En el desván hace mucho calor en agosto, así que no subo casi nunca.

Desván means attic or loft space in a house.

In Spain, desván is a very natural word for the space under the roof where people might store things.

It is not always the same as ático:

• desván = attic / loft space
• ático in Spain often means a top-floor flat/apartment or penthouse

So in this sentence, desván is the right word if the idea is the hot storage space under the roof.

Because en shows location, while a / al usually shows movement toward a place.

• En el desván = in the attic
• Al desván = to the attic

Here, the first part is describing what the attic is like:

• En el desván hace mucho calor = It’s very hot in the attic

So we need en, because we are talking about where it is hot, not moving there.

This is a very common Spanish weather/temperature structure.

Spanish often uses:

• hacer calor = to be hot
• hacer frío = to be cold

Literally, hace mucho calor looks like it makes a lot of heat, but you should learn it as a fixed expression meaning:

• it’s very hot

This is standard Spanish, and you use it for general conditions:

• Hace calor en verano.
• Hace frío en invierno.

Because calor is a noun, and mucho can modify nouns.

• mucho calor = a lot of heat / very hot
• muy is used with adjectives or adverbs, not nouns

Compare:

• mucho calor = a lot of heat
• muy caliente = very hot

So hace mucho calor is correct, but hace muy calor is not.

They are related, but they are used differently.

• calor is a noun: heat
• caliente is an adjective: hot

In this sentence, Spanish uses the noun expression:

• hace mucho calor = it’s very hot

If you use caliente, you describe a noun:

• La sopa está caliente. = The soup is hot.
• El desván está caliente. = The attic is hot.

That said, for general weather or temperature conditions, hace calor sounds more natural than está caliente.

Así que means so, therefore, or so that’s why.

It links the cause and the result:

• En el desván hace mucho calor en agosto = It’s very hot in the attic in August
• así que no subo casi nunca = so I hardly ever go up there

It is similar to:

• por eso = that’s why / because of that
• entonces = then / so

But así que is a very natural connector for spoken and written Spanish.

Yes. Subir means to go up, to climb up, or to go upstairs/up there, depending on context.

Here, no subo means:

• I don’t go up
• more naturally in English: I hardly ever go up there

Because the sentence already mentions el desván, Spanish does not need to repeat it.

You could also say:

• no subo al desván casi nunca

That would make the destination more explicit:

• I hardly ever go up to the attic

Because Spanish often omits subject pronouns when they are not needed.

The verb form subo already tells you the subject is I:

• subo = I go up

So:

• no subo casi nunca = I hardly ever go up

Adding yo is possible, but it usually adds emphasis or contrast:

• Yo no subo casi nunca, pero mi hermano sí.
  • I hardly ever go up, but my brother does.

Without contrast, leaving out yo sounds more natural.

Casi nunca means almost never or hardly ever.

• casi = almost
• nunca = never

Together:

• casi nunca = almost never

So no subo casi nunca means:

• I hardly ever go up
• I almost never go up there

In natural English, hardly ever is often the best translation.

This is normal in Spanish.

Spanish often uses negative concord, which means more than one negative element can appear in the same sentence without “canceling” each other.

So:

• no subo nunca = I never go up
• no subo casi nunca = I hardly ever go up

In English, using two negatives this way is usually non-standard, but in Spanish it is correct and normal.

A useful rule:

• If the negative word comes after the verb, you usually keep no
• If the negative word comes before the verb, no is usually not used

Compare:

• No subo nunca.
• Nunca subo.

Both are correct.

The normal order is:

• no + verb + casi nunca

So:

• no subo casi nunca is correct

You can also say:

• casi nunca subo

That also means I hardly ever go up, and it sounds natural.

But:

• casi nunca no subo is not the normal way to say this

That word order would sound odd because the negatives are not arranged in the usual Spanish pattern.

Because the sentence describes a habitual action or general pattern, not something happening only right now.

• En agosto hace mucho calor = in August, it is very hot
• no subo casi nunca = I hardly ever go up

Spanish often uses the present tense for habits:

• En verano voy poco a la playa.
• Los domingos no trabajo.

So subo here means something like:

• I don’t usually go up
• I hardly ever go up

Yes, that is also correct.

You may hear:

• No subo casi nunca al desván
• No subo al desván casi nunca

Both mean basically the same thing.

The original sentence leaves out al desván because it is already understood from the earlier part:

• En el desván hace mucho calor...
• therefore no subo casi nunca

Spanish often avoids repeating information when the context is clear.

Desván is pronounced roughly des-VAHN.

The written accent shows that the stress falls on the last syllable:

• des-ván

Without the accent mark, Spanish stress rules would suggest a different pronunciation.

A few pronunciation notes:

• desván → stress on ván
• así → stress on sí
• agosto → stress on gos

The accent mark is there to show the correct stress, not because the vowel is “longer” in the English sense.