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Soffit vent redux


kurt
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OK, so I've got the builder arguing that they don't have to have soffit vents. Plenty of ridge venting but no soffit vents. Muni passed it.

Muni is on the 2006 IRC. I've looked in R806.1-R806.3, and it only discusses soffit vents being necessary for roofs where the drywall is applied to the underside of the rafters, i.e., vaulted ceilings.

Where's the statement about soffit vents for your basic attic?

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Originally posted by kurt

OK, so I've got the builder arguing that they don't have to have soffit vents. Plenty of ridge venting but no soffit vents. Muni passed it.

Muni is on the 2006 IRC. I've looked in R806.1-R806.3, and it only discusses soffit vents being necessary for roofs where the drywall is applied to the underside of the rafters, i.e., vaulted ceilings.

Where's the statement about soffit vents for your basic attic?

There's no IRC requirement for soffit vents. They're just an option.

- Jim Katen, Oregon

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Hi,

You're right, it probably won't work but there's not a lot you can do to move an intransigent builder and/or muni. I normally just explain the issue to the client, tell the client that it's my opinion that it won't work and that I'll be writing it up that way, but not to expect the builder to do a whole lot about it, 'cuz it's been my experience that most builders and muni guys think that home inspectors like us are smokin' wacky tobaccy. I tell the client to insist on all of the answers from the builder and muni guy in writing, keep an eye on it if they buy it, and keep their litigation attorney on speed dial for the day that they discover that I was right and the builder and muni guy were wrong.

ONE TEAM - ONE FIGHT!!!

Mike

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Muni is on the 2006 IRC. I've looked in R806.1-R806.3, and it only discusses soffit vents being necessary for roofs where the drywall is applied to the underside of the rafters, i.e., vaulted ceilings.

Where's the statement about soffit vents for your basic attic?

R806.1 Ventilation Required. Enclosed attics and enclosed rafter spaces where ceilings are applied directly to the underside of roof rafters shall....

Kurt, I read that as "enclosed attics" and "enclosed rafter spaces" with the subsequent "ceiling applied directly to the underside of roof rafters" only applying to the bit after the "and". In other words, enclosed attics and/or cathedral ceilings are required to have ventilation.

I agree that R806.2 doesn't require eave vents for any attic IF the the 1/150 rule is followed...but at least 20% would be for 1/151 to 1/300. Still stupid not to have it though.

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So...if the average roof "mushroom" vent has a free opening of maybe 6"x6"(?), then a 1000sf attic would need 27 vents to meet the IRC 1/150 rule. Did you have that many?

I'm not sure what the free area of the various continuous ridge vents is but the biggest I can find after a quick search online are 18 sq" per foot. 1000 sf attic would require 53 feet of that ridge venting (for 1/150).

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Yep, another one of those common-sense items the code fails to nail down beyond the idiot of a doubt. What can you do?

I've seen it a few times, and I tried to explain to my clients that what they would have is really just half a ventilation system; air outlets, but no air inlets. They seemed to get it okay, whether they actually did anything about it or not. Misson accomplished.

Brian G.

Thousands of Rules & Regulations, But an Idiot Will Find the Holes [:-irked]

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I'm one of those folks. In this case, though, the house is done and it can't be converted to conditioned space.

This is just one of those stupid things that points out the stupidity of some aspects of the building code.

If it was a steep pitch roof, or had big air space, I don't think it would be significant. As it is, the roof pitch is 4:12, and there's almost no air space up there. I've seen enough of these turn to mold farms that I think it's gotta have soffit vents.

But, the guy will probably win because he's within "the law".

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Then there's the rising tide of folks that argue for attics being air-tight. Seal 'em up and make 'em part of the conditioned space.

Let's not go there right now.

I'm among that crowd.

Kurt's example will be a moldy mess in short order. The best one can do in that case is what Kurt has done... educate the client.

I inspected a rather large four square a few weeks ago. It was of the genre that includes a huge attic that could easily be converted to living space. For the last 105 years it's stood the test of time with no intentional ventilation but the roofer that last worked on the house studded the roofline with , get this, 11 box vents. It's truly lovely and one can stand at the top of the attic stairs and watch the door to the space strain to hold back the chimney effect. Open the door and it's like being in a trailer park in Alabama during tornado season.

More venting is always better. Right?

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I know Randy asked us not go there but....

...wrap your brains around this one guys, soffit vents cause ice dams.

If this caused your head to explode don't blame me, the logic behind this conundrum comes straight from the mind of Joe Lstiburek. If I follow it right, a sunny exposure on a 30 F day will raise the wall temp to around 40 F (even warmer for dark colors), and this warms the air adjacent to the wall which then is boyant enough to rise through the soffit vents where it melts the snow on the roof deck from the bottom up. If the snow on the roof is deep enough to insulate the overhang the melt water running beneath it freezes at the eave, if not, it freezes as soon as the sun goes down.

So why do we vent roofs like this?

Tom

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Because ice dams can be dealt with by installing WR Grace; condensation in the attic on the underside of the roof deck cannot be dealt with except by vents.

Or......

Completely rethinking how we insulate houses. I'm firmly in the icynene/no vents/condition the attic camp, although that could change if new information comes out contradicting what we thought yesterday.

My own house is solid masonry, no soffit vents, decent insulation, and I still get major ice dams in sunny weather. Sunlight is gonna melt snow on the roof.

Joe L. can think some of this stuff through too far, he's "right", but he's not right because this stuff boils down to a lesser of two evils thing. The problem isn't soffit vents, it's outdated insulation and building technologies prosecuted by completely untrained construction personnel. We're not going to change that, so vents will have to be used in some cases.

In my case (yesterdays inspection), I'm saying gotta have soffit vents regardless. How the heck is it gonna stay dry inside otherwise? Plus, this house is 100 years old with a stone foundation and damp bsmt. conditions. Stack effect is gonna play havoc with the attic unless it's ventilated.

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Originally posted by Chad Fabry

More venting is always better. Right?

I'm pretty much at the point where I don't think old houses with big attics need much, if anything, in the way of venting. I see a couple hundred a year, and there's never a problem. Problems come with new OSB sheathing, new tight windows, or other improvements that change the vapor and air transmission rates in the structure.

Your house (just described) didn't need vents. It was the untrained non-thinking installer that plugged in a standard formula.

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I always use the 1/150 and 1/300 rules and think about uniform air flow from the soffits up to the ridge. I don't like gable vents, pan vents, or power fans as these can be counter-productive and may, in some circumstances, pull in warm air at the ridge, for example. I know Certainteed requires gable vents, pan vents, or power fans be removed, if ridge/soffit venting is added on a reroof (taken directly from their Master Shingle Applicator book). The other top manufacturers (Tamko, Owens Corning, GAF) highly recommend the same.

I think IRC recommends soffits but doesn't require it. I would press the builder for soffit vents, and if you need to, use the shingle manufacturer's instructions and warranty paperwork to back you up.

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