Venting 21:12 cathedral church roof

I’ve got a church with shingles over tongue and groove boards that are exposed from underneath, about a 50’ height of roof at 21:12 pitch…I am very knowledgeable about roofing and ventilation, but why would I want to vent this?? After tearing off,what is adding battens and sheathing or a preformed system (ISO–gap–OSB) before reshingling it going to do for this roof. Maximizing the life of the roof and preventing condensation and ice damming are the 3 reasons for venting, but how is this going to help in this cicumstance?? Please don’t answer if you don’t REALLY know what you’re talking about.

I don’t know. Why WOULD you want to vent it.
An being as you are sooo “knowledgeable about roofing and ventilation”, why do you even ask?
Also, why would you "add battens and sheathing"
What do you mean ISO on a shingle roof?

Knowledgeable about roofing and ventilation on houses and normal residential applications…polyiso is also put on steep slopes to provide insulation on a compact system, not just low slopes. Battens and sheathing or sleepers, whatever you would call it, to create airspace between existing roof deck and new shingles. I have talked to a tech at AirVent and Certainteed, a Union HVAC superintendent and an architect and I have votes 2-2 to vent or to not vent the roof. My main competition is telling the church to vent it and when I go to see the board I want to be as educated as possible about it so Ican not only be awarded the job, but also so that I will do the job to the highest standards. I’ve left a message with an NRCA tech and am awaiting a reponse. The thing I love about this site is the few that answer with a smart comment instead of truly trying to be helpful.

Every cathredral roof I’ve done had insulation over the decking, none were vented. The primary concern with useing perlins and redecking is the fasteners can’t penetrate the ceiling which is the exposed decking on the underneath side. Thats a lot of weight to not be fastened properly in my opinion, but the older I get the more I find out how much I don’t know.

I’ll be watching this thread, I might learn something.


Churchs are different then houses. They heat them differently.

You say you are addressing ice dams. Does this church ever get ice dams???

I have not seen churches of the type you are talking have ice dams. So are you trying to treat a problem that does not exisit? I find that this happens a lot. Prople hear about ice dams and ventilation and do not consider if they even have a problem.

How long has the last roof lasted?

How would an ice dam form on the pitch you are talking about?

Knowledge may not get you the job. If everyone on the board watchs the home improvement shows, they may believe the tv personallity not the experienced roofer.

Throw away every ones opinions and contact the Shingle Manf for the shingle your going to use on the church.

Ask them how to correctly ventilate this roof so that after it’s installed the shingle will remain under the manf. warranty.

In this way your going to the authority for the shingles. Now take what the Manf told you and make sure it’s code for the municipality the church is in.

And is it really a question of, “Why would I want to vent it” or is it a question of, “How should I vent it”.

The way you phrased your post was hardly designed to elicit a cordial reply.
I am not going to waste my time pointing out how inarticulate and fractured it is.
You should have labeled your post “rhetorical question” and then offered up your “predicament” as a reason for asking it.
Look back some and take a lesson from “jcrew”.

The way you worded your initial post was just a bait to try and show some one how smart you are. Stop trolling so you can flame bait people.

With 50’ runs it is not going to vent very well anyway.
It probably doesn’t need it but if the people controlling the purse strings want it vented, bid it that way or both.

thanks bushhog and axiom for your input, I am not trying to show anyone how smart I am, that’s why I came asking for answers, there are quite a few guys here who’s knowledge I have a lot of respect for and I was hoping for some very technical input that I haven’t heard from the people I’ve talked to on the phone. Bushhog brought up a good point about the fastener and weight issue that none of the techs have mentioned and I will be using that with the church reps. I never said the church has ice dam problems, I stated that as one of the 3 main reasons you would normally ventilate a roof, but I had already ruled that out in this application. I pretty much ruled out condensation also because the airgap and the air in the peak of the chapel are still going to be very different temps in the winter and their is no airflow along the underneath side of the existing deck. The reason I said please don’t reply unless you really know what you’re talking about is because I’ve already talked to Certainteed, NRCA, Airvent, an architect and an HVAC guy so I was hoping someone would come up with something noone else has told me yet, I’m not trying to bait anything or be condescending. I’ve been roofing for 10 years, not long compared to alot of people and I respect that and thats why I would like to use this forum to gain knowledge, not really to help others becase you guys usually do that well enough when you don’t get sidetracked and your egos start causing squabbles that people really don’t care to hear. Thanks to anyone that gave me constructive advice and sorry to the others that misunderstood.


My comments are not directed towards you, rather another poster who came off condesending.

I helped as a sub for a contractor on a job just like you are describing. The goal was to get some insulation on a roof that was post and beam, 4x12 rafters 24"o.c.,w/2x6 deck,and 3 tabs. The system called for 2x 2-1/2" insulation boards,w/2x4s 24"o.c. screwed w/special screws(proper lenght)and then 5/8" plywood w/clips nailed conventionally to 2x4s.with ridge vent.
I hope this info was of some use to you!
Good luck in your venture…

Just an FYI…

I had 2 similar churches, both needed to be reroofed. the first church, after playing with the numbers, decided to go with 2 layers of 1 inch ISO and then shingles over the ISO. the other decided, after talking with the shingle manufacturer and architects, to have installed 2X6 standing on end on top of the T&G decking, fill 4 inches with EPS for insulation, and then 5/8 decking and lastly, the shingles.

the first church thought, given the extra costs, if they had to install 3 roofs in 30 years, it would still be cheaper than doing all the extra venting.

5 years later, the second church is already replacing the shingles. the manufacturer said something is wrong with the shingles.

the first church that used the same exact shingles, looks as good as the day we installed them?!?!?!

excuse me , uh, hawaii50,
da,da da,da daaa daaa , da,da da,da daaa.


can ya just please do the same thing that has worked
for the last how ever many years, please.

dont try to reinvent the wheel.

you may have 3" thick tounge & groove and not need
any insulation.