Raisedonadeere
Well-known member
My builder is doing metal roofing on my garage build. The metal is screwed to 2x4 purlins that run horizontally across four foot center trusses. The builder puts bubble wrap with foil on one side between the sheet metal and the purlins.
Foil needs an air gap to do any reflecting but he places the foil facing up and in direct contact with the metal roofing with the white side facing into the building. I have looked at several of his building and they are all done this way. The bubble wrap is acting as a vapor barrier to keep moisture away from direct contact with the cold metal and has enough insulation value that the inside surface of the wrap stays above the dew point - it seems to work in this area.
But why not face the foil down where I can see the shiny side looking up from the inside of the building. That way it would reflect.
My idea of the foil helping to reflect summer heat would be to install the purlins on top of the bubble wrap shiny side up, creating an air gap between the wrap and the metal roofing . But I have never seen it done that way. I wonder if perhaps moist air coming up through the vented soffits would condense and drip down onto the foil or just rust the metal from the inside.
So any thoughts on that would be appreciated but my ultimate question why not ask the builder to do everything like he normally does except face the foil down.
My builder is a gem, takes pride in his work, with most integrity I have ever seen in a builder and I do not want to go against his recommendation unless I have good information and a good reason.
Foil needs an air gap to do any reflecting but he places the foil facing up and in direct contact with the metal roofing with the white side facing into the building. I have looked at several of his building and they are all done this way. The bubble wrap is acting as a vapor barrier to keep moisture away from direct contact with the cold metal and has enough insulation value that the inside surface of the wrap stays above the dew point - it seems to work in this area.
But why not face the foil down where I can see the shiny side looking up from the inside of the building. That way it would reflect.
My idea of the foil helping to reflect summer heat would be to install the purlins on top of the bubble wrap shiny side up, creating an air gap between the wrap and the metal roofing . But I have never seen it done that way. I wonder if perhaps moist air coming up through the vented soffits would condense and drip down onto the foil or just rust the metal from the inside.
So any thoughts on that would be appreciated but my ultimate question why not ask the builder to do everything like he normally does except face the foil down.
My builder is a gem, takes pride in his work, with most integrity I have ever seen in a builder and I do not want to go against his recommendation unless I have good information and a good reason.
on staying up wind while the builder installs to avoid air from popping bubbles. His fee for guarantee not popping any bubbles was out the roof.