Proper order of layers

[bluedog225]

Good afternoon all,

Been a while since I visited. Happy New Year everyone.

I’ve been working on a small garage structure 25’x25’. About 28 feet tall. Garage on the bottom and small cabin on top.

So far, I’ve got it framed and sheathed in 3/4 ply, and a roof on.

Starting from the 3/4 ply, I was going to proceed as follows:

-tyvek
-3/4 foil faced polyioso (taped)
-3/4 treated battens at 16” o.c. faced with strips of ice/water shield or moisture stop to protect metal
-snap-lock metal siding attached through to 3/4” ply

Does this sound right? The battens provide an air space so the foil radiant barrier can work. I was specifically wondering if the tyvek ought to be directly under the metal instead of against the ply.

Either way the structure will dry to the interior as the foil-faced foam is not permeable.

I am in central texas.

Thanks

Tom

 

[K'ledgeBldr]

You had me at 3/4” ply sheathing!

No wonder lumber so damn expensive here! JK

...and no, you don’t need a permeable membrane if it’s going to be covered by a non-permeable sealed material.

 

[Jacobsen]

If I'm following right you intend to leave a 3/4 air space between the siding and sheathing. I would not do that. Siding should be flat against the substrate.

Also along the bottom I recommend strip of solid lumber not foam etc. Not what I did but would in future!

Also also. I would go as think on the ISO as you can stand. 2" iso is R 13 i believe. Just make sure siding nails would be long enough if you go thicker than the 1/2. Nobody regrets over insulating.

 

[jkeyser14]

If I'm following right you intend to leave a 3/4 air space between the siding and sheathing. I would not do that. Siding should be flat against the substrate.

Also along the bottom I recommend strip of solid lumber not foam etc. Not what I did but would in future!

Also also. I would go as think on the ISO as you can stand. 2" iso is R 13 i believe. Just make sure siding nails would be long enough if you go thicker than the 1/2. Nobody regrets over insulating.

The 3/4" gap is acting as a drainage plane and is a pretty common requirement depending on the type of siding you are using. Also if you read his post he is using them to provide an air gap so the radiant barrier face on the foam will work.

OP - I see nothing wrong with your approach. I would keep the Tyvek against the sheathing. The foam won't care if it gets wet and it will help protect the Tyvek from damage.

 

[Vintage Veloce]

Oops. Deleted.

 

[CraigStu]

My SIL was planning very similar for a metal roof on his new garage. Airspace under the metal.

 

[Jacobsen]

The 3/4" gap is acting as a drainage plane and is a pretty common requirement depending on the type of siding you are using. Also if you read his post he is using them to provide an air gap so the radiant barrier face on the foam will work.

OP - I see nothing wrong with your approach. I would keep the Tyvek against the sheathing. The foam won't care if it gets wet and it will help protect the Tyvek from damage.

Air gap is good for the radiant but I don't like to see the siding not fully supported. Depends on siding manufacturer, check their installation details to be sure.

The airspace should be direct with the foil. The housewrap creates break in that which dulls the effectiveness of the foil.

 

[bluedog225]

Thanks all. Good point about the support. I’ll have a solid treated 2x4 top and bottom. And a layer of 3/4 and 3/4 batten in the field. I’m hoping it will be enough. The metal siding is actually snap lock roofing panels. Fairly rigid vertically. I”m probably violating install instructions using for the wall.