Blow insulation over catwalk?

tombobOctober 5, 2009

I am planning on blowing in cellulose insulation in an addition that has traditional fiberglass batts laid in between the joists, even with the top of the joists. The contractors built a catwalk on top of the joists, two 2X6s side by side down the center of the attic space. The attic has trusses.

When I blow in, do I cover the catwalk?

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Cellulose packs down when walked on or even sitting things on it as light as a pipe wrench, for example. You didn't state what region you are in, but I would think 5-1/2" of blown in,( top of the catwalk), would be ample addition to the fiberglass. Be careful not to block any soffit or eave venting, and be careful around any lights/electrical,(such as recessed lighting), where the cans aren't rated for contact with insulation. Any other mechanicals that are safe to be covered, you might want to take note of where they are in case you need to access them.

    Bookmark   October 5, 2009 at 11:26AM
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As long as the area underneath the catwalk is fully insulated, putting insulation on top of it is unnecessary, and would be annoying if you ever go up there. The first inch of insulation always makes the biggest bang, and tapers off in its effect as you add more. If you have got batts already to the top of your joists, your blown in insulation overall will make a very small difference in heat savings for the whole space, and not having it on top of the catwalk will be an immeasurable difference. I won't go into the mathematical reasons, but going from, say, 6" of insulation to 12" does not save twice as much energy. For example, if 6" of insulation reduces heat loss by about 95% (which it does), that's great; however, the combined effect of 12" will only improve that to about 97%. So you are gaining only 2% efficiency by doubling your insulation.

    Bookmark   October 5, 2009 at 1:00PM
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The op's insulation is between the truss joists. Adding cellulose will help fill any voids, cracks, crevises that the batts do not take care of, but 5-1/2" is more than likely overkill. Agreed that you dont get double the r-value with twice as much insulation, in fact, with the air infiltration that fiberglass and cellulose allows, you're not going to achieve a true mfgr's claimed r-value anyhow. Best purpose in the op's case is to use it to fill voids and an even layer across the attic.Dependent on vent locations, i've seen attics where the wind coming in through the vents blew the cellulose out of the area and built up where the winds no longer reached it.

    Bookmark   October 5, 2009 at 1:57PM
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Why is there a 'catwalk'?

Is it required to access mechanical HVAC equipment in the attic?

If so, you cannot cover it, and the catwalk must remain open and accessible.

    Bookmark   October 5, 2009 at 8:03PM
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