In the crawl spaces beside my finished attic I think I am going to add more FG insulation as I have some serious ice dams even though I have proper ventilation.

On the bottom is ~2" of old rock wool with paper face down towards the lower ceiling, then about 10" of blown cellulose that is somewhere between 10 and 50 years old. Laying over that and the floor / ceiling joists is 1/2" OSB for a walking surface. (ascii diagram below)

1. Is there anything wrong with me adding a nice layer of new FG over all that old insulation?

2. Should I drill holes in the OSB to allow moisture flow from the lower insulation or should I just lay the new batts over the top?

Thank you for your help!


~~~~~~~~~~~~~~

Proposed new batts

============== OSB
* * *
* * *
* old cellulose
* *
* *
~~~~~~~~~~~~~~
Rock wool (paper down)
_________________
=============== Sheetrock

< First floor room>

 

It takes heat to cause the ice damms and by your statements it does not appear that adding more insulation will resolve the ice damm problem. The severity of the ice damms usually indicate the magnitude of the problem. Also certain types of construction, like having a finished attic, usually have similar flaws. In finished attic or Cape Cods the most prevalent problem is the attic by-pass phenomena. This is where heat by-passes the insulation and causes the ice damms. The most common cause are the attic entrances to these areas behind the knee wall. Another common cause is the floor directly below the knee wall. Other concerns are electrical outlet boxes and you would be surprized how much heat can escape through and outlet box in a knee wall, heating pipes and/or ducts. All of these things are simple to correct and are best done by the do-it-yourselfer. Another common problem with the attic by-pass phenomena with this type of structure are the ceiling and walls of the stairs leading up to the finished attic are usually poorly insulated.

 

Thanks for the reply!

I can beef up the area behind the access panels. The panels are 2x4 framed squares with 2" hard pink insul doubled up inside the frame. Then a piece of masonite on the finished side.

There are a lot of gaps between the frame and the foam on this door-- maybe that's it.

I thought this was ok when I built it, but if small cracks around outlets will hurt me, then these gaps certainly will.

Thank you.