Η εξωτερική θερμομόνωση είναι ενεργειακή παρέμβαση.

Η is the definite article meaning the.

Here it is:

• feminine
• singular
• nominative

It matches θερμομόνωση, which is a feminine singular noun.

So:

• Η θερμομόνωση = the insulation
• Η εξωτερική θερμομόνωση = the external insulation

Greek articles change form much more than English the does.

Because εξωτερική is an adjective agreeing with θερμομόνωση.

Since θερμομόνωση is:

• feminine
• singular
• nominative

the adjective must also be:

• feminine
• singular
• nominative

That is why you get:

• masculine: εξωτερικός
• feminine: εξωτερική
• neuter: εξωτερικό

In this sentence, the feminine form is required.

Θερμομόνωση is a feminine noun meaning thermal insulation.

A learner may also notice that it is a compound word:

• θερμο- relates to heat
• μόνωση means insulation / isolation

So the word literally has the idea of heat-insulation.

It is one single noun, not two separate words.

Greek often forms technical or formal terms as compound words, where English might use two words or a phrase.

So:

• thermal insulation in English becomes
• θερμομόνωση in Greek

This is very common in Greek, especially in scientific, technical, administrative, and formal vocabulary.

Είναι is the present tense, 3rd person singular form of είμαι = to be.

It means is here.

So:

• Η εξωτερική θερμομόνωση είναι... = External thermal insulation is...

Because the subject is singular, Greek uses singular είναι.

Greek often omits the indefinite article where English would use a/an.

So:

• είναι ενεργειακή παρέμβαση literally looks like
• is energy intervention

but naturally means

• is an energy intervention or more idiomatically
• is an energy-efficiency measure / intervention

You could also say:

• είναι μια ενεργειακή παρέμβαση

Here μια means a / one.
Adding μια makes the indefiniteness more explicit, but it is often not necessary.

Because παρέμβαση is a feminine noun, and ενεργειακή is an adjective describing it.

So they must agree in:

• gender
• number
• case

That gives:

• ενεργειακή παρέμβαση = an energy-related intervention

If the noun were masculine or neuter, the adjective would change too.

The main nouns here are in the nominative.

• Η εξωτερική θερμομόνωση is the subject, so nominative.
• ενεργειακή παρέμβαση comes after είναι and is also in the nominative, because Greek typically uses the nominative after the verb to be when identifying or classifying something.

So this is a normal X is Y structure.

Not completely. Greek word order is more flexible than English word order.

The neutral, straightforward version is:

• Η εξωτερική θερμομόνωση είναι ενεργειακή παρέμβαση.

But Greek can reorder parts for emphasis, for example:

• Ενεργειακή παρέμβαση είναι η εξωτερική θερμομόνωση.

That would put more emphasis on what kind of thing it is.

Even though Greek is flexible, the original version is the most natural for a plain statement.

Yes. In Greek, adjectives often come before the noun they describe, especially in straightforward formal writing.

So:

• εξωτερική θερμομόνωση
• ενεργειακή παρέμβαση

That is very normal.

Greek adjectives can sometimes come after the noun, but that often changes the style, emphasis, or tone. For a standard technical statement like this, adjective + noun is the expected pattern.

A rough pronunciation guide is:

i eksoterikí thermomónosi íne energiakí paremvási

A few helpful points:

• η is pronounced like ee
• ξ sounds like ks
• θ sounds like the th in think
• αι in είναι is pronounced e
• μβ in παρέμβαση is often pronounced like mv

The written accents show which syllable is stressed:

• εξωτερική
• θερμομόνωση
• είναι
• ενεργειακή
• παρέμβαση

Yes, it sounds natural, especially in:

• technical language
• construction
• architecture
• energy-efficiency discussions
• government or policy documents

Παρέμβαση literally means intervention, but in this context it often refers to a measure, action, or improvement made to a building.

So depending on context, a more natural English rendering might be:

• an energy intervention
• an energy-efficiency measure
• an energy-related improvement

Usually, for a general statement like this, Greek prefers the article:

• Η εξωτερική θερμομόνωση είναι ενεργειακή παρέμβαση.

Without Η, the sentence would sound less natural in standard usage, especially with a concrete noun phrase like this.

Greek uses the definite article much more often than English does, so English speakers often underuse it at first.