Αν δεν αερίζεις καλά το δωμάτιο, το ταβάνι και οι τοίχοι κρατάνε υγρασία.

Αν means if.

In this sentence, it introduces a condition:

• Αν δεν αερίζεις καλά το δωμάτιο... = If you don’t air out the room well...

This is the normal word for if in modern Greek when talking about a condition.

Modern Greek does not use the infinitive the way English does.

So instead of something like if not to air the room, Greek uses a fully conjugated verb:

• αερίζεις = you air / you ventilate
• δεν αερίζεις = you do not air / you don’t ventilate

Greek usually expresses actions with personal verb forms, not infinitives.

αερίζω means to air, to air out, or to ventilate.

So:

• αερίζεις = you air out / you ventilate

In this sentence, it means opening windows or otherwise letting fresh air circulate in the room.

Because Greek often uses the you form in general statements, just like English can:

• If you don’t air out the room well...

It does not necessarily mean one specific person. It can mean anyone in general.

καλά means well.

It modifies the verb αερίζεις, so:

• αερίζεις καλά = you ventilate well / you air out properly

It tells us the room is not being aired sufficiently.

το δωμάτιο is the direct object of αερίζεις.

You are ventilating the room, so Greek uses the accusative case here:

• το = neuter singular accusative/article
• δωμάτιο = room

So:

• αερίζεις το δωμάτιο = you air out the room

Greek usually repeats the article with each noun:

• το ταβάνι = the ceiling
• οι τοίχοι = the walls

So το ταβάνι και οι τοίχοι literally means the ceiling and the walls.

This is very normal in Greek. English can sometimes use one article for both nouns, but Greek commonly repeats it.

Because the subject is plural in meaning:

• το ταβάνι και οι τοίχοι = the ceiling and the walls

Even though ταβάνι is singular and τοίχοι is plural, together they form a compound subject, so the verb is plural:

• κρατάνε = they hold / they retain

Yes. κρατάνε and κρατούν are both present-tense forms of κρατάω / κρατώ.

In everyday spoken Greek, κρατάνε is very common and natural.

So:

• κρατάνε υγρασία
• κρατούν υγρασία

Both mean they retain moisture/dampness.

Literally, it means they hold moisture.

In natural English, this often means:

• they retain moisture
• they stay damp
• they trap dampness

Here it refers to the ceiling and walls becoming damp because the room is not ventilated properly.

Because it is being used as an uncountable noun in a general sense:

• κρατάνε υγρασία = they retain moisture

This is similar to English, where we usually say retain moisture, not retain the moisture, unless we mean some specific moisture already mentioned.

The first part is the condition, and the second part is the result:

1. Αν δεν αερίζεις καλά το δωμάτιο = If you don’t ventilate the room well
2. το ταβάνι και οι τοίχοι κρατάνε υγρασία = the ceiling and the walls retain moisture

This mirrors a very common Greek pattern:

• If X, Y

Greek word order is fairly flexible, but this order is very natural and clear.

Yes, very much.

In everyday Greek, saying that walls or ceilings κρατάνε υγρασία usually suggests a dampness problem in the building. It often implies poor ventilation and can suggest conditions that may lead to:

• condensation
• damp patches
• mold

So it is both literal and very natural in household/building contexts.

It describes a general or habitual situation.

The present tense here means something like:

• If you don’t ventilate the room properly, the ceiling and walls tend to retain moisture.

So it is not about one single moment, but about what generally happens under those conditions.