Adding a ridge vent without vented soffits
My parents have a 1970s brick ranch with a basic 5/12 Gable roof with 12″ overhangs. They will be getting a new roof in the coming months and I am wondering if there is anything wrong with adding a ridge vent knowing they have no soffit vents.
There current roof has lasted 28 years with just the two gable vents and about four metal roof vents along the 50′ ridge. The long term plan would be to replace the solid aluminum soffit with vented panels and then close up the gable vents and use strictly the ridge vent at that point, but knowing my dad, that may be another five years, so I am basically asking if it is ok to the put the ridge vent in now rather than waiting until we do the soffits.
Thanks,
Jacob, in Climate zone 5, SW Ohio
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Jacob,
No problem at all. Go right ahead.
Jacob,
Q. "Is there is anything wrong with adding a ridge vent knowing they have no soffit vents?"
A. Yes. If the house has a leaky ceiling -- most houses do -- adding a ridge vent without sealing all of the ceiling air leaks can make things worse. The new ridge vent contributes to attic depressurization, and the result is that more conditioned air is pulled through the ceiling leaks, raising your energy bills.
For more information on this issue, see "All About Attic Venting."
For more information on air sealing, see this article: "Air Sealing an Attic."
Martin,
i may have misunderstood, but i think Jacob is suggesting replacing the existing gable and roof vents with a ridge vent. I'm assuming there is no net difference at the venting near the peak.
Malcolm,
You may be right, in which case the danger I described is lessened. But improving air flow through a ridge vent often has the result I described. If the source of the air entering the attic is ceiling leaks, then a bigger ridge vent (or a new ridge vent where none existed before) makes the situation worse.
Let's guess that the air flow resistance of the gable vents is 2, the new ridge vent is 1 and the resistance of the attic floor is 100. Assuming the same pressure differential (should be about right given little difference in attic temperature/stack effect from changing vents), then the new vent will cause 1% more flow through the attic floor. Wind flow over different vents could have a much bigger effect, but who knows which direction that would be.
Jon R,
Your logic is impeccable -- which it should be, since the assumptions are all yours. If the attic floor has big holes, or the gable vents are blocked up, of course, the results would be different.
Thank you for your replies and information.
This is a classic case of getting educated a little too late, but I wanted to add a few other facts that I know are poor practices, but it is the facts regardless.
The house has electric baseboard heat and then central A/C in the attic that was added about 25 years ago. About two years ago new fiberglass was blown in the attic to about R-30 (previously about r-12) where the attic was physically deep enough to do so, the house does not have raised heel trusses, so it is pretty tight at the eaves.
I am sure the house has a leaky ceiling between two bath fans, a half dozen can lights, an attic access, and a big whole house fan in the hallway. As I write this, I am worried the house will become a case study for what not to do, but on the other hand there hasn't been any major problems in the first 45 years. That was what spawned the initial question of whether I should even add the ridge vent and possibly upset the whole apple cart.
Thank you for reading my grammatically incorrect ramblings...
Jacob,
Now that you have described your ceiling, my earlier worry about the possibility of big unsealed holes seems justified.
I advise you to save the cost of installing a ridge vent. A ridge vent is unnecessary and possibly counterproductive. Instead, devote your energies to sealing air leaks. Here are links to two articles to guide you:
"Air Sealing an Attic"
"Blower-Door-Directed Air Sealing"
Jacob,
It is possible to add the ridge vent later, when you can also do the soffits. During the reroofing, have the roofers cut through the sheathing to provide the slots necessary for a ridge vent. Then simply roof over the slots. If/when you finally get around to venting the attic properly with ridge and soffit vents, the ridge shingles can be removed and a ridge vent installed instead. It won't cost anything extra during the reroofing job and it provides a pathway for future improvements.
I completely agree with others that you need to seal the attic floor as a first step. The payback for this is often just a year or two in energy savings.