Some Roof Vent Questions

[ro]

In a small house/cabin, how important are roof vents?

In a small house/cabin where you're trying to maximize space with a loft, are they a detriment to overall insulation?

Is their primary function for heat or moisture control?

Are there particular climates that require roof vents more than others?

Are there openable/closable roof vents to adapt to different seasons? Or would small working loft windows serve the same purpose?

Are they better mounted in the actual roof or in the gable walls?



Thank-you in advance for any answers/ideas/provisos...

[MarkAndDebbie]

here is a pretty good rundown -
http://www.countryplans.com/cgi-bin/yabb2/YaBB.pl?num=1179830620/9

Basically you have to vent the space between the ceiling and roof to get rid of the moisture. Mount in soffit and a ridge vent. Windows would be below the ceiling. No need to open/close - open all the time.

THe other option is tight seal. check out the posts on iceen (sp sorry).

[ro]

Thanx M&D, that was a helpful thread!

(PS: I did search the forum before, but must have messed up, because that one didn't come up. )

[skiwest]

I'm doing a hot roof or artic roof so no venting.  


check out http://www.nuwool.com/products/technical/cathedral.html

http://www.dow.com/styrofoam/na/res-canada/installations/wallmate_tongue_groove_install.htm

http://www.dow.com/PublishedLiterature/dh_0036/0901b80380036189.pdf?filepath=styrofoam/pdfs/noreg/178-00790.pdf&fromPage=GetDoc

[glenn kangiser]

Icynene search should get you info on Okie BoB's favorite insulation - sealed system - sprayed on by installers only -- good but spendy.

[ScottA]

There seems to be alot of disagreement on this subject. Some say you must vent and others who are saying the vents cause more problems than they solve. I'm going unvented on my project by laying up foam board over the plank ceiling that'll be on top of the rafters (exposed rafters) with OSB and roofing over that. No air space at all between the roof and the inside. Another reason that was given for venting besides moisture was to keep the roof cool in summer, but studies have shown that roof color and not venting plays the biggest role in keeping a roof cool. I belive that codes in most areas now allow sealed cathedral cielings.

Scott

[John Raabe]

What I understand is in agreement with Scott. Venting is turning out to be less important in a roof (as it is in a crawlspace) than we had previously thought. Venting can sometimes cause more moisture problems than it solves.

There may be local climate reasons to provide venting (in a raftered roof) so check with the building department on what the local spec is on your situation. Yes, sometimes they can be helpful even if you don't get a permit.

[Okie_Bob]

Since Glenn so kindly mentioned my name in association with one of my favorite subjects, I thougt
I'd throw in my 2 cents worth. And as John so appropriately stated, venting is falling out of favor for cutting edge designs. Seeing as it is now into fall, we are into our fourth season change in our house with non-vented, fully sealed Icyene insulation and have experienced NO problems whatsoever. In fact, the longer it goes, the more we seem to like everything about it and have no dislikes yet, at all.

As Glenn pointed out, it is spendy and must be installed by a trained pro. I don't see that changing anytime soon, unfortunately but, there may be other similar products available now that are equal in value and less expensive and DIY'er friendly. At least I hope so.

BTW, this is my second investment with Icynene. The first was the garage with living space I have been in for 3 years now, I believe. I did not so a complete non-vent with it but, wish I had. No problems with it either but, I'm becoming convinced that it is not as efficient as the complete non-vented house. Just a suspician at this point, I can't back it up with numbers and doubt I ever will be able to.
If you want to go to my blog site, scroll way down and you'll see before and after pictures of an Icynene installation with the exception that I do not have any pics of the underside of the floor which also is completely sealed with Icynene.
www.bobdanaslakehouse.blogspot.com should get you there.
Okie Bob

[Okie_Bob]

Sorry, I just went to check out the pics and realized you now have to go WAY down to get to the Icynene pics. They are dated 06/03/07.
Okie Bob

[hnash53]

One could use fiberglass insulation with an unvented roof system if one put up a plastic vapor barrier over the insulation before putting on the finish surface.