I'm preparing to put the last layer of foamboard insulation on the rim joist--a foil-faced, fire-resistant layer as required by code. The black pipe for the natural gas supply runs along the top of the basement wall part of the distance I'm insulating. There isn't quite enough clearance between the existing foamboard and the black pipe for the additional layer of foamboard to just drop right in.

However, I discovered that if I pull the pipe inwards just a little, using very little force, the additional foamboard drops right in to place.

I'm certain it's not enough mechanical stress to affect the pipe or joints, but is it otherwise ok for that black pipe to be sitting up against that foil-faced foarmboard somewhat snugly?

Any code issues? Other issues?

Yep, that is fine. The engineers will tell you the R-value may be slightly reduced by foam board compression.

I'd maybe slip a little tar paper between the foil and pipe to eliminate the corrosive effect created by dissimilar metal contact. Just a thought.

quote:

Originally posted by Woodman:
Yep, that is fine. The engineers will tell you the R-value may be slightly reduced by foam board compression.

Thanks!

quote:

Originally posted by Expat:
I'd maybe slip a little tar paper between the foil and pipe to eliminate the corrosive effect created by dissimilar metal contact. Just a thought.

Turns out that isn't a problem for iron/aluminium contact: Galvanic Compatibility Corrosion Guide/Dissimilar Metal Corrosion Guide

Iron and aluminium have a max Anodic Index difference of 0.1. Even in harsh environments, which this will not be, differences up to 0.15 are acceptable.

Black “Iron” gas pipe is actually steel, not iron, but still is fine for contact with the foil face insulation.

quote:

Originally posted by Stlhead:
Black “Iron” gas pipe is actually steel, not iron, but still is fine for contact with the foil face insulation.

Thanks for the clarification and the reassurance.

A little bit of superficial research appears to suggest "black pipe" is carbon or other low-alloy steel, which has the same anodic index as iron.

Btw, Woodman: I'm not worried about the mild R-value loss from the mild compression. There'll be 3" of Owens Corning Foamular 150 between that 1" of fire-retardant stuff and the rim joist