[Greenbuilding] Weight of spray cellulose

Mon Feb 20 11:28:54 CST 2017

Regardless of the permeability of the foam, the asphalt shingles or metal roofing finish are almost perfect vapor barrier.
Unvented cathedral ceilings always have to dry to the inside.
Closed-cell foam insulation makes sure the water vapor never gets to the sheathing by diffusion or air leakage in the first place.

> On Feb 20, 2017, at 12:24 PM, Topher Belknap <topher at greenfret.com> wrote:
> 
> 
> Greetings,
> 
> What is the permeability of the spray foam?  If it is low, you will need
> to ensure drying to the inside, which seems problematic.  Have you run a
> WUFI simulation, or similar?
> 
> Thank you kindly,
> 
> Topher
> 
> -- 
> Topher Belknap
> Green Fret Consulting
> Kermit didn't know the half of it...
> http://www.GreenFret.com/
> (207) 882-7652
> 
> On 2/19/2017 11:24 PM, Sacie Lambertson wrote:
>> We're in Zone 4.  We will put in several inches of sprayed foam
>> immediately under the roof; sealed to the tops of existing walls.  Blown
>> in cellulose is the next layer.  Area/attic is _not_ ventilated.  The
>> house will be tight.
>> 
>> Will have an HRV system as well.
>> 
>> Should have described whole plan to begin with.  Again, appreciate the
>> comments.
>> 
>> Sacie
>> 
>> On Sun, Feb 19, 2017 at 9:16 PM, John Straube <jfstraube at uwaterloo.ca
>> <mailto:jfstraube at uwaterloo.ca>> wrote:
>> 
>>    There are numerous reasons to ventilate attics and cathedral
>>    ceilings: removal of moisture is the most important.
>>    Another reason is to limit ice damming in climates with sufficient
>>    snow and weather that cycles near to freezing temperatures. If you
>>    insulate enough, you dont need to ventilate for that reason.
>>    BUT, there is no way you can build cathedral ceilings with cellulose
>>    and NOT ventilate without taking serious risks.  Some cellulose
>>    companies have been selling this idea for years, and we (and most
>>    other forensic consultants) have seen sufficient failures to realize
>>    that it is too risky in most cases.  If the house below is super air
>>    leaky and hence very dry in cold weather you can often “get away
>>    with it” but modern houses in cold climates with higher RH levels
>>    (e.g. not 15%!) cannot tolerate small air leaks.
>>    Do a great job of air sealing, live in a climate that is not too
>>    cold (e.g. Zone 3 or 4) and you might be able to pull off a
>>    cellulose unvented cathedral. Still risky, but must less so.
>>    An alternate design is to put enough insulation outboard of the
>>    sheathing and cellulose. This is a good retrofit option. Fill up the
>>    available rafter space, then put an air barrier membrane on the
>>    sheathing, and add sufficient R-value on the exterior to avoid
>>    condensation (this amount varies ratiometrically with the amount of
>>    cellulose R-value, the outdoor climate, and the indoor winter humidity.
>> 
>>    PS I have R-100 in my house… roughly.  about 28” of cellulose in a
>>    flat ceiling under a well-ventilated attic. No furring, just 2x4
>>    bottom chords of trusses supporting 1/2” GWB with standard screw
>>    patterns. R-100 does not make a lot of sense, until you see the
>>    price difference between R-60 and R-100 is so small
>>    But Frank’s experience is worth a lot…. 30 houses over more than a
>>    decade.  That is worth more than any experiment in my books.
>> 
>> 
>>> On Feb 19, 2017, at 9:32 PM, Reuben Deumling <9watts at gmail.com
>>    <mailto:9watts at gmail.com>> wrote:
>>> 
>>> R80, huh? Wow.
>>> I'm curious, Frank, what you make of the article circulated here
>>    recently that suggested that (and I'm paraphrasing) above R30 the
>>    ventilation of cathedral ceilings could be skipped?
>>> 
>>> On Sun, Feb 19, 2017 at 6:05 PM, Frank Tettemer
>>    <frank at livingsol.com <mailto:frank at livingsol.com>> wrote:
>>> I agree with David's suggestion, to alleviate concern,
>>> However, for over a decde we have in 22 inches of blown in place
>>    cellulose = (R-80?). this had held up consistantly each year, We put
>>    up MemBrain by Certainteed stapled to the ceiling joists @ 24" o.c..
>>> Then, 1x4 spruce strapping on 12" o.c.
>>> 
>>> Then 1/2" drywall, double screwes into 1x4 on 9" o.c..
>>> 
>>> At least 30 ceilings and insulation installations over 14 years,
>>> with no failures except in my own garage ceiling where I stepped
>>    off the joists with my big bad foot.
>>> 
>>> Question?: Do you have a plan to block off the vented soffits, and
>>    allow ventilation channels from the vented soffit, above the
>>    cellulose, to the vented ridge, or, maximum vent box, or similar?
>>> More opportunities and good use of corrugated cardboard?
>>> Or inexpensive Moore vent/rafter vents, and vertical cardboad
>>    baffles, from outside face of the wall plate, up to the rafter vents?
>>> 
>>> Cheers,
>>> Frank Tettemer
>>> 
>>> On 2017-02-18 12:29 PM, David Wentling via Greenbuilding wrote:
>>> _______________________________________________
>>> 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>
>> 
>>    Dr John F Straube, P.Eng.
>>    jfstraube at uwaterloo.ca <mailto:jfstraube at uwaterloo.ca>
>>    www.JohnStraube.com <http://www.JohnStraube.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
>> 
>> to UNSUBSCRIBE or Change your List Settings use the web page
>> 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
> 
> to UNSUBSCRIBE or Change your List Settings use the web page
> http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org