Types of Dutch houseboats;

Basically there are Ships and “arks” [to use the Dutch term]. A woonboot or woonschip [ship for living] is a houseboat built on the hull of a ship or boat. When is a boat a ship? Beats me. For this purpose, we can say they are the same. I once read that if a vessel can sail with 40 loaded barrels on board, it may be called a ship instead of a boat.

There is a third category as well, a "woonvartuig" [vessel for living] which is between an ark and a ship. This is a term used by the city of Amsterdam for houseboats that are built on a ship's hull but that don't quite qualify as a ship for them, usually because there have been too many changes to the shape.

Anyway, a woonschip may have propulsion of its own or not. Most Amsterdam houseboats have had their engines removed. A bedroom is worth more than an engine room these days. See below for more on operational [varend] ships.

An Ark [woonark] is a houseboat built on a hull that was not built to move through the water, but as a static floating object. They may be steel or concrete [while other materials are possible in theory, I don’t know of any in this city].

Concrete arks are most desired; they never need to go to the shipyard. Some are 50 years old, and still sound.

The house [opbouw]

Generally, either wood or steel. I favor steel; when it's all welded together with no open seams, it lasts indefinitely with minimum maintenance.

But these days, steel work can't be done in your mooring, and pretty much has to be done at the shipyard. That makes it so expensive, it won't be done much anymore I'm afraid.

Steel can be bent and worked to harmonize with the lines of the ship. wood can be too, in theory. If you see a houseboat topside built this way, please send me a picture.

Wooden houses have been built for centuries, and there isn't  much different about building one on a boat hull; except that it's really difficult to make things that look ok. The city doesn't help, as it's rules specify maximum height, width, and length. This means if you build a brick, you'll get the most interior space [but the least attractive exterior for everyone else to look at]. And so most of the wood topped houseboats [ships and arks] are bricks.

Wooden houses generally have tar paper type roofing, which is good for up to 20 years. It doesn't look as good from the houses above as steel does, but you're not going to live up there anyway. They are more susceptible to catching fire from the outside, but in reality house fires usually don't come from outside.

A big problem is rain leaking in if the topside isn't built properly. Water running into your hull can't get out except by evaporation, and is the main cause of damp and hull damage in a houseboat.

If you have a catastrophic fire inside the boat, it will be completely destroyed whether wood or steel; the steel house will be so twisted and buckled, it won't be reusable.

Sailable houseboats;

A “Varend schip” is one that has propulsion; some are “vaar klar”, which means in addition to the propulsion system, there is onboard power and water, anchor, chain and windlas (if nessasary), radio, navigation lights, life preservers, and so on.