Structural capacity appraisal
An appraisal of whether an existing building can take a change of use, new loads or extra storeys.
About this service
Before you commit to a change of use, a new storey or a heavy piece of plant, you need to know whether the building can take it. A structural capacity appraisal answers that question. We establish what the building is made of, how it carries load today and what it was originally designed for, then calculate how much spare capacity it has and where it would need strengthening.
Our clients include developers buying offices or shops to convert into homes, freeholders exploring roof extensions, landlords adding rooftop plant or solar arrays, and businesses planning heavy storage or equipment. Buyers also use it for confidence before purchase. It is a feasibility tool that comes before detailed design, often alongside a structural alteration feasibility study while layouts are still being explored.
Many London buildings have been altered several times, often without records. A Victorian warehouse may have cast iron columns, a 1960s office a lightly reinforced concrete frame, and a parade of shops walls removed decades ago. Knowing the true capacity stops you buying a building that cannot take your scheme. Our appraisal reports are signed off by a chartered engineer (MICE), and the calculations go through our three-step quality control process with final sign-off by our Head of Engineering.
When you need it
- You're converting offices to homes or changing a building's use
- You want to add one or more storeys
- New plant, equipment or storage will add load
What's included
- Review of existing drawings and records
- Inspection of the existing structure
- Capacity calculations
- Feasibility conclusions and strengthening options
How it works
- Gather the recordsWe collect existing drawings, original calculations, Building Control records and earlier surveys. Even partial records help establish the original design loads and how the building was put together.
- Inspect the structureWe inspect the building to confirm the construction, member sizes, spans and condition, noting defects such as corrosion, cracking or past alterations that could reduce capacity.
- Investigate the gapsWhere key elements are hidden, we recommend targeted opening-up, concrete cores, cover surveys or trial pits, carried out by a contractor, to replace assumptions with facts.
- Calculate capacityWe calculate the capacity of floors, beams, columns, walls and foundations to current Eurocodes and compare it with the loads from the proposed use, storeys or equipment.
- Report the conclusionsWe set out what the building can take, where it falls short and practical strengthening options, so you can decide whether to proceed, change the scheme or walk away.
What you receive
Changing use, adding load and the limits of an appraisal
A change of use does not always mean more load. Offices are normally designed for higher imposed floor loads than homes, so an office to residential conversion can leave floors with capacity to spare. The extra weight tends to come from elsewhere: new screeds, acoustic floor build-ups, partitions, bathrooms and roof plant. Going the other way, from homes or offices to storage, a gym or assembly use, usually needs a much closer check.
An appraisal is only as accurate as what can be seen. Where records are missing and the structure is hidden, assumptions have to be cautious, which can make a building look weaker than it really is. Targeted investigation is usually money well spent because it can unlock capacity that would otherwise be written off. For hidden elements, our structural investigation and opening-up service can be arranged.
An appraisal is not the design. If the conclusions are positive, the next step is detailed design of the strengthening and new structure, for example through our additional storeys and upward extensions service. If you only need to check one floor for a particular load, a smaller floor loading assessment may be all you need.
Projects that used this service
Frequently asked questions
How do I know if my building can take an extra storey?
A structural engineer needs to check the walls, columns and foundations against the added load. That means establishing how the building is constructed, often with trial pits to expose the foundations, then calculating existing and new loads. The answer depends heavily on the foundations and the soil. A capacity appraisal gives you a clear yes, no, or yes with strengthening before you commit to design.
Can an office building be converted into flats structurally?
Usually, yes. Offices are generally designed for higher floor loads than homes, so the floors themselves often have capacity to spare. The checks focus on new loads from partitions, bathrooms, screeds and acoustic upgrades, new openings for stairs and services, fire protection to the structure and any roof plant. Older offices with unusual frames need closer investigation.
What loads are floors designed to carry?
Floors are designed for permanent loads, such as their own weight, finishes and partitions, plus imposed loads from people, furniture and equipment. The Eurocodes give typical imposed loads for each type of use, and offices, shops and storage areas are normally higher than homes. Older buildings may have been designed to earlier standards, so we compare their original basis with current requirements.
Can my roof take solar panels or a heat pump?
Most roofs can take a solar array, but not all, particularly older timber roofs or flat roofs with shallow joists. Heat pumps and other plant are heavier and create concentrated loads. A full capacity appraisal suits larger buildings or several items of plant, while for a single installation our roof load assessment is usually enough.
How much does a structural capacity appraisal cost?
Our structural capacity appraisal starts from £900 + VAT. The fee depends on the size of the building, the records available and how much inspection and calculation is needed. Opening-up and testing by contractors are extra if required. We confirm a fixed fee in writing before any work starts.