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Thomas Kasper Posted: Dec 10, 2006 08:57 PM	unvented roofs Here is something that has caught me off guard. I have done about 10 unvented roofs this year and was feeling confident about then until just the other day. We have had some cold weather lately down to zero a couple nights. The problem is some of these building are not heated all the time. They are heated just for a weeked and then no heat all week. When they get heated up the moisture from the frost drips off the vaulted ceiling down on the floor. The property owner that called me has one inch of ridgid foam is the vaulted ceiling. I told him he had to heat the house to 60deg all the time to prevent this. What do you guys think? If there was 6in of ridgid would this still happen? Thanks, Tom
Dave Strnad Posted: Dec 10, 2006 09:39 PM	I think you need at least 3" of rigid to prevent condinsation. 4" would be better. I'm not sure if it would make a difference if it were heated all the time or not. Why only 1"? Also what are they heating with? If this is a shop or something and they are heating with propane or kerosene torpedo heaters or any other ventless heater this could be adding to the problem. Fuel has alot of water in it and those heaters just put it into the air. If this is a house did you spray one inch of foam and then fill with fiberglass or something? Is it finished or is it just dripping off of the foam.
Thomas Kasper Posted: Dec 10, 2006 10:42 PM	It is a old house is going through a complete remodel. It has one inch of ridgid foam on the entire building envelope. There is no attic. The plan is to install fiberglass over the foam. The homeowner works on the house during the weekend and is gone all week. He uses a torpeto heater during the weekend and there isn't any heat during the week. I think he hasn't ben at the property for about a month this last time. The moisture is dripping off the one inch of foam onto the floor.
Posted: Dec 10, 2006 11:24 PM	The moisture has to come from somewhere, probably his heat source, the he lets it get cold, so it immediately forms condensation or frost. Even 4" of rigid wouldnt stop the condensation if he leaves it cold for a week. he should either heat it (with a low/no-moisture heat source)and keep it above freezing. Or not worry about the condensation until he's further along in the project. As for the unvented roof; the foam is not the problem if the condensation is on the underside of the foam. This would be expected under these conditions.
Dave Strnad Posted: Dec 11, 2006 08:24 AM	Keeping it heated all the time probally would help prevent this. Also one of the byproducts of burning fuel is water vapor so unless the combustion air is vented it just goes into the house. Torpedo heaters are known to form a lot of condinsation. In fact it is a catch 22 of spraying in cold whether. If you use those heaters they add a lot of condinsation, if you don't the surface temp is too cold. From what I was told and the research that I have done using 1" to seal the house can be done but it needs to be on the warm side of the house. The reasoning is that the surface temp of the foam would still be low enough to form condinsation and the fiberglass would allow moist warm air to pass through. If you only put one inch in, it needs to be covered from the top. THe folloing is a link to the R-value myth book which explains this better. http://www.dcsconstruction.com/R-Value.htm I'm not claiming to be an expert I am still learning, but from what I know appling 1" to the exterior and filling with fiberglass would cause problems especially in a cold climate.
Thomas Kasper Posted: Dec 12, 2006 02:08 PM	The foam is inside the house in the vaulted ceiling it is not on top of the roof deck. Thanks Guys, It's just amazing how fast the finger gets pointed at the foam and it's usually not the foam that causes the problem. Tom

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Comments

Thomas Kasper

Posted: Dec 10, 2006 08:57 PM

unvented roofs

Here is something that has caught me off guard. I have done about 10 unvented roofs this year and was feeling confident about then until just the other day. We have had some cold weather lately down to zero a couple nights. The problem is some of these building are not heated all the time. They are heated just for a weeked and then no heat all week. When they get heated up the moisture from the frost drips off the vaulted ceiling down on the floor. The property owner that called me has one inch of ridgid foam is the vaulted ceiling. I told him he had to heat the house to 60deg all the time to prevent this. What do you guys think? If there was 6in of ridgid would this still happen?
Thanks,
Tom

Dave Strnad

Posted: Dec 10, 2006 09:39 PM

I think you need at least 3" of rigid to prevent condinsation. 4" would be better. I'm not sure if it would make a difference if it were heated all the time or not. Why only 1"? Also what are they heating with? If this is a shop or something and they are heating with propane or kerosene torpedo heaters or any other ventless heater this could be adding to the problem. Fuel has alot of water in it and those heaters just put it into the air. If this is a house did you spray one inch of foam and then fill with fiberglass or something? Is it finished or is it just dripping off of the foam.

Thomas Kasper

Posted: Dec 10, 2006 10:42 PM

It is a old house is going through a complete remodel. It has one inch of ridgid foam on the entire building envelope. There is no attic. The plan is to install fiberglass over the foam. The homeowner works on the house during the weekend and is gone all week. He uses a torpeto heater during the weekend and there isn't any heat during the week. I think he hasn't ben at the property for about a month this last time.
The moisture is dripping off the one inch of foam onto the floor.

Posted: Dec 10, 2006 11:24 PM

The moisture has to come from somewhere, probably his heat source, the he lets it get cold, so it immediately forms condensation or frost.
Even 4" of rigid wouldnt stop the condensation if he leaves it cold for a week. he should either heat it (with a low/no-moisture heat source)and keep it above freezing. Or not worry about the condensation until he's further along in the project.
As for the unvented roof; the foam is not the problem if the condensation is on the underside of the foam. This would be expected under these conditions.

Dave Strnad

Posted: Dec 11, 2006 08:24 AM

Keeping it heated all the time probally would help prevent this. Also one of the byproducts of burning fuel is water vapor so unless the combustion air is vented it just goes into the house. Torpedo heaters are known to form a lot of condinsation. In fact it is a catch 22 of spraying in cold whether. If you use those heaters they add a lot of condinsation, if you don't the surface temp is too cold.

From what I was told and the research that I have done using 1" to seal the house can be done but it needs to be on the warm side of the house. The reasoning is that the surface temp of the foam would still be low enough to form condinsation and the fiberglass would allow moist warm air to pass through. If you only put one inch in, it needs to be covered from the top. THe folloing is a link to the R-value myth book which explains this better. http://www.dcsconstruction.com/R-Value.htm

I'm not claiming to be an expert I am still learning, but from what I know appling 1" to the exterior and filling with fiberglass would cause problems especially in a cold climate.

Thomas Kasper

Posted: Dec 12, 2006 02:08 PM

The foam is inside the house in the vaulted ceiling it is not on top of the roof deck.
Thanks Guys,
It's just amazing how fast the finger gets pointed at the foam and it's usually not the foam that causes the problem.
Tom

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