"Ghosting" on hardi-type siding

[Jim Baird]

House about 10 yrs old. This color diff pattern appears to show us stud locations, as the dark vertical lines coincide with face nails, but I don't know why. Guesses?

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[John Dirks Jr]

Insulation issues? Maybe temperature differential causing the finish on the siding to wear in that distinct pattern.

Which direction does that wall face? Was there similar patterns on other sides of the house?

[mjr6550]

Any idea what kind of wall sheathing? Any chance the siding is attached over furring strips?

[Jim Katen]

I don't know the reason, but I see it fairly often. (OK, maybe only once a year or so.) Perhaps it's the same thing as happens when the nails aren't driven quite far enough, touch the siding, and cause color changes.

[Jim Baird]

It's a full open eastern exposure. Other side is shaded by adjacent house for part of the day. I too think it is temp diff between area over framing and area over substrate, which is likely half inch isocyanurate and likely foil covered where structural sheathing is not applied. Also is likely the only coat of paint it ever had.

[inspector57]

Probably the same phenomenon as ghosting on the interior with candles, etc. Dust particulates depositing unevenly due to thermal differences showing thermal bridging at studs, etc.

I doubt there is foam board in those areas, but then 1/2 inch is pretty skimpy for much thermal benefit.

[Jim Katen]

Probably the same phenomenon as ghosting on the interior with candles, etc. Dust particulates depositing unevenly due to thermal differences showing thermal bridging at studs, etc.

I doubt there is foam board in those areas, but then 1/2 inch is pretty skimpy for much thermal benefit.

I thought the same thing, but it won't scrub off. The vinyl itself actually changes color.

[GMedich]

The photograph gives me the impression that there is also a dark horizontal strip approximately where the 2nd floor rim joist would lie. It appears to match the color of the suspected stud markings. If that coincides with the actual appearance, the framing is certainly affecting the issue if not directly causing it.

Another thought is that periodic, subsurface moisture might have "washed" some of the zinc from the fasteners slowly over time. Precise nailing on the studs would keep the drainage rather vertical. Weep holes would drain the wash close to the nails.

Are there any evidence of irrigation over-spray or misting?

[John Kogel]

Something I see here sometimes is frost forming only where the studs are.

Moisture collects on those cooler strips, but why that would darken paint, I don't know.

We sometimes get algae growth in that pattern, the green slime that turns dark when it dies.

[mlparham]

House about 10 yrs old. This color diff pattern appears to show us stud locations, as the dark vertical lines coincide with face nails, but I don't know why. Guesses?

Click to Enlarge

54.64 KB

Moisture movement from the interior to the exterior. Any water related issues in the home?