Я вмиваюся перед тим як виходжу із будинку.

Вмиваюся usually means I wash my face / I wash up, not necessarily I take a full shower. It often refers to the kind of washing you do at the sink, especially in a daily routine.

If you wanted to say I wash my whole body, other expressions might be more natural, such as миюся or приймаю душ, depending on the context.

The ending -ся is the reflexive marker. It shows that the action goes back to the subject.

So:

• вмиваю = I wash something or someone
• вмиваюся = I wash myself / I wash my face

This is very common in Ukrainian with everyday self-care verbs.

Because перед is a preposition, and a preposition normally needs a noun or pronoun after it. It cannot directly introduce a full clause with a finite verb.

So Ukrainian uses:

• перед тим, як виходжу = before I leave
• or перш ніж виходжу in some contexts

But перед як is not correct.

Because перед requires the instrumental case. The pronoun той changes to тим in the instrumental singular.

So literally, перед тим, як... is something like before that, when/how..., but in normal English you just translate it as before.

As a whole, перед тим, як is a very common way to say before when it is followed by a full clause.

For example:

• перед тим, як виходжу = before I leave
• перед тим, як лягаю спати = before I go to bed

So it is a clause-introducing expression, not something you should translate word by word in normal use.

Usually, yes. In standard writing, you will most often see:

Я вмиваюся перед тим, як виходжу з будинку.

So a comma before як is the safest standard choice here.

Because this sentence most naturally describes a habit or routine. Ukrainian often uses the present tense for repeated actions:

• Я вмиваюся перед тим, як виходжу з будинку. = I wash up before I leave the house.
  = This is what I usually do.

So the present tense here does not have to mean right now. It can mean as a regular practice.

Then Ukrainian would usually use perfective future forms:

Я вмиюся перед тим, як вийду з будинку.

That means I will wash up before I leave the house on a particular occasion.

So:

• вмиваюся / виходжу = habitual, repeated
• вмиюся / вийду = one completed future action

Because after з / із meaning out of / from, the noun takes the genitive case.

The dictionary form is:

• будинок = house, building

But after з / із it becomes:

• з будинку
• із будинку

So будинку is the genitive singular form.

Both з and із can mean from / out of here. Ukrainian often switches between з, із, and зі for smoother pronunciation.

So both of these are fine:

• з будинку
• із будинку

Learners should think of this mostly as a matter of euphony and natural sound, not a big change in meaning.

Not always. Ukrainian often drops subject pronouns because the verb ending already shows the person.

So both are possible:

• Я вмиваюся перед тим, як виходжу з будинку.
• Вмиваюся перед тим, як виходжу з будинку.

Including я can add emphasis, contrast, or clarity, but it is not required.

Both can be correct, but they are a little different in feel.

• з будинку = out of the house/building
• з дому = from home / out of the house, often more natural when talking about your home routine

So if you mean your usual home routine, many speakers might prefer:

Я вмиваюся перед тим, як виходжу з дому.

That can sound slightly more idiomatic than з будинку in everyday speech.