Het taxatierapport onderbouwt de WOZ-waarde.

Because Dutch nouns have grammatical gender/common article patterns:

• rapport is a het-word, so the compound becomes het taxatierapport
• waarde is a de-word, so the compound becomes de WOZ-waarde

A useful rule is: in a Dutch compound noun, the last word determines the article.

So:

• taxatie + rapport → taxatierapport → article comes from rapport → het
• WOZ + waarde → WOZ-waarde → article comes from waarde → de

It is a compound noun:

• taxatie = valuation, appraisal
• rapport = report

Together, taxatierapport means appraisal report or valuation report.

Dutch makes compound nouns very freely, much more than English does. Where English often uses two words, Dutch often joins them into one:

• belastingaangifte = tax return
• ziekenhuis = hospital
• taxatierapport = appraisal report

Onderbouwt is from the verb onderbouwen, which means:

• to substantiate
• to support with evidence
• to justify
• to back up

In this sentence, it means that the appraisal report provides the basis or evidence for the WOZ value.

So onderbouwen is stronger than just support in a vague sense: it usually suggests evidence, reasoning, or justification.

Because the subject is singular: het taxatierapport.

In the present tense, Dutch regular verbs usually work like this:

• infinitive: onderbouwen
• stem: onderbouw
• ik onderbouw
• jij onderbouwt
• hij/zij/het onderbouwt

Since het taxatierapport is a third-person singular subject, the verb is onderbouwt.

Yes. This is standard Dutch main-clause word order:

• Het taxatierapport = subject
• onderbouwt = finite verb
• de WOZ-waarde = object

So the structure is essentially:

Subject + verb + object

That is the normal pattern for a simple Dutch statement.

WOZ is a Dutch abbreviation for Waardering Onroerende Zaken.

It refers to the official valuation of real estate/property in the Netherlands, often used for municipal taxes and related matters.

For a learner, the important thing in this sentence is that WOZ-waarde is a fixed Dutch term meaning the official property value used for tax purposes.

Because Dutch normally uses a hyphen when an abbreviation is attached to another noun.

So:

• WOZ-waarde
• btw-tarief
• tv-programma

Without the hyphen, the word would be harder to read. The hyphen is the standard spelling here.

Because only the abbreviation WOZ is capitalized. The noun waarde is just a normal common noun, so it stays lowercase.

That is standard Dutch spelling for compounds with abbreviations:

• WOZ-waarde
• cao-onderhandeling
• EU-land

Yes, that is possible, but the nuance is a little different.

• onderbouwt = substantiates, provides evidence for, justifies
• ondersteunt = supports

In formal or administrative language, onderbouwt is often better because it suggests a stronger evidential basis. A taxatierapport does not just vaguely support a value; it is used to justify/substantiate it.

It is singular.

You can tell from:

• the article het
• the singular verb onderbouwt

The plural would be:

• de taxatierapporten
• De taxatierapporten onderbouwen de WOZ-waarde.

A natural past-tense version is:

Het taxatierapport onderbouwde de WOZ-waarde.

That uses the simple past of onderbouwen:

• present: onderbouwt
• past: onderbouwde

You could also use a perfect tense, depending on context:

Het taxatierapport heeft de WOZ-waarde onderbouwd.

Usually letter by letter, in Dutch:

• W = wee
• O = oo
• Z = zet

So WOZ is pronounced roughly as wee-oh-zet, but with Dutch sounds.

Yes. That is completely normal.

In this sentence:

• Het taxatierapport = subject
• onderbouwt = verb
• de WOZ-waarde = direct object

So Dutch allows:

• iets onderbouwen = to substantiate something

Examples:

• Hij onderbouwt zijn standpunt.
• De cijfers onderbouwen de conclusie.
• Het taxatierapport onderbouwt de WOZ-waarde.

No extra preposition is needed.