By contrast, houses in the Newark & Sherwood district are becoming more affordable.
Each year, the Office for National Statistics (ONS) calculates how affordable housing is, by dividing the median house price in local authorities by the median full-time annual income.
The higher the ratio is, the less affordable homes are to buy.
The ONS uses the median which is the middle number in a series, instead of the mean average, so the figures are not distorted between extreme highs and lows.
In Ashfield last year, the affordability ratio was 5.6 - the same as 2017 - but in Mansfield it was it was up from 5.4 to 5.8, while in Newark & Sherwood, it was down from 6.9 to 6.6.
The national average for England and Wales was 7.8.
The average house price in Ashfield has risen £4,000 to £142,000, while the average annual salary has risen to £25,366.
In Mansfield the average house price increased by £9,000 to £136,000, while the average annual salary was £23,647.
By contrast, yearly earnings in Newark and Sherwood rose by ten per cent in 2018, while the average house price only increased by six per cent
This general gulf between earnings and house prices highlights the impact of the housing crisis, with buying a home out of reach for many.
The drastic increase in house prices since 2002, when the ONS first began comparing this data, reinforces this.
The average home in Ashfield then cost £57,950, but the 2018 figure is 145 per cent higher.
In that time the average annual salary has only increased by £8,104, a 47 per cent rise.
It's the same story for Mansfield where, in 2002, the average home cost, £54,000, but that figure was 152 per cent higher in 2018, while the average annual salary has only increased by £6,102, a 35 per cent rise.
And in Newark & Sherwood, the average house price was £79,950 back in 2002, but the 2018 figure is 125 per cent higher, while the average salary has only increased by £8,286 - a rise of 44 per cent.
Polly Neate, chief executive of the housing charity Shelter, said: "The figures leave us in no doubt that owning a home is an all-but-impossible dream for millions of working families.
"Combined with the dire lack of social homes, this has left huge numbers of people with no choice but to rent privately."
“It cannot be right that so many families, especially those on lower incomes, now face a lifetime in deeply unstable private renting, where they’ll have to pay well over the odds to keep a roof over their head.
"More families desperately need the option of social housing, and they need it now."
Nigel Henretty, head of housing analysis at the ONS, said: "After five years of decreases, the estimated affordability of homes in England and Wales remained static in 2018.
"It's also notable that the estimates show newly built homes remained significantly less affordable than existing properties."