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Question DetailsAsked on 2/2/2017

How to stop condensation and mold on a newer roof without eaves? It has a ridge vent only.

The shingles and plywood had been completely replaced in 2007. Shortly thereafter I noticed condensation and mold started to grow. I have a cape type house so the entire roof is not exposed. There are crawl spaces running along the perimeter of the front and sides of the house. The problem is that although I have a ridge vent, there are no eaves along the border of the roof. I was advised by a roofer to install two fans with humidistat sensors on them which I did. Then I was advised by another roofer to install baseboard heat in the storage area to make the temperature rise closer to the interior temperature in the winter. Before I do this, I wanted to get other opinions as this problem seems to yield different answers from various contractor professionals. I don't feel like paying high heating bills to heat the attic is a viable solution. If I replace the roof, it will just happen again. There is no insulation on the plywood.

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2 Answers

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There are a LOT of previous discussions on this general issue in the Home > Roofing and Home > Insulation topics under Browse Projects, at lower left. Basically, you need expert input from an architect experienced in attic insulation and ventilation issues, or an energy and insulation specialist.


And absolutely, different professional will recommend different things because their experience and the type of work they do is different - roofers will tend to push ridge vents and maybe roof-mounted fans or vents, HVAC contractors commonly gable fans or whole-house ventilation systems, insulation contractors of course vapor barriers and insulation, soffit installers eave venting, etc. So you need a person trained across the board in ventilation and humidity control methods in attics - an architecture firm (who usually has a mechanical designer on staff or who may himself be trained in energy efficiency and building insulation and ventilation), some but not all energy auditors, some but not many roofing and insulation contractors.


You can get a lot of good input (realizing some, and especially many of the contractor/product sites, may be highly biased or dead wrong) by googling subjects like attic insulation, attic ventilation, and so forth. NACHI, Inspectapedia, This Old House, US government websites like EPA and DOE and EnergyStar are some sites with fairly reliable info - though many of the energy-saving sites are unduly optomistic about energy savings from insulation and such.


You don't say how long the previous roof lasted - but if the sheathing was replaced during the reroof evidently this is not a new condition - may or may not date to when the house was originally built, or maybe only to when the attic room was built if it was an add-on. Might be an idea to look closely at the trusses/rafters for rot too.


Certainly heating can help reduce the condensation - but that does not get rid of the moisture so it will just cause other problems by driving it elsewhere, or will promote more rotting in the plywood. Without ventilation to remove the moisutre, and cutting off the moisture sources (from inside the house almost certainly, so through the attic floor and from the attic rooms, and any kitchen or bathroom fans vented into the attic), all you will accomplish is a lot of wasted energy and improve the conditions (warmer) for mold growth.


Also - the fans (presumably gable or roof fans) would remove some of the humidity if the airflow could get to them around the walls of the attic room - but at the cost of removing condditioned air (leakage air) from the house probably since you have no eave vents, which means you would be using heated or cooled air from the house to ventilate the attic and be exhausted outside - so higher heating AND A/C costs. Plus that leakage air is high humidity so you might not get a reduction in moisutre levels at all.


Sounds to me like this was probably designed as a cold attic (whether a cold or warm attic needs to be determined before starting on a solution - but since uninsulated underside of the roof likely cold), and maybe the room(s) were added later and not properly sealed off from the attic, and/or may have taken away the ventilation that should have been left to provide a passageway for airflow from eaves to ridge vent. Assuming this was designed as a cold (rather than fully-heated) attic, the right thing is to put in eave vents (several ways to do that if your house does not have roof overhang, easily done if it does), properly penetration seal and vapor barrier and insulate the attic rooms AND crawlways to totally isolate them from the attic, and put venting space over the attic room walls (if not there now) where they meet the roof (restore the open rafter bays from eaves to ridge) so the air in the attic crawlways is mixed with outside air and can then vent freely to the ridge vents, removing both excess heat in the summer and that humidity from the house which the sealing off does not stop. Sometimes these crawlways need special eave baffling or supplemental fan-driven ventilation measures so the lower part against the room walls does not become dead space.

Answered 1 year ago by LCD

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Answered 1 year ago by Member Services




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