[GBlist] attic ventilation

["Alan Abrams, A.I.B.D." <awabrams@starpower.net>]

this is to seek advice on whether or not to ventilate an attic area which
will be used for heating and air conditioning equipment and associated
ductwork and mechanical connections.

the attic is above three habitable levels (including full finished basement,
which is 75% below grade).  the house is generally frame construction with
minimum of  3 1/2" of icynene insulation in the walls.  it is located near
washington, dc ("hazy, hot and humid" summers and relatively mild winters,
with a few weeks in mid Jan-early Feb were the temp may not get above
freezing.

the options, generally, are to insulate the upper ceiling with +/-4" of
icynene and 6-8" of batt, and ventilate the attic conventionally with soffit
and ridge vents--or to insulate the rafter bays, either shooting the foam
against underside of the sheathing, or creating baffles and air channels
under the sheathing, and insulating the bays.  baths and laundry will be
carefully ventilated, with provision for exterior make up air.

i would love to seal this space up and reduce the load on the hvac equip,
but i am concerned about moisture buildup.

alan abrams aibd


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