Gable vents help heat escape and help keep condensation from forming in the attic during winter months.
The use of ridge vent has increased greatly during the past ten years and when used with a soffit vent or vented drip edge, it is a very effective means of venting rafter bays, especially in cathedral ceiling areas. An air space in the rafter bay must be provided for full airflow. There are various styrofoam vent channels that, installed in the rafter bay, keep the insulation from fully filling the bay, to allow for air space. This can help keep condensation from forming on exposed roof nail ends and dripping onto the ceiling materials below during winter months.
When building a house or addition with a crawl space underneath, make sure to install a vapor barrier to prevent moisture infiltration into the floor system.
Welding inside of a shop or garage can create fumes. But they can easily be removed from the area by using industrial-type fans, or you can make your own from a recycled forced-air furnace fan. Check with the installers in your area for used fans; the cost may not be more than about $25, or they might even give you one. Cover the intake and all moving parts with heavy metal mesh, and run the power cord through a switch for easy on-off control.