Sorry, not VAT - but the value of the benefit you gain from working on your own property (presumably also if you're, say, a car mechanic and work on your own car, etc.) is subject to taxation. Mea culpa.
The obligation to pay tax only kicks in (as far as I can tell, IANAL) if the work is substantial and of a nature which requires professional skills.
Here's a recent link, though in Norwegian, I'm afraid:
https://www.fvn.no/abito/i/GM86x4/skatt-ved-arbeid-paa-egen-...