Depending on your house interior and roof framing design, cathedral ceiling ventilation can be treated as an independent or attic ventilation related condition.
Majority of problems with cathedral ceiling ventilation develop in structures where the ceiling framing, and roof framing are the same. What it means, that there’s no accessible attic between the ceiling and roof surface, only narrow, rafter / truss space which should be partially filled with insulation. Sometimes there’s partial attic, and you can see / look into the cathedral ceiling structure from accessible part.
“Safer” (from the cathedral ceiling ventilation point of view) types of cathedral ceilings are the ones, which have a separate from roof framing structure, which allows air to circulate more freely (image). But let’s talk about this first type. Depending on severity of the cathedral ceiling ventilation problem, you may, or may not see its consequences for a long time.
Some of the conditions, you’d be noticing are:
- roof surface deformation above the cathedral ceiling section of your house,
- moisture stains on cathedral ceiling surface,
- moisture dripping from recessed light fixtures or electrical boxes on the cathedral ceiling,
- moisture / water stains stains along the top section of the window located in the wall supporting lower end of cathedral ceiling,
- dark stains (ghost marks).
All of the above conditions are curable, but depending on the extent of damage, it might get expensive (lack of proper attic ventilation is a main cause of mold growth and ice damming). Basic principle for cathedral ceiling ventilation is pretty much the same as for any attic with a “twist” to it.
To prevent possibility of moisture condensation, you need constant air movement between the bottom and top of the roof, through the space between rafters / above the insulation layer installed on top of the finished ceiling. “Twist” is for extreme conditions, which in regular attic are easier to spot, and much cheaper to correct.
1. Insulation - if properly installed between the rafters, on top of the ceiling material (drywall, plaster, paneling sheets, etc.), there should be approximately 2″ of space left above it, which allows air to flow between the bottom and top of the roof. Ideal installation would also include vent chutes / baffles, secured to roof decking, which ensures proper insulation spacing and undisturbed air flow.
Check here your attic insulation amount recommendations.
Contractors who misunderstand principles of proper attic ventilation, never use vent chutes, use more or thicker insulation than required, packing it tightly into the rafter space, blocking completely air flow, and causing… costly “headaches”.
2. Roof bottom vents -because each rafter space is like a small, individual attic, it needs fresh air feed, which in most cases comes from roof overhang – soffit. With a variety of roof soffit designs, it is hard to suggest any particular type of vent, but continues one would probably cover all possibilities and ensure that each rafter space will receive fresh air. If there’s no overhang / soffit, “vented drip edge” can be utilized.
3. Roof top vents - depending on how your cathedral ceiling ends, different types of vents would be required: - if it goes all the way to the roof top / ridge / peak, where other side of cathedral ceiling starts, the only type of vent that should be installed is a ridge vent .
Some roofers prefer static roof louver vents, and if installed between every two rafters, it will do the job – but it doesn’t look nice, especially when you have a long ridge line. If your cathedral ceiling vents into an open attic, any type of properly installed vent will do, as long as it provides adequate output.
