- Measured Survey: Unlike estate agentsʼ floor plans, which can be imprecise with an accuracy of around ±5–10%, a professional measured survey provides reliable data suitable for construction and project planning. Undertaken by surveyors using precise 3D laser equipment, these surveys give the project team accurate measurements to work from. Costs typically start from £1,200 +VAT for a standard three-bedroom house.
- CCTV Drainage Survey: A CCTV drainage survey is often necessary when manholes are located within or near proposed extensions. It provides a detailed and accurate assessment of the propertyʼs underground drainage system, allowing the project team to plan rerouting or new connections with confidence. Prices typically start from £250–£400 +VAT for a standard residential property, depending on size and complexity.
- Thames Water Build-Over Agreement: If your proposed extension or building work is near or over existing public sewers, a Build-Over Agreement with Thames Water may be required. This agreement ensures that any construction does not damage or restrict access to the sewer, and it sets out responsibilities for maintenance and liability. Obtaining this agreement early in the design process helps prevent delays and unexpected costs. Application fees for typical domestic agreement start from £400.
- Planning Application Fees: When submitting a planning application for extensions, alterations, or new builds, local authorities charge a fee to cover the cost of reviewing and processing your application. Fees vary depending on the type and scale of the project. For example, a single-house extension typically costs around £206–£462, while applications for multiple dwellings or larger developments incur higher fees.
- Building Control Plans Check and Inspection Fees: When carrying out extensions, renovations, or new builds, your local authority or private approved inspector will charge fees for checking plans and carrying out inspections to ensure compliance with Building Regulations. These fees cover the review of detailed technical drawings and regular site inspections during construction. For a typical single-house extension, fees usually start from around £600–£3,000 +VAT, depending on the size and complexity of the project.
- Structural Engineering Fees: Structural engineers are engaged to assess, design, and certify the structural elements of a building, such as foundations, beams, and load-bearing walls. Their input is essential for extensions, loft conversions, or any alterations affecting the buildingʼs stability. Fees vary depending on the complexity of the project. For a typical residential extension, costs generally start from around £600–£1,500 +VAT, covering calculations, drawings, and certification required for Building Control.
- MEP (Mechanical, Electrical, and Plumbing) Engineer Fees: An MEP engineer designs and oversees the mechanical, electrical, and plumbing systems within a building, ensuring they are efficient, safe, and compliant with building regulations. Their input is especially important for projects involving significant alterations, extensions, or high-spec installations. Fees vary depending on the size and complexity of the project, but for a typical domestic extension, costs usually start from around £1,000–£3,000 +VAT.
- Party Wall Surveyor Fees: If your project involves building near or on a shared boundary, a Party Wall Surveyor may be required to prepare notices and manage agreements under the Party Wall etc. Act 1996. This helps prevent disputes with adjoining owners and ensures legal compliance before work begins. Fees vary depending on the complexity of the project and whether one or more surveyors are appointed. For a typical domestic extension, costs usually start from around £900–£2,000 +VAT per award.
- SAP Calculations: For extensions with large amounts of glazing, a SAP (Standard Assessment Procedure) calculation will be required to demonstrate compliance with Part L of the Building Regulations, which covers energy efficiency. These calculations assess the buildingʼs thermal performance, heating demand, and energy use. Fees vary depending on the size and complexity of the extension, but for a typical domestic project, costs usually start from around £250–£450 +VAT.
- Contingency: This is an amount set aside to cover unexpected costs that may arise during a construction project. Even with careful planning, projects often encounter unforeseen issues such as ground conditions, structural surprises, design changes, material price fluctuations, or delays. Including a contingency helps ensure that these surprises do not derail your project financially. For domestic extensions or renovations, a contingency of around 5–10% of the total construction budget is commonly recommended, though more complex projects may warrant a higher percentage.
