Holes cut in rafters to aid venting

I'm wondering if I can cut holes through my rafters to aid in cross venting between the "cells?" I'm adding a room above my garage and it will have the sheet rock nailed to the bottom of the rafters so I need some air flow but can't do ridge vent and don't want 40 vents on my roof - one for each rafter cell. Does anyone know the specs for drilling holes through my 2X8 rafters?

 

Don't do that, you will weaken the roof by doing this.

 

Its a fairly common practice for cathedral ceilings and hipped roofs.
One ventilation manufacturer recommends 6 - 1" holes in each rafter.
Do a web search for venting hipped roofs. You will most likely find more.

Good Luck!

 

Do not be cutting holes in fyour trusses. By doing so it will weaken the rafters. In fact most building codes across the country forbid any holes drilled in any trusses. You do not need a soffit vent between every truss. You could put on a gable vent on each end and solve the problem. For instance, I have a 3 car garage, all insulated, sheetrocked, with a 75000 btu furnace. I do not have any vents and really do not need any. No reason for any. Alot of this vent stuff is hype by the mfg. to get you to buy vents. The bad part is people believe them. Just my thoughts.

 

Trusses should not be modified as they are pre-engineered. Rafters however are different.

Excerpt from Uniform Building Code...."Holes bored in rafters or ceiling joists shall not be within 2 inches (51 mm) of the top and bottom and their diameter shall not exceed one third the depth of the member.