greater than 5m.


• Pile method of underpinning: Piles are driven on adjacent sides of the wall that support the weak foundation. A needle penetrates through the wall which is in turn connected to piles. These needles behave like pile caps. By using this method, the problem of soil settlement due to water clogging can be solved.


• Piled Raft Underpinning: When the entire building needs complete underpinning, piled raft underpinning is used. In this method, the internal floors are removed, and piles are driven in a normal way, forming a grid. Then a concrete raft is laid over the piles, and the floors are replaced. This is a complex and distributive method, and despite that, it also has the advantage of combining a complete raft of concrete, as with the mass concrete method, with the extra support of mini-piling.

Navigating The Underpinning Process: A Step By Step Guide

Hire underpinning contractors and plan a foundation that can last for years. Remember to ask your underpinning contractor when to temporarily move out before the underpinning process is started and when you can move back in. That way, you’ll easily plan on where to stay before your home is stabilised and safe. You can check the common steps of the plan below.

Step 1: Excavation

The process of underpinning starts with excavation. In this process, the soil around the foundation is excavated to create space to pour concrete below the foundation. In this step, formwork is introduced, and steel wires are set up for reinforcement. The formwork works like a frame to ensure the poured concrete matches the required shape and size and fits in the exact location.

Step 2: Preparation

If the mass pour method is to be applied, concrete will be poured through a hole around and/or under the foundation.

Formwork is then put in, and steel wires are set up for reinforcement. The formwork ensures the poured concrete matches the required shape and size and fits in the exact location.

Step 3: Reinforcement

When doing mass pouring of underpins, adequately mixed concrete is poured and given enough time to set in the formwork.

In case piles are to be introduced, they’re fitted into drilled holes or driven deep into the soil until they’re tied up on stable soil.

The process of underpinning starts from one corner and goes inwards underneath the wall being reinforced.

Step 4: Infilling

In this method, the soil excavated in the first step is backfilled as needed and compressed.

Step 5: Repair the building

Once your foundations have been stabilised to prevent any further structural movement, repair work can be done in the exterior and interior of the house.

Common repairs include fixing cracks, house restumping, and redecorating. This includes fixing damaged paths, garden walls, driveway, patio, and fences. Some home insurances cover the costs of such repairs. Thus, check with your insurer for possible coverage.

To plan your underpinning work, consider a suitable method and the cost of underpinning.