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Ridge Vent or Box Vents?

I have heard that ridge vents only work well if there are wide soffits, like 12" or more.

On houses with narrow soffits, box vents are recommended.

Any truth to this?

Reply to
DerbyDad03
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Don't see how the size of the soffits would matter. The area of the vents (equivalent opening) certainly matters. While they're related they're not the same. A 12" soffit isn't all that wide though.

Reply to
krw

It is compared to my 6" soffits.

12" or more was the number that a roofing estimator used when he recommended box vents for my house.

He mentioned box vents, I asked why not a ridge vent, he said my soffits are too narrow.

He then went on to explain that ridge vents only work well with wide soffits, 12" or more.

Reply to
DerbyDad03

The principle is that hot air rises. So, you want intakes near the bottom and outlets near the top. Whether the outlets are ridge or box vents isn't going to matter. What's more important is the square footage of each.

As to needing soffit vents that are greater than 12" wide, are we talking CONTINUOS soffit vents? If so, the roofer is nuts. Vents even 3 or 4" wide, run continously, are going to provide a lot of intake area.

I'd go with the ridge vent. And if the soffit vents aren't big enough, then I'd enlarge them, if possible. Many cases all it takes are one of the small cordless circular saws run down the length. Plus ridge vents, IMO, look a lot better.

Reply to
trader4

Your roofer sees a problem with using ridge vents and isn't explaining why very well. Perhaps you should talk to more roofers. If you have already hired him perhaps you could get him to elaborate.

Reply to
Pat

It seems to me that there might be some failure to communicate here (the forum). The OP is saying (taken literally) that his SOFFITS are

6", not his soffit VENTS. That leaves very little room for vents and maybe the roofer thinks he will need fans to pull enough air through? I don't know enough to offer an opinion on whether that would be correct...
Reply to
Larry Fishel

Thanks for correcting that. Even with 6" soffits, if you ran a 2 or 3 inch wide continuous soffit down it, that adds up to a lot of intake space, 24 or 36 sq inches per foot. The only reason that wouldn't work is if there were something in the construction blocking it. That something in many cases is insulation that gets shoved too far, right over the vents. To do it right, there should be plastic baffles that you can get at HD that get stapled to the underside of the sheating, at the soffits, that form an open channel for a few feet from the soffit so that air can flow.

A continuous soffit vent together with a continous ridge vent, IMO is the optimal solution. The ridge vent is typically a couple inches wide. A similar size opening along the soffit and you're all set.

Reply to
trader4

That can be done with smaller soffits, too. My last house had 6" soffits and a ridge vent. The soffit vent was continuous, however. It wasn't the perforated aluminum that I see elsewhere, some of which only has 1/3 perforated.

Reply to
krw

Basic rule: You can't have too much soffit vents.

At a minimum, you should have one sq ft of soffit vent for each 150 sq ft of floor space. This is one sq ft of unobstructed venting. Some screening material consumes as much as 2/3rds of the space. Refigure accordingly.

If you have a 1500 sq ft house, you need 100 sq ft of soffits, minimum. Assuming the screening material is hardware cloth or similar that consumes less than 20% of the opening, you should plan on 120 sq ft of soffit venting. Further, assuming small, six inch soffits on a 50 x 30' house, you have 160 feet of perimeter. That means only 80 sq ft, maximum, for available soffit vents.

Obviously this is woefully insufficient for the appropriate amount of passive ventilation. You'll have to move up a step in addition to ridge vents. Turbines are the next step and beyond that powered ventilators.

Reply to
HeyBub

(snip)

When, if ever, do you need to be concerned about having too much negative pressure in the attic? You don't want to encourage air to come up through the ceiling any more than necessary.

Reply to
Mike Paulsen

That's a lot of horse shit.

I've installed a few ridge vents, and you usually cut maybe a 6 to 8" wide gap in the decking at the very peak of a roof line (3 to 4 inches on either side).

To theoretically balance out the size of that ridge opening with a similar soffit opening, then a 6" fully-perforated soffit would work.

Also note that sometimes even a 2-foot-wide soffit isin't what it seems, because the bottleneck will be the gap or opening between where the deck passes over the wall header. Usually, the wider the soffit - the lower-slope the roof is, making for a not-so-large header gap.

A ridge vent will give you a more even airflow pattern along the underside of the decking compared to a few box vents.

Reply to
Home Guy

Huh, if your vents arent big enough they arent big enough no matter which you use. Soffit material is available that basically turns the whole soffit into a vent.

Jimmie

Reply to
JIMMIE

Excellent point! This could easily happen with aggressively powered fans and insufficient, or no, soffit vents.

Reply to
HeyBub

What do you klowns think is happening?

You think there is some big vacuum cleaner sitting on your roof, sucking air through your ceiling just because you have too much venting?

Stupid point!

What are the odds that someone is going to have powered roof fans *and no* soffit vents?

And think about this: Even IF you are somehow creating a negative pressure in the attic that IS pulling air through the ceiling - SO WHAT? This is going to be happening ONLY IN THE SUMMER. ITS NO BIG DEAL IF IT HAPPENS IN THE SUMMER. It's in the winter when you don't want that to happen, and who's going to turn on their roof fans in the winter ????

Reply to
Home Guy

in the summer with AC sucking cooled air from the air conditioned space is a poor choice, but at the same time its when having a cool attic is most important....

beyond which sucking on the living part of the home will create paths for the air from the living area to follow all the time.....

a real lose lose kinda situation.

roof fans in the winter help keep the humidity low in the attic which helps prevent mold growth

Reply to
bob haller

In the summer, if I had a choice between:

a) pulling 1000 cfm of air out of my attic using powered vents - with

950 cfm coming from the soffits (and/or gable-end vents) and 50 cfm coming from ceiling leaks - or

b) having NO powered vents (only passive vents) and therefore only getting 200 cfm of passive air movement out of the attic (and 0 cfm from ceiling air leaks) -

It's a no -brainer which one is better for the house and the roof.

And if I can pull more than 50 cfm from ceiling leaks, then the answer is NOT to turn off the fans. The answer is to fix the ceiling leaks (or just live with them) - not sacrifice the life of the shingles by letting attic temperatures soar.

I would bet that the vast majority of roof fans don't have humidity sensors - only thermostats (which means they only come on in the summer).

I know the theory of ventilating the attic in the winter to prevent mold, but explain to me how discharging cold, humid air from the attic and replacing it with cold, humid air from the outside is going to change anything.

If the air in the attic is more humid than outside air in the winter, it's because you have ceiling air leaks (or you're venting bathroom and kitchen exhaust fans directly into the attic). It's a no-brainer that you fix those situations first, eliminating the need for winter attic ventilation in the first place.

Reply to
Home Guy

That cost might be more than offset by the heat load I'm taking away from the interior ceiling area by ventilating the attic with 950 cfm of outside air vs 200 cfm of passive air.

Numbers like 1000, 200 and 50 (cfm) are all just hypothetical, but I still assert that interior air leaks into the attic are trivial (for any home built in the last 50 years) - not counting any bad practices like venting bathroom or kitchen fans into the attic.

Reply to
Home Guy

I'd ask why?

Seems to make no sense to me.

Sounds like he's saying you need larger intake vents regardless and he likes box vents. Maybe that's all he knows how to install?

Weird

Reply to
gonjah

Yep, you're right. My bad.

I appreciate the correction and congratulate you for preventing someone from making a grievous error based on my calculations.

Still, my answer was closer to being right than someone who announces "purple" as the solution.

Reply to
HeyBub

House was built 56 years ago.

There's a pull-down attic staircase in the hallway.

Reply to
DerbyDad03

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