[Greenbuilding] Weight of spray cellulose

Topher Belknap topher at greenfret.com
Mon Feb 20 11:24:25 CST 2017 

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:
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> 
>     Dr John F Straube, P.Eng.
>     jfstraube at uwaterloo.ca <mailto:jfstraube at uwaterloo.ca>
>     www.JohnStraube.com <http://www.JohnStraube.com>
> 
> 
> 
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