"Steve Walker" wrote in message
...
On 08/01/2020 00:53, Rod Speed wrote:


"Commander Kinsey" wrote in message
newsp.0d1qmig1wdg98l@glass...
On Tue, 07 Jan 2020 23:19:33 -0000, Rod Speed
wrote:



"Commander Kinsey" wrote in message
newsp.0d1n3vgmwdg98l@glass...
On Tue, 07 Jan 2020 21:55:04 -0000, Rod Speed

wrote:

Commander Kinsey wrote
Rod Speed wrote
Commander Kinsey wrote

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.

I wonder what the roof pitch has to do with it.

That's what determines whether you get the aerofoil effect.

When the pitch is too high, you don't.

But how can that get to the loft hatch?

The suction effect in the roof space sees air moved
out of the house into the roof space, lifting the hatch.

how could that happen? Surely aerofoil works on the roof itself,
lifting the tiles off.

The tiles arent an airtight surface like an aircraft
wing so you do get considerable movement of
air out of the roofspace before the tiles come off.

And my hatch is made of wood, way too heavy to lift like that.

You're wrong when the roof is of lower slope.

And hardly the end of the world if it opened, it might give me a fright
that's all.

Sure, but that's just as true of the other stuff like
shutters that it suggests should be shut and secured.

What of the possibility of air being able to rush from the house into the
reduced pressure of the loft, so suddenly changing the differential
pressure between the inside and outside of the roof and making it more
likely that the roof is damaged or ripped off?

It doesn't work like that, essentially because the hatch lifted by the
reduced pressure in the roof space doesn't see enough air moving
thru the narrow gap around the edges of the hatch to matter.