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Old 10-21-2013, 04:19 PM   #1
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Eclipse Foil Faced OSB question


I am about to start putting up insulation in my garage ceiling. Its a kind of cathedral ceiling with rafter ties about halfway up the rafters. Everything is 2x6, so I plan on R19 on the angles and r30 on the flat middle section. There will be insulation baffles up into the short attic space and a continuous ridge vent across the roof.

The question is that I was contemplating using Roy O Martin Eclipse foil faced OSB as the finished ceiling. My thought was that not only would it reflect the light around the garage, but some of the heat back radiating through the roof in the winter. I'd use unfaced insulation since the Eclipse panels act as the vapor barrier. My holdup is that I'm unsure of how this might act with the insulation. Typically these panels are used as wall sheathing or roof sheathing. In both applications the insulation is on the other side of the foil facing on the panels. I'm concerned with the heat and cold radiation from outside reflecting off the foil on the inside, rendering the insulation less effective.

Also, before anybody says it, I know what the code says about ceilings being fire rated. All pentrations and adjoining walls to the house have either 5/8 rock and or sealing foam. I'm more concerned with fire spread which has been already addressed than flammablilty.

I tell myself some insulation is better than nothing, but I don't want to unnecessarily waste insulation value for some extra light.

Here's a picture of the framing so you can see the layout.


Any thoughts?


Last edited by iminaquagmire; 10-21-2013 at 04:39 PM.
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Old 10-21-2013, 09:27 PM   #2
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Eclipse Foil Faced OSB question


Sorry. I don't know what to tell you about the radiant-barrier OSB. But I have some concerns with the design of that garage. If those 2x6s attached to the rafters are truly at rafter mid-point, then they suffice neither as rafter ties nor or as collar ties. Rafter ties should be within the bottom third of the roof height, collar ties within the top third. What this means is that your walls are vulnerable to spreading, and your roof is less likely to stay together in very high winds. I recommend installing collar ties and rafter ties 48" OC.

BTW, the rafter ties would not be necessary if you had a ridge beam, but it looks like you have just a ridge board.

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Old 10-21-2013, 10:08 PM   #3
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Eclipse Foil Faced OSB question


I understand the concern. The rafter ties are about a foot lower than midpoint which is not ideal I know, however they are tied to each rafter pair. There are collar ties as well, you just can't see them. There is also a post down to the stem wall on either end of the ridge board which is a 2x8 (which is still not ideal I know) but better than what you're concerned about.
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Old 10-22-2013, 12:34 AM   #4
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Eclipse Foil Faced OSB question


"Any thoughts? "----------- Scary; I agree with cortell (not scary that I agree with him...lol).... Wait until you add drywall, Fig. 22 and 21: http://books.google.com/books?id=iwS...joists&f=false

"The only time collar ties do any good is when they are specifically designed to be functional by an engineer or architect and are installed with meticulous care by the framer according to detailed drawings. Such collar ties are usually designed to resist outward thrust when there are no ceiling joists or structural ridge to serve the function. In these cases, structural collar ties should be securely fastened to the roof rafters with through bolts and spike grids. This hardware connects the collar tie to the rafter; a half-dozen nails don’t do the job." from; http://www.finehomebuilding.com/how-...llar-ties.aspx

"Collar ties are too high to keep walls from spreading and instead serve to resist uplift by holding the rafter together at the ridge." from; http://myconco.com/ComEngProb.html

http://publicecodes.cyberregs.com/ic...9_8_par022.htm

30# snow load, 20' span ?, 4/12 ?, 9-16d nails each side IF the rafter ties were down-- per code-- in lower 1/3; bottom chart; http://publicecodes.cyberregs.com/ic...?bu2=undefined

And 1/3 weight of your overhead door and the opener/track is hanging from the weakest point of the rafters- if the other side is supported by shelves. Framing appears new..... had a good snow yet?

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Last edited by Gary in WA; 10-22-2013 at 12:52 AM.
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Old 10-22-2013, 07:04 AM   #5
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Eclipse Foil Faced OSB question


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Originally Posted by iminaquagmire View Post
I understand the concern. The rafter ties are about a foot lower than midpoint which is not ideal I know, however they are tied to each rafter pair. There are collar ties as well, you just can't see them. There is also a post down to the stem wall on either end of the ridge board which is a 2x8 (which is still not ideal I know) but better than what you're concerned about.
Ah...I see those collar ties, now. So, sounds like you're OK on that front. But the lack of a proper ridge beam (a 2x8 across that span is all but useless as a beam) is still a big concern. At least you have the board supported with columns, but that beam is no match against a heavy Chicago snow load. I predict you're going to have significant deflection and those walls will spread.
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Old 10-22-2013, 08:57 AM   #6
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Eclipse Foil Faced OSB question


If this is an attached garage, I would be concerned if an OSB product would meet the fire code requirements. Typically it calls for 5/8" drywall.
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Old 10-23-2013, 09:29 PM   #7
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Eclipse Foil Faced OSB question


There have been several significant snow loads, one with 20+ inches as well as several 70+mph storms. There has been no deflection of the walls or the rafters.

I am not trying to justify the way it is installed, just stating facts. This was installed this way on suggestion from a contractor relative. Looking at the framing tables I believe that having the rafter ties where they are, it derates the rafter span roughly 40%. I am aware that it is going to be significantly more loaded with sheathing and insulation in place so I would like to get this fixed. Is there no adjustment for having the ties on every rafter vs every 4th the way it was?

I like the trayed ceiling and its dimensions and would rather not take it out to put a full ridge beam in. I also would rather not put the rafter ties lower. Like a lot of people, money is tight, so while trying to fix it correctly, the fix needs to be cheap, also meaning an engineer is out.


The plans I have (feel free to shoot them down) in my preferred order

1) Through bolt each rafter tie/rafter connection and install hurricane clips at the top plates (just to prevent slippage off the plates)

2) Create a raised tie truss like the paint sketch below (also through bolting rafter/rafter tie connection).

3) Sister the 2x6's with another 2x6

4) Sister the 2x6 rafters with 2x8's, thereby also increasing the insulation capacity and the strength.

5) 3/8 Cable through bolted through the rafters every 4th rafter (least desirable)

Any thoughts on these ideas to fix the issue?

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Old 10-23-2013, 09:43 PM   #8
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Eclipse Foil Faced OSB question


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Originally Posted by iminaquagmire View Post
Any thoughts on these ideas to fix the issue?
The idea I had in my head the other day was #5, assuming you're talking about running those cables just above the top-plate, and about 48" OC. But I've never seen cable used as rafter ties, so I shot the idea down.

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