Agree fully with DCD.
Don't be blinded by the tracker. A balance of €68k at 1% instead of 3% is saving you only €1,360 a year. And the savings fall every year as you reduce the balance outstanding.
So sell your property and build your home.
In practice, you may prefer to build your home first and then sell your former home.
Ask UB to remortgage your existing home. They might or might not. If they don't, Pepper will probably do so, but of course, you would lose your tracker.
Brendan