Replies

1. 
   DanH | Jul 16, 2013 08:48pm | #1

   What the inspector said was true -- in your area the dewpoint is always real close to the temperature.  Lots of things can happen.

   For instance, since you lack trees the roof of the carport will radiate heat into the sky at night and cool down rapidly (especially if it's a dark color). This will drop the temperature in the attic, causing dew to form on the carport ceiling (both sides) just as it forms on the grass overnight.  Venting may actually be counter-productive since it allows the attic to stay cooler during the day.

   A modicum of insulation over these areas might help -- just 4" unfaced fiberglass, maybe.  I'd also paint both sides of the plywood with mildew-resistant paint.

2. 
   IdahoDon | Jul 23, 2013 12:29am | #2

   If it's only a normal suface moisture issue and the wood is dry, simply have your painter use a mold inhibiting additive (available in any decent paint shop) to the paint.  Done!  Not much of an issue really.

3. 
   gbaune | Jul 25, 2013 06:46pm | #3

   Mold

   We worked on an extensive remodel last year, the new roof sheathng was installed in July and no ceilings or insulation installed through November.  This is about the time the mold started to grow, but like you said, only on some of the sheets.  I checked the sheets with the mold and they appeared to be of the same outer veneer, maybe poplar or cottonwood??  The sheets with fir/hemlock did not grow mold.  Ventilation could not have been the problem as the attic space was wide open.

   Final action was to spray the moldy sheets with a bleach solution, the mold stopped growing.  Any thoughts??

1. 
   kentkhi | Jul 25, 2013 07:40pm | #5

   gbaune, the owner seemed to think it was due to the specific sheets of plywood as well.  I think that is a contributing factor,  but I also think that it is more likely an atmosphere thing, as it happened all over the second story deck cover soffit, this soffit was 10 years old, and different plywood.  

   I guess my concern is more for the long term, how can I kill the exisitng mold as well as stop  any future mold growth? 

4. 
   kentkhi | Jul 25, 2013 07:31pm | #4

   Thanks Dan for your reply!  My question about insulation is, will mildew form within the insulation now that you are just moving the dew point to within it?  What are your thoughts about air movement, and installing a fan that would draw air through the attic when a certain humidity is reached?

1. 
   DanH | Jul 25, 2013 11:03pm | #6

   The purpose of the insulation would be to help the plywood retain heat and not get so cold due to the black body radiation from the roof.  You don't have a moisture problem, you have a cold problem.  There might be temporary condensation in the fiberglass, but it would be of no consequence, since fiberglass does not absorb moisture.

5. 
   IdahoDon | Jul 25, 2013 11:15pm | #7

   Surface mold on an unheated suface isn't a problem with how it's built - it's a problem with a surface that supports mold.  The SURFACE supports the mold currently.  Use a better product and it will go away. 

6. 
   Perry525 | Jul 27, 2013 07:02am | #8

   Mold condensation dew point wood solution

   Mould spores are all over the world, but you don't see mold

   everywhere, as mold needs food and water to grow.

   Mold feeds on wood and paper, it gets its water out of the

   air or the wood or paper it grows on.

   It also grows on dirty walls etc.

   You get condensation on surfaces, when the object is below

   dew point.

   Condensation forms inside untreated wood! The molecules of

   water vapor are so small, they can enter the surface of the

   wood (and some other things)

   You see condensation on windows, during cold weather, when

   the warm wet air inside your home condenses on the window

   surface that is below dew point.

   You see condensation outside on your truck, greenhouse etc

   as, condensation, dew, frost, ice - depending on the time

   of year.

   The air we breath out is 100% full of water vapor.

   Condensation does not form on surfaces/or in objects that

   are warm - that is to say, above dew point.You can pick up

   sheets of paper that are damp and limp with condensation.

   Condensation can form on many things, in most cases it

   merely dries out, evaporates and disappears into the air.

   Like when you get a can of beer out of the fridge, the warm

   wet air rushes to it, in no time it is covered in condensation.

   Then the can warms, the condensation dries and disappears.

   That's how water vapor, condensation works.

   To stop mold growing on any surface, wood -whatever, you

   need to deprive it of either food or water.

   You cannot deprive mold of water, as the water vapor is in

   the air. You must deprive it of food!

   You can do this by painting the surfaces with gloss paint

   or varnish - then like your beer can, the condensation will

   form and then dry/evaporate and disappear into the sky.

    

7. 
   calvin | Aug 01, 2013 02:16pm | #9

   Kent

   This may or may not be a possible answer to your problem, but it might be something to read through.

   This brand/type of plywood could have a propensity for mold growth.............

   http://forums.finehomebuilding.com/breaktime/general-discussion/anyone-use-sandeply