Replies

1. Expert Member
   Peter Engle | Jul 01, 2019 07:41am | #1

   Adhered stone veneer itself is the biggest risk in this scenario. Depending on the style of cap flashing above the veneer and drainage at the base, bulk water entrapment will be the biggest threat. If there is no cap flashing, and if the veneer continues down below grade without a drainage detail, it is installed wrong and it is likely to cause water damage regardless of your rim board insulation treatment.

   Also remember that there is no drying to the interior in winter. Moisture moves from warm to cold. The better you insulate the rim board, the less drying you will get. XPS or other closed-cell foam will reduce vapor flow from the interior to the exterior and therefore reduce the potential for condensation on the rim board in winter. But as you have realized, this will also slow drying of the rim board in summer.

   The bottom line with all insulation schemes is that you need to control bulk water first, before you worry about vapor migration. Adhered stone veneers are notorious for bulk water leakage problems. I generally do not recommend stone veneers over energy-efficient wall systems without a true drainage gap and aggressive drainage and flashing details.

1. 
   Jon_R | Jul 01, 2019 01:12pm | #5

   > there is no drying to the interior in winter. Moisture moves from warm to cold.

   I'd be cautious with such statements. It's closer to:

   a) from high to low (gravity moving bulk water)
   b) from high air pressure to lower air pressure (with airflow)
   c) from high vapor pressure to low (which can be from cold to somewhat warmer)

1. 
   2bablend | Jul 01, 2019 05:00pm | #8

   Thanks Jon.

2. 
   2bablend | Jul 01, 2019 08:02am | #2

   Thanks Peter!

   Yes, there is cap flashing and the veneer ends at grade. Weep flashing is also installed at the rim board/concrete transition. Would EPS be a better solution?

1. GBA Editor
   Martin Holladay | Jul 01, 2019 02:37pm | #6

   Craig,
   You wrote, "the veneer ends at grade." Ideally, the stone veneer should terminate at least 8 inches above grade.

1. 
   2bablend | Jul 01, 2019 05:00pm | #9

   Thanks Martin. I will fix that.

3. 
   Jon_R | Jul 01, 2019 11:42am | #3

   Yes, XPS could make things worse. Are there any signs that you currently have a problem that is worth the risk to fix?

4. 
   2bablend | Jul 01, 2019 12:57pm | #4

   Jon,

   No, there is no signs of water problems. Just trying to minimize warm air contacting rim board.

1. Expert Member
   Dana Dorsett | Jul 01, 2019 04:02pm | #7

   Sounds like you're trying to snatch a defeat from the jaws of victory here. Don't do it.

   An air barrier on the conditioned space side of the fiber insulation can help, and it helps even more if that air barrier is somewhat vapor retardent or a "smart" vapor retarder such as 2-mil nylon (Certainteed MemBrain), which is far cheaper and better than any foam board solution. A foam solution works best if it's fully adhered and guaranteed to be pretty air tight forever, such as sprayed polyurethane foam, but even then it can't be so thick/low-perm as to unduly limit the drying path.

   Using XPS for almost anything is the opposite of a "green building" solution, due to it's HFC blowing agents an less-friendly polymer. Most of the time it can (and should) be designed out.

5. 
   2bablend | Jul 01, 2019 05:02pm | #10

   Thanks Dana! I’ll look at the MemBrain as an alternative.