Cutting tree roots

[redwood1993]

Obviously cutting any tree roots would not be recommended but i have a customer putting in foundations for a garage that will come to about 3 metres distance of a 40ft horse chestnut tree and the roots will be affected. Im wondering if anyone can advise how to determine if this will kill the tree. The foundations will at their closet point be around 3 metres from the tree and cover 90 degrees of the trees root circumference. 

Tree DBH is 2ft

What are the chances of this causing tree death?
Would this affect the trees structural roots?