I am going to be building a home in heavy snow country. It is not unusal to have two or three feet of snow on the roof for a month or more at a time.
Part of the house would have a catheral ceiling, parts of it would be a story and a half, meaning knee wall with sloped ceiling and a very small attic space (vented in slope). Soffit vents would be present wherever possible, but some dead valley rafters would also be present.
To start with, let us assume we have soffit vents in a catherdal application. Are standard ridge vents good enough to keep the roof cool (assume R 40)? Are they good enough if covered in two feet of snow?
I was thinking about building a custom ridge cap by adding a mini roof to the peak of the roof. I would do this by adding 12 inch 2X2s nailed over the rafters at the peak on each side of the ridge. Then nail 18 inch 2 x2s on top of the 12 inch piece creating a 6 inch sheltered over hang. This would be sheathed over and roofed. Of course there are other details and screening. But the point is that the vent size would be much larer than factory vents, and a sheltered pocket would be provided. Still the air would have to move through the snow.
Would this improve the venting?
Before people think this is crazy, if you have been in heavy snow country you have seen these little roofs atop the roofs. I am only assuming they are there for vent purposes. But the question remains do they work better?
Replies
Roof Vents
Do people just not like this question?
doright
It might be that there's no informed opinion on the subject.
I know I have none. I'm not in "snow country', but for the past several weeks, there's been snow covering the ridge vents and most of the time the normal sq. roof vents. That's what happens when it snows and the roof doesn't melt off in the sun.
It's plenty cold in the attic so warm air isn't thawing out the vent areas. Problem? not that I'm aware of.
no "informed" opinions?
Maybe no one has an "informed" opinion on the subject? Since when has that been a deterent to responses on this board. LOL.
What you suggest is possible and even likely, but you have to admit what I just said above is also true. It is all good. No complaints, what can you expect on a message board. We all sift through the good bad and the ugly.
I just through my comment about no one liking the question as a when to bump the question back to teh top in case someone with an "informed" or otherwise comment missed it the first time around.
YOur vents are not melting clear. Ok. But you also say it is plenty cold. Therefore, the attic as you say is plenty cold. The issue I am thinking about is when temperatures are higher, or you have three feet of INSULATING snow on the roof deck. And even a bigger potential issue is in a cathedral ceiling where insulation is perhaps a lower R, and you only have that 1 or 2 inch air space. The air needs to move up and out.
Anyway, you have no "informed" opinion, so don't feel obligated to reply. But I am always happy to hear from you. Thanks for the banter.
I don't often do this...........
but you might go over to the other side and seek out Imerc. He lives in some serious snowy mts of Colorado. He might have and opinion for you. Be forewarned, he only uses a couple words.
I think the air flow you are thinking of is needed to cool the roof in summer months. I don't understand your concern over the lack of this air flow in winter with three feet of snow on the roof. It should be plenty cool then. Ventalating the attic I guess. Find something else to worry about :)
Ya never know what will happen here on BT. Sometimes threads with seemingly important subject matter attract little or no attention. Other times threads that seem dull attract a firestorm of posts.
There's no way to predict it...
Do Right,
A short answer to your question, IMHO, is yes the larger ridge vents you describe would help,or at least would do no harm, assuming your design has weather protection to keep rain and snow from entering the attic space.
A longer answer is that your "dead areas" should probably be insulated w/ a closed-cell spray foam in the rafter bays. The cathedral areas usually have a built up roof to allow for sufficient insulation (R-40 or greater) and ventilation. The key is to keep that attic area, or the underside of the roof sheathing as cold as the outside air from ridge to eave, that is what will prevent ice damming and the related water damage that comes with them.
The secret is to seal all the "leaks " of any air from the conditioned areas below, up into the attic, so that no warming of the roof sheathing is done from with-in the structure but rather only from the outsided,melting the snow cover naturally.
A key component is also to be sure you get sufficient air flow from the soffit area to create the"cooling" effect you need.
Hope this is of some help,
Geoff
Yes, you understand the question
You said "A (the) key component is also to be sure you get sufficient air flow .... to create the cooling effect you need."
Exactly! This is teh question regarding factory ridge vents. I am sure there is little problem with them in the summer for cooling. A hot roof under the sun heats teh roof and the air under the decking and you get one heck of a convection flow. In the winter the temperature differential is very low ... And .. did I say AND .... And if the ridge vent is unable to move any or little air out of the vent channel YOU MELT SNOW on the deck. So the question to all, was and is: do factory vents move enough air even when covered under snow AND / OR would a larger vent opening be helpful or would it still have the same problem moving air through the snow?
As for the guy saying the roof is plenty cold with all that snow up there... sure snow is cold, but it is also an insulator! It traps teh heat from the house and the heat melts melts the snow if it can not escape out the ridge. hence the question.
Thanks everyone.
Do
Keep the heat from getting in the attic and you'll only have roof heat to worry about.
period.
Hey Cal
Sure, but I guess I have always assumed that regardless of teh R value heat moves through the insulation. Simply put, the higher the R value the slower the heat moves but it does move. If this were not ture we could insulate a house, heat it up one time, and never heat it again. LOL. The point is some heat travels through the insulation, and if trapped it will melt snow.
I suppose one could say, since the it takes 80 calories to melt snow, as opposed to only 1 calorie to rise the temperature of water 1 degree C, it takes a fair amount of heat traveling through the insulation to start that melting process, which gives the air time to filter out the ridge vent and filter through the snow covering the vent.
I understand what you're saying, but..............
Block all forms of air leakage from the inside of the house, and there's no heat/air movement. Period.
Easier said than done? Sure, but if you try (building new, right?) you should be able to stop a whole lot more than you seem to think.
Airtite cans if you use 'em.
Caulk the plates and all joints in the framing. Caulk the wallboard to anything that doesn't move.
Don't forget sealant in all the electrical ETC, penetrations.
Foam your windows if that's what you like to do.
And more/more/more.
Sure Airtight
Maybe that is all that there is too it. But heat still moves through insulation, NO?
You say and foam your windows if you like? Why would that be an option? Or are you saying stufing FG in is good enough?
AIR can move through fibreglass the easiest.........
compared to blown celulose. Cold or warm, doesn't make a bit of difference. Air movement is what you should be trying to limit. 10 feet of insulation with air moving through it is ............a waste.
I'm saying about windows, that stuffing can be one way if the window is installed properly w/o a huge rough. Sealed well on the exterior, framing joined tightly and things like headers done well and air movement proof, perhaps a gasket sort of thing using backer-rod, and judicious caulking of plates, wallboard, etc....................yeah, good solid stuffing works at least as good as stingy application of the low expansive foam I run into.
You or someone else mentioned the blackened fibreglass look showing air momement through it.................well, you can often see that black on window stuffing.
But, you can also not see it.