# Vaulted Ceiling - Flat Roof - Heating Concerns



## Onarooftop (Oct 28, 2008)

Many different ways to complete this.

Low Slope 2/12
Vaulted ceiling below (finished off/drywall)
Aprox. 6 sq.
Ties into shingle 6/12
Customer Concerns - Very cold in that area of the house. 

How would you attack this project?

Onarooftop


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## shazapple (Dec 3, 2010)

There could be a lot of reasons why that area of the house is cold. Is the existing joist space uninsulated? Has he done any insulation or air sealing? Is there adequate return/supply air or heat? The customer should have an energy audit performed if he hasn't already. 

If he's been told that he needs insulation it would help to know what is existing. Maybe you can remove the existing roof and add new insulation over the existing deck.


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## Grumpy (Oct 29, 2008)

Let me get this straight, there is a ceiling beneath the flat roof, Correct? I'm assuming the ceiling is not vented, meaning fresh air is not being introduced into the conditioned space.

How much space between roof deck and ceiling? 12"? Treat it like a traditional cold deck design ?(shingle roof venting) You can remove the flat roof and substrate, fill with 1"" fiberglass insulation leaving as 1" space for air flow. A continuous intake, and exhaust would then be necessary. I'm assuming the air flows continuous into the shingle section, in which case an exhaust wouldn't be necessary. 

I haven't had the problems Mike described on the other forum with freezing condensation between rafters etc... WITH proper ventilation. If you do blow in (Better to use Bat), it will be hard to control the height in such a confined space and better to then use cellulose insulation which will settle to provide that space. So long as you have not less than 1" air space (preferably more) at the bottom of the sheathing and continuous ventilation so each rafter bay gets vented, you'll be OK in my experience. What Mike is describing about freezing condensation is what we call phantom leaks. Don't get me wrong we get a few leak calls every winter for phantom leaks. It's almost always a result of improper insulation and/or ventilation. 

If R ~30 (10") isn't enough, or you can't get an intake, or there isn't enough room for 10" of insulation then I would default to Mike's Recommendation of the warm deck. Although nobody around here uses a vapor barrier, it wouldn't be a bad idea.



From a risk management point of view, what ever you choose to do, be sure to CYA. Just because you improve the ceiling insulation does not mean you will solve their problem. Are the windows leaking? How much ventilation in the walls? Is the air duct feeding hot air blocked or under sized? I know from experience, having a similar situation with an addition that was improperly constructed before I bought my home, that the recipe usually has more than one ingredient. Even if you fix one of the symptoms, there could be more.


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## LCG (May 30, 2011)

Single ply tie in:

Warm deck as Grumpy calls it. I would take the the roof down to the rafters and fill the entire cavity with insulation. Install necessary Plywood. Then, add 1-2" of rigid poly-iso to the top deck. Install single ply as recommended by manufacturer.

or you can install single ply over the system recommended below.

Shingle tie in or single ply

Everything above applies, except.. Instead of installing rigid poly-iso you would install a cold deck panel by Hunter Panels (or whoever you choose). You can buy whichever thickness of Rigid-ISO you want. Then they install breather strips and a plywood/osb cover board of your choice. Install your roofing system as necessary.

***I am not a big fan of installing breather strips inside of rafter bays anymore. To be honest we have never had an issue with doing it that way but I feel there is room for error. The error comes from thermal bridging or blockage. If for some reason the ventilation fails then condensation WILL occur inside the rafter bay. Then you are chasing "phantom" leaks, again. Not that it's wrong, it isn't. There are just better products available for this procedure. Then again time and budget are always an issue. We installed it both ways last year!

The hunter panel will allow for a top deck installation allowing for the entire rafter bay to be insulated. That extra inch will give the homeowner and extra 3R minimum. Depending on your thickness of ISO on the top deck you can gain 7+ R per inch.

The biggest reason we prefer the cool deck is the fact that ventilation occures in EVERY DIRECTION. The entire deck breaths. It is nearly impossible for the ventilation to be obstructed. Granted some home owner could spray foam the intake rendering the entire system useless but homeowners tend stupid crap whatever the system may be.

We posted a job on this forum that we did this year with the coold deck. It wasn't some fabulous job but I thought it was a good way to show how the system works. Take a look. http://www.roofingtalk.com/projects/hunter-panel-cool-deck-w-slash-16-bridger-steel-sl-panel

Here is a link to Hunter Panel for further information http://hpanels.com/index.php/engineered-products

Again, you can use single ply over the top of this panel. Just make sure you over fasten the panel and use plywood as a top deck on both the home and panel to ensure your wind uplift rating is achieved.

Sorry for the long post. Hope it helps.:thumbup:


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