Slope of a Covered Porch

[Dennis_Kuhn]

I was wondering if there is a universal slope for the floor of a covered porch.  Some one told me it should slope 1/8 of an inch for every foot.  

[borgdog]

I'd have to measure again to be sure but I believe that is pretty close to what my 100 year old covered porch on my house is.  Doesn't get much moisture on it, but seems to deal with it fine.  I am going to have to replace 2 or 3 boards on the south end this this year, the weather and sun have gotten to them, but after 100 years I'll probably be pretty warped and cracked too.