According to Bernoulli's principle, ρv^{2}/2
+ p = const, where ρ is the air density, v is the wind speed, and p
is the air pressure. If
p_{0}
is the air pressure at v = 0, then ρv^{2}/2
+ p = p_{0}.
The roof will be blown away after the difference p –
p_{0}
will exceed F/A where F is the limit force (20555 N) and A is the
area of the roof.

The
wind speed at which the roof will be blown outwards can be found from
the equation ρv^{2}/2
= F/A.

Then v = √(2F / ρA) = √(2·20555 N / 1.29 kg/m^{3}
· 3.3 m · 4.4 m) = 47 m/s.