1. Bob Thoreson
   Member
   

   The two sides I've heard:
   1. Venting an attic that has been well air sealed and insulated only derates the R value because of whirling winds in the attic and a colder attic in the winter.

   2. Lack of attic vents can cut the life of a roof in half due to excessive heat buildup. Heat is what causes composition shingles to curl.

   When energy savings of an unvented attic is compared to a $10,000 roof, it doesn’t pencil out. I think I have a gap in my knowledge base. Please help me fill it in.

   Posted 1 year ago #

2. DanWildenhaus
   Member
   

   As per the life of the roof, I have heard this arguement before. I know the Canadiens have studied this and decided that this is only likely in the southern United States. I would only be concerned with dark roofing material that gets a lot of sun.

   http://www.efficiencyfirst.org/blog/2009/07/30/white-roofs-20-percent-reduction-in-energy/

   Another option? How about solar panels covering most of the roof once the venting has been sealed! Problem solved!

   The state building code has a proposal to allow for unvented attics in Washington State starting next July. It should be interesting to see what they put out.

   Posted 1 year ago #

3. RyanArnold
   Member
   

   What about the arguement that venting attics prevents moisture buildup and mold issues due to any minor roof leaks, humid climates, bathroom fan duct leak, etc...?

   Also, I agree that whirling winds may devalue the R-value of the insulation in the winter by allowing for a greater heat loss via the ceiling, wouldn't attic venting be preferable to allowing excess heat build up in the summer, which transfers heat back into the building and preventing an over night flush out keeping adjacent building envelope temps high?

   Why is WA considering allowing unvented attics? Is there additional benefits besides a small possible insulation devaluation when there are crosswinds?

   Posted 1 year ago #

4. Yves Vetter
   Vice President
   

   I believe vented attics have several drawbacks in addition to energy performance that aren't usually discussed:

   1) The venting is usually inadequate, so the supposed effects on heat, moisture etc are rarely realized (that's why it's usually so hot in 'vented' attics in summer).
   2) And in winter, moisture from the living area may condense on the underside of the cold roof deck. I've seen this often.
   3) The venting is often an entry point for mischief: critters enter there; moisture enters through the vents (wind blown or from e.g. drier venting); the phone company chops out screens to put cables in etc. I've seen this often.
   4) People always use attics for storage. Vented attics mean the ceiling insulation gets trashed because of this. I've seen this often.

   And there's more...

   Posted 1 year ago #

5. Mark Clouse
   Member
   

   Lots of good things said, yet I'm on the side of venting, and I do agree that most of the passive venting installations are poor. The typical backwords characteristic is the peak venting (if any) is very inadequate and limits the temperature reducing characteristics. Yves, some of your comments are accurate for an unretrofitted home. I think we should also discuss the topic from an "after retrofit" perspective.

   1) "swirling winds" - I guess it could happen in a storm, but I've never seen evidence of this that I can think of.

   2) An unvented attic with direct solar exposure is going to get very hot and negatively impact interior temp. gain during those hot summer days (remember last week? - are you insulating to a design temp differential of 100 degrees F.)

   3) If insulated and sealed adequately (stop stack effect) does it really matter to vent or not to vent, with the downside of not venting being increased indoor humidity and shortened roofing life with certain roof materials.

   4) A cool roof is desired for PV solar installation as the performance of Solar Modules declines significantly when the modules get hot. (20%+ performance decline when you thing it should be performing at it's peak)

   5) UV radiation on comp roofing shingles probably has as much to do with deterioration as heat.

   Fix the problems and it's probably not that big of an issue. IMHO

   Posted 1 year ago #

6. Scott Finley
   Member
   

   Years ago I used to preach the uselessness of attic venting. I believe lack of venting is not a primary cause of attic moisture and condensation, nor is adding venting a cure for these problems. However, over the years we have addressed literally hundreds of attic mold problems, and I have noticed a loose correlation between attic moisture and lack of ventilation. This is what I think is happening:

   In a perfect world, there is no air leakage through the lid between interior and attic, exhaust fans are all properly ducted, etc. In such a case attic venting is superfluous at best. In a newly constructed house where you can insure there is virtually no air leakage, there should be no problem with an unvented attic. Roofing lifespan will not be shortened by overheating, at least in this climate, according to research. The real solution to preventing moisture problems is, of course, sealing out as much interior warm, moist air as possible, however in the typical attic there is usually no way of assuring a complete air seal. In this case I believe some venting can dissipate a small moisture load. We don't usually ventilate to code levels, but I am not comfortable leaving a retrofit attic with no venting. When it is baffled properly there should be no significant problem with degradation of insulation R-value.

   Posted 1 year ago #

7. Yves Vetter
   Vice President
   

   Hi Scott, Mark, all,

   I didn't mean to suggest that we leave retrofitted homes with ceiling insulation and unvented attics. Just that the 'vented' attics I've seen often have many of the problems venting is supposed to address, as well as some unique issues. Whether the attic is vented with ceiling insulation, or unvented with roof deck insulation, each have their place, and both perform well or not based on construction quality and attention to detail, not on the particular design. The same old story!

   Posted 1 year ago #

8. Fred Mitchell
   Member
   

   All,

   I believe that states allowing unvented attics require that 40% of the void between rafters is filled with closed cell foam. The rest of the space can be filled with cellulose. How do you know if you have a leaky roof? Seems like you could do some serious damage to the roof deck?

   Posted 1 year ago #

9. Bob Thoreson
   Member
   

   40% closed cell foam seems to be going the right direction, but falls a bit short. It does the air sealing job intended, but as Fred points out, could lead to a problem in the rafters if there is a roof leak. If the foam were installed on the outside, in interlocking sheets, the only wood open to roof leak damage would be plywood sheeting that covered the foam sheets that the roofing was attached to. When re-roofing in the future, if there were a leak, damage would be contained to the plywood sheeting which would have to be replaced or patched when you re-roof, but the rafters stay safe.

   Posted 1 year ago #

10. Charlie_Rogers
    Board Secretary
    

    What about cathedral ceilings? I was under the impression folks were dense packing cathedrals with cellulose and not leaving any void. This would seem to be easily susceptible to a roof leak. What else can you do with a cathedral?

    Posted 1 year ago #

11. Yves Vetter
    Vice President
    

    Hi Bob, Charlie, everyone.

    In Seattle, now, we can use spray foam in a roof deck underside so long as we baffle the deck so that it can ventilate. (There is no 40% rule. 2" with net FG is typical). I've always thought of the baffle as unnecessary since the foam should prevent condensation problems by isolating the roof deck from household moisture, but perhaps it is appropriate if you're worried about ID'ing a roof leak, as it would leak out the bird blocking of the affected bay if the baffling were done right.

    Rigid foam from above is a retrofit I've seen in some places I've worked. Eaves and other details are important or it looks poor. It's also a more work and doesn't solve the air sealing problem.

    However, I'm not sure the leak thing isn't a red herring. I have replaced many roofs that were found on tear off to have had water damage, both from leaks and from condensation. But I've never replaced a roof specifically because of a leak ID'd from below the roof deck. So my experience is that the inspection value of an exposed roof deck underside is nil. Wayne?

    I am much more wary of cellulose in a cathedral as described.

    Posted 1 year ago #

12. Charlie_Rogers
    Board Secretary
    

    Thanks for the feedback Yves. So what do you reccommend for a cathedral that, for example, has 6" fiberglass and an exta 1' void? I would think tearing out the ceiling and spraying the roof deck with foam would be cost prohibitive. And if blowing full of insulation is a danger with potential roof leakage in the future do you simply do nothing with the cathedral?

    By the way, what spray foam are you using? (I'll start another topic for this subject).

    Thanks.

    Posted 1 year ago #

13. DanWildenhaus
    Member
    

    Wow-

    Great conversation here! Washington States proposal will be for 51% closed foam roofside and the rest using batt or other product.

    As for adding venting to an attic that we are separating from the house, it doesn't seem to make sense to add much if any ventilation if there is no indication of damage to the roof or supports. After retrofit there will be less heat and moisture getting into the attic then before. I always caution however that someone will eventually vent the attic because they believe they must. Therefore, perhaps best that we do the venting to close to code and do it with proper baffling.

    Cathedral attics would have the same potential of roof leak that a standard attic does. If you are putting R-20 in rigid foam directly on the roof deck and then filling the remainder with blown product or batt, then you have exactly the same risk as a standard attic where the roof deck is insulated the same way.

    Our state code is addressing this issue and should have information available soon regarding the July 2010 code change.

    Dan W

    Posted 1 year ago #

14. David Vollan
    Member
    

    I heard of one condensation induced failure in Portland due to packing a cathederal ceiling with insulation (cellulose I think). The ceiling construction was T&G boards and the failure seemed to be where the insulation wasn't packed densely around can lights in the rafter bay.
    See the following link from a cellulose manufacturer in Michigan on dense packed cathederal ceilings: http://www.applegateinsulation.com/Product-Info/Technical-Pages/249234.aspx

    Posted 11 months ago #

15. David Vollan
    Member
    

    My conclusion based on what I have read/heard is that if dense packing cathederal ceilings without ventilation in working in Michigan then it will certainly work here. We completed one job this fall where we insulated a 1960s era uninsulated cathederal ceiling. We cut in an access point at the top of the ridge and then dropped a tube down to fill the rafter bays from facia board to the top of rafter cavity. Interestingly, while the old roof had soffit ventilation it had no ridge vent insulation, so it would have been the perfect condensation trap, yet there was no damage to the drywall, so apparently if any moisture was condesning it wasn't very much. We also insulated the walls of this home and did a little air sealing in an adjacent space, the end result being a 43% reduction in CFM50.

    Posted 11 months ago #

16. Charlie_Rogers
    Board Secretary
    

    Home Energy Magazine recently had a letter to the editor inquiring on the same subject. Here is their reply:

    Bill Hulstrunk, a technical manager for National Fiber, a cellulose manufacturer located in Belchertown, Massachusetts, replies:

    The Weatherization Assistance program, one of the first building science-based energy efficiency programs, has been dense-packing unvented cathedralized and flat roof assemblies with cellulose throughout the Northeast for over 20 years. The reason that dense-pack cellulose works is that the 3.5 lb/ft3 density prevents moisture-laden air, the major transport mechanism for moisture, from entering the unvented roof assembly. Any diffusional moisture is handled by the hygroscopic properties of the cellulose and dispersed, preventing the formation of liquid water and its associated mold or rot. The borate-based fire retardants may also be of some help, due to their antimicrobial qualities. Some of the more forward-thinking cellulose insulation manufacturers even warrantee this use of their insulation in this application for the life of the building. Some day, maybe our building codes will catch up with the tens of thousands of durable and energy-efficient dense-pack cellulose unvented roof assemblies out there.

    Posted 7 months ago #

17. Randy Sibley
    Member
    

    Krigger/Dorsi in their 'Energy Auditor Field Guide' make the claim that 'adding attic ventilation won't cure a moisture problem caused by airborne moisture migrating up from the living space". You should air seal the ceiling. And further that 'excess attic ventilation can drive ceiling air leakage through the stack effect . . .' (pg. 49) But I assume he is not arguing for completely unvented attics even after you have air sealed the ceiling and the floor to reduce stack effect. Or is he saying its ok to have an unvented attic? Also I would like to copy this forum, delete names, and provide it as an example to my class, ENRGY 120, at EDCC as a great example of how to go about working through the issues for a typical home performance upgrade. Thanks!

    Posted 7 months ago #

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