Byggesøknaden må signeres.

Byggesøknaden is a compound noun:

• bygge = build / building
• søknad = application
• -en = the definite singular ending for many masculine nouns

So:

• byggesøknad = building application / construction application
• byggesøknaden = the building application

A very common feature of Norwegian is that nouns are often joined into one word like this.

Because Norwegian normally writes compound nouns as one single word.

So English often has:

• building application
• house door
• school bus

But Norwegian usually makes these into compounds:

• byggesøknad
• husdør
• skolebuss

This is very normal and something English speakers need to get used to.

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

So:

• en byggesøknad = a building application
• byggesøknaden = the building application

The ending -en already contains the idea of the, so you do not add a separate article before it.

Må means must or has to.

In this sentence, it expresses necessity:

• Byggesøknaden må signeres.
• The building application must be signed.

So it tells us that signing is required.

After modal verbs in Norwegian, you normally do not use å.

Common modal verbs include:

• må = must
• kan = can
• skal = shall / will / is going to
• vil = will / want to
• bør = should

So you get:

• må signeres
• kan gjøres
• skal sendes

Not:

• må å signeres

This is similar to English, where we say must sign, not must to sign.

The -s form here marks the passive.

Compare:

• De signerer byggesøknaden. = They sign the building application.
• Byggesøknaden signeres. = The building application is signed.
• Byggesøknaden må signeres. = The building application must be signed.

So signeres means something like be signed rather than signs in an active sense.

This is a very common Norwegian passive pattern.

After må, it functions as the verb that follows a modal, so learners often think of it as the passive equivalent of an infinitive.

The important practical point is this:

• after a modal like må, Norwegian uses the verb without å
• in the passive, that often appears as an -s form

So in this sentence, må signeres is best understood as:

• must be signed

You do not need to worry too much about the label at first; what matters is that signeres here is the passive form used after må.

The sentence does not say.

That is exactly what the passive does here: it focuses on the building application, not on the person doing the action.

So:

• Byggesøknaden må signeres. = The building application must be signed.

But we are not told whether it must be signed by:

• the applicant
• the owner
• an architect
• an official

If Norwegian wanted to say who does it, it could add that information separately.

Yes. That is also possible.

Two common passive patterns are:

• må signeres
• må bli signert

Both can mean must be signed.

Very roughly:

• må signeres is compact and very common in formal or administrative language
• må bli signert can sound a bit more explicit about the process of being signed

In many real situations, both are acceptable, but må signeres is especially typical in official written Norwegian.

This is normal Norwegian main-clause word order:

• subject: Byggesøknaden
• verb: må
• then the rest: signeres

Norwegian is a V2 language, which means the finite verb is usually in the second position in a main clause.

So here:

1. Byggesøknaden
2. må

That is exactly what we expect.

Yes, but the meaning changes slightly.

• Byggesøknaden må signeres. = The building application must be signed.
• En byggesøknad må signeres. = A building application must be signed / A building application has to be signed.

The first refers to a specific application.
The second is more general or introduces one not previously identified.

Yes, it sounds fairly formal or administrative, mainly because of:

• the noun byggesøknaden
• the passive construction må signeres

This kind of phrasing is very common in:

• forms
• instructions
• emails from offices
• official websites
• legal or bureaucratic contexts

In everyday speech, people might sometimes say something more direct, depending on context.

An active version would name the person or group doing the signing. For example:

• Du må signere byggesøknaden. = You must sign the building application.
• Søkeren må signere byggesøknaden. = The applicant must sign the building application.

The passive version avoids mentioning who does it and keeps the focus on the document itself.

Yes, it comes from the same basic idea.

• å bygge = to build

In compounds, the first element often gives the type or purpose of the second noun. So byggesøknad is an application related to building/construction.

English does something similar in expressions like:

• building permit
• driving licence
• swimming pool

Norwegian just tends to combine the parts into one written word more often.