Go Back  DoItYourself.com Community Forums > Exterior Improvement Center > Roofing, Gutters and All Waterproofing Anywhere
Reload this Page >

water damming caused wet sheathing and mold.... please help

water damming caused wet sheathing and mold.... please help


Old 01-25-09, 07:03 PM
Thread Starter
Join Date: Nov 2005
Location: canada
Posts: 175
Received 0 Votes on 0 Posts
water damming caused wet sheathing and mold.... please help

Okay so I'm about 90% sure water damming on my roof has caused it to soak water through the shingles and mold the bottom side of the OSB.

Signs are as follows. wet osb. worse mold lower down closer to the gutters when viewed in the attic. The 2X4 trusses have no mold on the bottoms of them but some mold/moisture present closes to the osb. this is mainly what leads me to belive the water came from above rather than moisture leaking from the house. (Also we just had a big snow and then melt here and there was a lot of ice dammed on the bottom section of the roof.

Assuming I'm right about the cause .(please chime in if you think it could be something else.) I'm thinking I need a new roof. The current roof is pretty well end of life and there is no point spending more than minimal cash and time on it.

My plan is tear the old roof off and new plywood/osb on the wet sections and re shingle. What I want to make sure of is the ice damming issue is resolved with the new roof. What can I do to ensure this? A friend told me I could seal the shingles with a caulk gun of tar so even if the ice damms again it won't sink in. Is this a good idea and what else should I do?


EDIT: i should probably mention this ice dam hasn't happened before however it may have been caused by the very very cold mass dump of snow then quick warm we had this year.

Upon more research here is what I'm thinking: The attic already had the first layer of blown insulation and a large second layer done much later so that is good unless I find trouble spots when the roof comes off. Replace the bad OSB, put on a new roof and install one maybe two wind turbines (is there a calculation by square footage to determine quantity?).. Currently only has a few roof top vents however they are only maybe 2 inches high and would have been covered for weeks with the last snow which is also how the bathroom vent was done. Should the bathroom vent have a stack to ensure warm wet air isn't blown into the snow while covered? Is there some kind of product to use on the say lower 3 feet of roof under the shingles in case some water dows get under the shingles?

Last edited by tha_dub; 01-25-09 at 07:46 PM.
Sponsored Links
Old 01-25-09, 08:04 PM
Join Date: Oct 2008
Location: Ohio
Posts: 27
Received 0 Votes on 0 Posts
Ice dams and condensation are the result of not enough insulation and/or not enough ventilation.

Check these links for more information.

Blockage of soffit vents;

Soffit Vents and Attic Ventilation

Proper roof ventilation;

Roof and Attic Ventilation
Old 01-25-09, 08:32 PM
Thread Starter
Join Date: Nov 2005
Location: canada
Posts: 175
Received 0 Votes on 0 Posts
Thanks for the info... I do have the Styrofoam soffit baffles in place however per previous post the roftop vents would be easily covered by a once or twice a year snowfall thus drastically reducing airflow.

mostly what I'm after is for someone to confirm my ice dam hypothesis and also to verify/modify my replace plan. Like i said the roof is old enough that it just needs to be replaced but I really don't want a repeat with a new roof.

Old 01-25-09, 11:21 PM
Join Date: Jan 2008
Location: rockland county,new york
Posts: 121
Received 0 Votes on 0 Posts
CALCIUM CHLORIDE,AND SNOW RAKES---YOU NEED TO ADD THE INSULATION,AND VENTING TO KEEP THE HEAT AWAY FROM THE BOTTOM of the roof,as far as soffit area venting,I drilled large 3" holes thru the existing fascia,added wood blocks over rafters for nailers,padded between with cobra vent,then installed new fascia over it,and capped it with aluminum

afterwards We cap the fascia,and aluminum cover with 3x3" backflashing that goes down below where the gutter will mount like this :

and then secure the gutter on top of the flashing,I also like to seal the back of the gutter to the 3x3 with Geocell tri-polymer sealant-I`m in Rockland county,deal with Ice dams all the time
Don`t caulk the shingles !

Sorry pics didn`t upload-be sure you install ice and water shield at your fascia eaves,so it runs at least 2 ft. past your bearing wall
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: