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Question DetailsAsked on 5/20/2014

A roofing contractor is telling me that I should have a ridge vent on my roof even though it is a cathedral ceiling

This is a cottage and there is no attic space between the drywall and the roof. The insulation is between the outside roof and the inside drywall ceiling. There are soffit vents along the front and back eaves. I have two round roof "vents" on the back slope of the roof. The cottage faces north. We do not use the cottage much in the winter but keep the heat about 50 degrees. One roofer is telling me no ridge vent. The other is telling me yes I need a Ridge vent but I need more round roof vents.

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5 Answers

2
Votes

The round roof vents are really useless if as you say you have drywall and then insulation before the underside of the roof sheathing. Hopefully you also have an airpace between the insulation and the roof sheathing. Since it is a seasonal cabin and not use much durring the winter you probably can get away without it though. The round vents are now just venting the rafter space they are directly over and a ridge vent would vent all that are inline with it. Generally the whole length of the roof up to about a foot or less of the gable ends. You have the soffit vent to provide airflo to the ridge vent and even if you do not have the required space above the insulation and the roof deck most of the moisture can find away out of the house. If you are in snow country make sure the roofer that wants to install the ridgevent uses the ones designed to stop wind driven snow.


Don

Answered 5 years ago by ContractorDon

1
Vote

Insulation right up against the roof underside is a no-no in most designs, certainly with a venitlated roof. However, to quote Popeye from your house's standpoint, I y'am what I y'am, so you work with what you have got. A Don said - go with ridge vent.


Ridge vent is far better for ventilation, cheaper than a bunch more round roof vents, and eliminates the leak potential from additional vent penetrations - so go with the ridge vent. Especially because it is cool and unused mcuh of the winter, be sure to get one with baffling to prevent snow blowing in if your winters have snow. Unless this is sprayed foam insulation, due to insulation settlement (especially if it gets wet) there will be at least a minimal airgap under the sheating to provide airflow space to help dry out any moisture that gets into your sheathing or insulation.


The only reason I could see needing more round roof vents is if there is blocking or someroof structure that blocks airflow to the ridge, then those specific locations might need roof ventsif the air cannot otherwise rise and escape.

Answered 5 years ago by LCD

1
Vote

I did not think about LCD's comment about the possibility of blocking in the rafter bays. Unless the contractor that is proposing extra round roof vents has used a thermal camera he would not know this and I would stay with the ridge vent. Even if one or two bays are blocked it will do the best job for you, especially since as I said before it is a seasonal cottage. If you were ever to retire and move in yearround then I would worry abut it.

That is the great thing about the ask a question feature, you can get advice from many with knowledge and each will catch what the other may have missed.

The other thing you have going for you that should ease your mind is since you leave the lodge with the heat on it is a very dry space since no cooking, showers and such are adding moisture.


Don

Answered 5 years ago by ContractorDon

0
Votes

Round turbine vents are THE last ditch effort to achieve the calcuated sq. in. venting required IF no other solution is present; these are only effective in open attic areas below. Silly waste of money if employed only to vent between two rafter-joists in most cases.


Ridge vents serve all rafter space they cross.

Even insulated rafter-joists USED to be required by VA/HUD/Code to have a 1" clear air space below roof decking. If not foamed (a contemporary practice) shut, then yes .. ridge vent is correctly prescribed. Go with this guy. Moisture damage from poor venting is not pretty & few like to fix it for you. It also attracts sugar ants, if not carpenter, leading to even more damage (look for frass).

Answered 5 years ago by tgivaughn

0
Votes

On the followup question posted asking why sugar ants are attracted (as noted in tgivaughn's reply) - damp (and also very hot - sap melting temperature) wood exudes sap and sap smell, which attracts sugar ants. Damp wood, for that reason or just because it smells like wood and the insects need dampish rather than totally dry wood to survive, also attracts certain species of termites, carpenter ants, post beetles, and such - along with the nasty mildew, mold, and fungal (dry and wet-rot) growth if the moisture is persistent and wet enough. So ALL wood roofs should be ventilated on the underside unless the attic is part of the "conditioned space" - included in the heat and air conditioned household space, though even then surface condensation and even frosting can be an issue in cold winter areas, or mildew/mold issues can occur if the air conditioning keeps the area too cold in the summer.

Answered 3 years ago by LCD




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