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Ceiling stains matching joist spacing

0 votes
We have a split level house, with open loft type attic/room over main area, which is used for storage, and a standard attic adjoining it/above another area of the split design. Originally we had a cedar shake roof with styrofoam insulation on top of the sheeting, so exterior insulation. We had to replace roof after hail damage. We could not/did not insulate directly under new roofing material. Instead, we used roxul insulation and a vapor barrier inside of  the lofted attic only. This area has some vents for heat/AC, but the temperature is usually 10 degrees F more/less than rest of house. Directly below this is our living room, and now I'm seeing shadowing on the stipling, in a pattern spaced as the floor joists would be. Did we over insulate, block too much ventilation, is this mold, or something else? (Live in southern Alberta, Canada, should that help) THANKS
asked in Attic Area by cameio (120 points)
edited by darekrudy
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1 Answer

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Hi Cameio,

Location helps, Alberta is definitely experiencing freezing temperatures during the cold season, that’s when such problems usually occur. Also, I don’t think that over-insulating would be an issue in this situation.
Assuming that:
In cold climates covering of the ceiling framing members sometimes helps to prevent dark ceiling stains from appearing. Therefore, if you have a single layer of batt insulation placed between the ceiling joists, and narrow, open spaces above the joists, this could be responsible for the stains. Blown in type insulation or dual layer of batts (second layer installed perpendicular to the joists usually prevents stains from appearing). 
The pattern of your stains suggests colder spots along the ceiling joists, discoloration may have different sources and my article - http://checkthishouse.com/2432/ghost-marks-and-soot-deposits-on-house-walls.html and Q&A in Interior Walls category - http://checkthishouse.com/qa/questions/interior-walls should give you a few ideas.
Please let me know if you have further questions, just click "comment" below.
answered by darekrudy (21,730 points)


Read the links you included below, THANK YOU. The information on cathedral
ceilings seems most relevant to our house design and the shadow stains.
This house is 35 plus years old, reinsulated about five years ago. House
is a split design, with the attic/loft/cathedral area being the
fourth/upper story. It is largely undeveloped, but has four windows, and
has had a full plywood floor the entire time. This space could have been
developed, but heating was an issue, as it's not as consistent as rest of
house. When we reinsulated, the roxul was brought along the top of the
rafters/trusses and right down to the plywood floor, along what would be a
knee wall built to shape the dormers. The soffit area, which was, and
still is not covered with plywood, but had batt insulation is now behind
the roxul and vapour barrier. I'm therefore wondering if we've cut off the
air circulation, causing these shadows. More are along the exterior wall,
but some are appearing six feet into the hallway. Shadowing is only
appearing on the stiple on the eastern side - other half of the house has
a painted drywall ceiling with western exposure, and I'm not seeing any
shadows on that side. The western exposure has a small overhang, the
offending eastern exposure has a six or eight foot overhand. We have had
more snow holding on that area of the roof since reroofing/resinsulating,
but we've also had significantly more snow in the last couple of years,
plus we've gone from a cedar shake roof to a composite rubber shake style.


Hi Cameo,
I’m not sure what you are referring to in your first sentence: “Read the links you included below”, there are no links in your response…
I can’t fully visualize your attic / loft from the provided description. Maybe if you can answer the following questons... pictures would be helpful.
  • Is that storage area / loft enclosed with walls or fully open
  • Are the loft’s ceiling / roof rafter spaces insulated / finished with drywall or anything else?
  • Is the floor (house ceiling) fully insulated and section of that floor covered with plywood?
  • Is the insulation under the plywood touching its surface or there's some air space left between the top of insulation and plywood’s surface?
  • If there’s some space between the floor insulation and plywood, did you block it by adding insulation around the plywood? 
  • Are the soffit vents open into the attic or they’ve been blocked with the new insulation?
  • Is there an air return vent installed in that area?
  • Are the stains located directly underneath the plywood floor?
  • Did you have a chance to check the temperature in those stained areas (during the winter)?
  • Can you take some pictures of that area and email them to me?
  • How old is your heating system (gas / oil)?
  • Is the vapor barrier paper? Is it exposed? 
  • Is the vapor barrier facing the conditioned space?
  • Has the vapor barrier been installed over any existing insulation?



:-) Hi Cameio
Sorry for "I’m not sure what you are referring to in your first sentence: “Read the links you included below”, there are no links in your response…" I must be tired after the weekend... :-)