Chimney flue location

Do you need to find the position of chimney flues? Our GPR surveys provide a fast and efficient means of locating chimney flues within walls. The surveys are non-destructive and non-intrusive, therefore, we can undertake them in occupied buildings with minimum disruption to the occupants.

The purpose of chimney flues

A chimney flue is a near-vertical structure made of masonry, clay or metal. Its purpose is to contain and transfer smoke and gasses from a fire or boiler to the outside. Find out more about chimney flues on Wikipedia.

Why locate chimney flues?

It is often necessary to accurately locate the position of chimney flues before opening up walls. This can be 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 more specifically, 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. GPR makes this possible 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 to the drastic change in material properties of the masonry wall and the flue void.

We can interpret the GPR data on-site in real-time to provide instant results with an on-site mark-up. However, we recommend off-site data processing and analysis. This produces better and more accurate results. Typically we save the GPR data electronically for off-site analysis. The position of detected flues is plotted on CAD elevation drawings.

Advantages of our GPR chimney flue surveys:

• Non-intrusive
• No damage to the building structure
• No noise or dangerous emissions
• Suitable for occupied buildings
• Minimum disruption to the occupants
• No need to remove decorative finishes
• Quick and efficient
• Flue paths plotted in CAD
• Flues marked-up in-situ if required

Site flue location surveys

Our chimney flue location surveys are carried out by Sandberg trained, experienced GPR surveyors. We scan nominated walls with horizontal scan lines at regular intervals. The spacing depends on site conditions, but typically we scan at 300mm centres.

In most cases, we use a GSSI SIR3000/4000 GPR control unit with a 1.5GHz antenna. On thick walls, we can use lower frequencies to provide greater penetration depth, but the resolution and detail of GPR scan data decrease with lower antenna frequencies. Therefore, it is 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, it does not work on panelling, dry lining or stud wall construction. Irregular surfaces, such as ornate mouldings, may result in poor surface coupling and antenna tracking problems. This can affect the positional accuracy of detected flues.

Deliverables

We present the results of our interpretation in a comprehensive factual report, issued in pdf format. The report includes CAD elevation drawings with the location of all detected flues marked. We also issue the original CAD drawings in AutoCAD .dwg format.