Is there an exception for hold down anchors in concrete using for wood-framed single family residences? If not, all my anchorage capacities have diminished greatly.
Don't know about that, but I know all my anchorage capacities for wind here in the US got cut by about 12% because the sheathing and nailing combination I always use was found to have some strange prying effect that reduces the overall capacity of the system. yay....
Im assuming your talking about Omega in the contexts of ACI Anchorage Calculations.
Theres no exception for hold downs, however there is one for wall sill plate anchorage.
But what I have seen does it to use the limiting load clause in ACI anchorage requirements for seismic rather than omega. Also some anchor manufactureres have proprietary anchors which have a tested allowable load, to me this is a justifiable means to not apply omega on your hold down anchors.
Ductilie crush of the sill plate at the hold down posts is one method I have heard tossed around to limit the anchorage load. This is also mentioned in the commentary of ACI Ch 17.2.3.4.3 (Option (c))