Best way to insulate vaulted ceiling and such

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  #1  
Old 02-19-16, 02:29 PM
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Best way to insulate vaulted ceiling and such

Hi,

I posted under attic ventilation fans forum before, but I think this is more appropriate place for my question.
I am replacing (hiring someone to replace) my failed Decra tile metal roof.
Would like to replace the insulation wherever it's not accessible otherwise and deal with the rest of it later - read never...
The vaulted ceiling above the living room and master bedroom are two spots. My rafters are only 6" so the max I can fit in there is probably R19. I ordered soffit vents from HD Amerimax Home Products 41 in. x 22 in. Accuvent Vinyl Attic Airway and Soffit Vent in Black-ACCUVENT - The Home Depot
and foil faced insulation from Attic Foil Attic Foil Radiant Barrier - Radiant Barrier Pricing - AtticFoil® Radiant Barrier Foil Insulation

Should I try installing the foil between the rafters first and then try fitting the R19 and probably end up compressing it, or it's better to still put down the foil and fit R13 so there's more room for it to breath? Or... better yet to nix the foil and just go with R19?
Thanks in advance,
 
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  #2  
Old 02-19-16, 04:30 PM
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How is the roof vented?
Compressing the insulation is just going to reduce the R value.
There needs to be air flow from the soffits to the roof vents.
Another idea is to go with having it spray foamed.
 
  #3  
Old 02-19-16, 09:33 PM
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With just 5.5" of rafter spacing you will fall far short of minimum insulation requirements and probably below code requirements. If you are replacing the metal roof, now is the time to consider adding a thick layer of rigid insulation above the rafters. There are also other options as well. here is a good article to get you started:
How to Build an Insulated Cathedral Ceiling | GreenBuildingAdvisor.com

Bud
 
  #4  
Old 02-20-16, 05:18 AM
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Thank you

Thank you Bud,
It seems just like anything else, opinions differ.
I am glad I read the article you posted though because the can lights, that I see a lot around here are not recommended. I also read somewhere that spray foam insulation has a very limited shelf life it shrinks and deteriorates quickly, in any case I wasn't going to use it.
When I asked my roofer to add the ridgid foam insulation below the roofing material he stated that it would actually be detrimental to proper roof ventilation because it will be blocking "dead air space" between the roofing material and the surface of the roof deck. His terminology, not mine...
I suspect my ceiling insulation is kind of doomed 😡 I am not going to add height for he rafters, it will end up lowering my ceiling.
If my roofer would be willing to add radiant barrier under the roofing material it would probably help a bit, but I doubt he would do that.
 
  #5  
Old 02-20-16, 06:03 AM
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LOL, on a scale of a "NOB" at the bottom and a top notch expert at the top, your roofer falls embarrassingly close to being a NOB. Despite thick rigid insulation above the roof deck being a relatively modern solution to insulating an attic, it is an approach that has long been (successfully) used in the log home industry, those beautiful vaulted pine ceilings. He needs to upgrade his "how to" knowledge bank.

CAL and other HOT areas deal with a lot more heat than I experience way up in the north east, but their solutions are well documented and proper use of a radiant barrier is one of their solutions. In the deep south they even use plywood that is covered with a layer or foil on the bottom. Anything you can do to block the heat before it enters the attic is a real benefit, even the color of that new roof. More reading:
Staying Cool with a Metal Roof | GreenBuildingAdvisor.com

I don't recall if you stated your intentions for that attic space, just trying toprotect the house below or create some attic living space?

Bud
 
  #6  
Old 02-20-16, 05:50 PM
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Thanks again,

And I am not sure if it's a lack of knowledge on the guy's part or him just wanting to get in and out result unfortunately the same.
I am trying to get the roofer, ANY roofer to actually start the work for almost 3 weeks since my roof was torn off on the Feb 1st.
I actually ordered this material to use it in my attic space - Attic Foil Radiant Barrier - Keeping Heat Out but I ordered only a 1000 sq ft and if I use it on my vaulted ceiling it's not going to be enough to cover everything I need.
Went to HD hoping to find 3/4" rigid foam this manufacturer recommends to be using as furring strips, they only have 3/4" foil faced, so now I am not sure if that's ok to use. Will call the manufacturer on Monday and find out and post if anyone cares.
And no living space from attic, just isolating from the rest of the house to keep it cool most of the time.
 
  #7  
Old 02-21-16, 09:45 AM
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One more question
Since I decided to use the radiant barrier on my vaulted ceiling, should I still be using these AccuVents I bought?

Amerimax Home Products 41 in. x 22 in. Accuvent Vinyl Attic Airway and Soffit Vent in Black-ACCUVENT - The Home Depot


Their "usable length" seems to be around 34-35", so am to place my barrier on top of them? - possibly blocking the air flow. Or on the bottom? - possibly nixing the effect of the radiant barrier. Or should I use them at all? - I kind of like the idea of having them because it looks like they could provide first line of defence against flying ambers in the wildfire situations if my soffit vents fail for some reason.
Your opinions please.
 
  #8  
Old 02-21-16, 10:04 AM
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Yes, you will want to use them to protect the ends of your insulation and hold that insulation back from falling into the soffits. I'm not a fan of bubble wrap being used anywhere as the companies selling it exaggerate it performance so much it is basically lying to their customers. But if you must, install it first against the bottom of the roof deck and secure it so it does not hang down, contact adhesive or staples. With the heat it will face it will be difficult to keep it in place. If you can't be sure it will not block the channels, don't put it in there.

Bud
 
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Old 02-21-16, 05:26 PM
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Thank you Bud,

So do I need to cut the AccuVents shorter to allow the foil barrier to go as close as possible to the vents? Then start with my foil.
I was not planing on using the bubble type barrier, just supposedly strong foil barrier - this one Attic Foil Radiant Barrier - Radiant Barrier Pricing - AtticFoil® Radiant Barrier Foil Insulation
nor I am sure of the difference.
 
  #10  
Old 02-21-16, 06:14 PM
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Being very thin and already perforated you can start as low as you can reach. I like an electric stapler in tight places where I cannot swing a staple hammer. Hold then tight to get a good set. If you have good hand strength the manual staplers may be fine. If you have 1/2" sheathing be sure to use an equal or shorter staple and lots of them to be sure the RB doesn't sag.

Then install the baffles right over the top. The baffle doesn't need to be a lot longer than the height of the insulation, but a little extra wouldn't be worth the effort of cutting them all.

Bud
 
  #11  
Old 02-21-16, 09:14 PM
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Thank you,

I will definitely use electric stapler, no arm strength any longer
and will probably be stapling to the rafters rather than sheathing, just in case.
 
  #12  
Old 02-22-16, 04:28 AM
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Stapling to rafters complicates the ventilation as you would then need to provide air flow between the RB and the roof deck as well as ventilation of the attic space. Stapling it directly to the bottom of the sheathing mimics a well tested approach of having the bottom of the roof covered with a RB.

You can attach it to the bottom of the rafters, but you will need to provide adequate air flow for above and below the RB and I don't recall the vent areas you have.

Bud
 
  #13  
Old 02-22-16, 07:57 AM
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I was going to attach the foil to the sides of the rafters, just following what they told me over the phone and what is shown on their video here - https://www.youtube.com/watch?v=CjwZXoRzRiM
and probably would have to monkey around with the AccuVents, just so the RB somehow lays on top of them to actually work.
I may talk to my roofing contractor ask him if he would put the RB right on top of the water membrane when installing the metal roof. Here they explain why it's better - https://youtu.be/EUiYtdqI1bU

Thanks again!
 
  #14  
Old 02-22-16, 09:28 AM
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A RB only works if it has an air gap on the reflective side. The method they are showing will have batt insulation installed against the foil so they need the gap above the foil for it to work. A RB can either reflect the heat (high reflectivity) or not radiate the heat (low emissivity). They work equally well in either direction.

What I was suggesting is the foil directly against the bottom of the roof to block the heat transfer by not radiating that heat into the attic. Then there is no spacing issue and it can go all the way down under the vent channel.

Bud
 
  #15  
Old 02-22-16, 09:45 AM
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I think we are talking about two different scenarios.

I have a vaulted ceiling in my living room, no attic space above it. I also reside in southern California where I am more concerned with heat transfer down from my roof rather than opposite direction.
If anything, foil should probably go directly on top of my decking surface?
 
  #16  
Old 02-25-16, 01:36 PM
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back at it

I am back to the RB questions

Roofers are in the process of removing the old roof and installing a new one.
Don't know if you can see well in the pictures, but
a. it turns out I had the RB with my old roof, it was a thin insulation with RB on top but non the less
b. the part of the RB that was under the wood battens stayed pretty shiny, but the rest of it looks very dull after the years of exposure.



I was going to take this insulation and lay it down inside the attic right on top of the ceiling joists and insulation to provide for some RB. Does it look too degraded to you so it's not worth doing that? Will I get any benefit from this insulation at all?

Thank you,
 
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