Driftskostnaden er høy.

Because -en is the usual definite singular ending for many masculine nouns in Norwegian. The base noun is driftskostnad (an operating cost / operating expense), and driftskostnaden means the operating cost.

So:

• driftskostnad = operating cost
• driftskostnaden = the operating cost

In this sentence, Norwegian uses the definite form directly on the noun instead of a separate word like English the.

The -s- is a linking element used in compounds. The word is built from:

• drift = operation, running
• kostnad = cost

Together, driftskostnad means operating cost. The s helps connect the parts smoothly. This is very common in Norwegian compound nouns.

You will see similar patterns in other words too, where an s appears between parts of a compound even though it is not a separate word by itself.

Because the noun here is singular, definite, and usually treated as a masculine noun, so the adjective appears in its basic form: høy.

Compare:

• en høy kostnad = a high cost
• kostnaden er høy = the cost is high
• et høyt nivå = a high level
• nivået er høyt = the level is high
• kostnadene er høye = the costs are high

So høy / høyt / høye changes depending on gender, number, and sometimes whether the adjective is used predicatively or attributively. In this sentence, høy is the correct form.

Because Norwegian usually puts definiteness on the noun itself. Instead of saying something like the cost with a separate article, Norwegian often uses a noun ending:

• kostnad = cost
• kostnaden = the cost

That is why driftskostnaden already includes the idea of the.

This is the normal Norwegian word order for a simple statement:

• subject + verb + complement

So here:

• Driftskostnaden = subject
• er = verb
• høy = adjective/complement

This is very similar to English word order in The operating cost is high.

If you turned it into a yes/no question, the verb would usually come first:

• Er driftskostnaden høy? = Is the operating cost high?

Er is the present tense of å være (to be). It is used the same way English uses is in sentences like The cost is high.

So:

• å være = to be
• er = is / are (present tense)

Since the sentence describes a state or quality of the cost, er is the natural verb.

Yes. Norwegian very often joins nouns together into a single compound word where English might use two words.

So English:

• operating cost

becomes Norwegian:

• driftskostnad

This is one of the most important habits to get used to in Norwegian. If you split compounds incorrectly, the result can look unnatural or even confusing.

Yes, in many contexts. Høy and høg are alternative forms, especially depending on written standard and style.

• In Bokmål, høy is very common.
• In Nynorsk, høg is common.

If you are learning standard Bokmål, Driftskostnaden er høy is the form you will most often see.

The plural would usually be:

• Driftskostnadene er høye = The operating costs are high

Changes:

• driftskostnaden → driftskostnadene
• høy → høye

That is because both the noun and the adjective must reflect the plural.

Yes, it sounds fairly neutral-to-formal and is especially natural in business, finance, administration, and technical contexts. The word driftskostnad belongs to practical or professional vocabulary more than everyday casual conversation.

In ordinary speech, people might sometimes choose a simpler or more specific phrase depending on the context, but this sentence is perfectly natural Norwegian.