There’s always the dilemma with extending an existing property over whether the extension should match the existing or contrast with it. How does the architect decide? Which is best? The answer invariably comes from the client; it is their personal preferences that generally sets whether the new part is to blend’ with the traditional or be contemporary and contrast with it. The planners can also have a big say in how they want the building to look unfortunately (more below on this)

Me? I’ve done and happy doing both. See opposite the modernist contemporary extension to a traditional rural two storey farmhouse in County Roscommon:

To this two storey extension (currently under construction) and proposed elevation:

Even this ‘matching’ extension is set back from the existing house to create a separation of the two buildings; there is also a greater contrast at the rear of the dwelling.

Each method has its own merits:

• Contrasting the new separates the old from the new, making the building easier to ‘read’ historically
• Matching the new blends the new in with the old and is probably a more ‘planning friendly’ route. Luckily the planning authorities where I work are reasonably progressive and can understand both sides to the argument and the County Mayo guide for dingle rural houses encourages contemporary design at the correct scale.
• But what was I taught at college? As discussed previously the design ‘Bible’ Responsive Environments by Bentley Alcock Murrain McGlynn Smith we used at Oxford Poly (now Brookes) was written by the tutors and is still in print HERE at AMAZON drew pn contextual cues from other adjacent buildings. The purpose of which was to ‘unite adjoining buildings of a disparate character’ with a contemporary version which neither exactly or contrasted completely with the surrounding architecture. This is illustrated brilliantly in the image below from the book showing a development in Bruges:
  

  Image from Responsive Environments

  What do you think? Comments welcome…