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Cathedral Ceiling Venting-Valley Raft...

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How soes one vent above valley rafters in a cathedral ceiling. The valley jacks block the air flow from the soffits. How are builders doing this and getting those areas vented above the insulation so it can run up to the ridge?

(post #177558, reply #1 of 14)

Bob - you might get more response if you post this question in the HVAC section. But you'd better have your asbestos underwear on! - jb

(post #177558, reply #2 of 14)



You kill me...........I laughed for 5 minuets
Joseph Fusco

(post #177558, reply #3 of 14)

Okay JB - Crazy Legs

Very funny - CL, I guess I could alos loook up capentry under wood. Attic venting an hvac question?? I don't think so, but my undies are on fire already just from your comments. No problem, I can take it, Steel Wool undies.

(post #177558, reply #4 of 14)



I think what jb, alludes to is the fact that this topic is always a "hot bed" of debate. You should wear "fire proof" gear if you wish to enter.

Joseph Fusco

Fusco & Verga Construction Co., Inc.

"The price of apathy towards public affairs is to be ruled by evil men." -- Plato

(post #177558, reply #5 of 14)


I do not vent my valleys but if I did this is how would do it..

The valley is usually not as deep as the plumb cut of the valley jacks. We rip and bevel a strip to make the top of the valley plane out with the top of the valley jacks. We also bevel the bottom of the valleys( Thanks Ken Drake for setting me straight on the bevels). To vent the valley drill holes in the strip that covers the valley then drill holes in the valley jacks. The holes in the valley jacks need to be towards the bottom end and close to the top of the board. I would make 5 or more holes 3/4 if possible. First check with engineer.

(post #177558, reply #6 of 14)

Hey Bob, sorry if I offended you. I meant to help you get response instead of ignored. I just looked, and you're right, the section is called "Energy: Heating, Insulating, and Venting a House" not HVAC.

There is a long established method of communicating here called "flaming". Venting is one of the more hotly argued subjects on this board. Many folks have strong beliefs, for, and against venting. So these topics often lead to "flaming posts" from folks.

Again, sorry if I offended you. I meant it as a good natured warning. - jb

(post #177558, reply #7 of 14)

No Prob. I have to ask such dumb questions to get all the facts mon.

As you can see one or two people did answer - and I did get the answer I suspected. They don't vent this space or they suggest cutting holes to let the air through- with questionable structural results.

Is is just that you don't need to do it because it doesn't present a problem of ice dams or whatever.? I think the Icynene insulation guys may have it right - NO air - NO sweat(ice).

This item is one of varied opinions as I have seen from other discussions and I don't know if anybody really has an answer. Whatever will be will be.

No offense taken - I understand that opinions are like a**holes - everybody has one. Expereince is what I am looking for - knowledge from doing it before and figuring out a great way to accomplish the job. We all want that I think.

(post #177558, reply #8 of 14)

Oh my Fred !! - Are you implying that you are not venting or not insulating. Surely you are insulating but not worrying about the vents. The money being made is for call backs on ice dams in valleys ???? Huuummmmm......

(post #177558, reply #9 of 14)

Dave - as I suspected - no vents. The hole method does scare me a little. Structural breaks in the rafters could weaken them I suppose, especilly under heavy snow loads in valleys where snow does not slide off the roof as easily. Have you seen anyone do it the way you suggest and what results?

(post #177558, reply #10 of 14)

Fred- thanks for the update. I will check out those articles. I have done some more research and I am definitely of the conclusion, based on sound research from other techinical experts in this field that the best thing to do with a cathedral ceiling is insulate it tight to the underside of the roof and seal the heck out of the ceiling to prevent indoor air from escaping to the rafter space.

There is no conclusive evidence that roof shingles wear out sooner even in warmer climates and ventilation of a cathedral ceiling or any other complicated roof with dormers, skylights, hips, valleys for that matter is next to impossible to properly and adequately ventilate naturally with soffit and ridge or other vents.

This is what I am going to do for my new house in Maine. Thanks for the input.

Oh- are you the Fred Lugano of earlier FHB fame. Are you still writing for FHB?

(post #177558, reply #11 of 14)


I have seen something similar to this done with TJI framed roofs. The TJI rafter is installed upside down(with the knockouts towards the top) and the knockouts are all removed. The idea is that you get ventilation not only from the eve to the ridge but also air flow side to side and into the valley jacks -almost a cold roof. I haven't done it myself and I won't be trying it any time soon. I haven't had any leaking problems in my valleys--yet.

(post #177558, reply #12 of 14)

Sound possible with TJI's but I am more of the opinion now that venting is an old science that has had its day. Not venting the attic is the way to go for a cathedral ceiling. It keeps the air from the house from rising into the air cavity and causing snow to melt/freeze etc. Check out FHB 125 article by Fred Lugano. I also have researched Icynene insulation and plan to fill my rafters to the brim with it. No vents, no ridge vents, no soffit vents. ASHRAE has extensive research that supports this and that is good enough for me. Good luck on your projects.

HOw is that unvented roof working for you? (post #177558, reply #13 of 14)

How is that unvented roof working for you?


do (post #177558, reply #14 of 14)

This thread is very old, might even  be from back in the real old days.  Guest is now listed as guest archive..........long gone.

A Great Place for Information, Comraderie, and a Sucker Punch.

Remodeling Contractor just outside the Glass City.