Your option #1 will perform significantly better according to WUFI.  The only thing I see getting your OSB wet would be a roof leak or flashing problem.  Positive pressure in a house would be unlikely except for stack effect at the upper areas - most things (exhaust vents, fireplaces, many gas water heaters, etc) cause negative pressure.  You will need a HRV and a humidity sensor to control and verify winter interior humidity.

Thanks Jonr. The only vents we'll have are the bath exhausts and kitchen. We will have an HRV with a humidity sensor, since we need the ventilation because we were planning on building so tight. And 1" cc foam will be cheaper than the 2", so that's even better.

To me things to think about are how water or vapor is going to get in and how it can get out. There are 2 ways for water to get in bulk water ie a leak and water vapor mostly carried by air leaks carry mosture to a condensing point.

From the outside block water flow with a rain screen. Any water that get through drains and a way for the back of the siding to dry without driving its water vapor in to the wall assembly. Also any water in the sheet can dry to the outside.

For inside the cavity dense pack cellouse as it is better at reducing air flow. If all the cavities are properly densed pack then only small amounts of vapor will be in the wall same basic level as in the interior. There will not be enough to condense.

Lately I have een recommendation of not using poly except in canada.

Posted By Roberth on 18 May 2010 12:02 AM
To me things to think about are how water or vapor is going to get in and how it can get out. There are 2 ways for water to get in bulk water ie a leak and water vapor mostly carried by air leaks carry mosture to a condensing point.

From the outside block water flow with a rain screen. Any water that get through drains and a way for the back of the siding to dry without driving its water vapor in to the wall assembly. Also any water in the sheet can dry to the outside.

For inside the cavity dense pack cellouse as it is better at reducing air flow. If all the cavities are properly densed pack then only small amounts of vapor will be in the wall same basic level as in the interior. There will not be enough to condense.

Lately I have een recommendation of not using poly except in canada.

The dew point of 70F 30% RH interior air is about 37F.  In the absence of an interior vapor retarder, any part of the cellulose is 37F or colder will experience condensation.  If it stays below that temp for extended periods of time (as it will for weeks on end in central IA) moisture will condense & accumulate in the cellulose. (And we're talking strictly from vapor diffusion, not air-transported water.)  Whether sufficient moisture accumulates to damage the cellulose or for it to lose R-value is a function of the local climate, but cellulose can handle significant moisture loads without damage. But there WILL be enough to condense- count on it!

The WUFI model jonr has been using is a well-evolved model based on lots of empirical data & testing.  The result using central IA weather showing 1" of interior SPF + 4.5" of cellulose keeps the OSB drier than 5.5" of cellulose jives well with simple paper models (and  physical intuition. )  With another R6 between the cellulose & exterior the amount of condensation/accumulation within the cellulose is better controlled, and since 1" of  SPF is only semi-permeable, not much of that moisture that does accumulate gets transferred to the OSB. And the semi-permeable SPF allows any moisture within the OSB to dry (albeit slowly) toward the interior most of the year.  In a significantly colder climate flash & fill won't be as protective.  The hygric buffering of the cellulose probably helps out a lot here- using fiberglass, rock wool in this exterior vapor barrier stackup would likely put the colder edge of the studs at risk.

"Greener to me right now is...R-60, native wood and ground up news papers"  I need to break this down into smaller parts.  I am having a hard time processing this.

How do you propose reaching R-60?  and at what cost?  R-60 with any insulation medium is going to break the budget.  I think your asking for a bit much with R-60 - we can all dream.  With plastic (SPF, SIPS, ICF, rigid foam board) your looking at about a 8.5" assembly.  With cellulose your looking at 17" thick assemblies.  You can't realistically reach R-60 without plastic (maybe with aerogel someday).  Regardless, R-60 is a bit much, you can build a net zero house with lower R-values.

I don't think the SPF industry deserves the blog slap.  Lets be real, if you are looking for an insulation option that air seals, provides heightened R-value and manages moisture, plastic is the way to go.  In fact, its the only way to go.  I don't care if your talking about SPF, SIPS or ICF's...guess what, its all plastic.  I know you die hard greenies hate to admit it.

Or we could put cellulose in our walls, or maybe hay.  Great idea, now we're introducing a hyrgoscopic material into the equation.  Lets really rot that wood. Cellulose has one good use, loose fill on an attic floor.   And don't get me started on batts - fiberglass, cotton, etc, any kind of batt is a waste.  BTW - for all you WUFI fanatics, I hope your using WUFI as a side line tool and not the end all be all silver bullet answering tool.  WUFI has its own problems.

Plastic plays a vital role in our lives whether you like it or not.  Now, I don't necessarily agree with how quickly most plastic comes into and out of the average american's hands (ie. starbucks iced coffee cup), but free market place has given the people what they want.

Reallistically, if we look at architecture from a macro perspective - what is green?  To me, its a high performing building that can last a life time and keep indoor airquality safe for building occupants.  ICC, energy star, BPI, etc etc have finally recognized the benefits of air sealing - how else are we going to air seal everyone's home?  Tree sap?  Maybe someday.  But for now, we have plastic. 

No I don't work for the plastics industry, but i consider myself someone who has weighed out all of the options and plastic is my final conclusion.  Cellulose is nice, but who wants nice?  You want air sealing and high R-value.

All that safety stuff your talking about is related to the way plastic is made.  If your making it in a factory (ICF & SIP) or custom fitting it for your wall cavities (SPF) there are hazards to associate to production.  SPF has garnered a lot of popularity over the last few years and as such will be regulated by the federal government (thank god).  I hate to admit it, your Apple computer (i say this because I bet you have one) has plastic in it, guess how it was made?  In a facotry with the same hazards associated to all plastic production.  There is only one difference,  your plastic insulation will still be working long and hard after the 5 years of use life you'll get out of your computer.

We have created a standard of living for ourselves that consist of indoor regulated temperatures and humidity levels that very few materials can maintain.  Unless we change our view of comfortability or more importantly goals in reducing fuel consumption - plastic in construction are here to stay.

Dana1

Regarding the dew point I have a question. If the cavity is full and there is no real air movement carrying more and more moisture will the insualtion get wet. I am assumming a textured ceiling that is not painted.  What would be the affect of painting the cieling.

What part of Ia are you in. Omaha here

Posted By Roberth on 19 May 2010 03:53 PM
Dana1

Regarding the dew point I have a question. If the cavity is full and there is no real air movement carrying more and more moisture will the insualtion get wet. I am assumming a textured ceiling that is not painted.  What would be the affect of painting the cieling.

What part of Ia are you in. Omaha here

The insulation will get wet via vapor diffusion through the building materials even when air-tight if it has no vapor retarder (as distinct from an air-barrier) on the interior side.  If the exterior side is highly vapor permeable it'll be able to dry somewhat toward the exterior from condensation events, but that process is extremely slow when it's below freezing.  In a roof or ceiling assembly we'd need to know what's above the insulation layer to estimate the hazard.

Air barriers aren't the same as vapor barriers.  Water molecules are extremely small- smaller than most of the gas molecules that make up the bulk of air, and it can pass through many types of materials where air can't.  Building materials are tested in several ways to characterize their ability to block or pass water vapor. The rate of vapor diffusion is expressed in "perms"- bigger numbers means vapor gets through more readily- lower means it's tighter.   For rules of them an easy nomenclature regarding vapor retarders, anything over 10perms is considered highly permeable, under 10 but above 1 is semi-permeable,  under 1 but above 0.1 is semi-impermeable, and under 0.1 perms is for all practical purposes a vapor barrier. Polyethylene sheeting is on the order of ~0.05 perms.  A sheet of relatively dry plywood or OSB is somewhere around 2 perms but will vary with the humidity content of the wood (higher internal humidity within the wood raises it's vapor permeance, and conversely.  OSB is typically less permeable than plywood as the humidity rises though, so it takes longer to dry.) 

In Omaha it's best to have a fairly impermeable interior side. Look up the permeance of the textured ceiling- (I never use it don't have a clue as to it's vapor characteristics).  If it's over 0.5 perms at the applied thickness it's probably too permeable to rely on it for an Omaha winter.  Standard latex paints run ~2-3perms, but specialized vapor retardent latex is typically 0.5 perms or lower, and may be sufficient depending on the rest of the stackup.

(I'm not in IA- the person who started this thread is.)

Johnny boy:  Nobody is giving SPF the "blog slap", it's just that it's too vapor retardent to use as cavity fill now that she has a highly retardent exterior sheathing.  SPF good stuff, when & where properly applied, but sandwiching wood between two highly vapor retardent layers has some risk to it.  Nobody here is down on SPF (quite the contrary), or is this just your standard rant whenever somebody recommends NOT using SPF (or other than all-SPF) in some application?

R60 is readily attainable, and yes, it takes a pretty thick wall to do it without foam, so?  In price per unit R it's hard to make the rationale for high R assemblies using SPF alone, but using it within a stackup for it's air-barrier and vapor retardency makes adjacent fiber layers work BETTER than they would otherwise.  Going high R with cellulose is far cheaper than with SPF. But it's for sure not an adequate air-barrier on it's own, even if dense-packed.  In combination with 1-2" of ccSPF it can be quite good, and far less expensive than going all ccSPF.

Cellulose wicks water away from building materials, protecting it rather than destroying it- methinks you've got that model turned on it's head.  Dense-packed or wet-sprayed it's dimensionally stable but flexible- can't crack or separate from other materials the way ccSPF can. It adds significant thermal mass to the structure, and buffers seasonal humidity (or even occasional minor bulk intrusions) in a protective manner.

Whether or not you can get to Net Zero with R60 walls is a function of climate. Net Zero  or PassiveHouse can be done just about anywhere in CA below 2000' of altitude with something like R35-R40 and some careful design.  But CA isn't MN, or even NY.  Show me an example ANYWHERE of a net-zero house in a 7000+ heating degree-day climate with less than R60. (Seriously- if one exists, I'd like to see how they did it!)  Even the Urbana IL PassiveHouse has R60 walls, in a ~6000HDD climate, and isn't Net Zero (but arguably could be with an investment in PV.)  The bulk of the insulation there was blown fiberglass (12"), with exterior sheet goods (4" of rigid EPS).   Getting to Net Zero with an array that can actually fit on the house in a cold climate just isn't gonna happen without high-R walls & roof, no matter how tight you can make it.

I'm not personally a WUFI fanatic, but recognize it's value as a tool.  It's but one of many tools but I'd be curious to know where you think it breaks down (beyond "garbage-in = garbage-out" arguments about naive, incompetent, or misinformed users.)

Johnny Boy... me likes Steve Jobs... and Android competing and have neither... am typing on a Vista/Acer pal.

Densepack cellulose... itself is enough tightness for a home... and the breathing through it ever so slowly is good for us inhabitants... no mechanical system needed.  Randiant heat.... no nasty air circulating that needs silly expensive filtering. No nasty carpets, or particle board..etc... nice clean air. Water based coatings...  lots of mass... no need for AC here in Lake George... some ceiling fans... which I like... never have liked the chill of running in and out of a freezer to a hot car... then turning it into a freezer... then on to the mall... me ... yaa... not a mall person... for almost 20 years now... movies at home... not at the big screen though I do miss that.

foam tight is not the answer... though I agree it works and do like 1/2 pound spray because it does breath.

Johnny.... Johnny... cellulose is not expensive to go high R... Foam is.

And yes... batt fiberglass has issues...

and one thing that is really silly... 5.5" thick walls full of wood!

Build the most passive home possible... insulate with cellulose dense packed.

For now... thick foam outside foundation and under slab

do not vent the roof... unless built into a double roof and totally isolated from warm inside air leaks. 

Seal all sills perfectly... seal drywall.... use paperless drywall if really wanting to be mold resistant.

No recesses lights... or other ceiling or wall penetrations. There are other ways....  and oops... may have to use a tiny bit of soy foam to seal what can't be sealed by subfloor glue...

by the by...who makes good bio subfloor glue??????????

aj

(is late... am tired and am not going to edit this one bit)

If you are concerned about air filtration, you can caulk all the interior seams between the OSB and the framing. It is labor intensive, but doable. Use good caulk, follow the directions for contact with the surfaces etc, and if you are going to do this invest in a powered caulk gun (I bought an 18Volt Ryobi). This way you get the filtration barrier without the moisture barrier.

Just an idea from an amateur DIYer

-Rosalinda

Posted By Rosalinda on 24 May 2010 03:33 PM
If you are concerned about air filtration, you can caulk all the interior seams between the OSB and the framing. It is labor intensive, but doable. Use good caulk, follow the directions for contact with the surfaces etc, and if you are going to do this invest in a powered caulk gun (I bought an 18Volt Ryobi). This way you get the filtration barrier without the moisture barrier.

Just an idea from an amateur DIYer

-Rosalinda

Rosalinda

Fiberglass - maybe Spider is the exception- is very air porous. To get fiberglass to work it needs to be in a reasonably airtight enclosure.  Fiberglass does not work well in leaky walls or attics.  It is well known that adding cellulose over fiberglass in an attic will help the fiberglass perform better because it is not as porous.  My question about JM's Spider is will it perform the same as or better than cellulose as lose fill in the attic.

Neither cellulose or fiberglass is going to be an air barrier.   To seal the attic floor 1 or 2 part foam is a better choice than caulk.  Commercial quality 1 part foam guns will allow better control of the foam to minimize waste/cost.

Normally I would be adverse to using fiberglass. It is labeled a possible carcinogen and generally does not perform well as installed. Spider may have over come many of the negatives but I would to learn the whole story.

Thanks for the advice and insight.

Dana 1,

As I've mentioned in previous posts, I think cellulose is a great product as loose fill in attic floors and dense packed in wall cavities. You might not get the air seal, but you have a tight home with good thermal mass properties.

Wetting it and flinging it into a wall cavity is another animal. I am all set with spraying wet newspapers in my walls. That practice is counter intuitive to everything that I know about

Posted By Johnny Boy on 17 Jun 2010 06:50 PM
Dana 1,

As I've mentioned in previous posts, I think cellulose is a great product as loose fill in attic floors and dense packed in wall cavities. You might not get the air seal, but you have a tight home with good thermal mass properties.

Wetting it and flinging it into a wall cavity is another animal. I am all set with spraying wet newspapers in my walls. That practice is counter intuitive to everything that I know about

"Wet" is a matter of degree. Wet-sprayed cellulose is just wet enough to make the water-activated adhesive tacky enough to stick, and bears no similarity to flinging "wet newspapers" into the wall.  It may come out of the spray gun ~30-35% water by weight feeling ever so slightly damp to the touch, but dries within hours or days (depending on conditions & insulation thickness) to ~20-25% where it feels quite dry.  In normal seasonal cycling it might hit a peak of 25% (just as dense-pack dry blown will), but it will usually peak well below 20% in most installations (just as dense-pack dry blown will).  It's not exactly a power spitwad-blaster, eh?

Wet spray cellulose isn't some new & untried technology- it has a decades-long track record, and generally a good one.  The only time it ever creates problems is if it gets covered when wet, which is a construction management issue- you need to give it sufficient drying time before the sheet-rockers & paint crews show up.

Wet sprayed cellulose in open-sprayed (as opposed to dense-packed) still has ~2/3 the thermal mass of dense packed, but allow measurably more air leakage (which is not a problem in a flash & spray), but if it has higher convective losses within the insulation they aren't readily measurable, and inconsequential from a practical point of view.

Wet-spraying into a 4.5" deep cavity (5.5" stud, less 1" of SPF) will dry somewhat quicker than a full-cavity 2x6 fill, and those are done successfully every day of the year. The only time I'd be concerned about wet-spray would be in super-insulation Larsen Truss, double-studwalls, etc, where the drying time for a 12-15" fill might take weeks or even months to get under 20%.