Styrofoam Insulation Question

[Old_Bobby]

Just now getting a new metal building. Located in central Texas, I am interested in keeping the heat out. I plan on using 1" styrofoam between the outside walls and the 3/4" plywood interior walls. I have a free source for the styrofoam. Question: Should I glue the styrofoam to the metal siding or should I glue it to the plywood? I am not sure if it makes a difference. Help is appreciated.

 

[astroracer]

How are you framing the interior walls? You will need something to attach the plywood to so just suff that framing with the foam and hold it in place with furnace tape (and a vapor barrier). You should stagger and tape all of the joints anyway so this seems like a simple solution.
Mark

 

[Old_Bobby]

I will be using 2x4 stud framing. So, it will be better to leave a vapor barrier both between the foam and plywood and between the foam and metal siding? Is that what you are recommending?

 

[dirttracker18]

I would hope you are just using the wrong term but you should not be using styrafoam. what you need is a foam board like extruded polystyrene.

That material is not only an insulator but a vapor barrier when sealed with sheathing tape.

 

[Old_Bobby]

Thanks for the advice. My neighbor has access to 1" foam and recommended that I use it for the insulation to save money. I do not plan on conditioning the air inside at all. My only concern is the extreme heat in the summer. I will have ventilation, but need to keep the heat down. Thanks again!

 

[mrodgers]

I would hope you are just using the wrong term but you should not be using styrafoam. what you need is a foam board like extruded polystyrene.

That material is not only an insulator but a vapor barrier when sealed with sheathing tape.

Psst.... Styrofoam is polystyrene, Dow Chemical's brand name for polystyrene in both molded expanded beads and sheet expanded panels.

The so called "extruded" polystyrene is expanded also, all foam products are expanded. It is just extruded into sheet form as opposed to extruded in strands and cut into pellets to expand foam beads.

All the molded polystyrene beads sheets I've seen are foil backed which is for the vapor barrier.

 

[astroracer]

I will be using 2x4 stud framing. So, it will be better to leave a vapor barrier both between the foam and plywood and between the foam and metal siding? Is that what you are recommending?

Probably be better to put the vapor barrier on the plywood side to keep moisture from condensing on the foam and steel.
I would like to see you leave an 1" airgap between the steel and foam AND the foam and plywood just to help insulate and prevent moisture from wicking between the panels if it gets a chance.
Mark

 

[dirttracker18]

Psst.... Styrofoam is polystyrene, Dow Chemical's brand name for polystyrene in both molded expanded beads and sheet expanded panels.

The so called "extruded" polystyrene is expanded also, all foam products are expanded. It is just extruded into sheet form as opposed to extruded in strands and cut into pellets to expand foam beads.

All the molded polystyrene beads sheets I've seen are foil backed which is for the vapor barrier.

Ture but styramfoam is much less dense giving it a very small R value with the denser polystyrene has a much better R value and is much more durable.

there is a difference

 

[Old_Bobby]

Probably be better to put the vapor barrier on the plywood side to keep moisture from condensing on the foam and steel.
I would like to see you leave an 1" airgap between the steel and foam AND the foam and plywood just to help insulate and prevent moisture from wicking between the panels if it gets a chance.
Mark

Thanks, that's what I needed to know.