It's pretty much a house for boats, used in winter time.

You would need a straight shoreline to build it upon.

To make it more than just look fancy we would probably need it to have a lockable door, so you would only happen to get it outside with a key.
Without a key there would only be the option to wreck the house wiht siege weapons (thus needing a lot more time and effort than just boating away with it).
We could debate over if the knarr would either be released when the house is broken or destroyed (which would feel more reasonable to me).
A middle way would be to salvage a nearly broken, slow version of the knarr stored.