When most people search for as-built drawing services
When most people search for as-built drawing services in the UK, they assume they need to commission a measured survey first. A surveyor comes to site, takes measurements, and the drawings are produced from the survey data. For many projects that is exactly the right approach.
But for the majority of construction and engineering projects, there is already enough information on site to produce accurate as-built drawings without a survey at all. Redline markups, site photographs, and annotated PDFs capture the changes made during construction — and that is all a specialist CAD outsourcing team needs to produce a complete, permit-ready as-built drawing set.
This is the service Outsource CAD provides. And it is faster, cheaper, and simpler than commissioning a measured survey.
What are redline markups and why are they enough?
A redline markup is a set of handwritten or annotated changes made to the original design drawings during construction. Site engineers, subcontractors, and project managers mark up printed drawings or annotate PDFs throughout the build — noting where pipework was re-routed, where dimensions changed, where equipment was relocated, where cable runs deviated from the design.
By the end of a project, a well-maintained set of redlines captures the complete difference between what was designed and what was actually built. That information is everything needed to produce an accurate as-built drawing set.
Outsource CAD takes those redlines — whether they are scanned paper drawings, PDF annotations, or photographs — and incorporates every change into the original CAD files, producing an accurate, complete as-built record without anyone needing to visit site.
When does a survey become necessary?
A survey is needed when there are no original design drawings to work from, when the redline record is incomplete or missing, when a high level of dimensional accuracy is required beyond what redlines can provide, or when a BIM model rather than 2D drawings is the required deliverable.
For existing buildings where no drawings exist at all — a heritage building, an older industrial facility, a property that pre-dates CAD — a measured survey or laser scan is the correct starting point. Outsource CAD provides point cloud to CAD conversion services for projects in this category.
But for the vast majority of construction projects — where original CAD drawings exist and redlines have been maintained throughout the build — a survey is not needed. The redlines are the record and Outsource CAD turns them into the drawings.
What types of projects does this apply to?
Redline-based as-built drawing production works across a wide range of project types and sectors.
Construction and M&E — floor plans, electrical layouts, ductwork and pipework routes, plant room drawings, and general arrangement drawings updated from site markups at practical completion.
Oil and gas — P&ID drawings, piping layout drawings, and equipment arrangement drawings updated from operational markups throughout the life of the plant.
Telecoms — site layout plans, antenna mount drawings, and construction drawings updated from as-built site records after installation.
Facilities management — as-built drawing sets for building handover, CDM health and safety files, and planned maintenance documentation.
CDM compliance — as-built drawings are a legal requirement under CDM Regulations 2015 for the health and safety file. Outsource CAD produces CDM-compliant as-built drawing sets from contractor redlines as a standard service.
How the process works
The process is simple. You send us your original design drawings in CAD format and your redline markups — in whatever format you have them. Scanned paper drawings, PDF annotations, photographs, or digital markups all work. We review the markups, confirm the scope, agree a turnaround time, and incorporate all changes into the CAD files.
The completed as-built drawing set is returned with a revision record, updated title block notation, and PDF copies for distribution and filing. Standard turnaround is 24 to 48 hours for straightforward packages. Larger programmes are tracked through a shared online register that gives you real-time visibility of every drawing in the set.
What if the redlines are incomplete?
Incomplete redlines are common on large construction projects where the markup discipline was not maintained consistently throughout the build. Outsource CAD flags any ambiguous or missing markup information before incorporating it — we never make assumptions on unclear changes without confirming with your team first.
For projects where significant information is missing from the redlines and the accuracy of the as-built record is critical, we can advise on whether a targeted survey of specific areas would close the gaps. But in most cases, the combination of redlines and site photographs is sufficient to produce a complete and accurate record.
Cost and turnaround
As-built drawing production from redlines is priced per drawing based on complexity and the volume of changes to be incorporated. Simple drawing updates cost significantly less than a full re-draw. Outsource CAD provides a clear, itemised quote before any work commences.
For ongoing programmes — oil and gas modifications, telecoms rollouts, M&E maintenance works — we offer dedicated team arrangements with agreed daily or weekly throughput targets and shared tracking.
Getting started
Contact Outsource CAD at info@outsourcecad.com or call +44 28 9009 8876. Share your original CAD drawings and redline markups and we will review them and provide a quote within one business day.
If your project involves redlines you have been meaning to incorporate for months — or a project that completed without a full as-built record — get in touch. We have turned around complex as-built drawing sets for major construction and engineering projects within 48 hours of receiving the markups.
