Hay humedad detrás del armario.

Because hay means there is / there are and is used to say that something exists or is present.

So Hay humedad detrás del armario means There is dampness behind the wardrobe.

You would use está if you were talking about the location of something specific and already identified. For example:

• La humedad está detrás del armario. = The dampness is behind the wardrobe.

In your sentence, the idea is more like there is some dampness present, so hay is the natural choice.

Hay is the present tense impersonal form of the verb haber.

It is very common in Spanish and means:

• there is
• there are

Unlike English, Spanish uses the same form hay for both singular and plural:

• Hay humedad. = There is dampness.
• Hay manchas. = There are stains.

In Spanish, abstract or uncountable nouns often appear without an article when you are talking about them in a general, indefinite way.

So:

• Hay humedad = There is dampness / moisture

This sounds natural because you are not referring to a specific, already identified patch of damp. You are just stating that dampness is present.

If you said la humedad, it would sound more specific:

• La humedad detrás del armario es preocupante.
  = The dampness behind the wardrobe is worrying.

Not always. Humedad can mean humidity, moisture, or dampness, depending on context.

In this sentence, dampness or moisture is the most natural translation, because it refers to a problem behind a piece of furniture.

Examples:

• Hay mucha humedad en el aire. = There is a lot of humidity in the air.
• Hay humedad en la pared. = There is dampness in the wall.

So the exact English word depends on the situation.

Because detrás is normally followed by de:

• detrás de = behind

So the full structure is:

• detrás de el armario

But in Spanish, de + el contracts to del:

• de + el = del

That is why you get:

• detrás del armario

This contraction is required.

Yes. Detrás de is the fixed expression, and the article changes depending on the noun:

• detrás del armario = behind the wardrobe
• detrás de la puerta = behind the door
• detrás de los libros = behind the books
• detrás de las cortinas = behind the curtains

Only de + el contracts to del. The others do not contract.

The accent mark shows where the stress goes: de-TRÁS.

Without the accent, it would not follow the normal stress pattern for Spanish spelling. The written accent helps you pronounce it correctly.

So say it with the stress on the last syllable:

• de-TRÁS

Armario usually means a wardrobe, cupboard, or cabinet, depending on context.

In a bedroom, armario often means wardrobe.
In a kitchen or elsewhere, it might be better translated as cupboard or cabinet.

So in this sentence, wardrobe is probably the most natural choice, but the exact translation depends on what kind of furniture is meant.

Because Spanish normally uses the definite article with nouns in cases where English often does not.

Here, del armario means behind the wardrobe. It refers to a specific piece of furniture, even if English might sometimes sound okay with less explicit wording in other contexts.

So Spanish prefers:

• detrás del armario

not:

• detrás de armario ❌

Yes. Tras can also mean behind, and in many contexts it is similar to detrás de.

So this is possible:

• Hay humedad tras el armario.

However, detrás de is often more common and clearer for learners. Also note the structure difference:

• detrás de + noun
• tras + noun

So:

• detrás del armario
• tras el armario

Both are correct.

A helpful approximation is:

eye oo-meh-DAD deh-TRAS del ar-MA-ryo

A more natural breakdown:

• Hay → like eye
• humedad → the h is silent
• detrás → stress on -trás
• del armario → in connected speech, it flows smoothly together

In Spain, armario is usually pronounced with a clear Spanish r and a vowels:

• ar-MA-rio

Usually humedad is treated as an uncountable noun, so hay would still stay the same:

• Hay humedad detrás del armario.

If you wanted to talk about several visible marks or patches, you might use a countable noun instead:

• Hay manchas de humedad detrás del armario.
  = There are damp patches behind the wardrobe.

Notice that hay still stays hay, because it works for both singular and plural.