Sonetaket er gult.

In Norwegian, the definite article is usually attached to the end of the noun instead of standing as a separate word.

So in this sentence:

• sonetaket = the sonetak
• the base indefinite form would be et sonetak

That -et ending is the definite singular ending for a neuter noun.

Er is the present tense of å være, which means to be.

So here:

• er = is

The sentence structure is therefore the same basic idea as English: [noun] + is + [adjective].

Because the noun is neuter singular.

In Norwegian, adjectives often change form to match the noun they describe. The adjective gul becomes gult when it matches a neuter singular noun.

So:

• gul = common gender singular
• gult = neuter singular
• gule = plural

That is why the sentence has gult.

Because gult is a predicative adjective here: it comes after er and describes the subject.

Predicative adjectives in Norwegian agree in gender and number, but they do not take the special definite adjective form.

Compare these:

• det gule sonetaket = the yellow sonetak

  • here gule comes before the noun, so it uses the definite form

• sonetaket er gult = the sonetak is yellow

  • here gult comes after er, so it only agrees as neuter singular

This is a very common point of confusion for learners.

The word order is:

• Sonetaket = subject
• er = verb
• gult = subject complement / adjective

So the pattern is:

subject + verb + adjective

That is very similar to English:

The sonetak is yellow.

The dictionary form would normally be the indefinite singular form:

• et sonetak

The sentence uses the definite singular form:

• sonetaket

So when you look up Norwegian nouns, you usually want the indefinite form, not the form with the attached definite ending.

Very often, yes. Many Norwegian adjectives change according to gender and number.

Using gul as an example:

• en bil er gul = a/the car is yellow
• et hus er gult = a/the house is yellow
• bilene er gule = the cars are yellow

So gult in your sentence is part of a larger pattern, not a special one-off form.

Yes, if the context already makes it clear what you are talking about.

• Det er gult = It is yellow
• Sonetaket er gult = The sonetak is yellow

The second version is more specific because it names the thing directly.