Learn Hardcore Japanese: tonari no heya ha urusai desu.

Japanese i-adjectives like うるさい already function as predicates (they contain the idea of “to be”). So 隣の部屋はうるさい literally means “As for the room next door, (it) is noisy,” without needing a separate “is” verb.

What does の do in 隣の部屋?

の links two nouns, making the first one modify the second. 隣の部屋 = “the room next (to us)” / “the room next door.” Think of it as “adjacent’s room” turning into “adjacent room.”

Why is は used here instead of が?

は marks the topic and often adds a contrastive feel: “As for the room next door, it’s noisy (others may not be).”
が identifies or answers “which one”: 隣の部屋がうるさいです is natural when specifying which room is noisy (e.g., in answer to “Which room is noisy?”).

Is は pronounced “wa”? Why?

Yes. The topic particle is written は but pronounced wa. It’s a historical spelling convention.

Can I drop です? What changes?

Yes. With i-adjectives, です adds politeness but isn’t required.

Polite: 隣の部屋はうるさいです。
Casual: 隣の部屋はうるさい。
Soft/explanatory: 隣の部屋はうるさいんです。 Don’t use だ with i-adjectives.

Why can’t I say うるさいだ?

だ attaches to nouns and na‑adjectives, not i‑adjectives. For i‑adjectives, use the adjective as-is, optionally with です for politeness: うるさい（です）. You can say うるさいんだ／うるさいんです (explanatory tone), but not うるさいだ.

Does 隣の部屋 mean “my neighbor’s room”?

It means “the room next door.” If you specifically mean “the neighbor’s (person’s) room,” say 隣の人の部屋. In apartments, 隣の部屋 usually implies the adjacent unit.

How do I make it negative or past?

Present: うるさい（です） = is noisy
Negative: うるさくない（です） / more formal うるさくありません
Past: うるさかった（です）
Past negative: うるさくなかった（です） / more formal うるさくありませんでした

How do I say “The room next door is quiet” instead?

Use the na‑adjective 静か:

Polite: 隣の部屋は静かです。
Casual: 隣の部屋は静かだ。 Note the difference: 静か (na‑adj) needs だ／です; うるさい (i‑adj) does not.

Can I say 隣に部屋はうるさいです?

No. Use の for “the room next door”: 隣の部屋はうるさいです。 Use に for location in existence sentences: 隣に部屋があります (There is a room next door).

Does うるさい also mean “annoying”?

Yes. うるさい can mean “noisy,” “annoying,” “fussy,” or “overly particular.” For example, あの人はうるさい can mean “That person is a pain/fussy,” depending on context. Shouted as うるさい！, it can mean “Be quiet!/Shut up!”

How can I soften this complaint?

Add softeners like ちょっと or ね, or refer to the sound rather than accusing the room:

隣の部屋はちょっとうるさいですね。
隣の部屋からの音が少し大きいようです。
隣の部屋の音が気になります。

Why are there spaces between the words here?

Spaces were added for learners. Ordinary Japanese writing doesn’t space words: 隣の部屋はうるさいです。