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-   -   ventilation baffles in cathedral ceiling (http://www.diychatroom.com/f19/ventilation-baffles-cathedral-ceiling-70320/)

HHac8014 05-01-2010 09:35 PM

ventilation baffles in cathedral ceiling
 
I have a great room with a cathedral ceiling that contractors have recently removed a 4 foot strip (at the top peak) of drywall from. The ridge of the roof has a ridge vent. However, I'm not sure the ridge vent is doing its job - because I'm not sure air has a good passage from soffits to the ridge vent.

I'm familiar with the short fat rafter baffles to use in an attic - but is there a looong skinny rafter baffle available that could inside the six inches of a cathedral ceiling from soffits to the ridge vent?

RoyalAcresRod 05-02-2010 06:28 AM

It is difficult to get sufficient insulation when only the depth of a vented 2X6 is available. Typically 1.5 inches is needed for ventilation (a 1X2 nailed to the roof side of the 2X6 can provide a nailing surface)

That leaves you 4 inches for insulation. Even with high-value polyisocyanurate, you'll only get R-26 or so in that 4 inches.

HHac8014 05-02-2010 03:25 PM

I think I've got about that in ventilation space. The insulation used was build foor 2x4 walls, so when placed in the 2x6 cathedral ceiling, it's got some breathing room above it.

My concern is that it likely is bunching or sliding at spots, and thus losing ventilation flow. Perfect situation would be a long skinny 10-foot baffle to slide in each of the rafter bays. I see nothing on the market like that.

RoyalAcresRod 05-02-2010 04:16 PM

You nail a 1X2 to the roof side of the rafter bay (nail to 2X6). Get a sheet of polyisocyanurate foam board, and cut it to the width of the bay. Nail foam board to the 1X2 with plastic-capped nails. This will give you a 1.5 inch ventilation "shaft."

However.....not to nag, but if you use fiberglass for the remainder of the insulation fill, your total R-value will not be very high. R-4 approx for the 1/2 foam board, and R-13 for the fiberglass...only an R-17 ceiling....not very high for a ceiling!

rod

Gary in WA 05-02-2010 07:35 PM

The baffles should be installed before the insulation. If you don't use baffles, the insulation will be wind-washed by the incoming air from the soffits all the way to the ridge- taking your heating dollars with it. R-13-15 is not enough insulation. Furr-out the rafters to get the recommended R-value for your area: http://www.ornl.gov/sci/roofs+walls/...on/ins_16.html

Be safe, Gary

Scuba_Dave 05-02-2010 07:49 PM

Quote:

Originally Posted by HHac8014 (Post 436653)
I think I've got about that in ventilation space. The insulation used was build foor 2x4 walls, so when placed in the 2x6 cathedral ceiling, it's got some breathing room above it.

My concern is that it likely is bunching or sliding at spots, and thus losing ventilation flow. Perfect situation would be a long skinny 10-foot baffle to slide in each of the rafter bays. I see nothing on the market like that.

Where are you located ?
I have min R30 in my (older) cathedral ceiling & newer ceilings with 2x12's will have R38
You will pay more in heating/cooling costs unless you have more insulation
Its well worth it to fir this out to fit more insulation in

HHac8014 05-03-2010 07:58 AM

1 Attachment(s)
I'm in Decatur, Georgia. So, technically R26 should be OK... I like the ideas of the 1x nailer, but I only have access to the top 2 feet of the cathedral ceiling.

So, it sounds like another option would be to use expandable spray foam, and fill up the bays completely. Right? If I fill them up completely with spray foam (essentially becoming a solid), ventilation isn't necessary right? (And in theory, I could get rid of the ridge vent (?))

RoyalAcresRod 05-03-2010 08:30 AM

Yes, you can spray foam the entire rafter bay...but at what cost? Using that scenario, all the drywall is going to be torn off. You really need to look at the entire cost of what you are intending to do, and the resultant utility costs.

I'm somewhat befuddled at your statement that you only have access to the top two feet, then talk of foaming the entire bay. You know all the drywall going to have to come down and go back up to foam the bays, right? And you'll still have less than R-38 in that instance.

I believe your most cost-effective option is to furr out your existing rafters with 2X6 or 2X8s to get additional depth. YOu can either use use the method I detailed above for an air channel, or staple commerically available air chutes.

I realize some use foam for the entire bay, but I believe it important to have ventilation area/

As in all things in life, you can go the cheaper route initially, but will pay more in monthly energy costs moving forward.

You really need to calculate all your costs for various scenarios, including how long you intend to stay in this home.

Scuba_Dave 05-03-2010 09:01 AM

Some roofing Mfgs require ventilation for their warranty
In a hot location I would never eliminate the ventilation
Better to tear down the ceiling, fir it out & spray
Cathedral ceiling in your area they say up to R38 is best
Meeting the min is not a good idea, always better to max out the insulation

HHac8014 05-03-2010 10:08 AM

Royal, I admit I didn't actually understand the furr'ing process being mentioned, now I get it though. That may make sense.

I had thought spray foam could be sprayed in from the top of the cathedral, using gravity and velocity to go all the way to the bottom of the rafter bays. But, yes, if all the drywall has to come down, it seems like furring and adding stronger r-value insulation would make sense.

Would re-drywalling that ceiling cost me a fortune? I don't have the equipment or skills to do that high of a ceiling.

RoyalAcresRod 05-03-2010 10:32 AM

I don't think you've mentioned the size or height of the room, so of course we couldn't comment on the cost. Some measurements and a few phone calls will give you some ballpark figures.

There are always used drywall lifts on Craigslist and ebay.....I know many who have bought new or used ones, then re-sold them after they're done with them.

These projects are invariably expensive and/or time-consuming to do correctly. But the pride afterwards often makes it worthwhile and gratifying to many of those in these precincts.

And of course the project can be broken up into bits of DIY and hired work...depends only on your pocketbook, level of self-security in doing the work, time available, and your comfort in performing some tasks for the first time. But there are plenty of folks on this site who will take their time to walk you through the process.

rod


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