How model assisted valuation delivers large-scale property valuations

When undertaking a large-scale valuation exercise, mass appraisal is a modern, efficient and cost-effective way of providing consistent and accurate valuations.  

Mass appraisal is the valuation of a group of properties using common data, standardised methods and statistical testing. 

Mass appraisal is commonly used in countries that base taxes on the value of property. It is also used in the private sector, for example, most initial mortgage valuations are from mass appraisal models.  

An Automated Valuation Model (AVM) is a key element of mass appraisal.  

Similarly to valuers, AVMs use data about sold properties, including their sales price, property characteristics and location. Whilst valuers typically focus on a small group of comparable properties at a time, AVMs use algorithms and statistical techniques to produce estimates of property’s value at a set point in time for all properties. 

An AVM provides a fair and consistent basis for a valuation, because all properties with the same characteristics will be valued in the same way.  

Currently the Valuation Office Agency (VOA) is using mass appraisal to support Welsh Government’s Council Tax reform agenda.  

The VOA has adopted a model assisted valuation approach, to help target its valuer resource when valuing properties at scale. 

The model is being used to support the valuation of 1.5m domestic properties for a Council Tax revaluation in Wales in 2028. 

VOA valuers underpin each stage of the model assisted approach.  

First, they ensure the property data and sales used are accurate. They then collaborate with analysts to build and refine the AVM.  

Valuers sample model valuations to ensure the model is accurate and to understand where valuer reviews should be targeted. 

Groups of properties, with similar characteristics in the same location, are then reviewed. The focus of valuers is on reaching the right Council Tax band for each property.