soffit and ridge vents and/or/with attic fan?

ruthgardenSeptember 17, 2006

We'll be replacing our two story contemporary saltbox homes's roof. The roof is ventilated with continuous soffit and ridge venting. We also have a non working attic fan that has burned out two motors. Our home is 20 years old and this will be the third roof. Because of premature failure, Celotex replaced the shingles approximately 10 years ago. We've also experienced ice dams twice on the cathedral ceiling portion of the roof.

After reading the postings on this forum, I assume the roof problems: early failure, ice dams, and leaking happened because the vent system is not working. Maybe there is insufficient air flow up the bays between the rafters? What needs to be done to make sure the soffit and ridge venting is working, especially in the cathedral ceiling part? And once the venting is working, should the attic fan be replaced or is it not necessary with soffit and ridge venting? About 20 feet of the roof is a half story higher than the other 25 feet; should there be two attic fans at the highest part of each ridge?

Also, over the attic part, the roof appears to be ridged and sagging--not between the trusses but parallel with the eaves.

Any advice would be appreciated! Thanks!

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Is insulation blocking the path between the soffits and attic? This needs to be open (1" gap minimum) so air from the soffit vents can get into the attic and up and out the ridge/attic vents to carry moisture away. Check this, you may need to add insulation baffles. Also, their needs to be adequate soffit and ridge/attic vent area available. The rule of thumb is the net free area of open ventilation needs to be 1/150 of the attic floor area, split evenly between soffits and ridge/attic vents. This is the same as 1/300 for soffits and 1/300 for ridge/attic vents. IMO, many homes are underventilated. Go to a web site for a manufacturer of attic vents to get more info, Lomanco is one, or will have tech resource info on venting.

    Bookmark   September 17, 2006 at 10:13AM
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thanks for your reply. i'm going to the sites now.

    Bookmark   September 17, 2006 at 1:00PM
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I would make every effort to dump the power vent. They just consume power and eventually burn out. I guess they have there place when you have a problem and do not want to attack it directly by increasing the venting, but if you are doing it, do it right and dump the vent.

    Bookmark   September 19, 2006 at 7:47AM
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hi, i also have a problem. i have a ridge vent and soffit vents,but have noticed condensation in my attic. could this be from clogged soffit vents? i have 2 gable vents one on each side of the house could these be disrupting the flow of the air? i really have no idea what to do, but the problem is getting worse. any info will help alot! thanks

    Bookmark   February 22, 2009 at 10:55PM
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Nick, If your soffit and ridgeventing is installed properly with no obstructions, you need to seal off the gable vents as, yes, they are interrupting the flow. You dont have to necessarily remove the gable vents, you can seal them off on the back side as long as you have access to them. If no access, you will have to tackle them from the front side which means removal. For astetics or not involving removing siding if possible, you can simply seal them off and repalce them or remove them altogether, fill in the opening, and patch the siding. It all depends on your siding type, gable vent install, acess or no acess, etc.

    Bookmark   February 23, 2009 at 10:30AM
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I thought more ventilation was more betterer, or is that just an issue with ridge vents? I have soffit vents all round, and two whirlybird type mechanical ventilators (I do need to add more insulation to combat ice damming) plus two gable vents that seem to be covered with a tyvek- type material, you can see light through it and, apparently insect screen so either they were covered, or they're supplied that way so are mostly decorative? I had considered removing that material, are you saying it would disrupt my air flow too?

    Bookmark   February 23, 2009 at 12:19PM
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Continous soffit/ridgeventing is designed to keep air flow with the pitch of the roof. Gable venting distrupts that flow. I'm not sure if you relyed on the whirlys as a substitute for ridgeventing if that would keep the flow inline or not. As it stands, though, i feel your gables unblocked would cause an interupption of flow to the whirly's. Out here, whirly's are used for the most part to pull hot air out of the attics. They aren't used a whole lot anymore, but in the winter, the whirly's were usually tie wired to keep them from turning, acting only as a roof vent similar to a dormer type roof vent. If you are getting close to needing a new roof, you might consider installing a continous ridgevent, or consider one anyhow as it wouldn't be that big a project to retrofit to your existing as well as removing the whirly's and patching those areas.

    Bookmark   February 23, 2009 at 12:55PM
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Venting of rafter bays is for moisture control. To prevent ice dams you need to prevent heat from melting the snow with more insulation. A "cold roof" will also prevent ice dams but that would involve adding a second roof 2 or more inches above the existing one, not just additional venting.

    Bookmark   February 24, 2009 at 7:49AM
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I agree with the more insulation thing, I would have probably done it already but to claim the BC govt subsidy I have to have an energy assessment/blower door test (which is kind of stupid because what older home will NOT benefit from additional insulation?) and I also want to add some ceiling lights first so want to get that out of the way before I add blown-in, I don't want the hassle not to mention it doesn't work as well once you start wading through it.

The cold roof idea is interesting, unfortunately my roof was just replaced. I don't know if anyone in Kamloops BC here uses ridge vents, I'll have to see what they look like. They do sound like a good idea.

The whirlys are just left as they are, there's not too much wind in winter in my spot so they don't turn much. I had considered some sort of insect/weather protection underneath, I think I saw a plastic mesh arrangement that is supposed to do just that.

We have very hot summers and the whirlys seem to do a reasonable job, the attic is quite well ventilated. I also had whirlys in Australia, a retrofit to an attic that had no ventilation, they made a huge difference.

    Bookmark   February 24, 2009 at 12:13PM
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don't mix ventilation stratagies.
gable ends
soffit and ridge vents
soffit and passive venting (whirlybirds)

each works as a stand alone, but when you mix them
up you change the dynamics of the air flow.

I've seen people seal off gable ends with clear
plexiglass when installing rigde vents.

power vent fans use energy and create a negative pressure
on the house causing air infiltration and make
duct leakage sites worse.

building science also has excellent info on unvented

pbj, blower door tests are done before additional insulation is installed so that air leakage pathways
from attic into conditioned spaces can be identified
and sealed.
insulation does not perform when air is
moving through it.
once additional insulation is installed
it will be next to impossible to seal all the leakage areas.
(testing the ductwork & sealling would also be to your benfit)
first you have to seal for the air barrier, then the insulation for the thermal barrier.

Best of luck.

    Bookmark   February 24, 2009 at 7:33PM
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I lived in my house for 20 yrs before I got an ice dam problem, and it was a big one. It was easy to understand. It was due to a particular set of weather conditions: a foot of snow on the roof, some melting, enough to fill the gutters with ice and onto the roof, and then a rain.

My solution was to install anti-ice dam sheeting. I was due for re-shingling the roof, so I had the roofers to install an anti-ice dam sheet and there had been no problem since.

The discussion below assumes there is already ONE layer of shingles on the roof.

The anti-ice dam sheet is a waterproof, elastomer sheet that must be applied on the bare roof boards along the lower edge. It may be from 3 ft to 6 ft wide, the wider, the better. Any existing shingles must be removed, but only need to be removed where the sheet will be. The old shingles can be then re-installed over the sheet. The sheet is held in place with adhesive and will seal around nails driven through it. And then, the new, second layer of shingles can be applied over the entire roof.

If the old shingles were not re-installed, then new shingles must be put in their place to avoid an unsightly ridge on the roof were the roofing changes from 2 layers of shingles to 1 layer. This ridge should be avoided since the top layer of shingles may tend to crack and/or break along this transition line. When finished, there should be two layers of shingles everywhere. An alternative is to remove all of the old shingles and discard.

Ridge vent versus roof vents:

When my house was built in the 1970s, the builders in my area were using soffett vents and roof vents. Recently in my neighborhod, I have noticed that roofers have been installing ridge vents when repairing old houses that did not have much in the way of roof vents. Ridge vents seem to more popular at present. A hail storm came through 2 years ago and many roofs were re-shingled (by the insurance companies), so I got to watch several repair jobs recently.

    Bookmark   March 7, 2009 at 1:09AM
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I live in a house with NO soffit vents and NO ridge vents. There are gable end vents and a power vent that has functioned for the 22 years we have lived in the house. I know this is not a good solution, but it is what is in place. The power vent is set to come on when the temp in the attic reaches 95 degrees.It is remarkable that it has never failed.

I assume the next time I have a roof done a continuous ridge vent should be installed. Should soffit vents then be cut in the soffits? And the gable end vents sealed?

    Bookmark   March 19, 2009 at 10:04PM
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Don't bother withe the ridge vent. Just cut in the soffit vents,make sure they are clear of insulation and leave the gable vents alone.

The reason I said don't bother with the ridge vent is the fact they do not really work all that well. See the link below to the article. You can go with more traditional venting options if you want to supplement the power vent

Here is a link that might be useful: Ask the builder

    Bookmark   March 20, 2009 at 3:32PM
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I'm no expert here but I question the "physics" in that article. My understanding is that the "wisdom" is to use a ridge vent with an equal area of soffit vents. This creates the maximum differential to induce air flow. Introducing additional vents doesn't seem to be advised since it short circuits the ridge/soffit system. The author says his ridge vent doesn't work - but then doesn't say whether he has adequate soffit vents - and then claims he has an assortment of other types of vents. All of which may be causing the ridge vent to not function properly.

    Bookmark   March 21, 2009 at 3:56PM
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As the black sheep of the group, dump all ventilation. It is an outdated solution for attic health. It had its place when heat and moisture from the home migrated into the attic, causing ice damming, mold growth, higher heating bills, etc. Today's foam insulation has extraordinary R value and provides 100% air sealing, so air and moisture from the home can't penetrate into an attic to begin with - thus making ventilation unnecessary. For retro-fitting into existing homes, all ventilation is removed and the foam is applied directly to the underside of the roof decking. It's good stuff and will be the modus-operandi of the future. For more info just check building science sites and green technology sites.

Here is a link that might be useful: Craftsman Home Inspection

    Bookmark   March 28, 2009 at 12:44PM
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Here is good way to learn more about attic ventilation. Try to keep the concepts of moisture control and reduction in heat gain separate in your mind even though they can be indirectly related.

Here is a link that might be useful: attic ventilation

    Bookmark   March 28, 2009 at 1:43PM
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