On 07/01/2020 20:35, Rod Speed wrote:


"Commander Kinsey" wrote in message
newsp.0d1gkmz9wdg98l@glass...

Why secure a loft trapdoor in a storm?

And what's the roof pitch to do with anything?

In theory you can get a suction effect similar to
what you get with an aircraft aerofoil section.

In practice it isnt seen often enough to matter.

"Close and secure loft trapdoors with bolts, particularly if roof
pitch is less than 30°"

https://www.metoffice.gov.uk/weather...afe-in-a-storm


I agree. A low pressure from the outside will pull on a roof's attic
space to try to equalise with the internal pressure of the attic/home.

If the roof opens a pathway is created. If the attic door opens,
another pathway is created. This very small pathway then becomes subject
to the mass of air in the home. This mass compresses and speeds up as it
passes through the smaller hole and can be a very strong rush of air.