QUESTION: Our church worship hall has exterior walls around the entire area. It is an extremely large space with room for over 600 people to be seated. The worship area is painted white. On the exterior walls you can see a faint dark line where each stud is behind the wall. We were thinking of repainting the walls but for a space this large it is quite a costly undertaking.
Do you think this condition is manifesting itself due to inadequate insulation or vapour barrier? If we paint the space, do you think in a few years we might be facing the same problem?
Thanks, Frank Conway, Winnipeg
ANSWER: The issue you are seeing on the inside of the exterior walls of your church may be due to building envelope defects typical of many older buildings, which are not normally easy to rectify. I will provide you with an explanation of the phenomenon and some things to avoid that may help, but remediation may be difficult and costly.
The good news is that the "shadows" on the walls are primarily cosmetic and rarely are a sign of any significant defect in the wall system. These vertical lines can be quite common and are simply due to specific areas where particles in the air in the building adhere to the wall. These particles are not attracted to the surrounding area, so the dark discolouration appears as lines only in these specific sites.
You are correct that this phenomenon normally appears only where the studs are installed. The reason for this is primarily due to "thermal bridging", which is caused by a direct connection of the wood or steel studs in the outside walls to the exterior siding. This will cause the entire stud to be slightly cooler than the surrounding wall cavity, which may be moderately insulated. Even with decent insulation and a polyethylene air/vapour barrier, this can still occur.
Because the studs are colder than the surrounding wall, this thermal bridging can also extend through, and make the drywall or plaster covering these areas cooler. The cooler wall may attract more airborne particles than the surrounding, warmer wall surface.
The airborne particles may be fine dust, smoke, or dirt that normally is carried throughout the building by the forced-air heating system. These particles will be darker in colour than the white walls in your sanctuary, so they will appear as shadows or dark lines.
I've been aware of the cause of this phenomenon for quite some time, but always thought the particles in the shadows were sticking to the walls due to condensation on the cooler surface. This may not necessarily be the case. I read an article a while back, authored by a physicist, who explained this issue at a molecular level. He said that fine particles in the air would adhere to cooler surface of walls because the lower temperature causes subatomic particles (electrons) to move slower than on the surrounding wall surface. These slower molecules would then "plate out" on the slightly cooler surface, whereas the warmer ones would simply keep moving and not stick to the warmer sections.
Further details on this were beyond my level of comprehension, but the theory seemed to make sense to me. This theory seemed more valid than that of condensation because the temperature difference may not be great enough to cause that to occur.
My own experience has shown that this wall staining can happen in one area of a home or building and not in others. I typically see it in areas like family rooms where vaulted ceilings and fireplaces are present. I also have observed it in homes with heavy smokers. Other colleagues of mine from across the country have found this happening in homes where candles are frequently burned.
Because of all these observations, I feel that one of the main variables is a high concentration of smoke particles in the air in buildings where this is seen. These smoke particles may indeed be highly susceptible to the subatomic effects described by the physicist, and plate out more frequently due to the nature of the dissolved smoke particles in the indoor air.
Following this reasoning, it's possible that your church is seeing the "shadows" occurring due to smoke particles in the indoor air. Because indoor smoking in all public places has been banned in Manitoba for several years, and I doubt that there is a wood-burning fireplace in the church sanctuary, I would suspect that the smoke may be coming from candles. If your congregants or clergy regularly burn large numbers of candles, which burn at a fairly cool temperature and emit black, carbon-rich smoke, this may be the source of the dirty air particles.
It may be possible to paint the inside of the walls of your church with a good primer and highly washable paint that will be easy to clean, but that may not prevent future staining. Without major renovations, the thermal bridging will continue and the shadows may return.
If my theory about the candles is correct, addressing that issue with better ventilation in the areas where they are used may help more than re-painting. Washing the walls, if they are not coated with flat-finish paint, may minimize the shadow effects by removing the excessive particles at a much lower cost than painting.
Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the President of the Canadian Association of Home & Property Inspectors - Manitoba (www.cahpi.mb.ca). Questions can be emailed to the address below. Ari can be reached at (204) 291-5358 or check out his website at www.trainedeye.ca.
trainedeye@iname.com
