As Built Drawings: What They Are and Why They Matter
As built drawings are the set of plans that show a building as it was actually constructed, including every change made on site after the original design was drawn. If you are having a loft conversion, extension or garage conversion done in the UK, they are the document that tells you where the steel, pipes and cables really ended up. Ask for them before you make the final payment.
TL;DR
As built drawings record what was built, not what was planned. Design drawings show intent, as built drawings show fact.
For most UK home projects no law uses the phrase “as built” by name, but accurate records still feed your completion certificate, your sale and any future work.
“As built”, “record” and “measured” drawings are three different documents. Know which one you are asking for.
Ask your builder at the quote stage to hand over a clean, marked-up set at completion, and tie final payment to it.
No drawing is perfect. Concealed pipework in particular is often shown diagrammatically.
Table of Contents
What as built drawings actually show
Design drawings are made before work starts. Things then change: a joist turns out to be in a different place, a pipe has to be rerouted around a beam, a window moves 100 mm to suit the brickwork. As built drawings capture the result.
According to Procore’s guide to as-built drawings, they are a factual record of the completed state, including deviations and field changes, and they cover structural layout, concealed services and final dimensions. They are also used to show that a contractor delivered what the contract required.
For a homeowner, that translates into practical questions the drawings answer:
Where does the new steel beam sit, and what does it carry?
Where do the drainage runs, water pipes and electrical conduits go behind the plaster?
What are the final room dimensions and window openings?
Where was the structure altered compared with the planning drawings?
As built, record and measured drawings: three different things
These terms get mixed up, and the confusion causes real disputes about who is responsible for what. A guide from the Ontario Association of Architects and the Ontario General Contractors Association sets out the distinction. It is written for Canada, but the logic holds for UK projects too.
Document | Who usually prepares it | What it is | When you use it |
As built drawings | The contractor | Site mark-ups (often in red) showing changes from the design | At handover, to record what was built |
Record drawings | The designer or architect | A formalised, tidied set compiled from the mark-ups and site information | Long-term reference and the project file |
Measured drawings or survey | A surveyor | A baseline survey of the existing building, made before design starts | The start of a project, to produce the “existing” plans |
The See3D explainer on as-built surveys and measured surveys makes a related point: the survey is the measuring process, while the drawings are the product that comes out of it. When someone says “as built drawings” they may mean either, so say clearly which you want.
In practice, a London homeowner will meet all three. A measured survey at the start, a contractor’s marked-up set during the work, and, if you pay for it, a formal record set at the end.
Are as built drawings a legal requirement in the UK?
For a typical house project, the phrase “as built drawings” does not appear as a stand-alone legal duty. But the paperwork around your job still depends on accurate information about what was built.
Higher-risk buildings. Under the Building Safety Act regime, the Building Safety Regulator’s Gateway Three guidance lists as-built drawings among the evidence required for a completion certificate application. This applies to higher-risk buildings, not to a semi-detached house with a loft conversion. The related golden thread guidance on GOV.UK explains the duty to keep a digital record of building information.
The health and safety file. Where CDM 2015 applies, the principal designer prepares a health and safety file for whoever will maintain or alter the building later. Its contents include as-built drawings of the building, plant and equipment, and the location of significant services. That page also notes that the commonest failure is a gap between the drawings and the building handed over. Whether a full file is needed on a small domestic job depends on how the project is set up, so ask your designer or contractor who holds that responsibility.
Building control. Where designs change on site, especially for structure, drainage or ventilation, your building control body will want to see that the final work matches what it approved. Our guide to loft conversion regulations and the completion certificate explains how that sign-off works and why a missing certificate causes trouble when you sell.
The honest summary: for most homeowners it is a contractual and practical matter rather than a statutory one. That makes it something you have to ask for, in writing.
Why homeowners should care
Future building work
The next person to open up your wall, whether an electrician, a plumber or the builder doing your next project, needs to know what is behind it. A set of drawings showing the real pipe and conduit routes saves exploratory work and avoids drilling through a live cable or a heating pipe.
Selling or remortgaging
Buyers’ solicitors ask for planning and building regulation paperwork. Drawings that match the finished building make that conversation simple. Drawings that show a different layout from the one in the house raise questions.
Planning and the next project
The Planning Portal explains that planning applications need drawings showing both the existing property and the proposed development. If you extend again in five years, your starting “existing” plans should reflect what is really there, not the original design from the last job. Mismatched existing and proposed sets are a common reason for an application to be returned or delayed, as a London measured-survey firm notes.
Keeping the building maintained
Records of what is installed and where make it far easier to service a building properly. Even outside construction, the principle is the same one that makes a service asset register useful for a business: knowing exactly what you own and where it sits is the basis for maintenance, repairs and later upgrades.
How accurate does an as built drawing need to be?
Many homeowners assume “as built” means millimetre perfect. It does not. Accuracy is a specification for the particular job.
RoomPlot’s guide to as-built floor plans says that modern mobile LiDAR can capture dimensions within roughly 1 to 2 cm, which is enough for space planning and early quotes, whereas party wall disputes or complex structural steel packages justify a chartered measured survey with much tighter tolerances. Match the method to the use:
Space planning and an early budget: a quick digital scan or careful tape measurements may do.
Structural design, steel, party wall matters: commission a professional measured survey.
Handover records: the contractor’s mark-ups, cleaned up, with photographs of services before they are covered.
Two cautions. First, hidden services are often drawn diagrammatically, so a pipe shown on the plan may sit a little to one side in reality. The AIA and ABA joint committee guidance on drawings and specifications recommends a note stating that drawings are a convenient reference rather than a guaranteed map. Second, treat the drawings as a guide, and still use a cable and pipe detector before you drill.
How to get a useful set at the end of your project
Start with a good baseline. For an extension or loft conversion, a measured survey at the start gives the architect and the builder the true dimensions. That is what makes a fixed-price quote reliable.
Put it in the contract. Write into the agreement that you will receive as built drawings at completion, in PDF and, if you want, editable format, and say who prepares them.
Ask for photographs before covering. Dated photos of pipes, cables, steel and insulation before plasterboard goes up are the cheapest as built record there is.
Agree a mark-up routine. Contractors usually keep a red-line set during the work. Ask to see it at key stages, such as after first fix.
Request the formal set before final payment. Contractors keep red-line mark-ups during construction. Ask for them to be turned into a clean set before you release the last stage payment, because that is when you have the most leverage.
Store everything together. Keep the drawings with your building control certificate, structural calculations, electrical and gas certificates, warranties and party wall award.
Our perspective on as built records
We build loft conversions, extensions, garden rooms and garage conversions across Greater London and Essex, and we see the same pattern. Problems rarely come from the building itself. They come from information that was not written down when the work was hidden.
That is why we think of transparency as more than a sales line. Our clients can follow live projects through virtual tours before they hire us, so they see how work is set out, how it is managed and how it is finished. The same attitude should apply to records. If you are choosing a builder, ask how they document structural changes and hidden services, and ask to see what a typical handover pack contains. Raise it when you request your quote, not at the end.
We also handle party wall agreements and manage projects from planning through to completion, which is where accurate drawings earn their keep. A party wall surveyor, your neighbour and your structural engineer all work from the same set of dimensions, and an error at that stage costs time on site.
Our view is simple: a good project leaves you with a building and with a clear account of what is inside it.
— Florin
Planning a project? Start with accurate numbers
If you are considering a loft conversion, extension or garage conversion, we give detailed quotes within 24 hours, so you can compare options without waiting weeks. Loft conversions start from £35,000, and our residential building services page sets out the full range of what we build. If you already have drawings, send them with your enquiry. If you do not, we can talk you through what to commission first. You can request an instant quote here, or look at our home extension specialist page for rear, side return, double-storey and wrap-around options.
Common mistakes to avoid
Assuming the planning drawings are the as built drawings. Planning drawings show the proposal. Site changes are rarely reflected unless someone updates them.
Skipping the survey to save money. A small survey fee is cheap compared with a redesigned steel package or a rejected application.
Accepting a handover with no paperwork. Verbal assurances do not help the next owner.
Treating the drawing as a guarantee. Use it as a guide, and verify before cutting or drilling.
Confusing the roles. Decide in advance whether the contractor, the architect or a surveyor produces the final set, and who is paid to do it.
FAQ
What is the difference between as built and record drawings?
As built drawings are usually the contractor’s marked-up set showing changes made during construction. Record drawings are a formalised version compiled by the designer or architect. The OAA and OGCA guidance treats them as distinct, so state in your contract which one you expect.
Do I need as built drawings after a loft conversion or extension?
They are not usually a named legal requirement for a standard house project, but they are strongly advisable. They help with your completion certificate paperwork, with a future sale and with any later building work. Higher-risk buildings are different, and the Building Safety Regulator requires as-built drawings for completion certificate applications.
How do I create an as built drawing?
Record the real dimensions and positions of what was built, then mark them over the original design drawings or redraw them. Photographs of services before they are covered help a great deal. For anything structural or contentious, have a surveyor measure the building rather than relying on tape and memory.
Who pays for as built drawings?
It depends on your contract. Some builders include a mark-up set in the price, while a formal record set drawn by a designer is usually an extra. Settle this before signing, not at completion.
Sources
Recommended
Comments