Technical thread on shelter/exposure

Hi all - bit of a specialist one here - I'd decided that a wall behind my greenhouse would be a good place for a couple of climbers. As the wall's south-facing and presumably masked from winds by the greenhouse, I thought it'd be a sheltered location and planned a rose and a clematis cirrhosa.



I was working in this passageway at the weekend and was hit by pretty hefty gusts of wind, suggesting there's some kind of chimney effect pulling wind through the pasasgeway which might be too much for the cirrhosa (perhaps the rose'll be fine as they're pretty tough).

2 questions:

1) anyone have any experience of roses/cirrhosas in (occasionally) gusty situations? I'd imagine the pasageway's the warmest place in the garden, so I think we're talking more about wind exposure than temperature issues.

2) anyone managed to limit wind effect in a chimney/passage thing? I haven't got much to play with tbh - I can't put a full-height screen up, but could potentially put some kind of lower barrier up. RHS say:

"Shelter can improve growing conditions for up to 30 times the height of the shelter. The closer to the shelter the more pronounced the effect, but the greater the potential for shade."

In my mind, this suggests that some kind of barrier to say 1ft-2ft (perhaps a small conifer or similar MIGHT just break up / direct wind up enough to limit damage to the climbers.

Thanks!


Rob

 

Hi @Robodendron in my experience a barrier is worse, because the wind goes up and over. Next to my house is a wind tunnel due to a solid gate at the end. I am thinking of replacing it with a fancy metal one with lots of holes to dissipate the flow. And the wind effect is curious - the flow over the top can send things flying towards the gate instead of away!
So it might be worth looking at something open and trellis like to break up the airflow.

 

I agree.
I found this image that shows the effects that @CarolineL describes and why it causes things to fly toward the gate -
Not very sharp images, but the best I could find

Top image shows a solid gate - bottom one a wrought iron or similar gate

 

Great - thanks @CarolineL and @Pete8 - I've done a quick diagram of the area



Given that Google AI (no idea if right ) agrees with you that:

Permeability is Key: Good barriers should not be entirely solid, as they create turbulence. A semi-porous barrier (40–60% density) allows some wind through, which lifts the remaining wind up and over, providing the best protection.

and that south-westerly's presumably the prevailing wind, what would you reckon to a 40%-60% trellis/similar to baffle the gusts at either A or B?

Thanks again - appreciate it!

Rob

 

Looks fine to me, and in whichever position works best for you, though A may be more efficient, but maybe less practical.
40-60% permeability should do a good job of slowing the SW winds down.

 

Thanks @Pete8 !

 

You should always try to slow the wind rather than a solid block, which is why hedges work better than fences.

 

I knew the fluid mechanics course I did about 50 years ago would be useful!