Chimney flue location survey
A GPR survey traces chimney flues inside walls without removing bricks or plaster, so you can drill, fix or alter a wall without breaking into a flue.
What the survey finds
When you need a flue location survey
Flues in older buildings rarely run straight. They bend and merge as they rise through the building, and their routes are seldom on any drawing. A flue location survey is usually commissioned before:
- drilling into or through a wall for fixings, services or ventilation
- installing a new flue, stove or boiler
- removing or altering a chimney breast
- refurbishing listed or historic buildings where opening up is restricted
Breaking into a flue in use can let smoke or fumes into the building. In a disused flue it can create new defects on top of those already there.
What the survey finds
The survey shows where each flue runs inside the wall, where it changes direction and how many flues share a stack. It can also show changes along a flue that may indicate blockages or infill.
How it is done
We move a GPR antenna across the wall in lines. The radar sends a signal into the masonry and records reflections from the flue walls. Results can be read on site and marked straight onto the wall. Where you need a record, the data is processed in the office and the flue routes are drawn in CAD with a short report.
A small job usually takes a day or less on site. The equipment is quiet and safe, so surveys can take place in occupied homes and offices.
Limits you should know about
GPR works best on plain masonry and plaster. Metal lath, foil-backed boards, tiles with metal backing and very thick walls reduce the detail. Where a flue has been fully filled with material similar to the surrounding brickwork, it may show only faintly. We will discuss the wall construction with you before the survey.
Why use GPR
- No damage to walls, plaster or decoration.
- No drilling or removing bricks to insert a camera.
- Quicker and cheaper than opening up.
- Suitable for occupied and historic buildings.
Questions we're asked
How were flues traced before GPR?
By drilling holes or removing bricks, then feeding a borescope or CCTV camera into the flue. This was slow, costly and damaged the wall. GPR is now the usual first choice.
Is this the same as a chimney survey?
"Chimney survey" is used for two different jobs. A chimney specialist's survey, often with a CCTV camera, checks the condition of the flue and whether it is safe to use. A flue location survey, which is what we do, traces and maps where the flue runs inside the wall, before drilling, fixing or building work. If you need both, we can work alongside your chimney specialist.
How long does a flue survey take?
Most smaller projects take one day on site. Larger buildings with many walls and floors typically take two or three days.
Do I need to maintain an unused flue?
Yes. An unused flue should still be ventilated and inspected, because weather and moisture can damage the masonry over time. A chimney specialist can advise on the right maintenance.