Swedish Svartbygge (lit. black construction)A building raised without a building permit.

https://sv.wiktionary.org/wiki/svartbygge 'Construction' is in the noun sense (something constructed). Nisses båthus är ett svartbygge om jag känner honom rätt = Nisse's boat house is a svartbygge if I know him correctly The svart- prefix is often used for illegal/sketchy things in general, like in German and Dutch: Svartklubb = speakeasy/underground club Svarttaxi = illegal taxi service (dictionary says 'gypsy cab'... had never heard that :P) etc.