Presiding officer George Reid yesterday revealed that the bill for repairing the rogue strut will cost £130,000. That does not include scaffolding and other related costs.
And the cost for hiring temporary venues for parliamentary debates has climbed to £250,000 since the beam fell on 2 March.
Confirming the figures, a spokesman admitted costs could escalate even higher because contractors had not yet submitted final invoices.
Structural engineers Arup and Atkins have recommended all beams inside the chamber be reinforced. This will involve small unobtrusive pins, known as dowels, being inserted through the shoe and the strut. Once fitted, only the outside edge of the 20mm-diameter dowel would be seen, which, with suitable buffing and polishing, is unlikely to be visible.
Reid said: 'Liability remains an issue for the future and while it is unwise to speculate, we have repeatedly stated we will do everything possible to redeem the costs to the public purse.
'This near invisible mend ensures that the problem is treated and the Corporate Body considers it the best way forward. We have now instructed officials to progress this solution and come forward with more detailed costings which we will publish.'
Arup and Atkins are aiming to complete the project before MSPs return from their summer recess on 3 September.