I am subject to rules of my rebates organization, that I must break in correct service of my customers.The rules that have troubled me most are the call of a vapor-permeable air barrier on the exterior side of knee walls, and the 100% rule for vapor retarder placement.
1. Vapor-Permeable Air Barrier:
(From July, 2009 Insider, for example)
One clue of error in reasoning, is the application only to human-contact areas. The real and only purpose, applicable even in a hard-to-crawl, small knee wall alley, is to keep ill-sized, non-retained batts, from falling down. Isn't it?
Another clue of error in reasoning is the practical exclusion of non-air-barriered low-density, loose-filled attic floors, from enforcement. That fact is proof concerns are neither wind-washing, nor protection against dust. I have challenged my enforcement contact to find an insulation manufacturer spokesman who will say there is special concern of wind-washing in a knee wall, or that there is any consequence to R-value, of wind-washing on an attic floor.
I break the rule, where the expected compliance is stapling up a few hacked pieces of house wrap. That won't even retain a batt that wants to fall. It certainly adds no air-tightness. I was very disappointed in my one experiment in thus-compliance. I don't think any house wrap is sold with a useful tape to join panels, and bond to other structures. I had heard some contractors are complying, where anyone might check, by stapling up visqueen, and slashing it. My contact denies this would be approved. I'm not convinced it doesn't happen. Slashed visqueen is in fact not inferior as hold-up band-aid, to pieces of house wrap. My careful framing and double-layering is NOT a band-aid. R15 and less is NOT ENOUGH, where more will fit.
I seek change to an "R30 Rule" for knee walls and all permissive vertical walls, in part by example in my work. Please see my discussions and experiments, here, and here. My recent post on insulation of skylights inspires this fresh summary. Rules on security and amount of vertical-wall insulation, where thickness is not constrained, must apply equally to knee walls and to skylight shafts. Would there be any virtue in stapling some house wrap to try to stabilize precarious skylight insulation? Much better to use containing framing and crossing batts, for a standard R30 minimum.
2. 100% Rule for Vapor Retarders:
This is stated many times in 2010 Energy Trust Specifications, for example, here:
In attics with no pre-existing insulation, vapor retarders shall face the heated area of the building. Do not install new insulation with a vapor retarder on top of pre-existing insulation. There should only be one vapor retarder in the assembly, and it should be in contact with the heated ceiling. If existing attic insulation has a vapor retarder on top surface, slash with razor knife every 6 inches before adding more insulation.
I apply the common Two-Thirds Rule. Please see discussion here, and here.
My excellent examples of better service to customers by use of a Two Thirds Rule, are numerous. I don't like to break rules. It teaches disrespect. It makes me seem to be disrespectful, and in that I am being abused.