According to:  The Effect of Radiant Barriers in an Attic Application on Exterior Roofing Materials – Technical Bulletin 103

It does raise the temperature but not much and the few degrees does no harm to the exterior roof.

… The results of this study are:

* Roof shingle temperature increases due to attic radiant barriers are 2 to 5 degrees Fahrenheit.

* Roofing material warranties are not affected by the installation of attic radiant barriers.

read the whole article here via Radiant Barriers in an Attic on Exterior Roofing Materials; Technical Bulletin 103 – RIMA-I.

Technorati Tags: effects, exterior roof, heat, radiant barriers