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

[Reuben Deumling]

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>
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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