Rhonemas - 13 November 2006 11:48 PM

Well Precaud, I owe you an apology because you were right!  I dug around in my energy books and low and behold there’s a tiny blurb that states the temperature difference also affects it (see picture).  That’s all I could find anything about the rated R-Value of batts decreasing with temp difference, doesn’t mention how much or to what degree, but something I passed over.  I’m assuming it happens to all insulation, nonething I have mentions it happening to cellulose but I feel the higher the temperature difference the more force but I have to assume fiberglass batts is most susceptible. 

Here’s the pictures of what this years energy book says, along with the chart explaining how devastating the smallest gaps have on fiberglass batts.  Oh well, the book recommends if I have fiberglass to blow cellulose over it saying the cellulose will fill any gaps/cracks I missed so I get full R-Value of the fiberglass batts and add it’s own R-Value.  Maybe after I’m done remodelling Enjoy

I believe it’s recommended that fiberglass batts be layered in the attic at right angles to each other for this reason. First layer between the ceiling beams, then the next layers put down at right angles to the joists.

BeGreen - 13 November 2006 11:59 PM

How did you locate these openings precaud?

By getting up there with a light and looking along the wall intersections…

<snip> rated R-Value of batts decreasing with temp difference <snip> I’m assuming it happens to all insulation, nonething I have mentions it happening to cellulose but I feel the higher the temperature difference the more force but I have to assume fiberglass batts is most susceptible.

Seem like it’s just a function of the porosity. A material where the air pockets are trapped and sealed won’t allow penetration.

Here’s the pictures of what this years energy book says, along with the chart explaining how devastating the smallest gaps have on fiberglass batts.

OMG! 50% loss of R value with R38 and 1% gaps! That’s huge.

Oh well, the book recommends if I have fiberglass to blow cellulose over it saying the cellulose will fill any gaps/cracks I missed so I get full R-Value of the fiberglass batts and add it’s own R-Value.  Maybe after I’m done remodelling Enjoy

Yeah, it can wait...! The only downside I’ve read to doing that is that the cellulose, which is quite a bit heavier than the fiberglass, compresses the batt. Nevertheless, it seems like the way to go.