It’s long been taken as read that high tech company salaries push up housing costs in the surrounding areas, but the WSJ commissioned home tracking company Zillow to provide some hard data. By tracking the increase in values of homes owned by Apple employees, it was able to prove that home values in those areas rose further and faster than in surrounding areas with similar demographics.

The piece notes that zoning laws and regulatory red tape also have a significant effect, by limiting the supply of housing at a time when demand is increasing, but the comparison does suggest that there is a direct link to tech companies like Apple.

The problem of lower-paid workers finding it hard to find housing within reasonable commuting distance of tech companies like Apple has been highlighted in the past. Apple took the decision back in March to hire the majority of its previously contracted security guards as staff, providing them with health insurance and retirement benefits. The company also arranged for its contracted shuttle bus workers to get an improved deal.

Homes occupied by Apple workers are appreciating at 18% a year, compared with 11% for San Francisco as a whole and 12% for San Jose. Since iPhone sales launched in June 2007 [and stock values rose], the Zillow analysis found, the average difference between the median home value of Apple workers and San Jose workers has swelled to 20% from 13%.