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

[Michael O'Brien]

Hi, again-

Here’s a list of products with tested reflectance and emissivity:

http://coolroofs.org/products/results

Best,

Mike

On Nov 26, 2016, at 10:00 AM, Reuben Deumling <9watts at gmail.com> wrote:



On Sat, Nov 26, 2016 at 9:42 AM, Michael O'Brien <obrien at hevanet.com <mailto:obrien at hevanet.com>> wrote:
Hi, Reuben--

I think some metal roofing has high reflectance and emissivity, would reduce the heat in the attic. I wonder if a foil sheet stapled to the bottom of the rafters would add more reflectance, 
When you say 'bottom of rafters' can you explain? Are you saying staple the foil sheet to the inside faces of the purlins - which would then touch the back side of the drywall? 
 
not sure of your configuration.
standing seam painted metal roof -> tar paper -> 5/8 plywood -> 2x6 rafters +insulation batt -> 2x4 purlins (horizontal)+insulation batt -> sheet rock -> prime+ paint 

Best, Mike
Sent from my iPhone

On Nov 26, 2016, at 7:20 AM, Reuben Deumling <9watts at gmail.com <mailto:9watts at gmail.com>> 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/ <http://www.greenfret.com/>
> 
> _______________________________________________
> Greenbuilding mailing list
> to Send a Message to the list, use the email address
> Greenbuilding at bioenergylists.org <mailto:Greenbuilding at bioenergylists.org>
> 
> to UNSUBSCRIBE or Change your List Settings use the web page
> http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org <http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org>
> 
> _______________________________________________
> Greenbuilding mailing list
> to Send a Message to the list, use the email address
> Greenbuilding at bioenergylists.org <mailto:Greenbuilding at bioenergylists.org>
> 
> to UNSUBSCRIBE or Change your List Settings use the web page
> http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org <http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org>
_______________________________________________
Greenbuilding mailing list
to Send a Message to the list, use the email address
Greenbuilding at bioenergylists.org <mailto:Greenbuilding at bioenergylists.org>

to UNSUBSCRIBE or Change your List Settings use the web page
http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org <http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org>

_______________________________________________
Greenbuilding mailing list
to Send a Message to the list, use the email address
Greenbuilding at bioenergylists.org <mailto:Greenbuilding at bioenergylists.org>

to UNSUBSCRIBE or Change your List Settings use the web page
http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org <http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/greenbuilding_lists.bioenergylists.org/attachments/20161126/9be548bc/attachment.html>