Amounts contributed to the Roth 401(k) do not reduce the compensation available to support an IRA contribution. The amount that will support an IRA contribution is the amount in box 1 of your W-2 minus any amount in box 11. Depending on your modified AGI for the purpose of a Roth IRA contribution, your eligibility to contribute to an Roth IRA might be limited. Your modified AGI for the purpose of deducting a traditional IRA contribution prevents you from being able to deduct a traditional IRA contribution, but your spouse might be eligible to deduct a traditional IRA contribution depending on your modified AGI for the purpose. (I assume that your spouse is not covered by a workplace retirement plan.)
