Breakdown of Er is iets in het gebouw in deze straat.
zijn
to be
in
in
deze
this / these
er
there (existential)
Questions & Answers about Er is iets in het gebouw in deze straat.
Why do we use Er is at the beginning of this sentence?
Can I just say "Iets is in het gebouw" instead of using Er?
You will be understood, but it sounds very unnatural in Dutch. When you want to say that an indefinite person or thing (like iets, meaning "something") is in a certain place, Dutch strongly prefers to start the sentence with the "there is" structure: Er is.
Why is it deze straat and not dit straat?
Because the word for "street" is a de-word (de straat). In Dutch, you use deze (this) for all singular de-words. If you wanted to say "this building", you would use dit (dit gebouw) because gebouw is a het-word.
Does the preposition in work exactly the same as in English here?