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HeyBub[_3_]

Tim Watts wrote:
On Thursday 21 February 2013 20:52 HeyBub wrote in alt.home.repair:

wrote:

All sections have continous soffit venting, about 2" wide.
All 3 roofers say that is sufficient and doesn't need to be
improved.

Without a bit more info, I can't say for sure, but I'm betting your
soffit vents are woefully too small.

The "standard" * is 1 sq ft of soffit vent for every 150 sq ft of
attic space. If your house, for example, is 50 x 50 feet (2500 sq
ft), you need about 20 sq ft of soffit, or At your 2" wide existing
soffits, and ignoring dimunition for screening, you'd need (mumble,
mumble, carry the three...) 2880 sq inches of soffit. At 2" wide,
that works out to be 1400 linear feet.

Now since this example house's perimeter is only 200 feet, well, yep,
you're under-soffited!

There IS a fall-back rule and it's this: You can't have too much
soffit venting.

--------
* I think this "standard" is for passive ventilation. If you have
fans that are putting the big suck on the attic, you can probably
get by with much less.

The UK guideline for building regs is 1" continuous equivalent.

That means a 1" wide slot all the way around - or the equivalent
area. As this is obviously bad for letting mice in, it's usually
implement as a 2" wide series of slots (50/50) or a 1" wide slot with
mesh.

That's the soffits - obviously it needs to be balanced with vents up
top.

I strongly disagree, for reasons I worked out above using real math.

Further, the notion of "balance" is foolish. If you have too little soffit
vents, you're not getting maximum ventilation. If you have too much, they're
not doing any good.

Remember, you can't have too many or too much soffit vents.