OK strange question....

[Kels]

I was outside and looking at my shop when i noticed something strange...

the roof had a color change on it (Assuming DEW forming) between the purlins and the insulation.

Very similar to what you see on a poorly insulated house when the snow melts and you can see the frame work.

I haven't noticed this before and am stumped on what would cause this. the roof does have the standard metal building condensation blanket on the roof 2" thick fiberglass with the vinyl backed. Building is not heated or cooled currently. walls are steel and tyvek and wood framing.

temp is about 83 hi and low 56 humidity ~55% http://www.weather.com/weather/today/Bremerton+WA+98312:4:US not sure if this is a factor.

so any ideas why this is happening?

was also on the lower 2/3rd of the roof.....

lol, not sure what info is needed....

 

[atfulldraw]

Mine does that in the mornings.

I solved the problem by sleeping later.

 

[nehog]

Mine does that in the mornings.

I solved the problem by sleeping later.

So does mine. The purlins conduct heat and cold better than the insulated parts which causes the problem. In the winter if I'm working in the shop a lot, I can see the purlins in the snow cover (if the snow is only about 4" deep) too because the purlins conduct the shop's heat up to the roof sheeting.

If nothing else it shows very well how fiberglass insulation when compressed doesn't provide a lot of insulation capability!


I'll have to keep that sleeping later solution in mind--that may work for me too!

 

[Falcon67]

Same with houses - with just the right dew or light frost, you can sometimes see the rafter lines. Some of the metal buildings around here look almost like an x-ray in the right conditions.

 

[Kels]

Yeah, I thought that was it.... I'm planning on insulating the shop... and was going to make it a cathedral ceiling to avoid loosing height... would putting a layer of foam board over the purlins on the inside take care of this? Had no idea how much the wood was a conductor!

 

[Old Steamer]

Same with houses - with just the right dew or light frost, you can sometimes see the rafter lines.

Every home in my neighborhood does this and is most noticeable when there is frost.

 

[78Bird]

i see it on cars too, all the time.

the tonnau cover on my truck is fiberglass, and real often in the morning dew or frost i can clearly see the thicker reinforced center part outlined.

the 'vette trunk does the same thing if exposed in the right conditions, the structure shows clear as day in dew or frost.

when there's a difference in materials or thickness that causes temp variations on a surface, the right conditions will do this.