After waiting almost a year to claim a victory in the longest format, two comfortable wins have seen the hosts edge closer to a series triumph, but Root is fully aware that England cannot afford to relax.
"You come out of two games where we've played some really strong cricket and there's a lot of confidence," the batsman told Sky Sports News.
"I think the key now is to go into Friday and continue that, to build on what we've done so far and remember this is just the start of where we want to be.
"We can't rest on just two Test wins, we have to capitalise on what we've started and really cement what we have done to take this series home."
The fifth Test begins at The Oval on Friday morning, with England needing only a draw to secure a series victory.