As with any house, the cost of a four-bedroom home in Ireland is driven by floor area, build form, specification and site conditions rather than by bedroom count. Larger houses usually mean more floor area, more bathrooms and larger heating and ventilation systems, all of which increase both the construction cost and the compliance work needed.
A four-bedroom house typically has a larger gross floor area than a three-bedroom equivalent, and cost scales broadly with area. However, the increase is not purely linear: extra bathrooms, larger spans, bigger heating systems and more extensive external works all add cost, while some fixed costs such as connections and site setup do not increase.
Because larger dwellings have a bigger heat loss envelope, meeting Part L of the building regulations may require a higher specification of insulation, glazing and renewables, which should be priced at design stage rather than discovered during construction.