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Are there any issues with Spray-foam next to Batt insulated walls?

We have a project where we there are additions and renovations to an existing residence that has batt insulation throughout. We have specified closed cell spray foam insulation to be used in the addition walls floor and sloped ceilings and batt in flat ceilings. In the existing part of the house where some exterior walls will be renovated we have specified spray-foam. The remaining existing house will not receive new insulation. My questions is, are there any issues with condensation using both insulation types adjacent to each other? A spray foam contractor has brought this up, but I can not find any research on this.

Thanks

Asked by Martin Brown
Posted Oct 31, 2012 11:25 AM ET

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2 Answers

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1.

There are no inherent issues with condensation with foam in one stud/rafter bay and fiber in another. In general the foamed part of the assemblies will be more air-tight than the fiber-insulated assemblies (unless there was significant air-sealing detailing on the fiber-insulated parts.)

Making the whole house more air tight raises the humidity levels inside an occupied house, but that is independent of the insulation, and needs to be monitored & controlled in any tight house. If it's staying well above 35% RH @ 70F indoors even during a week of weather where the daily high temps never break +20F, mechanical ventilation (preferably a heat or energy recovery type) under dehumidistat control keeping it at 30-35% RH would be a good idea, which would lower the risk of moisture buildup in the sheathing of the fiber-insulated part.

Answered by Dana Dorsett
Posted Oct 31, 2012 3:53 PM ET

2.

Dana, Thank you for your assistance...this was very helpful

Answered by Martin Brown
Posted Oct 31, 2012 4:55 PM ET

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