Housing markets have several problems with regard to affordability.

First of all, the land costs are 60% of the total costs in building a decent home, which is probably due to the fact that there is an "urban limit" that prevents building more houses at affordable prices. (how does this urban limit work?)

Second, the cost of building a house in Auckland is about 25% more expansive than in Melbourne.

This could be due to the fact that building materials and regulatory fees are more expensive here in Auckland than in Melbourne.

Third, there are covenants attached to lands which mean that you have to build buildings of a certain size, and not allowed to build a smaller house even if you wanted to. (covenants??? not sure what you mean here. It's a rule?)

Fourth, the transport costs are very expensive, which add to the already high building costs. (the link between transport costs and building costs isn't clear)

There are several ways to help keep the housing prices down.

For one, the "urban limit" could be relaxed a bit to keep the land prices down. (wouldn't the urban limit affect the price of the buildings and not the land itself?)

Secondly, being flexible in land covenants to allow for the building of affordable houses.

And third, planning a better transport system, which would reduce the costs of transport fees as well as allowing the urban sprawl to keep the land prices down.