Saturday, November 14, 2009

Fire Safety and Insulation

Talk of vapor retarders, linked to fire safety issues, should be followed by more independent thought on the fire safety issues. Everything in life is compromise against competing concerns. I'm proud to present a clean, physically-safe attic. Yet, I can not offer a maximum in fire safety. I'm stuck with lots of pre-existing features not open for discussion or change. Residential codes allow a bias in favor of usability and resale value, and I think that is where I am aligned. I put in clean, serviceable batt insulation, when starting with none. I don't mind a bed of rock wool or cellulose to start, leaving in-place with contribution to better fire safety, in addition to avoiding land-fill even for some dirty stuff. Cover the dusty stuff, I will, and in an attic floor, I doubt covering batts degrade fire safety.

I have taken the step of burning samples of Tenoarm and old, reject batt kraft facing, in my garage. Both do burn. The tarred kraft facing with some ready fury. The Tenoarm, not contained, sustains flame, but progressively falls out of the flame in drops of melt. I don't know how to proceed further, and leave advising to some Federal consumer-protective force.

Through a customer, I am awakened to concern for fire safety in the insulation of sloped ceilings, that connect knee wall closets with an upper attic. Such passages are found with various draft-stop provisions, more often wide open than draft-stopped. When wide open they tempt provision to moderate roof temperature, by baffling over new insulation. If roof joists are 2x4, I argue that R15 batts, pressed-down, leave sufficient breathing space, and that works even if the bottoms of the slope cavities are draft-stopped. I recently completed a new-drywall insulation placement with 2x6 roof joists, where breathing spaces were forced by DuroVent plastic baffles. Upon prompt by drywall contractors, I must reduce the applied insulation from R21, to R15. I may instead argue that the spaces should be draft-blocked, removing the baffles.

I wish a blog or some other internet forum might moderate discussion toward appropriate compromises.

Thursday, November 12, 2009

Vapor Retarder Two-Thirds Rule

When placing insulation in Portland, Oregon, I rarely use material with a bonded-on vapor retarder (kraft face). I am aware of propaganda favoring cellulose, and raising fear of fiberglass batts, in The Big Burn Video. Proponents of cellulose have dealt with criticism of organic cellulose as inherently less safe than inorganic mineral insulation, and tilt the table too far in the other direction. The video presents ideal cellulose, and fiberglass with no description. I imagine the fiberglass was a least-favorable setting, with air channels (chimney path) the length of flammable kraft facing. A fair comparison would have fiberglass totally filling joist bays, with no kraft facing.

I will never use kraft facing in a wall or in a new-construction ceiling. There I use complete, taped sheathing with polyethylene sheeting designed for the purpose, Swedish Tenoarm. Aside from fire safety concern, I save time and get better fit, in custom-cutting unfaced batts. I also follow the advice of the USA importer of Tenoarm:

I will use kraft batts in an attic floor, to isolate new material from found loose-fill insulation. I use original reasoning in study of dew point data for my location, as reviewed in this posting, with a current update. The commonly-understood two-thirds rule states that a vapor retarder should be to the warm side of two thirds of the applied insulation.