Geo-Serv Ltd offer a premium-quality level monitoring service nationally at competitive prices.
Take the guess work out of subsidence claimsUsing the most accurate instruments on the market and experienced personnel, precise levelling can reliably measure foundation movements to a fraction of a mm. Graphical presentation against time produces a clear picture of which parts of the house are moving and by how much.
- implicated trees are readily identified
- misdiagnosis is eliminated
- limited underpinning schemes can be designed in the knowledge that they are stabilising the right parts of the structure.
Cost effectivePrecise levelling is more expensive than simple crack monitoring, but the benefits easily outweigh the additional cost.
- fewer surveys are needed because the degree and pattern of movement is identified more rapidly - usually within 6 months
- tree owners, especially Local Authorities, find the evidence difficult to refute and escalation of the damage is avoided
- inappropriate underpinning is eliminated
The typical cost of monitoring a domestic property over a one year period is about the same as a soil investigation. See Standard Charges for further details.
ReliableChanges in crack width can provide a useful indication of what is happening to the structure and, in simple cases, these changes may reflect what is happening to the foundations. Unfortunately, in many cases the changes in crack width bear little resemblance to the recorded foundation movements. Cracks can remain stable while the foundations continue to move seasonally or new cracks can open in locations that are not being monitored. Equally cracks can open without corresponding subsidence or heave, which is positive proof that the cracks have been caused by processes other than subsidence. Even in simple cases, crack widths give no quantitative information on how effective tree control or other remedial measures have been. See Case Studies for further details.
Application of the resultsIn most cases, the cause of the subsidence and broad recommendations for remedial measures (e.g. tree management, drain repairs, underpinning, etc.) can be based on the results of the monitoring alone. Moreover, the complex cases where further investigations are needed can be readily identified and targeted.
- Digest 386 - To ensure accuracy, it is important that the right technique is employed. Geo-Serv have developed a levelling technique based upon the recommendations set out in Building Research Establishment Digest 386 "Monitoring building & Ground Movement by Precise Level Monitoring".
- Precise level - A precise level works on the same principle as the Engineers Level or Dumpy Level seen on most building sites. However, it has one fundamental difference: it is fitted with a parallel plate vernier which allows measurements to be recorded to the nearest 0.01 mm, compared to an Engineers Level which can be read to ±0.5 mm. The difference in accuracy between a Precise Level and an Engineers Level is therefore very similar to the difference between a ruler and a digital caliper. Very few investigators would use a ruler to record changes in crack width and the same principle should apply to recording vertical movements with an Engineers Level.
- Levelling stations - Monitoring points consist of No 8 Brass slotted round wood screws plugged and resin-bonded into pre-drilled holes so that approximately 15 mm protrudes beyond the wall. Where practical, the screws are fixed into the same mortar course, at a height of between 300 mm and 600 mm above ground level. As a minimum, points are fixed externally at the corners of the house, midway along the accessible elevations, and either side of any major fractures in the brickwork. Additional points may be required to record relative movement between the house and bays, porches, external stairs, extensions, etc..
- Survey datums - For straightforward cases, it is not essential to provide a deep datum and the survey can be referenced to the point on the house furthest from the perceived area of movement. However, wherever practical, a drain or other feature on a relatively deep foundation is included in the survey as a check on the stability of the reference point. Where there is a suspicion that the whole house is moving (e.g. as a result of heave following the removal of large trees), a dedicated sleeved datum can be installed to a depth of at least 5m in an area remote from any retained or removed trees.
- Closing error - To check that the survey has been carried out correctly, it must start and finish at the same monitoring point or datum. The closing error is the difference in the two readings obtained and, unless there are extenuating circumstances, it should not exceed 0.5mm. When comparing our services to our competitors, customers should be wary of any monitoring companies that do not quote closing errors.
- Repeat surveys - Unless an alternative interval has been specified by the client, we normally recommend that surveys are carried out initially every two months and the frequency then reduced to every three months unless the results appear unusual.
- Results & Feedback - The recorded results are tabulated in an Excel spreadsheet and presented graphically as recommended by BRE Digest 386. Results are normally sent electronically to the client and/or the instructing engineer within 5 working days of the survey. Our report includes any comments made by the homeowner at the time of our visit.
- Analysis - For a small additional charge we will include a brief analysis of the results based on information supplied by the client. Any unexpected results are flagged for the attention of the instructing engineer and/or client. Click below to see a sample monitoring report. If required, we can provide additional consultancy services ranging from an informal review of the file to undertaking an independent inspection of the property.
Click on link below to open up a sample monitoring report in Adobe format. Adobe Reader required. Sample report
Geo-Serv currently operate throughout England and Wales, including the Isle of Wight.
Our standard charge for precise level monitoring a domestic property is £175 per survey, plus VAT. This includes:
- Installation of up to 12 external monitoring points at no additional cost
- Monitoring up to three external cracks, provided these are accessible from ground level or a telescopic ladder
- An initial brick course survey to record out-of-level
- Provision of standard Monitoring Report
- Travelling costs (for all properties within the Home Counties)
- Additional external monitoring points
- Additional crack measurement points
- Internal monitoring points
- Travelling in excess of 50 miles from London
- Analysis and interpretation of the results
Case StudiesComing Soon - The following case studies in PDF format will be available to download. Adobe Reader required.
- Seasonal movement
- Tree growth
- Removal of large trees
- Tree reduction
- Root barriers
- Long term heave