It rather depends on the house in question.

Many houses were actually based on Elizabethan (or earlier) constructions, only to be later remodelled, sometimes quite heavily. Osterley Park in west London being one such house, which still retains its original Tudor stable block, but the house itself was re-modelled in the mid 1700’s to its current form.

On the other hand, Scotney Castle in Kent was originally a moated castle built around 1180, and subsequently partly replaced with an Elizabethan house in the 1580’s within the original moated perimeter. In the 1780’s a new ‘castle’ was built on the hill overlooking the original, the latter being deliberately ruined to make an elaborate garden ornament(!)

The oldest parts of Knole, in Kent, just outside of London, date back to the 1450’s with much of the house actually dating to a century later and has remained substantially unchanged since then.

Perhaps one of the finest such houses is Blenheim Palace, built for the Duke of Malborough, ancestor of Winston Churchill, to commemorate the Duke’s victory at Blenheim. It dates back to 1722, the house itself covering an astonishing 7 acre plot. Try hoovering that on a Sunday morning, and you’ll understand why the owners of these houses tended to keep a very large number of servants on their payroll.

Some parts of Lanhydrock House dates back to the 1620’s but more or less the entire house as it currently stands is Victorian.

Polesdon Lacey in Surrey was a Regency villa, substantially remodelled in 1906 in Edwardian fashion but with Jacobean oak wood panelling and moulded ceilings giving a superficial impression of greater age.

Still later, Castle Drogo was only completed in the 1930’s, though never a very successful building – Designed by Edwin Lutyens, it was a castle in name only and suffers from damp ingress through its solid stone walls.