Ridge Vent / Soffit Vent Question

Posted by on August 31, 2005, 3:51 am

Greetings:

I bought a 30 year old house with absolutely NO ventilation in the
attic, which is about 1000 square feet.

This summer, I spent a few days with a hole saw drilling into the
soffits. Every 4 feet, I drilled three holes (two and a quarter inch
diameter) and covered it with a vent. This had to go not only through
the vinyl, but also through a wooden soffit that was underneath the
vinyl.

Then, in the attic, I inserted and stapled styrofoam baffle vents into
the eaves where I had drilled the holes allowing for the air to come
through. All tested OK as cool air came through.

Questions - for the size of the attic, was this enough, too much, or
too little ventilation? My brother in law is a contractor, and he is
coming in shortly to do the ridge vent, presumably along the entire
length of the house.

AND, I was only able to vent about 75% of the soffits to date, as some
of them were too high for me to use a ladder safely (prone to vertigo!)
Should the entire perimeter of the attic be vented? At present, all of
the shadier side of the house is vented, with about half of the sunnier
side.

Thanks,

Dave

Posted by kevin on August 31, 2005, 5:05 am

In general, the more the venting, the better. In the ideal case, the
attic will never be above freezing unless the outside temp is too. In
other words, the attic should be same temp as outside in the best case.

The only caveat is that sometimes it is better to strategically add
vents to get good cross-ventilation, rather than just haphazardly. The
recommended way is a continuous ridge vent (across the whole roof), and
continuous soffit vents (a single opening along the entire soffit).
What you have done is most of the way there...

Posted by on August 31, 2005, 5:58 am

Not knowing where you are, be careful of ridge vents, heavy rains tend
to bounce or push water into them, snow WILL blow into them. I can't
tell you how many houses i've had to show a home owner a pile of snow
in the attic.

Posted by on August 31, 2005, 7:38 am

I'd say it's very likely you don't have enough soffit venting. A 2 1/4
inch one every 4 feet isn't very much. IMO, it probably would have
been a lot more effective to run a saw down the underside of the soffit
and install a continuous vent.

Posted by on August 31, 2005, 12:16 pm

>I'd say it's very likely you don't have enough soffit venting. A 2 1/4
>inch one every 4 feet isn't very much.

IIRC, it was 3 holes every 4', ie 0.083 ft^2, or half that as open area and
twice for both soffits. If each 600 ft^2 of attic needs a 1 ft^2 vent, with
a vapor barrier in the ceiling and equal high and low areas, those 3 soffit
holes can vent 49.7 ft^2 of roof, ie a 4'x12' section. We might want 6 holes
per 4' of 24'-wide roof, or a 2"x14.5" screened soffit slot.

As an alternative, a WXL' attic might have WL/600 ft^2 of screened vents
at the top and bottom of each endwall. A 30'x40' attic might have 4 1'x2'
gable vents placed high and low, which might be covered in wintertime to
conserve heat. IMO, continuous ridge or soffit vents are not required to
eliminate "hot spots," since air can flow freely inside an attic.

Nick

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