U uredu je bilo toliko sparno da smo otvorili sve prozore čim smo došli.

Because u can mean either in or into, depending on the case:

• u + locative = in
• u + accusative = into

Here the sentence means in the office, not motion toward it, so Croatian uses the locative:

• ured = office
• u uredu = in the office

Compare:

• Radim u uredu. = I work in the office.
• Idem u ured. = I’m going into/to the office.

Je bilo is the Croatian way of saying it was in an impersonal sense.

In this sentence, bilo je sparno means it was stuffy / muggy / close. Croatian often uses bilo je for weather, atmosphere, or general conditions:

• Bilo je hladno. = It was cold.
• Bilo je tiho. = It was quiet.
• Bilo je sparno. = It was stuffy/muggy.

The word je is the present tense of biti (to be), and bilo is the past participle. Together they form the past tense.

Because this is an impersonal construction.

When Croatian says things like it was hot, it was late, it was difficult, there is no real subject like a person or object with gender. In that situation, Croatian normally uses the neuter singular form:

• bilo je vruće = it was hot
• bilo je kasno = it was late
• bilo je sparno = it was stuffy

So bilo is neuter singular, used because there is no specific masculine or feminine subject.

Sparno describes air that feels stuffy, close, muggy, heavy, humid, and unpleasant, especially indoors or before a storm.

It is often used for weather or room conditions:

• Danas je sparno. = It’s muggy today.
• U sobi je sparno. = The room is stuffy.

So in this sentence, it suggests the office air felt unpleasant enough that they opened all the windows.

Toliko ... da means so ... that.

It introduces a result:

• toliko sparno da smo otvorili sve prozore
• literally: so stuffy that we opened all the windows

This is a very common Croatian pattern:

• Bio je toliko umoran da je odmah zaspao. = He was so tired that he fell asleep immediately.
• Bilo je toliko glasno da se nismo čuli. = It was so loud that we couldn’t hear each other.

So toliko intensifies the adjective or condition, and da introduces the consequence.

Both are possible, but Croatian often places the auxiliary smo in second position in its clause.

The past tense is made with:

• auxiliary: sam, si, je, smo, ste, su
• past participle: otvorili

In a clause like da smo otvorili sve prozore, the word smo naturally comes very early, after da.

You could also hear da smo otvorili much more naturally than da otvorili smo, which is incorrect.

Croatian clitic auxiliaries like je, smo, su usually go near the beginning of the clause, not wherever English would put have or were.

Otvorili is the past participle of otvoriti (to open), and it agrees with the subject.

Here the subject is we, understood from smo, and the form otvorili tells us the group is:

• masculine plural or
• mixed-gender plural

If the speakers were all female, it would be:

• otvorile smo

So:

• smo otvorili = we opened

Because otvoriti takes a direct object, and direct objects are usually in the accusative case.

• svi prozori = all the windows (nominative)
• sve prozore = all the windows (accusative)

So:

• otvorili smo sve prozore = we opened all the windows

Singular and plural forms can be tricky here, but the important point is that prozore is the accusative plural of prozor.

Čim means as soon as.

It introduces a time clause:

• čim smo došli = as soon as we arrived

It shows that one action happened immediately after another.

Examples:

• Nazvat ću te čim stignem. = I’ll call you as soon as I arrive.
• Čim je ušao, sjeo je. = As soon as he came in, he sat down.

Both are possible, but they mean slightly different things:

• kad smo došli = when we arrived
• čim smo došli = as soon as we arrived

Čim is more immediate. It emphasizes that they opened the windows right away, with no delay.

So in this sentence, čim fits very well because the stuffiness caused an immediate reaction.

Croatian often omits subject pronouns when the verb already makes the subject clear.

Here:

• smo otvorili = we opened
• smo došli = we arrived

The form smo already tells you the subject is we, so Croatian usually does not need mi.

The participle došli is plural because the subject is plural: we.

If you added the pronoun, it would be:

• ... da smo otvorili sve prozore čim smo mi došli.

But that would usually sound unnecessary unless you want emphasis or contrast.

Yes, both are perfective, and that does matter.

• otvoriti = to open (completed action)
• doći = to come/arrive (completed arrival)

This sentence describes completed events in sequence:

1. it was stuffy
2. we arrived
3. we opened all the windows

Perfective verbs are very natural here because the actions are viewed as finished whole events.

If you used imperfective verbs, the meaning would shift:

• otvarati = to be opening / to open repeatedly
• dolaziti = to be coming / to come habitually

That would not fit the sentence nearly as well.

Croatian word order is flexible, and the beginning of the sentence often gives the setting or what the speaker wants to highlight first.

Starting with U uredu sets the scene:

• U uredu je bilo toliko sparno... = In the office, it was so stuffy...

This is very natural because it tells you immediately where the condition applied.

Other word orders are possible, but they may shift emphasis:

• Bilo je toliko sparno u uredu...
  still grammatical, but the focus feels slightly different

Croatian often moves time/place expressions around for emphasis or style.

Yes, that is a very close literal translation.

A more natural English version might be:

• It was so stuffy in the office that we opened all the windows as soon as we arrived.

The Croatian sentence is built very similarly to English:

• U uredu = in the office
• je bilo toliko sparno = it was so stuffy
• da smo otvorili sve prozore = that we opened all the windows
• čim smo došli = as soon as we arrived

So the structure is actually quite learner-friendly once you understand the cases and verb forms.