Clear or Opaque?

[Chris Johnson]

I'm planning on building an extension on the side of my workshop/garage; it faces east. This abysmal wet and cold May has reinforced the opinion that to grow specialist plants on the west coast, wind protection and cover is almost essential.

The workshop is 8 metres long and the extension will be 4 metres wide. I intend using triple- or multi-walled polycarbonate but can't decide on clear or opal. Although the intention is to grow semi-shade loving plants, I'm not convinced that light-diffusing opal is necessary. There will be a window in the south end and the east side will be 50% shade netting allowing plenty of ventilation.

Does anyone have any experience with these materials and can offer an opinion?

[Maggi Young]

"Borrowing "  forumists Michal Hoppel's photo from Facebook - you'll see that he has used  opaque for his  covers over his walk-through, sunken, alpine area in his garden in Poland

[Chris Johnson]

Thanks for searching, Maggi. I don't have the doubtful pleasure of Facebook.

Being open on all sides, he has ample additional light. I wonder what the orientation is?

[Maggi Young]

Tis a doubtful pleasure indeed, Chris!

I cannot remember the orientation of Michal's set-up- he spoke of it in his talk to the SRGC Discussion weekend the other year when he was just building it.    Will message him to see if he'll come and comment.

[Chris Johnson]

Thanks Maggi.

Any general comments also welcome, whether from experience or not. My feeling is that multi-walled polycarbonate will have a natural amount of diffusion and the opacity of the opal range might be too light-limiting.

[Michal Hoppel]

My roofing is oriented south with the bigger sheet,
the smaller and more steep is on nothern s.
My previous roofing in old garden was oriented east-west with polycarbonate 16mm with X structue inside, clear type. It  was blocking too much light for alpines .
The new one is made of 10mm without extra structure .
l'm sure that it should be clear, not dimmed . It blocks UV light and some visible light as well and after some time it will be not as clear as after fixing .
l'd recommend acrylic glass sheets as transporting UV light So important for plants.
Here in Poland there's hotter summer than in UK
Michal

[Maggi Young]

Thank you , Michal 

[Chris Johnson]

Thank you, Michal, for the extra information. I couldn't see the north-facing sheets from the photograph and the trees in the background are obviously not quite as close as they look. I'm impressed with your design.

That nicely answers my initial question, I now need to decide on the thickness. My research suggested 25mm multi-walled would be the strength needed here where severe gales are prevalent, but it will be sited away from the prevailing winds. Perhaps 16mm with narrower panels is the way to go? I've not looked at acrylic sheeting but will do so.

Regards, Chris

[Michal Hoppel]

Chris,

Thanks
I don't think that very thick plates are necessary. Thickness may be obtained from the construction as the whole, density of mounting, thickness of the construction etc. Quite dense mounting e.g 60-80 cm in my opinion makes 10mm PC useful even with strong wind conditions.

I don't know your climate and wind strenght, my experience is that investment in thicker PC may not be worthwhile, if money doesn't matter - acrylic glass would be best as it pass UV-light. I 'm considering exchange one of my PC sheets with acrylic glass in near future - maybe one of three and only this bigger south-facing. Wood used for the construction should be well-seasoned and dried to not release the resin in contact with PC, of course aluminum is better.

I'll post some more photos in next post, maybe my previous glasshouse as well
If you have more doubts let me know.

Michal

Michal

[Michal Hoppel]

More pictures attached. This wooden construction is definitely too strong but fits to the style of my garden.

[Michal Hoppel]

My old alpine-house with 16mm PC roofing with X structure - definitely too strong.
Sides detachable - 10mm PC,
aluminium construction, east-west orientation.

[Chris Johnson]

Michal

Thank you for the extra photographs and information. I like your design very much and being a little over-engineered is preferable to not being strong enough.

Having investigated acrylic sheeting; it's not an option. Apart from being very expensive in this country, 4 metre long sheets are not available. I'm waiting for a couple of suppliers to come back to me with their recommendations but will consider the 16mm triple-wall option again.

This site is the second windiest place on the planet and winter storms regularly register between 110 and 145 kph. This winter we had a hurricane registering 175kph. Not an element to take lightly.

Best wishes, Chris

[John85]

Chris,
Don't use white but clear poly.I have used some white ones because I got some cheap second hand.All the plants went leggy.Orientation is South West.
I advise you to paint the wall of your shed white.
I live not that far from the sea ,so it can be very windy here too.
What kind of "rafters" are you going to use?The top cover that hold the poly.must be of excellent quality.I had to replace them with a system that uses bolts and aluminium cover instead of a butyl one that clips onto the aluminium profile.

[Chris Johnson]

John

I've now ordered the roofing and fortunately it's in keeping with you observations.

The rafters are 6 x 2 in old money (150 x 50mm). There was a choice of rafter fixings with a considerable difference in price. However, the more expensive was not only a stronger manufacture, but a screw-down system rather than clip-on.

The larch cladding with be removed from the shed wall revealing what I anticipate as fairly rough block-work. I have a dislike of painted walls especially brick and block, which never looks nice in my opinion, and requires repainting on a regular basis. Bear in mind this is meant as a semi-shade bed and will give us the opportunity to grow plants that wouldn't survive our climate otherwise.

[Chris Johnson]

The construction is now well under way. More images of the construction can be found on my blog: New Rock Garden and Greenhouse - Ardivachar