Smoke Testing My New Ridge Vent

[DerbyDad03]

I'm looking for opinions about what I'm seeing when I smoke test my new ridge and soffit vents.

I had my roof replaced and a ridge vent was installed. I also had full soffits vents cut and then covered with perforated vinyl. My soffits are about 6" wide, so there's about 4" of perforated vinyl showing.

The roof is framed such that I have about 3 feet of slanted ceilings in the bedrooms, and the crawlspace attic itself is about 4 feet from the top of the ceilings joists to the rim.

There is bat insulation on the floor of the ceiling that extends part way down the rafter bays towards the soffit. When I pull the insulation out of the rafter bays, I can see light from the newly cut soffit vents. The contractor said that the soffits themselves are free of insulation.

I installed 4 feet of baffles in each rafter bay, pulling them back about 4" from the soffits, per the contractor's instructions. I then put the bat insulation back in the rafter bay making sure the tops of the baffles are open. The insulation does not extend more than 2' beyond the top of the baffle so I know it's not covering the soffit vent.

Last but not least, I have a 12" x 12" gable vent at each end of the house, which I have not yet closed off.

I bought some smoke matches to check the air flow and this is what I found:

The weather conditions were mid-50's F, thunderstorm, breezy. The attic itself was fairly cool. I closed the access staircase so the attic was closed off as it will be under normal conditions.

Holding a smoke match up inside a rafter bay near the ridge, there was some movement up and out, but also a lot of smoke spreading down and across the top of the attic. The was certainly no indication of the smoke being rapidly sucked up and out through the ridge vent.

Holding a smoke match inside a rafter bay near the top of a baffle, there was movement up the rafter bay towards the ridge, but it seemed more like natural up flow as opposed to strong breeze blowing it upwards. If there was a breeze, it was not significant.

Finally, holding a smoke match within an inch of either gable vent showed significant outflow through the gable vent. It was literally being sucked out of the vent at a rapid pace. If I backed away from the gable vent 4 to 5 inches, the smoke just floated upwards towards the ridge vent.

I suspect that I need to cover the gable vents, but based on what I have described, do I need to be concerned that the soffit and ridge vents are not operating properly? Do I need to wait until it's really hot and try another smoke test?

Thanks!

[Limp Arbor]

Not an expert but from what I've read about it you need the gable vents closed off for the ridge vent to start the chimney effect. You should be able to test by covering the gable vents with plastic.

When I recently re-wired my house I put fireproof caulk in all of the holes in the basement and the attic where the wires were run. The difference was amazing as far as temperature in the basement. The chimney effect was obviously the culprit.

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[krw]

The gable vents should permanently be closed off or the ridge vents will just draw from them instead of the soffits.

In the basement. Interesting. I've seen the wiring caulked in the attic but not the basement.

[DerbyDad03]

Yet, as I stated in my description of the smoke test, the gable vents are drawing air *out* not in.

"Finally, holding a smoke match within an inch of either gable vent showed significant outflow through the gable vent. It was literally being sucked out of the vent at a rapid pace. If I backed away from the gable vent 4 to 5 inches, the smoke just floated upwards towards the ridge vent."

[DerbyDad03]

Still seems strange that the gable vents were drawing out, not in.

It could have been caused by Bernoulli's principle since the wind outside could have caused less pressure outside the gable vents than inside. However, I would think that the same thing would have happened at the ridge, yet the ridge vent did not show any significant draw either in or out.

I'm trying to make sure that everything is working before I pay the contractor. He still has to install the gutters and the contract is "payable upon completion". While I trust him to come back if there's a problem, payment has a way of changing people's priorities.

Anyway, the forecast for weekend is mid-60's and sunny, so I'll probably block the gables and see what happens. I may still have to wait for a really hot day to see significant draw through the ridge vent.

[trader4]

I would not cover the gable vents. IMO, it just serves as more outlet area for the rising hot air. Even if you got some air coming in from one or the other, hard to imagine that it's not going to help cool the attic.

Your tests on a 50F day aren't going to show much. You want a day with temps in the 70s+ and full sun.

If you want to experiment, try holding a smoke source at the soffit vents with and without the gable vents blocked. I'll bet you can't tell any difference.

[DerbyDad03]

Testing with the gable vents blocked was going to be my next step...I just didn't have time last night.

I'm waffling about covering the gable vents. In talking to both contractors and others, the majority say that they should be covered but its sure not 100%.

The guy that actually did the roof basically shrugged and said it shouldn't matter...it was up to me.

[DD_BobK]

Please explain......

You caulked the holes and it had an effect on basement or attic temps?

I would suggest that basement temp correlates well to soil temp and less well to outside air temp. Attic temp is a function of air temp, solar radiation and roof construction.

I'd be hard pressed to belive that caulking Romex holes would have much effect on basement temp..... maybe attic temp, but not a strong effect.

cheers Bob

[DD_BobK]

Talk about a 2nd order effect......... I wonder how much good caulking plate holes really does. The holes do have a piece of Romex in them and if the stud bays are insulated, then caulking plate holes would seem to fall into the ream of "turd polishing".

Any one know the gensis of the requirement to caulk plate holes?

I know that in concrete structure floor to floor slab penetrations (as for drain plumbing) require the use of fire-stop caulk to seal the annulus around the pipes. However this gap has a much higher total area then the un-filled portion of a hole for Romex.

A 1/2" gap around a 4" pipe is nearly 8 sq in... a 3/4" hole is only .44 sq inches (an that's without the Romex) Figure the Romex takes up 1/2 the area, we're down to .22 sq inches.

Any have some research data or code section that requires this?

cheers Bob

[Limp Arbor]

Based on this thread it is handled differently in diferent locales. (like most things)

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[Limp Arbor]

While running the wires when I was in the attic (winter) I could feel the heat and the 'breeze' flowing through the holes in the top plate of the second floor. That air was coming from various places up the stud cavities into the attic.

With all of the time I spent in the attic and seeing gaps only sealed by drywall tape and other ill-fitting framing. I am starting to believe some of the stuff that Mike Holmes and his tuck-tape crew do.

All I can say is it made a difference. I did caulk everything in the basement including: the old holes where the wires were pulled out around the drain & vent pipes The panning around the return bays (forced air)

One hole and I'd agree with you. Start adding up every hole in the basement that has a wire, pipe, CATV cable, phone, or just empty running through the walls. Probably would add up to having a wide open stud bay running from the basement to the attic.

My basement was much waremer. All I can attribute it to is the warm air near the ceiling wasn't running up the walls to the attic.

I can see how all of this sealing off of air could lead to problems. Seems to me that the newer homes that are tighter have a higher incidence of mold than the older homes that 'breathe'.

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[Ed Pawlowski]

"DerbyDad03" wrote

I don't find it unusual at all. You have all the inlets at one level along the soffits. Then you have a "group" of outlets five to ten feet above that level that can allow the warm air to vent. The flow may change depending on temperature, wind strength and direction.

[Larry Fishel]

You said it was "breezy". My money is on the wind hitting one wall and being deflected up, through the soffit vents, raising the pressure in the attic and blowing the smoke out the biggest hole(s) not on the same wall...

[DerbyDad03]

Wind was mainly from the west, hitting the side of the house where there are no soffit vents. The soffit vents are on the north and south walls of the house, so the wind would have been blowing across them.

In fact, there is a gable vent on both the east and west side of the house. Both gable vents showed significant outflow, even the one on the west wall.

[DerbyDad03]

[e-mail]:

Wow...those would have to be some pretty dumb and/or non-caring roofers.

Besides, they didn't use tar paper on my roof.

I went with the GAF Lifetime Roofing System and no, they didn't cover the vent with the Deck Armor.

[DerbyDad03]

An update:

Quite a bit warmer in the attic today and quite a bit more air flow from the soffits up through the ridge vent.

I still haven't decided what to do about covering the gable vents...need to do a little more research.

In any case, I'm quite happy with the roof/soffit/gutter installation. The contractor was paid this morning.

[besttar]

Isn't there a "NO SMOKING" sign in your attic? If not, there should be one. Buy one at Walmart and install it immediately!

Smoking is dangerous and bad for your health!

[Home Guy]

DerbyDad03 used improper usenet message composition style by unnecessarily full-quoting:

I don't buy the basic argument for that product.

I don't want the underlayment to "breath".

=========== Helps prevent inside moisture from becoming trapped within your roofing system ? and causing mold, mildew, and expensive structural damage ===========

If it can let water vapor / moisture pass through from the attic to the outside, it can also let moisture pass the other direction as well. The whole point of a roofing system is to have a water-tight covering over the roof deck.

That GAF "Deck Armor" is a crock of shit. You don't solve an attic humidity problem by having a "breathable" shingle underlayment. You solve an attic humidity problem by (a) not venting kitchen and bathroom fans into attic, and (2) have proper soffit and roof vents.

As for testing your ridge vent, don't bother doing any testing or measuring on a cloudy day.

Go to any hardware store and buy a $5 or $10 digital thermometer that has an indoor and outdoor temperature capability and it uses a small thermocouple connected to 3 feet of wire as the outdoor sensor. If you're handy with a soldering iron, extend the length of the wire with some extra wire and place the outdoor sensor in the attic near the peak, maybe a foot under the deck surface. Mount the readout unit somewhere in the house where it's convienent.

I've done this, and mine will record min/max temperature as well, so I know how hot it got on any given day.

If the max temp you ever see on the hottest day doesn't go above 120, then you really don't have to do anything more or be too concerned. If it hits 140 then you definately need to do something (like add a ventilation fan).