Learn Hardcore Spanish (Spain): Ella apenas duerme cuando hay ruido en el edificio. - She barely sleeps when there is noise in the building.

More natural: Apenas duerme cuando hay ruido en el edificio.
With emphasis/contrast: Ella apenas duerme... (implies “She, unlike others, hardly sleeps...”)

What does “apenas” mean here? Could it also mean “as soon as”?

Here it means “hardly/barely.” In some contexts, especially in Latin America (and also understood in Spain), apenas can mean “as soon as”: Apenas llegó, se acostó (“As soon as she arrived, she lay down”). In your sentence there’s no second event, so only the “hardly/barely” meaning fits.

Can I say “No duerme apenas” instead of “Apenas duerme”?

Generally, no. Apenas already carries a negative/limiting sense, so adding no is usually considered redundant in standard Spanish. Better options:

Apenas duerme.
Apenas si duerme. (a bit more formal/literary)
Casi no duerme. (very common)

Where should “apenas” go? Can I say “Duerme apenas”?

Put apenas before the verb or right after the subject:

Natural: Apenas duerme... / Ella apenas duerme...
After the verb (Duerme apenas) sounds odd or ambiguous in most contexts.

Why is it “cuando hay” (indicative) and not “cuando haya” (subjunctive)?

Because it’s a habitual/general statement. With cuando, use:

Indicative for habits or facts: Duerme mal cuando hay ruido.
Subjunctive for future/unknown/pending events or commands: Dormirá bien cuando no haya ruido. / Cuando haya ruido, cierra la ventana.

What’s the difference between “hay ruido,” “hace ruido,” and “está ruidoso”?

Hay ruido = “There is noise” (noise exists/present in the environment).
Hace(n) ruido = “It/they make noise” (a source produces noise): Los vecinos hacen ruido.
Está ruidoso = “It’s noisy” (adjectival description), less common; more idiomatic is Hay mucho ruido or Es ruidoso (talking about a place/person generally).

Should it be “ruido,” “un ruido,” or “ruidos”?

All are possible, with nuances:

Hay ruido (uncountable, general background noise).
Hay un ruido (a specific, identifiable noise).
Hay ruidos (several distinct noises).
Your sentence uses the general, uncountable sense.

Why “en el edificio” and not “del edificio”? Do they mean the same?

En el edificio = location (“in the building”).
Del edificio = origin/source (“from the building”).
Use en if she’s inside and the building is the setting; use de(l) if you’re outside and emphasizing where the noise comes from: Hay ruido del edificio de al lado.

How is this pronounced in Spain?

Ella: the “ll” is typically a “y”-like sound [ʝ].
apenas: stress on -pe-: a-PE-nas.
duerme: “ue” as a diphthong; stress on duer-.
ruido: “r” is a single tap; “ui” sounds like
hay: like English “eye”; silent “h”.
edificio: in most of Spain, ci is [θ] (“th” in “think”): e-di-fi-THio [eðiˈfiθjo].

Why “duerme” and not “dorme”? What’s the verb pattern?

It’s the verb dormir, which has a stem change o → ue in the present tense for all forms except nosotros/vosotros:

duermo, duermes, duerme, dormimos, dormís, duermen.

Why “cuando” without an accent? When would it be “cuándo”?

cuando (no accent) is a conjunction/relative (“when”) in statements: ... cuando hay ruido...
cuándo (with accent) is interrogative/exclamatory in direct or indirect questions: ¿Cuándo llegas? / No sé cuándo llega.

Could I use “si hay ruido” instead of “cuando hay ruido”? What’s the nuance?

Yes:

Cuando hay ruido ≈ “whenever there is noise” (habitual trigger).
Si hay ruido ≈ “if there is noise” (conditional).
Both work; cuando sounds more like a regular pattern; si frames it as a condition.

Are there natural alternatives to say the same thing in Spain?

Yes:

Casi no duerme cuando hay ruido en el edificio.
Apenas puede dormir cuando hay ruido en el edificio.
Very idiomatic: No pega ojo cuando hay ruido en el edificio. (“She doesn’t get a wink of sleep...”)