RG Stones (Buildings) Ltd had been contracted to replace the canopy between two temporary buildings at Lakelands School on Oswestry Road in Ellesmere when the incident happened last August.
William Phillips, 52, of Weston Rhyn, was standing on the canopy with two colleagues when he fell three metres between the timber joists onto the concrete floor below.
He fractured his back, breastbone, six ribs and right wrist and has not yet been able to return to work.
Shrewsbury Magistrates’ Court heard that the company had not installed any edge protection to prevent a fall.
It had put two soft landing bags on the floor to mitigate the effect of any fall, but neither were in the area where the work was being carried out.
RG Stones (Buildings) ltd, of Wrexham, Clwyd, pleaded guilty to safety and was fined £6,500 and ordered to pay costs of £3,105.
After the hearing, HSE inspector Guy Dale said: “This incident was entirely preventable. The company had obviously appreciated the risks of a fall, as shown by the provision of the landing bags, but it’s a shame they didn’t think to put them under the area it was most needed.
“Work at height is a high risk activity and needs to be properly planned. Had that happened, a man would not have been left with debilitating injuries.”