"Mike" wrote in message
oups.com...
I'll bet this is it: a kerosene heater has been used to keep the
temperature in the addition around 50 F at night (so the drying plaster
does not freeze). The heater throws off a lot of carbon when it runs
low on kerosene, as it does around 6am.

Now we have an extra layer of dust on the instulation. Any reason to
think that this is a problem?

The layer of dust on the insulation is not a problem. What is a potential
problem is your lungs. If it got onto the insulation, it also got into your
lungs if you were there when the heater was running. If is was used during
construction it is probably not that big a deal, but be sure to keep it in
the unoccupied space