Can you make your own roof vents?
Short answer. You can, but you usually should not: a homemade roof vent has no tested net free area rating, no proven way to shed wind driven rain, and no manufacturer instructions for code compliance. The parts of a vent system that are legitimately built on site are the ridge slot, intake openings in soffits, and custom sheet metal vents made by a skilled metal fabricator.
Why manufactured vents are the norm
- Rated airflow. Store vents are labeled with net free area, which you need to size the system to code.
- Weather protection. Baffles, louvers, and filters are designed and tested to keep out wind driven rain and insects. A plywood box with a screen rarely does both.
- Flashing flange. Factory flanges are sized to weave into shingle courses. Homemade flashing often relies on caulk, which fails in Georgia sun.
- Code and warranty. The code calls for vents installed per the manufacturer's instructions, and shingle warranties assume proper ventilation products.
What can be built on site
- The ridge slot under any ridge vent is cut by the roofer.
- Soffit vent openings can be cut into wood soffits and covered with screened vent strips or louvered covers.
- Rafter baffles can be made from rigid foam or cardboard to keep insulation out of the eaves.
- Custom metal vents, such as copper or painted steel vents for historic homes or unusual roof shapes, can be fabricated by a sheet metal shop with proper flashing and screens.
If you are tempted to improvise
The usual motivation is an odd vent size or a hard to find replacement hood. Most standard vents fit common openings, and a roofer can resize the opening and reflash it. See roof ventilation basics and roof flashing explained.