Anyone else prefer Silverboard over the standard pink NGX for old walls?

I went with the 1-inch Silverboard on my 1924 bungalow last summer becasue I was terrified of trapping moisture against my original fir sheathing. The biggest issue with the pink Owens Corning XPS is that it doesn't breathe well at all. In an old house that wasn't built with modern vapor barriers, you realy want that higher perm rating so the wall cavity can dry out if anything gets in behind the siding. The graphite-infused EPS (Silverboard) gives you about R-5 per inch, wich is pretty close to the pink stuff anyway, but without the risk of creating a moisture sandwich. I found the boards a bit easier to cut around my funky old window trim too. If you go with the pink boards, you’re basicly wrapping your house in a plastic bag. For a century home, I'd stick with the GPS every time just for the peace of mind regarding rot.

I actualy went the opposite route and stuck with the 1.5-inch Owens Corning Foamular NGX for my 1910 Victorian. Everyone gets worked up about perm ratings, but in my expirience, the structural stiffness of the pink board is a massive advantage when you’re dealing with wonky, century-old balloon framing. The Silverboard is a bit too flimsy for my liking; it tends to telegraph every single dip and bow in the old sheathing right thru to the new siding.

Instead of worrying about the foam breathing, I focused on creating a real drainage plane. I taped the seams of the XPS with 3M 8067 and then ran 3/4-inch furring strips over the top to create a rainscreen. That gap does way more for protecting your sheathing than a slightly higher perm rating ever will. If you’re spending the money on new siding, you might as well get the better R-value of the XPS. My heating bills dropped nearly 30% the first winter, and the walls have stayed bone dry beacuse the airflow behind the siding handles the moisture.

You shoud look into Halo Exterra instead of the basic Silverboard. I used it on a 1915 farmhouse and the integrated water-resistive barrier is a massive help. It’s a GPS board so you get that R-5 per inch and the high perm rating you need for old walls to breathe, but it has a much tougher perforated film. It holds up better during the siding install and saves you time on the housewrap if you tape the seams well. It’s the best middle ground for these old builds.

This is so cool! I'm just getting started on my first fix-er-upper and seeing all these options is making my head spin in the best way posible! I'm defintely leaning toward the GPS stuff now after reading this. Quick question though—since we're talking about old framing, has anyone noticed if these foam boards help much with soundproofing? My house is right near a busy bus stop and I'm dying to know if the Silverboard or the pink stuff helps block out that engine noise while it's keeping the heat in!

This is all so helpful beacuse I honestly had no idea there were so many types of foam. I'm still a total newbie at this, but I'm curious about the 'wonky framing' mentioned earlier. If my 1912 walls aren't perfectly flat (they definatly aren't), does the GPS board acutally bend to fit those curves, or do you end up with gaps behind it? I'm worried if I use the stiffer pink stuff it'll just crack or leave huge pockets of air. Does that mess with the insulation value if it's not sitting flush against the old wood?

Quick update—thanks for the suggestions! I’m really leaning toward that Halo Exterra now since the integrated barrier sounds like a massive help for my old walls. I am curious about the point on stiffness though. For those who used GPS, did you have any issues with it conforming to wonky studs, or did it hold up well enough to keep the siding flat?