GPR is very effective in locating chimney flues

GPR provides a fast and efficient means of locating chimney flues within walls. The surveys are non-destructive and non-intrusive, hence can be undertaken in occupied buildings with minimum disruption to the occupants.

Why locate chimney flues?

It is often necessary to accurately locate the position of chimney flues prior to opening up walls, either for access, connecting adjoining properties, or reusing redundant flue voids as ventilation or service ducts. In building refurbishment works it is also frequently necessary to locate flues, or rather areas of solid masonry away from flues, to support structural steel beams. A GPR flue location survey can provide essential information during preliminary feasibility studies, or the planning stage, with no damage to the building fabric or decorative finishes.


Advantages of a GPR chimney flue survey

GPR detects changes in the sub-surface. In the case of flues, the flue void is detected due the drastic change in material properties of the masonry wall and the flue void. Typically the collected site data is analysed off-site and the detected flues marked onto a CAD elevation drawing.

Advantages of a GPR chimney flue survey include:

  • Non intrusive
  • No damage to the building structure
  • No noise or dangerous emissions
  • Can be undertaken in occupied buildings
  • Minimum disruption to the occupants
  • No need to remove decorative finishes
  • Quick and efficient
  • Flue paths can be plotted in CAD

Site survey

Chimney flue location surveys are carried out by our trained and experienced GPR surveyors. Nominated walls are scanned with horizontal scan lines at regular intervals;  the exact spacing is determined on site, but typically scans are collected every 300mm.

A GSSI SIR3000/4000 GPR control unit is generally used with a 1.5GHz antenna. Lower frequencies can be used to provide greater penetration depth, but the resolution and detail of GPR scan data decreases with lower antenna frequencies; it is therefore desirable to use the highest frequency possible, while still meeting the objectives of the survey.

GPR works on most materials; however, the GPR signal does not travel well across voids, therefore will not work on panelling, dry lining or stud wall construction. Irregular surfaces, such as ornate mouldings, may result in a poor surface coupling and antenna tracking problems. This can effect positional accuracy of detected flues.

Scanning a wall using GPR to locate chimney flues

Scanning a wall to locate chimney flues

Deliverables

Our reports include CAD elevation drawings with the location of all detected flues marked. Reports are issued in pdf format; the original CAD drawings are also issued in AutoCAD .dwg format.

Chimney flue location survey results plotted in CAD

Chimney flue location survey results plotted in CAD