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1. Which absorbs more moisture (when exposed to exactly same relative humidity); FG or Cell ?
2. Which transports water faster (across its mass); FG or Cell ? Will moisture penetrate one faster and or deeper in one or the other ?
3. Which retains its loft and insulation value better, when wet; and, when frosted/frozen; FG or Cell.
4. Which dries faster (evaporates out water more efficiently)? Is there any difference in evaporation performance under different rates of air flow across their surfaces ?
5. Are either types of insulation suseptable to any form of decay from either fungis or from chemicals or off-gasing from other building
materials ?
Replies
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ECW,
WET?...Homes aren't submarines.....Lets keep the insulation dry....
Jack : )
*Hi Jack,Sure we all would love to keep our houses dry, but the fact is moisture will breach the shell from time to time, be it via humidity or via leaks. It's not unreasonable to ponder what will happen under these circumstances.I'll take a crack at the questions, though I'm only parroting back what I've read from various other people at various times.1) FG won't hold moisture. It is hydrophobic. Cells will diffuse moisture evenly throughout its mass.2) I've no clue.3) good question. I don't know.4) I would assume since the FG doesn't want to hold the water, it will dry faster, but is the wall drier or has the moisture just puddled up at the bottom or soaked into the sheathing?5) I've no idea.Now that I've shown myself to be the ignoramous that I am, I would love to know the answers too, and their relevance, positive or negative, to total system performance.Steve
*Steve,Relevance...thats the point I was making...Not building submarines or insulating them...and especially b not analysing them,Jack : )
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But Jack ...Steve's point is really your point (if I might be so bold). How can you prevent moisture and even bulk water from entering the insulation. Aside from building your house in a garbage bag, filling it with dessicants and then heat sealing it.
In decades of camping, canoeing, kayaking, I never saw a system that could keep out moisture. We tried everything; air tightness does not mean water tightness. Water has the insidious ability to migrate into the most expensive water-tight design.
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Tedd,
My house is bone dry...inside and in the walls...
The only place I see moisture problems is when the occupants add it by the bucket load (see my other posts) or when a builder builds a house in a body of water (wet soils!!!) with drain schemes that do diddley!!!
And by the way if 40% of the homes in the USA have a problem...then I would say 99% of the problems are caused by the two items mentioned above.
Dry to bone,
Jack :
*FG with only 5-10% moisture (which still feels dry) looses 1/2 of its r value. Cels with 40-50% moisture loose only a few % of their origional r value.
*Hi Ron,Do you have a verifiable source for this info?Thanks, Steve
*Steve,Its been years, I think it may have been from Oak Ridge. If I run across it I will post it. I have run thermal imaging of damp walls with cels and fg myself on the same house and the cels was far better.Ron
*Ron,How do you have access to thermal imaging equipment? I would love to look at my house, and several others that I have worked on. Is it rentable?Steve
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So Jack ... there is no humidity change in wall and roof cavities in your place ? Maybe humidistates would be good things to have there.
Tedd
*Yea ... I would like to know more about tests and measurements on live buildings and comparisons in insualtion performance including humidity affects. Who's doing this kind of analysis ?My mind can't compute FG being less efficient from humidity and water than cellulose. Someone explain this to me.If FG fibers are not water absorbant, and condensed humidity drains down and through the batts how can R value be comprimised ? Unless, water sticks to the fibers and fills the air spaces ? Wouldn't cellusose actually saturate and expand when wet, filling the air spaces with the turgid paper ? Tedd
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Tedd,
About my home...It's built in gravel area...cellar temperatures are winter 48 degrees at coldest wall base and 55 degrees for the rest of the concrete...humidity is reading 35 percent...In the insulation that I have recently checked I find all dry as a bone...I did feel air flowing up and down the vented spaces that lead to ridge vent, mildy windy day..cold air outside air...There was an area that had dirty fiberglass...from air movement...
So I have very little if any moisture coming in from the cellar...and I do not add much...
I still would like to upgrade the building envelope...and probably will as I get a feel for what can be done economically.
Chillin in Upstate NY,
J
*Fred. On your point 5a. Fiberglass will decay: break down under the right temperature and moisture conditions. See Dr. Low's paper, "Material Degredation of Thermal Insulating Fibres,"published in ASTM STP 922, _Thermal_Insulation: Materials and Systems, page 477.You may also recall my post on the homeowner in Missouri who found his 30-year -old attic fiberglass insulation had deteriorated into a powdery mass full of rat droppings, and insect shells and had shrunk from 6-inches down to 1-inch. TEDD, et al. As for the effects of moisture on cellulose's R-value, the Swedish building scientist Dr. Sandberg in his report "Determination of the Effects of Moisture on the Thermal Transmissivity of Cellulose Fibre Loose-fill Insulation," published in the _Thermal_ Performance_of_the_External_Envelopes_of_Buildings_V, 1992, showed that moisture or wetting has only a minor (8 percent)effect on the thermal performance of cellulose insulation. Cellulose insulation then, is more resistant to the negative effects of moisture, heat, and cooling than fiberglass.And finally, TEDD, the last sentence of the last paragraph of your March 2, 1999 #3 post, " Water has the insidious ability to migrate into the most expensive water-tight design."should be posted in the largest fonts this page will take. Those of you who wonder why the change from barrier to retarder should be required to read this statement from Tedd, every morning over coffee. GeneL.
*Gentlemen.Fred is right on soaked cellulose and fiberglass. One of my arguments against gable-end louvered vents is that in the Ameroican and Canadian Prairaries high winds often blow several inches of snow inot the attic space.But it is also common in non-prairie regionsI had this happen in my 1968 laboratory in Pepperell, Massachusetts. Because thius is a common occurence in Canadian Prairies, a Manitoba building scientist decided to find out how well do fiberglass and cellulose recover their R-values when covered with 4-inches of snow that melts or from excessive wetting caused by rain penetration or roof leaks.Fifteen inches of cellulose and fiberglass were blown dry inot a special chamber. The R-values were measured, and then the samples of both insulations were wetted to 5 pecent moisture content by volume.This high moisture loading was considered to be equivalent to four inches of snow melting into the insulation.The R-values of the wetted insulations were measured and the insulations were allowed to dry for 25 days at 70 degrees F and 40 percent relative humidity.The drying samples were remeasured at 5 days and at 25 days. Results. After drying for 25 days the cellulose had regained only 78 percent of its original R-value. The fiberglass regained 86 percent. The title of the paper is "An Evaluation of Cellulose Fibre Loose-Fill Attic Insulation for Manitoba Housing." The report may still be available from Msnitoba Housing or from Professor Chant (204)474-9463. GeneL.
*Gene,It looks like cels perform better than fg at the moisture content that they might get to from condensation from moisture that comes from inside of the house but fg performs better from a soaking standpoint.
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1. Which absorbs more moisture (when exposed to exactly same relative humidity); FG or Cell ?
2. Which transports water faster (across its mass); FG or Cell ? Will moisture penetrate one faster and or deeper in one or the other ?
3. Which retains its loft and insulation value better, when wet; and, when frosted/frozen; FG or Cell.
4. Which dries faster (evaporates out water more efficiently)? Is there any difference in evaporation performance under different rates of air flow across their surfaces ?
5. Are either types of insulation suseptable to any form of decay from either fungis or from chemicals or off-gasing from other building
materials ?