kekkou furui tatemono desu ga, naka wa omotta yori kirei deshita.

It’s quite an old building, but the inside was cleaner than I expected.

Breakdown of kekkou furui tatemono desu ga, naka wa omotta yori kirei deshita.

• は: topic particle
• です: to be
• より: comparative particle
• が: conjunction particle

Questions & Answers about kekkou furui tatemono desu ga, naka wa omotta yori kirei deshita.

What does けっこう mean here?

Here, けっこう means fairly, quite, or rather.

So けっこう 古い 建物 means a საკმაოდ old building / a fairly old building.

A useful thing to know is that けっこう can have different meanings depending on context. For example, it can also mean fine, all right, or even no thank you in other situations. But in this sentence, it is simply an adverb modifying 古い.

Why is it 古い 建物 and not 古な 建物?

Because 古い is an i-adjective.

In Japanese, i-adjectives directly modify nouns:

• 古い 建物 = an old building
• 新しい 車 = a new car

You do not change 古い into 古な because な is used with na-adjectives, not i-adjectives.

What is the role of ですが in this sentence?