tatemono no naibu ha sizuka desu.

の links two nouns together. In this sentence, 建物の内部 means the interior of the building or the building's interior.

So the pattern is:

• A の B = B of A / A's B

Here:

• 建物 = building
• 内部 = interior, inside
• 建物の内部 = the interior of the building

は marks the topic of the sentence. It tells the listener what the sentence is about.

So in:

• 建物の内部は静かです。

the topic is 建物の内部 = the building's interior.

A very literal feel is:

• As for the interior of the building, it is quiet.

Japanese often uses は when introducing or describing a topic, even where English would simply use the subject.

Both can sometimes be possible in similar sentences, but they give slightly different nuance.

• は = presents something as the topic, often neutral or contrastive
• が = marks the grammatical subject more directly, often with a sense of identifying or emphasizing it

So:

• 建物の内部は静かです。
  = As for the interior of the building, it is quiet.

This sounds like a general statement about it.

If you said:

• 建物の内部が静かです。

it would sound less natural in many ordinary contexts, unless you are specifically emphasizing that the interior is the quiet part.

For a basic learner, the safest understanding is:

• は is used here because the sentence is simply describing the building's interior as a topic.

静か is a な-adjective.

In Japanese, there are two main adjective types:

• い-adjectives: like 大きい
• な-adjectives: like 静か, 有名, 便利

Even though 静か ends in か, it is not an い-adjective. It is a な-adjective.

That matters because it behaves differently depending on what comes after it.

Because な-adjectives only use な when they directly modify a noun.

For example:

• 静かな部屋 = a quiet room

But when the adjective comes before です or acts as the predicate of the sentence, you do not use な:

• 部屋は静かです。 = The room is quiet.

So in your sentence:

• 建物の内部は静かです。

静か is not directly modifying a noun, so there is no な.

です makes the sentence polite and completes the statement.

So:

• 静かです = is quiet

In plain form, it would be:

• 静かだ

But learners are usually taught the polite form first:

• 静かです

So です does not mean exactly the same thing as English is in every situation, but here it works very much like is in translation.

The structure is:

• 建物の内部 = the interior of the building
• は = topic marker
• 静かです = is quiet

So the pattern is:

• [noun phrase] は [description] です

A more literal breakdown is:

• As for the building's interior, it is quiet.

This is a very common Japanese sentence pattern.

Japanese does not have articles like a, an, or the.

So a noun like 建物 can mean:

• a building
• the building
• buildings

The exact meaning depends on context.

In your sentence, English may translate it as the building or the interior of the building, but Japanese does not need a separate word for the.

Both can refer to inside, but they are not exactly the same.

• 内部 = interior, inner part; a bit more formal or technical
• 中 = inside, in, within; more common in everyday speech

So:

• 建物の内部は静かです。 sounds slightly more formal or written
• 建物の中は静かです。 sounds more everyday and natural in casual conversation

Both are understandable, but 内部 has a more formal feel.

Yes, absolutely.

• 建物の中は静かです。
  means nearly the same thing and is often more natural in everyday speech.

The difference is mainly tone:

• 内部 = more formal, more precise, sometimes more written
• 中 = more common and conversational

So if you are speaking casually, 中 is often the easier choice.

It is pronounced:

• たてもの の ないぶ は しずか です
• tatemono no naibu wa shizuka desu

A few notes:

• 建物 = たてもの
• 内部 = ないぶ
• は is written ha but pronounced wa when it is the topic particle
• 静か = しずか

So the full pronunciation is:

• tatemono no naibu wa shizuka desu

No. Japanese is normally written without spaces.

So this sentence would usually appear as:

• 建物の内部は静かです。

Textbooks and beginner materials sometimes add spaces to make the grammar easier to see, but in normal Japanese writing, you should not expect them.

Yes, it is natural, especially in a formal, descriptive, or written context.

Because 内部 is a somewhat formal word, the sentence sounds a little more formal than everyday casual speech. In ordinary conversation, many people would more naturally say:

• 建物の中は静かです。

But 建物の内部は静かです。 is still perfectly correct and natural.