Hi!

We are building a new 2 story house for our family. I know many of you love spray foam but we decided against it mainly because my wife is very sensitive to chemical smells and we just didn't feel 100 % comfortable with it after reading some EPA notices and watching that canadian documentary about botched installations.

So instead, we designed to put all our HVAC and ducts in conditioned space (fur downs) and will go with 2x6 walls (ZIP sheathing) and a traditional vented attic with blown in insulation and Techshield radiant barrier decking.

I have now been reading about damp spray cellulose vs BIBS fiberglass for literally 10 hours and it seems like both sides make good arguments. The web is full with scientific studies that appear to be funded by industry lobbies of each group.

My main concern is again health and indoor air quality. Fiberglass is now formaldehyde free but the Internet says I should worry about the fiber particles entering the house plus that the rodents love it. With cellulose the Internet tell me there is also dust that can become air born and there are tons of chemicals that Cellulose is treated with.

Then there is the humidity and MOLD. Intuitively it sounds not too smart to put paper in an attic in a climate like Houston where humidity around 80-90 % happens almost every night ... I also read that for proper damp spray application the humidity should be less than 40 % to ensure proper drying ... which is basically never in Houston. Most positive articles I read about cellulose are from cold climates.

Then the air sealing (not substituting proper air sealing with foam and caulk) which in the 2x6 walls appears to be equal if the fiber glass is dense packed to R23 but in the attic where the fiber glass cannot be dense packed, cellulose appears to be the better choice for air sealing.

As you can see I have read most info out there. The question is just what fits best for Houston, TX climate and is best for somebody with sensitivity to chemical smells.

Price difference here in Houston appears to be very minor ... what should we put in?

Walls: BIBS or Damp Spray Cellulose?

Attic: Loose Fiberglass or Loose Cellulose?

Thanks,

Robert

1: With wet-spray they can mix in a small amount of adhesive as well. That will help keep down the amount of dust.
2: You can also specify for low-dust cellulose which will help decrease the dust situation rather dramatically. Especially if combined with option #1.

3: Have you thought about simply putting the insulation on the OUTSIDE of the structural wall/roof assembly? Either foam sheet or cellulose with a larsen truss/I-beam truss type setup?  Then topped with a fascia wall/roof.

This would mean perfectly clear wall chases inside for running all your utilities. And the insulation would be sealed between the inner structural wall and the outer fascia wall with minimal bridging.

You would also be able to get away with standard 2x4 framing.


Also, while I understand your reticence.  The canadian "We had to rip the whole roof off" documentary is about the dangers of foam when the vendor doesn't know what the hell they're doing and are operating in a shady manner.  Don't just write off an entire sector because of one crappy trades-shyster.

we already have our plans finalized and permitted for R21 (or higher) cavity walls. Plus unfortunately with our budget anything except cellulose or bibs would not work. My main preference, being European, was to go with Rockwool. But this product seems wildly overpriced here in the US. And for some reason nobody makes it as a blow-in product ...

but sounds like you would vote for the cellulose instead of the bibs?

My vote would be damp sprayed cellulose.

If you have an Applegate Cellulose installer in your area, I would recommend you talk with them. Here is a link to their website along with several imbedded links relating to borate only stabilized cellulose:

http://www.applegateinsulation.com/Product-Info/Insulation-Products/Stabilized-Cellulose-Insulation/default.aspx

Damp spray cellulose takes a bit of time to dry out, vs BIBS. So you need to give the wall time before you put the sheetrock up.
But it generally goes in tighter and has better sound-deadening than BIBS fiberglass.
Also, in an open wall. construction setup, the application of either is nearly identical, other than the drying time.

In an air conditioned house in Houston you can even safely apply damp sprayed cellulose to unvented cathedralized ceilings. See Table 3 of this set of WUFI simulations performed by building science types (not insulation industry folks.)

https://buildingscience.com/sites/default/files/migrate/pdf/BA-1001_Moisture_Safe_Unvented_Roofs.pdf

Look at the second column, second row to see how a north facing roof deck fares in Houston under a couple of different roofing types. According to the simulations, under a tile roof the moisture levels at the roof deck on a north facing pitch will be above 16% for part of the year, but still fewer than 1000 hours total and it could be above 28% for as long as a week, but not longer. Under darker less hygroscopic roofing materials it stays below 16% all year long. This implies strongly that it's pretty mold-safe.

IRC 2015 would require that you have at least R5 above the roof deck for moisture control at the roof deck, but IRC prescriptives are nowhere near as location-specific as WUFI. While it's not a bad idea to put an inch of foil-faced polyiso above the roof deck (Labeled R6, good for at least R5.5), the simulation indicates it's not really necessary.

Also note, looking at the first column, without insulation above the roof deck the simulation indicates that 1.8lb dense packed fiberglass has much higher moisture levels in the roof deck than with cellulose, potentially above 28% for 4 weeks in the tiled roof case! For that reason alone my personal inclination would be for damp sprayed cellulose over fiberglass BIBS. YMMV.

dana, thanks for that, this really means that I don't have to worry about the moisture/mold issue. BTW: are you the same Dana that provides countless detailed responses on GBA as well?

I reached out to applegate to get an installer reference, but so far haven't heard back from them. One cellulose installer I liked in Houston is using a product called Celbar that is apparently made here in Houston primarily from Cardboard. It says "celbar has always been formulated with borates and is free of all ammonia additives". Is that good enough as far as sulfates are concerned? Not sure if it meets the "low dust" category though ...
http://celbar.com/wp-content/themes/celbar/assets/pdf/Celbarinsulation_2011_web.pdf

Regarding air sealing on the ceiling plane: should i insist that the builder caulk the drywall to the top plates or is this less needed if I have a 10" cellulose layer covering the whole attic (R38)?

Posted By rhawke on 01 Aug 2017 11:24 PM
dana, thanks for that, this really means that I don't have to worry about the moisture/mold issue. BTW: are you the same Dana that provides countless detailed responses on GBA as well?

I reached out to applegate to get an installer reference, but so far haven't heard back from them. One cellulose installer I liked in Houston is using a product called Celbar that is apparently made here in Houston primarily from Cardboard. It says "celbar has always been formulated with borates and is free of all ammonia additives". Is that good enough as far as sulfates are concerned? Not sure if it meets the "low dust" category though ...
http://celbar.com/wp-content/themes/celbar/assets/pdf/Celbarinsulation_2011_web.pdf

Regarding air sealing on the ceiling plane: should i insist that the builder caulk the drywall to the top plates or is this less needed if I have a 10" cellulose layer covering the whole attic (R38)?

In a vented attic with either cellulose or fiberglass on the attic floor there is potential for moisture on the ceiling gypsum if air conditioning the interior to some low temperature well below the dew point of the outdoor air, but under normal conditions the ceiling would be vapor permeable enough to pass that moisture through via vapor diffusion to be managed by the air conditioning. But the ceiling needs to be air-tight, with all seams & penetrations sealed. At 10" loose blown celluose is fairly air retardent, but it's not an air BARRIER.

Rather than micro-managing the air sealing methods, ask that as a condition of commissioning the house that they blower test the house and prove that it is below 3 air exchanges at 50 pascals pressure. (That is required by code to get a certificate of occupancy for new houses in some states.) If you're concerned about potential dust filtering down from the attic it's fair to insist that they caulk with a polyurethane caulk or can-foam all seams & penetrations.

As long as the cellulose is borate only, with no sulfates, it's good enough.

And yes, I'm that Dana.

Well Dana, then let me first say thanks for your advice here and your many, many answers and comments I have read over at GBA. Unfortunately, their website marks me as SPAM so I am unable to post any comments there .... I have one question that I have been trying to post as a comment for 5 months now. I will create a separate thread here and would welcome your opinion.

Regarding the air sealing: I have met with 7 very reputable custom home builders, some even calling themselves "green builders" or "energy efficient builders". When i ask them how many ACH50 their blower door tests usually come back with, they had no idea. They don't even know what ACH50 is. After explaining it, I asked all of them if they would be willing to guarantee 3ACH50. They all said: no, i will only guarantee that we will "pass inspection". At first I thought I just found the wrong builders. But after the 7th one I gave up and decided that I will just have to micromanage the air sealing process, especially at the ceiling to the attic. The builder we will most likely go with now is at least interested in the topic and said he welcomes an additional set of eyes and ideas to get the house as air tight as possible.

But in general I have been extremely surprised how little the builders here really care/know about building science. When I asked them if they always slope their window sill pans they looked at me as if I'm crazy. I suggested to put all the ducts and mechanical equipment in conditioned space and I got: "why make it so complicated when you can just put it in the attic" or "that can only be done with spray foam". When I mentioned that I would like to have a 3rd party design the HVAC system, all but one said "why, we always have our HVAC sub do it", etc. Not sure if this is just a TX thing where energy is cheap and we don't have cold weather or if this is the norm everywhere.

Your builders are (unfortunately) pretty typical of contractors. A few states have at least some enforcement of air tightness standards written into the codes. Most states don't enforce it even if it's on the books, and the inspectors are (no surprise) as clueless about it as the contractors.

Codes for city of Houston include an amended IECC 2015, which in climate zone s 1 & 2 (Houston is zone 2) requires <5 ACH/50. That's not exactly a tough hurdle to clear, but it's not a stripe on the floor either- more of a threshold-height speed bump, that's usually retro-fittable after a failed test unless there were some egregious errors. Even 3ACH/50 isn't tough to hit for houses with simple shapes, as long as the contractor & subs are given notice that air tightness is something they need to pay attention to.

I heard that the city of Houston inspectors have become a bit more stringent on the prescriptive air sealing methods (I believe most of them are mandatory even with u-value offset or performance method), at least for the main items like between attached garages and living areas, behind the bathtubs, kneewalls, etc. aka the really big holes.

I'll report back in a couple of months when we have our blower door tests done, to see what we were as a team able to achieve.

Thanks again for your help!