I am sure the plumber put it at that height for the inspector.
													
																	Plumbing vent pipe height above roof. 
									
		
	
	
		
	
	
		
	
	
		
	
																	Open vent pipes that extend through a roof shall be terminated at least 6 inches 152 mm above the roof or 6 inches 152 mm above the anticipated snow accumulation whichever is greater except that where a roof is to be used for any purpose other than weather protection the vent extension shall be run at least 7 feet 2134 mm above the roof. 
																	All open vent pipes that extend through a roof shall be terminated at least number typically 6 inches mm above the roof except that where a roof is to be used for any purpose other than weather protection the vent extensions shall be run at least 7 feet 2134 mm above the roof. 
																	You are letting air into the plumbing system of the house. 
																	On a sink that would be either the rim or overflow hole. 
															
													
									
		
	
	
		
	
	
		
	
	
		
	
																	Above the roof plumbing vent height. 
																	I have a main vent and a sink vent and both are only 6 high above the roof. 
																	But it is on the edge of the roof so that should not be a problem. 
																	A note on the main drain. 
															
													
									
		
	
	
		
	
	
		
	
	
		
	
																	The 6 you describe should be just fine. 
																	All open vent pipes that extend through a roof shall be terminated at least 6 inches 152 mm above the roof and not less than 2 inches 51 mm above the invert of the emergency overflow except that where a roof is to be used for any purpose other than weather protection the vent extensions shall be run at least 7 feet 2134 mm above the roof. 
																	A vent stack is not like a chimney which requires 2 higher than any roof within 10. 
																	However it needs to be at least six inches above your fixture s flood level to keep from getting wet. 
															
													
									
		
	
	
		
	
	
		
	
	
		
	
																	Each vent pipe or stack shall extend through its flashing and shall terminate vertically not less than 6 inches 152 mm above the roof nor less than 1 foot 305 mm from a vertical surface. 
																	Upc i 906 1 and 906 2. 
																	You should be able to cut that vent shorter but stay above the roof line. 
																	Open vent pipes that extend through a roof shall be terminated at least 6 inches 152 mm above the roof or 6 inches 152 mm above the anticipated snow accumulation whichever is greater except that where a roof is to be used for any purpose other than weather protection the vent extension shall be run at least 7 feet 2134 mm above the roof. 
															
													
									
		
	
	
		
	
	
		
	
	
		
	
																	Vent pipes should extend to outdoors above the building roof and should terminate vertically not less than 6 above the roof surface nor more than 24 and must be at least 12 from any vertical surface such as a nearby sidewall. 
																	The slope is about 4 high for every 12 horizontal.