in floor heat effect on floor framing

huangyhg

in floor heat effect on floor framing
i design in an area where most homes have in floor heat.  many of these systems utilize a staple up tubing method where the heat tubing is stapled directly to the underside of the floor osb then the joist bays are insulated with foil backed insulation to keep the heat reflecting upwards.  the water temperature on a cold day can reach 165degrees.  the heating contractor insists that the engineered joists and osb is weakened due to these temperatures.  the top surface of the osb reaches 90degrees, so i'm guessing that most of the members in the area only get to 120degrees on the underside.  i suppose the osb in contact with the tubing gets pretty hot.  what are your thoughts on if this is a legimate structural concern, especially with engineered materials which have a lot of glue in them? is the diaphragm strength weakened?
thanks,

i've messed with some radiant heating systems, and the information i've gotten from radiantec has been pretty accurate and helpful.  i did a quick search on their site, and they've actually addressed your question to some extent:
to carry minerk's comment one step further, that's why the floors have a 3" concrete or tile topping - the heat sink for a more even distribution of the heat.  with the concrete on top, and the tubes in the concrete, degredation of the osb is a non-issue.  i typically spec 3/4" t&g plywood for these applications though, not osb.  the extra concrete affects the framing   
but there is a system that doesn't use a mortar bed, the pex tubing is literally fastened to the underside of the subfloor or snapped into channels in reflector plates that fasten to the underside of the subfloor.  these can be in any room and the finish floor can be wood, vinyl or any number of products that do not use a mortar base.
typically they are not pouring the concrete on many of these floors for cost reasons, thus there is no thermal mass (not very energy effecient i know).