insulating between old shingles and new metal roof

Rod Tustin
Hi. Am looking to add new metal roof over existing shingles. Cottage has a ridge vented cathedral ceiling and I would like to add a layer of 2" rigid insulation between the shingles and metal roof. Is this a good idea? Have had some issues with condensation since new windows were installed. Thanks, Rod
Eric Novotny
An informed customer is the Best Customer!
The house is effectively "tighter" with the new windows and you are not controlling the moisture levels. That is an issue that needs to be addressed on its own and is really separate from the roofing consideration. Next, you are mixing ventilation types here. If you are going to use foam, you would need to treat the roof as an insulated roof deck and close off the soffit area along with the ridge. Nothing about the foam or venting is going to necessarily address the condensation issues inside the home though. Those need to be addressed on their own. Are you running a whole house humidifier? If so, turn it off and bring it back online slowly. Humidity shouldn't be above 35% in the winter if you are in a colder area and even that is pushing it.

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