A professional contractor such as Affordable Quality Roofing is able to measure your home properly to determine and recommend the type and amount of ventilation your home needs. There are a number of factors to take into account when determining the type and volume of ventilation your roof needs, and whether the ventilation you already have is sufficient or if you need extra ventilation added when the roof is replaced. Your roof and insulation will not function properly without sufficient ventilation, so be sure to ask your roofing contractor if you have enough, and if you need more.