VELUX KLA 100 Rain Sensor The Roofing Outlet Sale! from £210.00 £210.00 (inc VAT) £175.00 (ex VAT) Qty. Add to Basket This item is currently on backorder but you can still purchase it now and we'll ship as soon as more become available. VELUX KLA 100 rain sensor for automatic closure of VELUX smoke ventilation windows in case of rain. Grey finish 80 x 80 x 55mm The rain sensor closes the window provided that the smoke ventilation function is not activated.