Expert: Bruce E. Johnson - 10/11/2008

Question
The corrugated tin roof in my outhouse drips dew during the winter season. We have been covering it with hay for some years now to stop dew formation. That requires changing the hay cover each year after the rainy season and before the winter sets in. But could there be a more efficient way to stop dew formation? Like, is there any paint, coating etc. that can help?

Answer
Hi Rajiv, dew is formed during the transfer of heat from hot to cold thus the term "dew point".  By putting the hay on top of the roof you are in essence insulating the roof to stop this heat exchange.  If you have other means to insulate the roof this will work also.  Maybe putting a layer of insulation inside up against the bottom of the roof.  I can't think of any paint that will keep the dew from forming.  Another alternative would be to put a layer of visqueen or plastic on the inside and slope it to the outside wall so that any water dripping from the roof would hit the plastic and run down to an area of your choosing.  I hope this information helps feel free to write again regarding this or other matters, sincerely bruce e johnson..bejohnsonconsulting.com