Thread: Stains/shadow lines at truss locations

I have seen this before but I can't remember what causes it. Light stains/shadows were visible on vaulted ceiling at truss locations near outside wall. There were no sings of moisture intrusion. I would have to guess that water from ice damming traveled along the trusses and caused the stains.

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Consider candle soot plating out on the cooler walls or areas where air flow might cause impact of soot particles. There has been an extensive discussion of this here in the past.

Originally Posted by Trent Tarter

I have seen this before but I can't remember what causes it. Light stains/shadows were visible on vaulted ceiling at truss locations near outside wall. There were no sings of moisture intrusion. I would have to guess that water from ice damming traveled along the trusses and caused the stains.

Trent,

Could also be due to inadequate ventilation. If the roof framing is rafters, were there eave vents at each rafter bay and complete ventilation at the top of the roof, such as a ridge vent? If the roof framing is truss, then ventilation may not be a problem.

I find that most attics around here are marginally ventilated.

Originally Posted by Gunnar Alquist

Trent,

Could also be due to inadequate ventilation. If the roof framing is rafters, were there eave vents at each rafter bay and complete ventilation at the top of the roof, such as a ridge vent? If the roof framing is truss, then ventilation may not be a problem.

I find that most attics around here are marginally ventilated.

No it was truss framing. Attic had soffit and ridge vents.

Try this thread:
http://www.inspectionnews.net/home_i...ior-walls.html

Trent;
Called in by owner who had primed and painted area several times over several years, but discoloration returned.

Found similar situation that was a result of insulation (loose fill) not covering the area.

Redistributed the insulation. Interior ceiling was cleaned, primed and painted. Discoloration never returned.

It looks like it could be "ghosting". Do they burn a lot of candles, fireplace with poor draft, or other sources of soot and dirt in the home? Here some links:

Ghosting of ceiling joist in tight home - JLC-Online Forums

How to Recognize & Diagnose Thermal Tracking (and Thermal Bridging), Ghosting, Heat Loss, Soot Stains, Thermal Bridging, Soot from natural gas, soot from oil burners - an explanation and advice for home owners and home inspectors - recognizing stuff

I'm posting some pics of a 1950 house with ghosting on the walls. You can see where the studs are. I suggested it could be soot from scented candles (or the old oil furnace, but it had been removed), and condensation forming on the cold surface. This is plaster on gypsum, probably no insulation in these walls.

Not quite the same as what you have, but poor insulation could be the root cause.

Yep, appears to be classic ghosting.

Easily confirmed with cleaning/streak test, moisture readings and Thermal imaging.

Presuming all is as it should be regarding vapor/moisture barrier, ventillation openings/ratio/balance, un-clogged chutes, R values. I suspect there is no isolation/thermal break - cold/damp wicking truss chords. On walls, even if all seems as should be, sometimes in your region it is a lack of a (properly installed, lapped, taped) rain/water screen and wind barrier behind siding that's the culprit for air/moisture migration.

R-value of wood significantly lower than surrounding insulation. See this a lot in pre-fabs/modulars and truss vaulted ceilings.

Hence the roof-over-roof "solutions" promoted over a decade ago, still requires isolation at ends to work, but has its own potential problems and load considerations, esp. in tropical climates. One method included isolating deck with a mini SIP sandwich before superroof structure - heavy solution usually exceeds snow/ice and wind/sheer loading.

Appears ceiling was installed directly on chords, not strapped and not isolated/insulated. Dropping ceiling, support structure to isolate/insulate from chords *might* work. Also heavy, lose headroom, and increased uplift issues and a cracking wall/ceiling intersection joint - hide with floating crown.

I believe that it's soot, most likely came from burning candles. The soot is attracted to the cooler surfaces where the trusses are located. The ceiling was vaulted so there was no practical/safe way of accessing the area above from the attic.