Build two houses

[Rudy Manna]

I own a rental property in Seattle. The house is in Ballard location which is desirable one. The house in a 5000 sqft lot.

Quite a few builders in my block bought houses and then build two houses after tearning down the old one. I did the math and it would be profitable to it. But to start with I need to figure out the city permits and steps involved. 

Can the experts please point me to:

1. The rules involved in building two houses.

2. Additional permits required.

3. The timeframe required to get the permits and all so building can be started.

4. Pitfalls  should be aware of.

Thanks in advance.