After sin, con, tener, buscar, haber when the indefinite article (un or una) does not refer to a quantity or the numerical concept of one then you don't use use un or una....por ejemplo ¿Tienes novio? - Do you have a boyfriend? Hope this is clear.
The one form in English that occurs to me is my dad once said in English "We're moving house"... not a common thing in English but i have heard it.
meaning that in certain contexts, even English eliminates the article. Similarly, in American English, we say "I was in the hospital last week" whereas in England (I think) they would say "I was in hospital"... just interesting to realize that the language I supposedly know so well in fact has interesting variances I'd never thought about until I'm learning how this or that is said in Spanish. Fascinating
I think it is this case of not using: When not referring to a specific item, but rather the idea of the thing. E.g.:
¿Tienes coche? (Have you got a car?) Tengo un coche rojo. (I have a red car.)
So would it be correct to say "No vamos a tener una casa." too.... if so, does it change the meaning?
I'm not sure, but I think "No vamos a tener una casa." would mean something more like "We are not going to have one house", like how you have to say "No tengo ningún secadora" as opposed to "No tengo una secadora" in Spanish. As you probably picked up, the first sentence would literally, in English, mean "I do not have no dryer", while the second one would be correct in English, but in Spanish the second one would translate more into "I do not have one dryer", meaning you could have hundreds of dryers. It's just the way the language works. Of course, I'm not a native speaker, so feel free to correct me if I'm wrong about something.
Look for "Omission of un/una after other verbs", and you should be able to dial right into Butt & Benjamin saying:
Spanish does not use un/una after a number of verbs such as tener...comprar...sacar...buscar...llevar...haber..., when their direct object is a noun referring to things of which one would normally have or carry only one...Omission is normal when the object is something typical or expected...one would say María tiene perro...but María tiene una tortuga...
In the 5th edition the discussion is expanded and explains that un/una is used if the noun is qualified and not generic (llevaba una falda blanca, but eres [un] hombre respectable), may be understood to be other than generic (siempre escribe sus novelas con un bolígrafo, could mean any pen or a certain pen, but without 'un' it's any pen), is associated with a suppressed comment (tiene una casa...and some house it is), or its number greater than one would be normal (¿tienes UN hermano?).
if it isn't is just because DL is wrong, because "No vamos a tener una casa" is sentence with perfect sense
So if we wrote 'una casa' would it be wrong or would it just have a slightly different meaning?
It would mean "one house"
have a house - "tener casa" have one house - "tener una casa"
My understanding is that saying 'una casa' in this sentence would imply that there is a specific group of houses that you're talking about, and you're not planning on having one of them. But you're just saying that you're not going to have a house in general.
Perhaps the way to understand "casa" in this sentence is more akin to the English "home": We are not going to have a home. It's the concept of a home, not the actual house that is in question, so you don't need to put "una" there (which is a specific house).
I think the idea here could be, for example, that you are going on vacation, and you plan to stay in a hotel, when in the past you rented a house.
Alternatively, I have known consultants who travelled so much that they didn't have a fixed residence...they went to difference places each weekend (friends, relatives, vacation areas, etc.) and they literally did not have a house or a home for that matter.
Another possibility might be that you are getting married and plan to rent an apartment...so you will not have a house. In short, I think there are many situations where this sentence could make sense.
In doing a web search for "tener casa" I also came across articles discussing homelessness and alternatives to home ownership.
In all of these situations the sentence means that you will not have ANY house by not using "una" and the same concept is achieved in English while using "a" if it is said in the right context. As I understand it, in Spanish "No vamos a tener una casa" could mean "We are not going to have one house." which could mean that you plan on having MORE that one house in the right context In English we would always say "I am not going to have only (or just) one house!"
I believe the sentence "Let's not..." would require an imperative case, implying that the speaker wishes to action to be completed, whereas this sentence is simply stating a fact
My prof said to me, for exemple, dame un boligrafo or dame el boligrafo, but if you say dame boligrafos, it means a few or one or another. But if you use the two first exemples,it's because you know exactly what you want. And with the sentence with "casa", you don't know the house that they're talking about, so the article isn't necessary.