One of the costs of renovating is to allow for alterations within the existing footprint – such as modifications of the floor plan, partial demolition, roof framing changes, re-allocation of spaces (say bathrooms) and creation of openings in the walls of an existing home.
None of these alterations add floor area to a building so they could be overlooked as cost items when estimating the cost of a home renovation project. This is especially likely if you estimate project cost on the basis of how many extra square metres of building you’re home is going to have!
Estimating on a per square metre basis can account for the cost of new construction, but some allowance needs to be made for alteration works as well. The only way to do this with any certainty is to base your estimate on a design so the extent of any alteration work is clear, particularly for roof/wall alterations and new services which are – in most cases – out of sight and out of mind.
Archicentre Australia architects can assist by preparing a tailored design feasibility sketch and an opinion of probable cost for you – see the sample report in the Property Design – Residential Renovation Feasibility page.
By the way, so many homes have been renovated during the last 30-40 years that they can often be big enough to meet today’s needs. They may need some alterations, but working within the shell of an existing building – while it will cost some money – will be less expensive than adding extra space.
Think about it before you decide to make the building bigger; it may just need altering.