How strong is the sun in Johannesburg, month by month
People ask me why they need shade in September when it is not even properly hot yet. Heat and sun damage are not the same thing. It is the UV that takes your dashboard apart, not the temperature.
Johannesburg is a difficult place for anything left standing outside. We are at roughly 1 700 metres above sea level, we get very little cloud cover through the dry months, and the sun sits high overhead for a long stretch of the year. Thin air and a high sun mean more ultraviolet reaching the ground than most people expect.
What the numbers look like here
The UV index is a simple scale. Anything from 3 is worth taking seriously, 8 and up is Very High, and 11 and above is classed as Extreme. Johannesburg spends most of the year in the top half of that scale.
| Month | UV index | Rating |
|---|---|---|
| August | 7–8 | High |
| September | 11 | Extreme |
| October | 11–12 | Extreme |
| November | 11–12 | Extreme |
| December – March | 12–15 | Extreme |
| April – July | 4–7 | Moderate to High |
Typical midday values for the Johannesburg area under clear skies. Actual readings move with cloud cover and the time of day.
The part that surprises people is September. We are still in jerseys in the morning, but the index has already climbed to Extreme. At an index of 11, unprotected skin can burn in roughly fifteen minutes. That is the walk from the parking bay to the office and back.
What it does to things that are not skin
UV breaks down the bonds in plastics, rubber, paint and fabric. It is slow and it is cumulative, which is exactly why it gets ignored — nothing looks wrong until it all looks wrong at once.
- Vehicles. Dashboards crack, door seals go hard, headlight lenses cloud over, and paint loses its depth. On a fleet parked in the open, that is real money off the resale value.
- Stock and equipment. Anything in plastic housing, anything with a rubber seal, anything printed or labelled. Packaging fades, labels lift.
- People. Staff walking across an open yard at midday, customers loading a car, a school field at break time.
- Plants. For the agricultural clients we do work for, it is the opposite problem — the crop needs light, just not all of it, and not the harshest part of it.
What shade netting actually does
A shade net is not a roof and it does not pretend to be one. It is a filter. A net rated at 80% is designed to block roughly 80% of the light passing through it, and the fabrics we install are UV stabilised so that they hold that rating for years rather than months.
What that means practically: the surface under the net stays considerably cooler, the UV load drops sharply, and the slow breakdown of everything underneath slows down with it. You still get airflow, which is why a netted structure does not turn into an oven the way a solid roof over a closed space can.
Percentage is a choice, not a ranking. For cars and people we normally go high, because there is no reason to let the sun through. For crops it depends entirely on what is growing — that is a conversation, not a default. There is more on the fabrics and what each one is suited to on our colours page.
The honest version
Netting does not stop UV completely, and anybody who tells you it does is selling. What it does is cut the exposure down to a level where the damage becomes slow enough to stop mattering over the life of the asset. That is the whole point of it.
Where the netting itself sits in all of this
The netting is outside too, taking the same punishment. Good UV-stabilised fabric from a proper supplier will give you ten to twelve years in Gauteng conditions. Cheap netting will look fine for two summers and then go brittle and tear along the stitch lines, usually in the first real wind after it has gone.
This is where I differ from most of the industry. When a net starts to go, the frame underneath is normally perfectly sound — it is galvanised steel, it has years left in it. Replacing the net on an existing structure is a fraction of the cost of a new build, and it is what I will recommend if that is genuinely what your site needs. We maintain before we replace.
What to do about it
If you have existing structures, the time to look at them is before September, not after the first storm. Check the tension, check the stitching on the seams, and check the cables. A net that has gone slack takes far more strain in wind than one that is properly tensioned.
If you are covering something for the first time, work backwards from what is standing there. Vehicles, people and stock all want a different answer, and so does a nursery.
Send me a photo of what you have. I will tell you honestly whether it needs replacing or whether it just needs attention — and if it is the second one, I will say so.