George is right. Derating for residential is overblown.
If there is tight packed cables run through tight packed insulation You might just heat up your cables somewhat, but up to 90 degrees centigrade? I doubt it. First we should be looking at the loading on the cable runs in a dwelling. Most are underloaded from the branch circuit rating. Where you are more likely to find wires or cables that should need de rating is in the commercial or industrial setting. I'm sure most of us have run across those way to warm or hot runs of conduit that somebody packed up with too many wires. Especially true where lay in flourescent lights keep getting added to existing circuits. But truthfully have any of you inspectors or fire marshall's out there ever seen a fire start because someone pulled more than 3 runs of romex thru a series of drilled holes? Be honest about your answers now.
