http://en.wikipedia.org/wiki/Mews

4. DESIGN STANDARDS FOR MEWS HOUSES

Design of mews houses will require to meet all the under-noted criteria:

(a) The scale and massing of any new development will require to be subordinate to the surrounding properties and constructed in the style of a mews house up to a maximum height of two storeys, (in some sensitive locations a maximum height of one and a half storeys, or even one storey, may be considered more appropriate);

(b) If the building adjoins, or is in proximity to, an original mews house or group of mews houses that pre-date 1919, then it would be appropriate to form a new mews building up to, but not exceeding, the dimensions of the original mews, provided that there is no adverse effect on neighbouring properties;

(c) All new buildings shall have pitched roofs, clad in slate, with gable ends;

(d) All walls facing on to the lane shall be finished in natural stone in conservation areas. Whitewashed walls could be considered acceptable in less sensitive locations, (or where this style of mews house predominates locally);

(e) Second floor accommodation, if proposed, shall be lit by conservation-style rooflights, rather than dormers;

etc.

Подводя итог - mews house - не выше двух этажей. Terraced house - как правило 4-5 этажей.