condensation issue

[diesel06]

Anyone ever have condensation issue by putting your insulation right below metal roofs? I recently insulated my shop this way at the time the condensation didn't cross my mind. I plan on finishing the walls and ceiling with white metal.

 

[meboatermike]

Where are you located? What kind of insulation is it? Here in Maine it gets cold and there could be all kinds of condensation issues below a metal roof.

 

[diesel06]

Located in Pennsylvania, using r13 fiberglass batt insulation

 

[keith5064]

I recently found myself in this predicamwnt. Its a one car garage with some rafters that someone cobbled together, soo being how the rafters were so low I decided to just staple some insulation to the bottom side of the roof..worked great until I noticed a drip coming from the ceiling, turns out the whole bottom side in between the insulation was ALL frost! I'm sure its partially to do with my ventless blue flame heater..now I'm trying to figure out what to do!

Sent from my XT1080 using Tapatalk

 

[anthony666]

ventilation is as important as insulation when controlling condensation

 

[DC73]

Building experts are able to calculate the amount of insulation needed under a roof for various climates to prevent the condensation issue. Fiberglass is not recommended for this type of installation because even if you get a high enough R value, fiberglass lets warm air come through and get to the cold roof surface where it condenses.

One solution is to spray closed cell foam on the underside of the roof in sufficient thickness to prevent the condensation (again this is a calculation) and then finish getting the needed R value with fiberglass batts. This is known as flash and batt technique.

I'm sorry but I don't know the actual calculations to help. I live in a dry climate and won't have this issue so I've never needed to make the calculation. I've gotten most of my information on this from BuildingScience.com. Click on the Information tab and then review most of the links to the left. I also purchased their Builders Guide for my climate. An extremely helpful resource. You might also find some information on GreenBuildingAdvisor.com.

Good luck.

DC