I’ve written about typical things people miss in their renovation construction budget. There are also costs which we call unknowns. Unknowns are costs that we renovation contractors can sometimes predict but can only confirm by taking your home down to the studs and checking with local building bylaws. When going into a renovation, consider a contingency for unknowns. Value your contingency at approx 20% (above your renovation budget) for single family and 10% for condominiums. The older the building, the higher the percentage.