Snow in attic with ridge vents

[Greg Wayman]

I've been inspecting for 9 years now and this a first for me. I had a 4 year old tract built home with gable style roof and a continuous ridge vent. There was about 3"-6" of snow piled up below the ridge vent running half the length of the home. I've seen snow come in turtle vents, but never ridge vents.

My question: Is there a maximum width the ridge vent is to be cut? Is there supposed to be a felt membrane in the ridge vent that would block the snow? Or is a driving wind an acceptable excuse for this much snow penetration?

[Markus Keller]

That much snow isn't normal, at least not around here. We have ridge vents and maybe once a winter I'll do a house and see a little bit that has come through the ridge vent. We get some pretty hard winds, so a little doesn't make me write like crazy. 3-6" there has to be something wrong. Imagine what is going to happen to the interior as that much snow melts.
As far as what is required, you would need to have an idea of what type of ridge vent it is. The metal cover that nails to the ridge, the mesh stuff that just gets nailed under the ridge shingles and creates ~ 1/2+ gap, etc. There are some variations and each of course has it's own manufacturer specifications.
If you got a picture of the material, I would suggest identifying it and then seeing what is required for that material.

[Greg Wayman]

Markus,

Thanks for the fast response. Your concerns are exactly what mine where. When that snow melts, there's going to be some not-so-pretty stains forming in the ceilings. I let the Seller know so they can hopefully get right on that. I did refer it out of course so I'm not worried about liability. I'll have to do more research on the ridge vent type. I've got an expert that sells the vents that may be able to shed some better light on the specs.

[John Kogel]

It sounds to me like the house is oriented in a way that catches an unusual amount of wind at the vent. In fact, you don't normally want that much wind entering the attic, with or without the snow. They may be better off with conventional roof vents on the lee side of the roof. Anyways, a repair is called for. I'll bet you get a few windy days in the winter in Nebraska.

[Bruce Adams]

Greg
Sounds like you have one of two problems here. Improperly installed Ridge Vent or a cheep vent that should have never been used in Nebraska. Snow blowing into the attic has been a problem with some brands of ridge vent in the northern states.
There are some roofers in the northern states that will not install Ridge vents because they installed a cheep product and then had to go back and replace it. They should have done there homework and installed a good product.
The ridge vent has been proven to be the best product to vent the attic known today. It should be installed the full length of the ridge. with proper soffit vents. The ridge vent should have external baffles. And be centered on the ridge and secured with proper nails.
If you are seeing any snow in the attic something is wrong. Most likely the wrong product. I would recommend that the ridge vent be replaced with a better product that has been tested in the northern states to work. I do not recommend replacing the ridge vent with box or turtle vents. If the correct product is properly installed you will not see snow in the attic in the worst of conditions.
Bruce Adams

[Door Guy]

When ridge vents first came out many of the continuous aluminum vents didn't have any filter or roll on the bottom egde to deflect wind or snow. Caused many problems...

A ridge vent shouldn't be cut more than 2-1/2" on each side of the ridge. Properly installed quality vents shouldn't cause any problems. If you don't have the right vent or installed properly you will have snow infiltration. When it gets very cold, snow becomes very fine and it really doesn't take much wind to blow it through very small spaces or gaps.

[Door Guy]

Greg
Sounds like you have one of two problems here. Improperly installed Ridge Vent or a cheep vent that should have never been used in Nebraska. Snow blowing into the attic has been a problem with some brands of ridge vent in the northern states.
There are some roofers in the northern states that will not install Ridge vents because they installed a cheep product and then had to go back and replace it. They should have done there homework and installed a good product.
The ridge vent has been proven to be the best product to vent the attic known today. It should be installed the full length of the ridge. with proper soffit vents. The ridge vent should have external baffles. And be centered on the ridge and secured with proper nails.
If you are seeing any snow in the attic something is wrong. Most likely the wrong product. I would recommend that the ridge vent be replaced with a better product that has been tested in the northern states to work. I do not recommend replacing the ridge vent with box or turtle vents. If the correct product is properly installed you will not see snow in the attic in the worst of conditions.
Bruce Adams

I agree, a ridge vent works much better than box vents...removing it would be a dis-service to the owner. I would also recommend a shinlge over vent vs. a continuous aluminum. They look better and perform better.

[Bruce Low]

A pretty good resource for attic ventilation can be found at Air Vent (http://www.airvent.com).

What you observed may be rare due to an unusual weather event. Can you make any correlations.

With luck there will be little damage to the insulation, and little or no damage to the ceiling, as the snow disappears. Of course conditions will dictate what really happens, but quite often the snow will sublimate, leaving little or no trace. Although the amount of snow is less than you observed, I experience this first-hand in my garage.

Nevertheless, there is no substitute for properly installed quality vents.

Oh, and a Happy New Year to Y'all :)

Bruce Low
Bottom Line Home Inspection
Luxemburg, WI
Bottom Line Home Inspection | Through an Engineer's Eyes (http://www.bottomlinehomeinspection.com)

[Hank Spinnler]

I have observed similar issues with entry of leaf litter and moisture into the attic whenever the ridge vents had no filter media installed to minimize or block entry.

[Mike Schulz]

Filter media missing is probably the cause. They are just laid in the vent with little or no attachment. They can be a real pain and allot of roofers would throw it away.
Newer designs may not need a filter do to baffle design and as stated above literature on the product is needed.
If it's not a reoccurring issue and no noticeable adverse effects to other materials it may not be an issue. Sort of like rain blowing in gable vents which leaves water stains in substrate on the gable walls. It's not right, it hasn't t caused any damage so it's a judgment call on correcting.

[Peter Russell]

Greg, this is what we use here in NH. The plywood is cut back about 1'' to either side of the ridge. the cobra vent is installed and then the caps over it.

It's important to note the the cobra vent should not extend all the way to the gable ends of the roof. App. 3 feet from the end and the cap should completely lay over the end of the cobra vent to prevent water intrusion.

I have never seen this venting system leak water or snow.

GAF Roofing – Cobra Vents - Cobra Exhaust Vent (http://www.gaf.com/roofing/residential/products/roof-vents/cobra-exhaust-vent/cobra-exhaust-vent.aspx)

For those of you who are interested there are some interesting studies that show roof venting may do more harm than good. I believe these apply to colder climate where cold air infiltration is more of a concern than moisture control. Proper air sealing of the thermal boundary is a must for non-vented roof systems.

BSD-102: Understanding Attic Ventilation — Building Science Information (http://www.buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation?searchterm=roof+venting)

[Door Guy]

Greg, this is what we use here in NH. The plywood is cut back about 1'' to either side of the ridge. the cobra vent is installed and then the caps over it.

It's important to note the the cobra vent should not extend all the way to the gable ends of the roof. App. 3 feet from the end and the cap should completely lay over the end of the cobra vent to prevent water intrusion.

I have never seen this venting system leak water or snow.

GAF Roofing – Cobra Vents - Cobra Exhaust Vent (http://www.gaf.com/roofing/residential/products/roof-vents/cobra-exhaust-vent/cobra-exhaust-vent.aspx)

For those of you who are interested there are some interesting studies that show roof venting may do more harm than good. I believe these apply to colder climate where cold air infiltration is more of a concern than moisture control. Proper air sealing of the thermal boundary is a must for non-vented roof systems.

BSD-102: Understanding Attic Ventilation — Building Science Information (http://www.buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation?searchterm=roof+venting)

Thanks for the link to attic ventilation... I personally believe certain situations are better without ventilation, cathedral, heating system in attic (which I would never recommend in cold climates) etc. You also can loose heat through vented attic by wind washing. Ventilation will actually pull the heat from deep in the insualtion. I'm not saying don't ventilate, but some cases I think would perform better without it.

On the cobra vent, why would you only cut it back 1", we normally cut in back 2". If you only cut 1" your only getting 1/2 the ventilation. We also ran it complete length with no leakage problems, just run a foot or so of cap under the vent on the gables. It just looks better that way.

[Peter Russell]

Thanks for the link to attic ventilation... I personally believe certain situations are better without ventilation, cathedral, heating system in attic (which I would never recommend in cold climates) etc. You also can loose heat through vented attic by wind washing. Ventilation will actually pull the heat from deep in the insualtion. I'm not saying don't ventilate, but some cases I think would perform better without it.

On the cobra vent, why would you only cut it back 1", we normally cut in back 2". If you only cut 1" your only getting 1/2 the ventilation. We also ran it complete length with no leakage problems, just run a foot or so of cap under the vent on the gables. It just looks better that way.

Hi Randy, we cut it back about an inch probably more like 1 1/2. We also leave it back about three feet from the gables because I'm close to the ocean and during a " Nor Easter " the rain will come down side ways and combined with near hurricane force winds they will leak.

I agree with you on air washing. I've done many TI inspections and have seen how cold the top of a wall can get. I have yet to see any insulation company install proper vents correctly so that the soffit is completely air sealed around the vent. Most of the time roof vent are not performing and venting the roof because of this. I would rather see a warm wall and a completely seal thermal boundary than a roof that is vented.

[Greg Wayman]

A BIG thank you to all who have posted their responses! I've attached pictures of the snow in the attic and the only 1 I had of the ridge vent. Sorry I didn't get any close-ups of that.

Did I mention this house also has over 100 nails poking the shingles up because whoever installed the roof didn't nail them flush to the roof deck? Fun things that we find;-)

[Peter Russell]

Greg, that is definitely an unusual amount of snow to be in the attic.
Do you have a picture from outside? Did this happen after a big storm?


Here is another link to an interesting experiment done in Sweden. I would like to know more about it but I think it may be a good solution for attic ventilation.

Basically you would completely seal the attic and then introduce ventilation mechanical utilising sensors to control the fans instead of guessing whether the proper vents and ridge vents are working correctly.


http://www.ventotech.com/docs/Kallvindar%20K%c3%b6penhamn%202008.pdf

[Bruce Adams]

[quote=Peter Russell;155454]Greg, this is what we use here in NH. The plywood is cut back about 1'' to either side of the ridge. the cobra vent is installed and then the caps over it.

It's important to note the the cobra vent should not extend all the way to the gable ends of the roof. App. 3 feet from the end and the cap should completely lay over the end of the cobra vent to prevent water intrusion.

I have never seen this venting system leak water or snow.

GAF Roofing – Cobra Vents - Cobra Exhaust Vent (http://www.gaf.com/roofing/residential/products/roof-vents/cobra-exhaust-vent/cobra-exhaust-vent.aspx)

For those of you who are interested there are some interesting studies that show roof venting may do more harm than good. I believe these apply to colder climate where cold air infiltration is more of a concern than moisture control. Proper air sealing of the thermal boundary is a must for non-vented roof systems.



I'm not a proponent of Cobra vent. Tests have shown that it is not one of the better venting systems Externally baffled vents have been known to vent better. Of a independent study of six brands Filter vent and Shingle Vent came in best both external baffled. Then came Cora-vent, Cobra Vent, Roll Vent, and Vent Sure in order. You can get a copy of the report by writing Air Vent Inc.at 3000 West Commerce Street, Dallas Texas. 75212.
There are several brands on the market. Need to look at what gives the best service for the area that you are in. When properly installed all will correctly vent the attic. Some better than others. Several have been known to allow water and snow intrusion into the attic in high wind areas.
Venting has three purposes. To remove moisture from the attic area. To cool the attic in the summer. And to prolong the life of the roof covering. If that ridge vent is not drawing air from the attic it's not doing these things.
The pictures indicate that it was caused by a negative air flow. Again looks like wrong product for the area.

[Door Guy]

A agree with Bruce, it almost looks like air is pulling snow in instead venting air out. BTW I used to use Cobra vent and never had any problems, switched to Shingle vent because of testing results, very satisfied with that product also.

[Greg Wayman]

We had about 50 mph winds and only a few inches of snow.

[Bruce Adams]

We had about 50 mph winds and only a few inches of snow.

Again wrong product for the area. I would recommend that the ridge vent be replaced with a better product. If they were to replace it with an externally baffled vent they would get good venting for both summer and winter and better life of the roof covering. The External baffle causes the air to flow over the vent creating a vacuum.
And have someone to install the vent that knows what they are doing. Even the best product can be the worst if not properly installed. In your area you are going to get those High winds and that fine blowing snow. If there is no damage this time, over time there will be.

[Ken Bates]

One might at well use a poor performing Cobra vent if the ridge is not perpencular to the prevailing winds.

Old fashion baffle vents work nicely when the ridge is perpendicular to the wind. The Bernouli effect can suck up wind from the soffit vents.

the Cobra will keep out debris.

[Peter Russell]

Again wrong product for the area. I would recommend that the ridge vent be replaced with a better product. If they were to replace it with an externally baffled vent they would get good venting for both summer and winter and better life of the roof covering. The External baffle causes the air to flow over the vent creating a vacuum.
And have someone to install the vent that knows what they are doing. Even the best product can be the worst if not properly installed. In your area you are going to get those High winds and that fine blowing snow. If there is no damage this time, over time there will be.


"and better life of the roof covering".


Bruce, recent studies are showing that ventilation has little effect of shingle life, This is why most roofing companies are starting to warranty their shingle's on non-vented roof assemblies. There is a lot to know about building science and ventilation for roofs. The old saying that roofs must be vented to save the shingle's just isn't true anymore.

[Peter Russell]

Here is an excerpt from the study I posted above.

The amount of cooling provided by a well ventilated roof exposed to the sun is very small. Field monitoring of numerous attics has confirmed that the temperature of the roof sheathing of a un-vented roof will rise by a few to no more than 10 F more than a well ventilated attic.


This study was done by the Building Science Corporation.

Building Science Corporation (http://www.buildingscience.com)

[Door Guy]

Here is an excerpt from the study I posted above.

The amount of cooling provided by a well ventilated roof exposed to the sun is very small. Field monitoring of numerous attics has confirmed that the temperature of the roof sheathing of a un-vented roof will rise by a few to no more than 10 F more than a well ventilated attic.


This study was done by the Building Science Corporation.

Building Science Corporation (http://www.buildingscience.com)

I agree the jury is still out on the best method... to vent or not to vent. However, I also believe 10 degrees hotter over 10 or 15 years will shorten the life of the shingles.

[Bruce Adams]

[quote=Peter Russell;155551]Here is an excerpt from the study I posted above.

The amount of cooling provided by a well ventilated roof exposed to the sun is very small. Field monitoring of numerous attics has confirmed that the temperature of the roof sheathing of a un-vented roof will rise by a few to no more than 10 F more than a well ventilated attic.


OK there is always one. Can you name any roof covering Manufacture that is going to tell you that there shingle is not going to last better on a properly vented roof. I do not know of any. Most roof covering Manufactures only have a ten to twelve year warranty on the 20 year shingle and 12 to 15 year warranty on there 25 year shingle. As long as I have to tell the persons that I deal with that there shingle may not be warrantied by the manufacture because of improper venting I will have to go along with the Manufacture.
The manufacture is warranting there covering over an insulated deck not an improperly vented attic.

[Peter Russell]

[quote=Peter Russell;155551]Here is an excerpt from the study I posted above.

The amount of cooling provided by a well ventilated roof exposed to the sun is very small. Field monitoring of numerous attics has confirmed that the temperature of the roof sheathing of a un-vented roof will rise by a few to no more than 10 F more than a well ventilated attic.


OK there is always one. Can you name any roof covering Manufacture that is going to tell you that there shingle is not going to last better on a properly vented roof. I do not know of any. Most roof covering Manufactures only have a ten to twelve year warranty on the 20 year shingle and 12 to 15 year warranty on there 25 year shingle. As long as I have to tell the persons that I deal with that there shingle may not be warrantied by the manufacture because of improper venting I will have to go along with the Manufacture.
The manufacture is warranting there covering over an insulated deck not an improperly vented attic.

Hi Bruce, I'm not trying to be confrontational, hope you didn't get the wrong impression. Just a healthy discussion about building science.

You are correct about the MFG but rarely do the ever warranty their product anyway. In my experience the only time I have seen this is when multiple roofs fail in the same region. This is usually caused by some type of MFG defect, remember Bird? or how about Certainteed or GAF.

I always tell my clients the straight up true about roofs. Due diligence of the installer is key to a long lived roof. No amount of ventilation is going to help you with a claim if it's not installed correctly.

If your familiar with IKO in your area take a look at their Iron Clad warranty about non-vented roofs.

[Bruce Adams]

[quote=Bruce Adams;155554]

Hi Bruce, I'm not trying to be confrontational, hope you didn't get the wrong impression. Just a healthy discussion about building science.

You are correct about the MFG but rarely do the ever warranty their product anyway. In my experience the only time I have seen this is when multiple roofs fail in the same region. This is usually caused by some type of MFG defect, remember Bird? or how about Certainteed or GAF.

I always tell my clients the straight up true about roofs. Due diligence of the installer is key to a long lived roof. No amount of ventilation is going to help you with a claim if it's not installed correctly.

If your familiar with IKO in your area take a look at their Iron Clad warranty about non-vented roofs.

I was not taking it as confrontational. In fact I would say that more than 90% of the roofs out there have no MFG warranty. Most new homes have no MFG warranty. In order for the manufacture to warranty there roof covering it has to be installed to there installation instructions and by a qualified roofer.
In order for me to certify a roof it has to be according to the MFG.
Have you ever tried to breath in a un-vented or improperly vented attic.

[Jerry Peck]

Have you ever tried to breath in a un-vented or improperly vented attic.

Seems to me that there is a possible mis-use, or mis-application of some terms here, such as "Have you ever tried to breath in a un-vented ... attic."

An "un-vented" attic is no problem to breathe in if you are referring to a sealed attic (which is "un-vented") and which has the insulation applied to the underside of the roof sheathing - that attic will be within a couple of degrees of the temperature in the rooms below that sealed "un-vented" attic.

Now, if you are referring to an unvented attic which is not a sealed attic ... well, it would be vented if not sealed, right? Unless that attic is simply "improperly vented", then that is a different story altogether.

[satcat69]

Up here in Alberta we get a lot of snow and high winds,sometimes together. The best ridge vent, I Have ever seen installed, Is the WeatherPRO PRORidge "Not plugging a product, just information " Snow infiltration is almost impossible,and their is no mesh to clog up. They have an incredible, Test video, on their website.110 MPH wind with a simulated torrential downpour ..No water infiltration. A Typical "mesh" vent would have flooded the attic.Their are some good products on the market..Do some research ,and determine what is best for your situation..