I've come across a situation that seems unlike any I've seen discussed\nhere, but this is probably common in 30-40 year old houses. This is an\napprox 20x80 sq ft raised ranch (a basement and 1 floor of living\nspace) with a hip roof. The attic has loose fill fiber, about 4", but\nit's pretty uneven and dusty (30 years will do that). In addition,\ninsulation has settled deep into the bathroom and kitchen walls, so\nthat if the vanity cabinet in the bathroom is removed, the bathroom\nwall is open to the attic. There's a ridge vent running along the\nmiddle 2/3 of the length of the ridge, and 3-4 passive vents halfway\ndown the roof. While adding some batts seems an obvious way to increase\nthe efficiency of the roof, there are two problems.\n- the hip roof overhangs about 3 ft in the front of the house, and this\nis the only place where there are 2 soffit vents\n- with the lack of soffit vents along the other 3 sides, air may short\ncircuit between the ridge and passive vents\n\nI was wondering if, after adding another 8" of batts, it makes sense to\nhave a small (6 or 8") fan going at low speed, at around half the\nheight of the attic. This could circulate the air enough that moisture\n(and heat in the summer) would circulate with the outside air through\nthe vents.\n\nAlso wondering if laying some Tyvek before laying down the batts where\nthe roof is open to the walls of the living space would be advisable.