ir a or ir a la + noun (place)

Question

HELP: Translation of "He goes to his friend's house"

1 Va a la casa de su amigo

2 Va a casa de su amigo

Is the definite article "la" casa necessary or does it make no difference?

Are both correct with no subtle difference in meaning?

I have searched the internet and KWIZIQ and can find no answer.

Many thanks,

Ian

Answer

Hola Ian
The most common way to say this is "a casa de..." without the article. It is not incorrect to use "a la casa de..." though. When we may want to add the article is when you are not talking about someone's house as their permanent residence, for example:
Voy a la casa de la playa de Miguel. - I'm going to Miguel's beach house.
Or for example when it's someone different to someone you know well, more of a distant acquaintance:

Voy a la casa de unos amigos de mis padres. 
I'm going to some friends of my parents' house.

Saludos
Inma