The society lent £14.9bn, up from £13.1bn in the corresponding period last year.
In the process Nationwide upped its profit by 34% in to £802m, up from £598m in 2014.
Graham Beale, chief executive of Nationwide, said: “This has been our best ever half year of mortgage lending.
“Our first half performance reflects the growing strength and security of the society with all of our core product areas delivering standout results.
“We have also continued to deliver better customer satisfaction than our high street peer group, achieved excellent financial results and further improved our capital position.”
Nationwide commented on “healthy employment growth and robust demand from investors – including buy-to-let” which has resulted in London prices rising rapidly.
But it added: “Such outperformance is unlikely to be sustained over the long term, given that key measures of affordability are already stretched.”
