Fellesarealet er stengt.

Because Norwegian very often forms compound nouns by writing them as a single word.

• felles = shared, common
• areal = area
• fellesareal = common area / shared area
• fellesarealet = the common area

So where English uses two words, Norwegian often uses one compound word instead.

The ending -et marks the noun as definite singular for a neuter noun.

Here is the pattern:

• et areal = an area
• arealet = the area
• et fellesareal = a common area
• fellesarealet = the common area

So the English word the is often attached to the end of the noun in Norwegian instead of standing in front of it.

You learn it from the dictionary form or article:

• et areal = a/an area

The article et tells you it is neuter. That matters because neuter nouns affect other words in the sentence, such as adjectives and participles.

That is also why the sentence has stengt and not stengt/stengte in some other form.

Er is the present tense of å være = to be.

So:

• jeg er = I am
• du er = you are
• det er = it is
• fellesarealet er stengt = the common area is closed

It works just like English is in this sentence.

Because stengt agrees with a neuter singular subject here.

The noun fellesarealet is neuter singular, so the word describing its state takes the neuter form:

• Døren er stengt = The door is closed
  (dør is common gender, so no -t)
• Vinduet er stengt = The window is closed
  (vindu is neuter, so -t appears)

Since fellesarealet is neuter, Norwegian uses stengt.

In this sentence, it is best understood as a past participle used adjectivally.

It comes from the verb å stenge = to close / shut.
So stengt literally means closed/shut.

In sentences like this, Norwegian often uses er + past participle to describe a state:

• Butikken er stengt = The shop is closed
• Døren er stengt = The door is closed

So grammatically it comes from a verb, but in use here it functions like an adjective describing the condition of the place.

Yes, in many contexts you could, but stengt is often more natural when something is closed to access or use.

A rough distinction:

• stengt = closed, shut, not open, not available
• lukket = closed, shut, sometimes more physical or formal, and also used in other senses like closed group/system

For a common area in a building, stengt sounds very natural if the area is unavailable.

Because Norwegian usually puts the definite marker on the noun itself.

Compare:

• English: the common area
• Norwegian: fellesarealet

That -et at the end already includes the idea of the.

If an adjective comes before the noun, Norwegian often uses double definiteness, for example:

• det felles arealet would not be the normal way here
• more natural with a regular adjective would be something like det store arealet = the big area

But in your sentence, felles is part of the compound noun, so fellesarealet is the correct form.

The normal word order is:

subject + verb + complement

So:

• Fellesarealet = subject
• er = verb
• stengt = complement

This is the standard declarative pattern in Norwegian, just like English:

• Fellesarealet er stengt. = The common area is closed.

If you turn it into a yes/no question, the verb comes first:

• Er fellesarealet stengt? = Is the common area closed?

Yes. It is a fairly general word for a common/shared area.

Depending on context, it could mean:

• a shared room in an apartment building
• a communal lounge
• a shared kitchen
• a common area in an office or housing complex

So the exact place depends on the situation, but the grammar of the sentence stays the same.

A simple learner-friendly approximation would be:

• fellesarealet ≈ FEL-less-ah-reh-AH-let
• er ≈ a short ehr or sometimes very reduced in connected speech
• stengt ≈ stengt with a clear final t

A few helpful notes:

• ll in felles is pronounced like a normal l
• the r in Norwegian is usually more clearly pronounced than in many English accents
• the final -et in fellesarealet is not silent

If you want to sound natural, focus on saying the compound as one unit:
fellesarealet

Yes, absolutely. It sounds very normal and natural.

You might see it:

• on a sign
• in an email from building management
• in a notice in an apartment block
• in a message about maintenance or cleaning

It is a standard way to say that a shared/common area is not available for use.