Monitoring an adjoining owner’s property during the course of a building owner’s construction works ensures that any movement is detected at the earliest stage possible while also ensuring there is a full record of the movement in place.
There are a number of different approaches to movement monitoring, however generally speaking the monitoring system will be calibrated to detect as little as 1mm movement. Being able to detect early movement means the movement issue can be addressed at the first instance and in advance of becoming or leading to a severe issue.
Movement monitoring systems are installed to the adjoining owner’s property before the building owner commences their construction work and will generally be installed to a number of different predetermined points on the property such as the front, rear or flank walls.
The first readings that are presented are the ground readings and establish the base for which comparison can be provided during the course of the works. Once the base readings are established, the trigger points can then be set. For example, a trigger of plus or minus 1mm may be set for a property that sits on soft ground, whereas a property on firmer ground which is less likely to be affected by movement, may have a trigger reading of plus or minus 3mm.
Once the monitoring tags are installed, they will be read throughout the course of the works usually with as much frequency as once a week and will remain in place for a number of weeks once the construction work is complete.
This comprehensive approach ensures that movement is detected early and when found can then be easily cross referenced to the works taking place on site, meaning that the contractors can react and redesign the method of works, if the movement readings are higher than they should be.
The weekly movement reports and readings, tend to be presented in an easy to follow traffic light system with the obvious reading of green meaning no movement to red, meaning severe movement.
What happens when Movement does occur?
When movement does occur and cracks are noted within an adjoining owner’s property, it then becomes a matter of establishing if the movement is still live. The best method for doing this and recording and measuring crack movement is through the installation of a crack monitors or tell-tales.
There are a wide variety and type of crack monitors, however in my experience the most popular tends to be an “off the shelf” plastic grid measure. The measure will be installed over the crack and then monitored over a set period of time at regular intervals to identify any movement.
Once the readings are in place, it will give the engineer who installed them a clearer idea of the potential cause of the movement while also importantly enabling the appropriate rectification works to be planned.
What are the Costs?
In our experience, we tend to find that an initial set up cost for base “ground” readings and the installation of the monitoring tags/targets tends to be in the region of £800 + VAT.
Given that the monitoring is usually once a week, there will also be the ongoing weekly cost for the tags to be monitored and the reading reports to be presented to the project team, in our experience this tends to being the region of £300 + VAT per visit.
As with all technology these days there is also the opportunity for the monitoring tags to run on a continual 4g phone line, meaning that as soon as movement occurs, it automatically informs the monitoring company by email and even SMS text! However, this type of remote monitoring system is usually in the region of £10,000 plus, therefore it is unlikely to be used in a conventional residential context.
The installation of movement monitoring is a fairly substantial cost and will likely equate to in the region of £3,000 – £6,000 + VAT over the course of the project. It is therefore important that careful consideration is given to works that are taking place and the type of properties that surround those works. In our experience we tend to see movement monitoring installed on structurally complex works such as substantial demolition or deep excavation.
If you are planning on undertaking extensive structural works to your property, we would advise speaking to your project team about movement monitoring at an early stage to ensure that it has been considered.
We are seeing movement monitoring becoming an increasingly common request by adjoining owner’s surveyors therefore we would recommend budgeting it into the project costs sooner than later.