I have a Silver Maple tree in my backyard I want to build an addition along with a basement onto my house the tree is about 3ft in dia and I would be doing the construction about 8ft away from the tree. I do not want to take the tree down if it is not necessary. We will be cutting down through the roots, will this kill the tree? Or will the tree be alright? Please HELP?

8 foot away is pretty close, i would gather the foundations to your extension of your property will be under the actual crown of the tree?-if not then first thing i would suggest is restricting access beneath the dripline of the tree-underneath the whole canopy-to help prevent compaction and damage to branches and bark during the construction of your new basement and extension.
A good rule of thumb is that you are pretty safe to remove up to a 3rd of the root system.
If you have a decent tree officer in your area working for the local government then they should be able to give you good advice and should come and see the tree itself.
i was just reading through these and thought i would post my bit-im sure others will be able to post more.
1 thing i would say is that my brother-in-law was to build an extension which would have been very close to a weeping willow-he asked me to remove it-i did and a week later i planted another at the bottom of the garden.
hope it all goes well.