Why do firefighters break windows and cut holes in roofs when the fire is inside a building? 

It may appear that by breaking windows or cutting holes in roofs cause more damage than the actual fire.  However, internal building fires create a lot of heat and smoke and firefighters must remove the heat and smoke before they can get close enough to put out the fire.  Heat and smoke rise, so cutting a hole in the roof and breaking out windows in planned locations force smoke to vent upwards, allowing cool air to enter the building from below.  This is called “ventilation.”   This also improves visibility and lowers heat conditions for the firefighters inside, allowing them to quickly and safely extinguish the fire.  Heat and smoke can cause extensive damage; ventilation will actually reduce overall damage to a building and contents.