Chet wrote:

You solve high attic humidity by having a proper vapor barrier
between your ceiling and the attic space above it, as well as
having proper soffit ventillation.

Soffit vents are for "intake" of ventilation, where the cooler
air infiltrates.
You need additional vents to "exhaust". Power vents are much
like your information you have, USELESS. They don't work in the
winter.

Power vents *can* work in the winter. Some attic fan control modules
have humidity sensors in addition to temperature sensors. They can come
on in the winter based on the need for humidity control.

A vapor barrier does nothing for the attic as far as heat loss to
the attic in the winter.

We aren't talking about heat loss as much as we are talking about
interior house water vapor rising up into the attic. If you humidify
your house in the winter, you do not want that interior air to get into
the attic where it will condense on cold surfaces like the underside of
your decking and rafters and cause rot and mold.

Heat WILL still escape into the attic, even with PROPER INSULATION.
The vapor barrier is for the "interior" or "thermal envelope"
of the structure.

That envelope includes the boundary between your ceiling and attic - not
just the walls.

If you have a proper vapor barrier between your ceiling and attic, you
will by definition have an air-tight barrier and no (or very little)
interior humid air will find it's way into the attic.

Now if you are dumb and you exhaust your bathroom and kitchen fans
directly into the attic space, then naturally any vapor barrier you have
up there is wasted and you are causing the humidity problem that you
claim is bad.

Heat loss is up to the attic is not the same as humidity or air leakage
into the attic. If I had to choose between a good vapor barrier between
my ceiling and attic, vs having any insulation in my attic above the
ceiling, it's no contest - the vapor barrier wins hands down. But
(naturally) it's not a choice between having one or the other - you can
(or should) have both.

With a working vapor barrier, you don't need to have attic ventilation
in the winter, but you really can't totally stop the ventilation either
- even if your roof vents are covered in snow. Because if you have
soffit venting, then winds blowing against one side of your house will
flow up and into the soffit on that side, through the attic and out the
soffit vents on the other side.

At least read up on this stuff, since you have no real
experience with it.

Speak for yourself.

Here's a hint, read about condensation. You probably think a
cold glass of iced tea in the summer, is leaking tea through
the glass.

Here's a hint: Any condensation or frost forming on any surface inside
your attic is coming from water vapor that leaked into your attic from
inside your house or was dumped inside your attic by an interior vent
fan.

Air containing any humidity percentage you care to name will not
condense on a surface that's at the same ambient temperature as the air
in question. Air thats inside your house thats leaking into your attic
will me MUCH warmer than the temperature of the surfaces it encounters,
and hence the water vapor it's carrying will condense or form frost on
those surfaces when it hits them.

Outside air thats at the same temperature as your roof decking will not
condense it's water vapor on your roof decking when it enters your
attic.