Learn Hardcore Finnish: Keittiö on jo imuroitu, mutta olohuone on vielä imuroitava. - The kitchen has already been vacuumed, but the living room still has to be vacuumed.

imuroitu
- This is the past passive participle (also called the second passive participle).
- It roughly means vacuumed, that has been vacuumed.
- With olla it forms a result/state:
  - on imuroitu ≈ has been vacuumed / is (now) vacuumed.
imuroitava
- This is the (present) passive participle in -tava/-tävä.
- It basically means to be vacuumed, that must/needs to be vacuumed.
- With olla it gives a sense of obligation or something remaining to be done:
  - on imuroitava ≈ must be vacuumed / needs to be vacuumed / is to be vacuumed.

So the sentence contrasts a past-result state (on jo imuroitu) with something that is still to be done (on vielä imuroitava).

Why do we say Keittiö on jo imuroitu instead of something like Keittiö imuroitiin jo?

Both are possible Finnish, but they focus on slightly different things.

Keittiö imuroitiin jo
- Uses the past passive tense (imuroitiin).
- Focuses on the event in the past: at some point, someone vacuumed the kitchen already.
- Roughly: The kitchen was already vacuumed (as an action).
Keittiö on jo imuroitu
- Uses olla + past passive participle (on imuroitu).
- Focuses on the current result/state: right now, the kitchen is in a vacuumed state.
- Roughly: The kitchen has already been vacuumed / The kitchen is already vacuumed.

In this sentence, we are contrasting:

one room that is already in a finished state (kitchen), and
another that still belongs to the tasks that must be done (living room).

That idea of a current resulting state is expressed more clearly with on imuroitu than with imuroitiin.

What is the literal structure and meaning of olohuone on vielä imuroitava?

Grammatically, it is a simple copula sentence:

olohuone – subject (the living room)
on – verb olla (is)
vielä – adverb (still / yet)
imuroitava – passive participle used as a predicative adjective

Literally you can think of it as:

The living room is still a to-be-vacuumed (thing).

In natural English that becomes something like:

The living room still needs to be vacuumed.
We still have to vacuum the living room.

There is no separate word for must / need in the Finnish sentence; that meaning is carried by the -tava participle together with olla.

Does on imuroitava always mean must be vacuumed? How strong is the obligation?

Olla + -tava/-tävä often expresses some sort of necessity or requirement, but the strength depends on context.

In everyday neutral context, on imuroitava ≈ needs to be vacuumed / should be vacuumed / has to be vacuumed.
In instructions, rules or technical texts, on X-tava can sound quite formal and duty-like, closer to must.
- Hakemus on palautettava perjantaihin mennessä.
  – The application must be returned by Friday.

Compared with other options:

olohuone täytyy vielä imuroida – stressed obligation, like must.
olohuone pitää vielä imuroida – also obligation, often slightly more colloquial.

So on vielä imuroitava is impersonal and can be read as has to be / needs to be; the exact strength is interpreted from context and tone.

Who is doing the vacuuming in Keittiö on jo imuroitu, mutta olohuone on vielä imuroitava?

The sentence uses Finnish passive/impersonal forms, so the doer is not mentioned:

on imuroitu – has been vacuumed (by someone / by people / by us)
on imuroitava – must be vacuumed (by someone / by people / by us)

Typical interpretations:

Generic someone/they: Someone has already vacuumed the kitchen.
Often we if the speaker is part of the group doing the work: We’ve already vacuumed the kitchen, but we still have to vacuum the living room.

If you wanted to explicitly name the agent, you would normally use a different construction, e.g.:

Keittiö on jo meidän imuroimamme. – The kitchen is already vacuumed by us.

But in everyday speech Finns usually leave the agent implicit, exactly like in the original sentence.

Why are Keittiö and olohuone in the nominative case here? Aren’t they more like objects than subjects?

In these sentences they are grammatical subjects, not objects.

Keittiö on jo imuroitu.
- Keittiö = subject (nominative)
- on = copula verb
- imuroitu = predicative (a state the subject is in)
Structurally this is like:
Keittiö on puhdas. – The kitchen is clean.
Only here the descriptive word is a participle (imuroitu) instead of a plain adjective.
olohuone on vielä imuroitava.
- olohuone = subject (nominative)
- imuroitava = predicative adjective (what kind of state the living room is in: to-be-vacuumed)

So even though in English kitchen and living room feel like objects of the vacuuming action, Finnish reorganizes the sentence:
they become subjects whose state is being described by a participle.

Is imuroitava functioning like an adjective describing olohuone?

Yes. Participles in Finnish are verb forms that can behave very much like adjectives.

imuroitava olohuone – a living room that needs to be vacuumed / a to-be-vacuumed living room
korjattava auto – a car that needs to be repaired / a to-be-repaired car
luettava kirja – a book that must/should be read / a to-be-read book

In olohuone on vielä imuroitava, the participle imuroitava is not placed in front of the noun, but it still describes the living room via the copula on:

The living room is (still) a to-be-vacuumed one.

So grammatically it is a predicative adjective formed from a verb.

Could I say the same thing with pitää or täytyy instead of on imuroitava?

Yes, there are several natural alternatives. For example:

Olohuone täytyy vielä imuroida.
Olohuone pitää vielä imuroida.
Olohuone on vielä imuroiden – not correct; don’t use this.
Olohuone on vielä imuroimatta.

Differences in feel:

täytyy / pitää + imuroida
- More directly expresses obligation (must / have to).
- Slightly more colloquial and spoken than the -tava construction.
on vielä imuroitava
- More impersonal and descriptive: the living room belongs to the set of things that are still to be vacuumed.
- Common in written language, instructions, schedules:
  - Seuraavat kohteet on vielä siivottava.
on vielä imuroimatta (using the -mA + -tta form)
- Literally is still un-vacuumed.
- Emphasizes the fact that the job is not done yet, rather than the obligation.

All of these can describe the same practical situation, with slightly different nuances.

Why is on repeated in the second clause? Could I say Keittiö on jo imuroitu, mutta olohuone vielä imuroitava?

In standard, neutral Finnish, you repeat on:

Keittiö on jo imuroitu, mutta olohuone on vielä imuroitava.

Each side of mutta is its own clause with its own finite verb:

Keittiö on jo imuroitu.
Olohuone on vielä imuroitava.

Leaving out on in the second clause:

… mutta olohuone vielä imuroitava

is possible only in very elliptical or note-like / headline-style language, where verbs are often dropped:

Keittiö imuroitu, olohuone vielä imuroitava. (for example in a checklist)

As a normal, full sentence in conversation or prose, you should keep on.

Where do jo and vielä usually go in the sentence? Could I move them somewhere else?

In both clauses, jo and vielä stand just before the participle they modify, which is a very typical, neutral placement:

on jo imuroitu
on vielä imuroitava

Other positions are possible, but they can slightly change emphasis or feel:

Keittiö on imuroitu jo. – also grammatical; can sound a bit more emphatic or contrastive about the timing (already).
Jo keittiö on imuroitu, mutta olohuone… – puts strong emphasis on jo (already even the kitchen is done…).
Olohuone vielä on imuroitava. – unusual in everyday speech; sounds marked/poetic or used for specific emphasis.

As a learner, placing jo/vielä just before the main participle or verb (as in the original sentence) is a very safe and natural default.