[Greenbuilding] thermal implications of a vault vs flat ceiling at R-38?

[Topher Belknap]

Greetings,

Sadly, all I have is empirical evidence that stratification isn't an
issue.  But I do have that.

Venting's purpose is to move moisture past a (roughly) impermeable
barrier.  You can do without it by arranging you surfaces in reverse
impermeable order (i.e. most permeable outside).  Metal roofing however
is pretty impermeable (as if tar based roofing paper).  I would want
ventilation below those two things.

Sure, fill the entire triangle.  Moisture only tends to condense on
solid surfaces within a wall (at least at first).  Filling the whole
cavity leaves no interior places able to support condensation.

Thank you kindly,

Topher

-- 
Topher Belknap
Green Fret Consulting
Kermit didn't know the half of it...
http://www.GreenFret.com/

On 11/26/2016 10:20 AM, Reuben Deumling wrote:
> Thanks for your reply, Topher, and good to hear from you. This list is
> not quite what it once was... Have folks drifted elsewhere, and if so I
> wonder where those places might be?
> 
> 
> On Sat, Nov 26, 2016 at 7:03 AM, Topher Belknap <topher at greenfret.com
> <mailto:topher at greenfret.com>> wrote:
> 
> 
>     Greetings,
> 
>     Thermal losses should be considered on the basis of surface area, not
>     volume.  
> 
> Agreed.
>  
> 
>     Heat stratification (for good or ill) is pretty insignificant in a
>     modern, well insulated and sealed house.  
> 
> I've noticed this myself and tried to discuss this with the heating man
> who came to advise/make a bid for the additional duct work to the new
> upstairs rooms), but I don't think I was able to persuade him.
>  
> 
>     Venting ought to be the same for either option (if I am envisioning
>     correctly).  Since it should
>     run up the outer surface, not the interior.  
> 
> I am aware that standard practice has me installing vent channels
> between the insulation-in-the-rafter-bays and the sheathing, that
> connect vents at the bottom to ridge vents--we've discussed this here
> over the years--but I also think I remember folks arguing that in
> certain situations one could skip those channels. Am I misremembering
> this or just experiencing wishful thinking? I confess that getting the
> venting right seems to me the biggest challenge at the moment.
>  
> 
>     My concern would be ensuring that the vapor barrier (if your climate
>     wants one) is put in
>     the right place.  
> 
> Ah, vapor barriers. I'd love advice on this. There is currently a layer
> of roofing felt on the outside of the sheathing. The batts of insulation
> I'm planning on using for the walls and sloped roof sections of the
> envelope are paper-faced fiberglass. I was going to rip the paper off
> the batts that run vertical and keep it on the inner layer that runs
> horizontal. Is that a viable approach?
>  
> 
>     If you decide on the flat ceiling, fill that space with insulation.
> 
> I was certainly planning on insulating above the horizontal sheet rock,
> but are you suggesting filling the entire triangle? 
> 
> 
>     Thank you kindly.
> 
>     Topher
> 
>     --
>     Topher Belknap
>     Green Fret Consulting
>     Kermit didn't know the half of it...
>     http://www.GreenFret.com/
> 
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