老式房屋设计。

old fashioned apartment structure

a more colloquial (British) way of expressing the concept. I think you might be wise to avoid the word "old", because it doesn't mean old as in 100-year ago. There's an ambiguity in the English "old" which is not there in the Chinese.

"Our new flat is just a bog-standard shoebox, but it's quite big, and it's close to my mum's."

or...

is a box, but a big box
isn't architecturally exciting

I would just say 'old fashioned house' in English.
我们的新房也是"老户型"，但是不算小，离我娘家很近。
(Our new house is also an old fashioned house, but I wouldn't regard it as small, and it's very close to my mum's house.)

Our new place is an older apartment, but it's not particularly small, and it's pretty close to my mom's.

Instead of going with 'old' perhaps you could go with 'older', suggesting that the apartment was older than the surrounding apartments, or appartments in surrounding buildings.

I've dropped the 型, which could be translated as fashioned (in this context), or model/type, as 'older fashioned apartment' sounds a bit long-winded to me. I think 'older appartment' works fine in this context. Though, it may be helpful to know if the new house is a single standing structure, or is actually part of a block of apartments.

我同意Phil Hand說的關於用'old'一詞的問題。'dated'在這裡更恰當一些。
’老戶型‘在中國住房裡，具體指的是’大臥室，小廳，小廚衛‘的格局。以前的住房裡幾代同堂的情況比較多，一般臥室設計得比較大，而起居室/廳 設計得很小，而且通常廳是暗暗的。現在的’新戶型‘不是這樣的了。更多地考慮了’社交‘的問題。而且使用者相對結構比較單一（與父母或祖父母同住的少）。新戶型都是臥室小，廳大。