Lot of frost in attic

I have a 2007 built home. I by chance went into the attic recently and was shocked by the amount of frost on all the roof decking and all the nails looked like snow cones. Of course as this melts it is wet and there was signs of this happening over time. I have vented soffits. However there are some on the front and very few on the back of the house by design. I can see plenty of day light from these, they are not packed with insulation. I borrowed a smoke machine and filled the attic on a windy day. I did not notice any movement of the smoke toward the ridge vent. Not sure if it is plugged by snow or if it is not working at all. Looking from the outside it is a very shallow vent. I need to correct this ASAP this year. I plan on pulling up all the insulation and air sealing wire holes, pipes, recessed lighting and any gaps etc. Also there is a bathroom fan with what looks like too small a hose just run over and plopped in one of the soffits. I plan on using a 4" insulated flex to and outside vent on the adjacent gable. This should reduce the moisture going up. However I am concerned about the lack of air flow. I am looking for any input on if I should have my ridge vent replaced with something better like the Shingle Vent II or should I install two gable vents. I read that you should not have both a ridge vent and gable vents. However if my ridge vent is ineffective, would installing the gable vents be a non issue and help evacuate the moist air that is going up? Thank you for any input. If helpful I can add photos of the house roof.

 

The frost is likely from penetrations that are not air sealed, allowing warm moist air into the attic. The improper bath fan exhaust doesn't help. There will always be some moisture coming through the ceiling whether the penetrations are sealed or not, since ceilings rarely have a vapor barrier. If the humidity in the attic is high it could possibly be because the humidity in the house is too high, so you could look into that.

As far as air flow, without specifics on the exact amount of soffit vents and their sq. area as well as the exact amount of ridge ventilation in linear feet, it is hard to say if the ratio or amount of ventilation is correct. (plus we don't know the length and width of the house) Maybe the sheathing was not cut back enough at the ridge. (usually a 2" wide gap at top, or if there is a ridge beam, 1" of clear area on each side of the ridge beam) We would also need to know the type of ridge vent to have some idea about how much free area it actually provides per foot.

Hopefully the majority of your rafters have styrofoam baffles with insulation stuffed below them to insulate the top plate. This limits the airflow to that fresh air comes directly from the soffit vents and it encourages that top to bottom air flow rather than a horizontal soffit to soffit air flow. Keep in mind that the main driving force in soffit to ridge ventilation is heat, since heat rises. In the winter when it's cold there just isn't going to be a lot of heat rising, so I would not expect a lot of smoke to clear out of the attic as if there was an exhaust fan running. That just isn't how it works, nor should it be. When air flow is increased in an attic (like via a power exhaust vent) it often sucks air and heat away from the home which can actually increase your energy bills. If you tested with smoke when it was windy outside, you probably would have seen dramatically different results.

You are correct that you do not want to mix gable vents with ridge and soffit vents.

 

First, ridge and gable cents work fine together along with soffit vents, the caution you hear is an old roofing myth that got traction and is now very hard to eliminate. The long explanation is available any time.

A common mistake is for the roofers to cover over the ridge vents during the shingle process and forget to cut it open as the ridge vent is installed. Since you saw no movement of the smoke, your conclusion of snow or the vent was never opened seems possible. You can carefully inspect that ridge from inside to see if the plywood was cut back, probably was, and that they cut the underlayment back so you can actually see the vent material. From outside it may look covered with snow if it was not cut back. Depending upon the opening you may be able to resolve the issue from the attic. Take a look and tell us what you see up close.

Bud

 

First, thank you VERY much for the information. I would like to hear more about how the gable vents and ridge vents can be done together. I did the smoke test on a cold day but the wind was blowing. It has been very cold here for weeks now, zero, sometimes below and today was around 21. Best I can tell the cut back is about 2 inches on either side of the beam. What is there is scotch brite type material, the mesh under the ridge vent. The paper and shingles seem to be but back as well. The photos show from what I can see what soffit venting I can see light from on the front of the house (noted by the green arrows). The red arrows I don't see anything from in the attic. On the rear of the house (I don't have a photo) there are two spots where light shows for soffit venting. Both spots are around the size of the area shown in the green circle. The type of ridge vent I am not sure. It looks very flat compared to some of the other houses here. That's why I was was wondering if an external baffle type ridge vent would be better. If it creates a suction when the wind blows etc.. Thanks again ! I am kind of broke at this point and don't mind doing what I can myself, but I don't want to do it the wrong way. Just trying to save my roof and prevent mold. My kids have enough medical issues..

 

Good, at least the ridge vent is open as it should be. In Maine we did get a bunch of freezing rain which created an ice layer over the snow and I did notice a lot of houses with ridges completely covered with snow. Can you see the ridge vent from outside?

As for ridge vents working in conjunction with the gable vents, the air coming in the soffits is pushed in by the weight of the colder outside air. Just like a boat is buoyed at the surface, the force comes from below, thus regardless as to where the warm air is pushed out, the fresh air will continue to come in. The only concern is where prevailing winds may blow snow or rain into a gable vent, but that is a concern all vents have. That's the short explanation, I have a worksheet that explains how house pressures develop and are calculated.

There may be better ridge vents, but what you have should be working. It isn't clear that you have sufficient soffit venting. When you did the smoke test, was the attic access open? If it was there should have been plenty of pressure to push that smoke out of the ridge vent. Is it possible the "scotch brite type material" has frosted over on the outside? With the humid air exiting to the cold it could do that. Those soffits should have a lot of venting everywhere the rafter tails overhang the wall. Look for perforated vinyl soffits from the outside.

Wind also helps, but natural pressures work 24/7 with just a little temperature difference.

"X" covered most of the moisture issues and ditto that bath exhaust needs to vent out somewhere other than below a soffit vent.

It does look like you are having a mild winter .

Bud

 

I will try to get better pictures soon of the ridge vent outside soon. When I did the smoke test yes the attic access was open, yet the smoke just kind of sat there. The front of the house faces West and the rear East. The prevailing winds are front to back so gable vents on the side should be ok for blowing in. Due to the winds being that way, my interest was spiked by the shingle vent II. It shows the external baffle working like a wing and pulling air out. We have a lot of wind so that might be good. I have no issue doing the vent my self, however my roof is quite high and I stink at heights . I figured putting a better ridge vent on, verifying all soffit vents are open and air sealing the best I could along with moving the vent fan outside would be good. When I get the pics of the ridge vent from outside I will post. I am curious to what you have to say. My builder is not that good, there have been many other issues with this house. Thanks Bud.

Mild winter ?! What the heck kind of temps are you getting your way if mine are mild ?

 

I was looking looking at the green grass LOL.
Your list looks good.
Recommended vent area is about 1 sq ft of net free vent area for every 300 sq ft of attic floor. Double that for homes where the ceiling plane has not been well air sealed. half high and half at the soffits.

With the attic hatch open there should have been more than enough pressure to exhaust that smoke out the ridge. It does sound like it may be blocked.

I'll attach a link for air sealing so maybe you can spot some of the low hanging fruit. There are often a couple of large bypasses delivering most of the warm air. Also, air seal the attic access.

http://www.efficiencyvermont.com/ste...ide_062507.pdf

Bud

 

Thank I will look at the PDF now. Those pictures I used of the exterior were from Years ago and during the warm season. If I took them now it would be all white

 

I sure wish I could find it, but there was a pretty detailed article regarding this in JLC years and years ago, and I don't recall that it was a myth. It seemed to be well illustrated and proven science that the mixture of multiple types of ventilation would result in a haphazard ventilation that had the potential to create swirling "dead zones" in the attic, along with cross flow, possible downdraft problems (snow) etc. plus the possibility of introducing straightline winds into the mix, possibly causing downdrafts from the ridge. Maybe, Bud, you have come across the article and know which one I am referring to.

At any rate, if there is new information and you have a link handy why don't you go ahead and share it with us. I'm all ears.

The closest thing I can find is an illustration (pg 33) in the June 2003 JLC, but that's not it, as these illustrations don't depict the downdraft, dead air zones, and cross winds that were studied. The specialist quoted in this short Q&A I can find was Mike Keogh who stated, "if you choose to add ridge vents (to an existing soffit and gable vent setup) you must either remove the gable vents or seal them up."

Bill Rose seems to take the complete opposite tack, "Gable venting and ridge venting are both fine. Soffit venting with baffles is fine. Combinations are fine."

The book "Complete Building Construction", on page 605 contains 7 specific criteria for an effective attic ventilation system, showing areas where gable venting really doesn't bring anything to the table, when compared to soffit-ridge ventilation.

Companies that specialize in ridge ventilation generally will say that gable ends should be closed off when used in conjunction with their products, so all things aside, end users who don't close off gable vents are really not following the mfg's guidelines. (of course, this could be driven by their desire to promote their own products).

 

I too on a few places in my reading over the past few days saw that the two should not be combined. Think they said it could make the ridge vent an intake at times as well. I am all for the set up I have now. I just need to verify all soffits are in fact open if they are there. That front peak may be covered with insulation. I have to crawl in there to see for sure. I still think my ridge vent stinks and is the cheapest one they could put on. That is this builder's style. With the high winds here and my house facing East / West the external baffle vent like the shingle II would make good use of that wind. It seems to stand higher off the surface as well (if that makes any sense). The one I have now seems very flat and would not take much to block it. Again I will get a closer look when wx permits and will post the pics here for you guys to verify. I know I need to seal the bathroom and vent that exhaust fan and the attic access.

 

The best feature of that type of ridge vent is that when the wind is blowing the baffle creates low pressure above the vent (uplift) like an airplane wing, so that it helps create some airflow, rather than blowing straight into the attic, or worse yet, blowing in one side of the ridge vent and out the other. They are also less likely to introduce snow and rain as a result.

 

That's why I was leaning toward replacing my ridge vent with the better kind, air sealing, moving bath vent and verifying soffit vents for obstruction. I am going to be watching the new thread on gable / ridge combos though to learn as much as possible.

 

Here are pics I took today. My vent seems to be very flat and non effective seeing as it looks to be filled with snow. Now the two house across the street seem to have what looks like a more substantial ridge vent that shows a gap and looks as though they deiced themselves.

 

Does this look like a Cobra vent I have ? Just the filter stuff with shingle caps on top ? Not much of a gap and seems to get plugged easy. I was looking into possible costs to have it replaced. At face value it didn't seem that big of a deal except I found online if a roof is not walkable. Mine seems pretty steep and no I have not measured the pitch yet. I guess those type of roofs cost more to have done

 

Cobra vent is plastic, has vertical louvers and a baffle, and the filter is located on the interior side of the cobra vent so that it filters air coming in/out of the attic and/or louvers. If you'd like to see pictures of it, just go to Google Images and compare yours to it.

 

Matt, your comment "seeing as it looks to be filled with snow." may actually be ice due to the moist air indicated by the frost in the attic. If we eventually get enough warm weather you might re-check to see if you see any smoke exiting the ridge.

Bud

 

I was wondering if I have this type of ridge vent :

The Ridgevent Installation Video - YouTube

It's kind of what it looks like. I think I would be better served with an external baffle one. I thought this type in the video was called a Cobra vent, that's why I said that in my previous post.

 

Have you ever measured the relative humidity within the house, and with a reliable instrument, not some cheap $10 devise?

I noticed from your pictures that the roof sheathing is osb. This is not the best for issues where moisture may be of some concern as it does not offer the ability to store moisture without quickly showing signs of visible condensation. Not to say you should change your roof....I am just saying that osb is the least forgiving of sheathing materials.

Keep in mind that water vapor entering the attic, whether it be from vapor diffusion or leakage paths, does NOT know that there are ventilation paths for it to follow to. Sometimes the condensation will be inevitable and the ventilation can only provide a means of air movement that will help to dry out the affected surfaces.

There are many factors at play and this winter is certainly bringing about a number of them that will adversely affect even the most well planned ventilation and insulation assemblies.

 

No I have not. We do have a whole house humidifier. It's manual and I think failing to turn it down when the outside temps get so low has been an issue. That's our fault. I did turn it down recently after all this was noticed. There are a few places that OSB shows signs of damage from moisture. If I air seal a bit, move the bath vent, get a better ridge vent and manage the humidifier maybe I have a chance ?

 

madmattz,

How much insulation do you have in the attic? It appears to be batt insulation, since it seems that we can see the tops of the joists. Is there a poly VB below the insulation, or is there kraft facing on the insulation? Just curious.

 

It is faced insulation. Nothing between it and the ceiling drywall. I would say it's about a foot or so ? You can see how thick the bats are in this photo by that one piece on top.

 

Glad you realized the humidifier to be a source of excess humidity. Most people who have them have no clue that they need adjusting relative to exterior temperatures. The problem is that there is a latent reaction to these adjustments meaning that you should turn down the moisture contribution several days in advance of the cold weather forecast.

Do you tend to have condensation forming on the windows, especially on the north side of the house.

 

I was not aware of the latency issue. Yes, there were a few times in December that I noticed moisture on the windows. That's when I turned it down. I was not sure if it was that or the fact we had more people in the house at the time. Since then, even with these recent cold snaps I have not noticed any moisture at all on the windows. I have to be more diligent with the setting. Funny enough I recently assisted my neighbor in wiring in his WHH. Same manufacturer except his is auto and has the external temp probe to adjust as needed. That should have been a wake up call. There is def too much coming up through the ceiling though. Like I said I will have to relocate the bath fan exhaust and seal some stuff up better. What is the best way to install the vent on the side of the house for the bath exhaust so that it won't leak ? Also should it be a 4" insulated hose connecting the fan to the vent ? That is not what is on it now.

 

Just a note. Most bath fans have an internal damper which tries to block cold air from coming back in. However, that damper is pointed in the wrong direction to prevent warm air leaking out and on a second floor, the winter air pressures are pushing in the attic direction. There probably is a steady slow flow of warm humid air leaking into the attic. Were the frosty nails near (above) the end of this exhaust?

Bud

 

The issue of placement of the duct and exhaust port for a bath fan has always been handled poorly on most new homes.

Ideally the vent line should go down an interior wall and exit the side of the house at a point well below the eave or go through the ceiling and follow to a gable end wall where it would vent to the exterior without concern for it to rise into the attic space. The issue is that you need to have a fan that is powerful enough to move the air through the various turns and distances that may be required to accomplish proper exhaust at a point where it won't re-enter the attic. This may involve spending more than most builder's want to devote to something that most people don't give two hoots about.

The exhaust line should be under the ceiling insulation wherever possible or it should be enclosed in some significant level of duct wrap to keep condensation from occurring when attic temps. drop to levels that would allow the dew point to occur for the level of RH in the vent line. I have picked up many flex duct lines in attics only to have many of them dump gallons of water out the eave, having accumulated condensation over weeks of use in cold weather.

There are back draft blockers that can be placed in-line that are very effective in eliminating cold air from travelling back through the fan. One that comes to mind is sold by "batticdoor.com" and I am sure there are others.

I want to clarify the comment I made in the previous post about a latency period with regard to humidifiers. Consider that when the humidifier is running all of the porous substances in the home are accumulating moisture. When the outdoor temperatures drop, the moisture that has accumulated within the house will need a period of time to exhaust itself into drier air so that the interior RH is not too high when exterior temperatures drop to very low levels. That is why you have to be a few days ahead of the extreme plunge in temperatures so you can keep the "current" humidity level in line with the recommendations for the settings on the humidifier. Hope that is all not too confusing.

 

I didn't seem to notice a concentration of frost in any particular area. All of the nails were covered and the sheathing was frosted in no particular pattern.

I understand what you are saying about the latency. That makes sense.

The bathroom fan is pretty weak and plan on replacing it with a better one. I think I will use an insulated hose and run the vent to the gable side wall that has no soffit intakes above it.

 

The insulated flex is hard to keep straight/level. Well not exactly level, a bit of a down slope to the outside. I prefer metal rigid duct and then wrap it in insulation. They make delay timer switches so that when you turn the fan off it will continue for an additional set time. This removes excess moisture in the bathroom and ensures the duct comes up to temperature and clears itself of any condensation. A short on/off cycle will leave that moisture in the duct to freeze.

Bud

 

Thanks Bud.

I will be able to maintain a slight down slope to the vent. The master bath has a raised tray type ceiling. This what the top looks like in the attic. A box I guess you could say.