House cards are available at all times EXCEPT during combat.
Not entire combat. Just for a moment (really a moment) when players are choosing cards to revealing them.
The rules say not available when players are choosing House cards. In practice, not available to be viewed from the moment when the player picks them up to select their house card until after combat cards are revealed for that combat.
"Note: All House cards, whether available or used (i.e.,
discarded), are public knowledge. As such, a player’s discard pile
or hand may be examined by others players at any time except
during Step 3 of combat."
"The contents of a player’s House card discard pile and his hand of
House cards is open information except when players are choosing
House cards during Step 3 of combat."
Errata and FAQ version 1.0:
"Hidden information of discarded House cards: All
players’ discarded House cards are always considered
open information. A player’s House card discard pile
can always be reviewed by any other player at any
time, including during all steps of combat."