0 Helpful?

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.


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


2 Answers

Select your preferred way to display the comments and click "Save settings" to activate your changes.

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


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

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

Other Questions in Green building techniques

Should I go with chimney vent or power-vented water tank for cost savings?

In Energy efficiency and durability | Asked by Alan B | Sep 26, 15

How is thermal bridging prevented?

In General questions | Asked by S. Schneider | Oct 5, 15

Attic insulation

In Energy efficiency and durability | Asked by Quinton Bryant | Sep 28, 15

Advice regarding adding insulation to log home with added siding

In GBA Pro help | Asked by Debbie Baskerville | Oct 12, 15

How do you assess flash-and-batt installations?

In Building Code Questions | Asked by Robby Schwarz | Oct 11, 15
Register for a free account and join the conversation

Get a free account and join the conversation!
Become a GBA PRO!