  Using atomistic simulations we determine the roughness and the thermal
properties of a suspended graphane sheet. As compared to graphene we found that
hydrogenated graphene has: 1) a larger thermal contraction, 2) the roughness
exponent at room temperature is smaller, i.e. $\simeq$ 1.0 versus $\simeq$ 1.2
for graphene, 3) the wave lengths of the induced ripples in graphane cover a
wide range corresponding to length scales in the range (30-125)\,\AA at room
temperature, and 4) the heat capacity of graphane is estimated to be
29.32$\pm$0.23\,J/molK which is 14.8% larger than the one for graphene, i.e.
24.98$\pm$0.14\,J/molK. Above 1500\,K we found that graphane buckles when its
edges are supported in the $x-y$ plane.
