I have a problem with mold on the ceiling in a house with no attic space. The problem has worsened since we installed double pane windows and doors. I bought the house when it was about seven years old and don’t know how the roof/ceiling construction was done but I think there is no ventilation space between the sheet rock ceiling, the insulation, then sheathing and shingles. There are no soffit vents or roof top vents. The house is in the mountains (4,000 foot elevation).
Any suggestions on appropriate ceiling changes that would fix this?
I am considering building a new, lower ceiling which would be open to a vent space and adding gable end vents (not powered).
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I have no answer, but this will "bump" your posting up so it doesn't drop off the bottom of the list. Maybe someone else will have an answer.
Thanks for the "bump"
Your problem may not be related to anything in the roof assembly (lack of roof ventilation.....) Although there may be problems brewing in there.
The mold may be a symptom of high relative humidity in the building coupled with a cold ceiling surface. Even though warm air rises in the room, the surface if the ceiling may be cold. You may not have a roof assembly problem even without ventilation.
The old windows may have been leaky and the new ones not so you may not be getting as much 'natural' air exchange as before.
If it was my house, I'd first get a RH sensor (not a regular %humidity sensor but a unit that automatically does the calc with temp and humid to get RH), If you're up in the 60+ range you have an IAQ problem. Remember that once the mold takes hold, it can grow at lower humidity levels. It could have begun in winter when the ceiling was at it's coldest and doors/windows remained shut. Warmth of summer can cause it to blossom and appear to be unrelated to elevated RH in winter. If you think the RH is the problem, just control moisture vapor inside the house with ventilation (not roof ventilation but inside the house ventilation).
Then I'd borrow a moisture meter and stick the ceiling to see if moisture is building up in drywall; it can over time just from household moisture vapor.
I'd also cut a section of the drywall out and have a look at the roof assembly. If you don't want to patch the drywall, you can also remove roofing and cut through the sheathing- sometimes this is a less problematic route.
If you really think after all this that venting the roof is the fix, I'd skip the inside ceiling idea and instead lay furring strips (2x3) over the roof, sheath over the furring to create ventilation channels. Use venting drip edge for air intakes and ridge vents for exhaust. If there happens to be OSB roof sheathing under the shingles, you may want to drill some holes in it to let moisture vapor that migrates through the insulation -get out.
Mike;
Thanks for the response. I will get a sensor and check the RH before going on to the next steps.
I believe there is moisture buildup in the roof/ceiling assembly as there is mold growth around a ceiling light fixture. Other spots are not associated with a ceiling opening but are at the highest point if the ceiling.
Assuming the roof isn't actually leaking, it's probably poor roof design. Precisely what's wrong with it is hard to say at this distance, but a combination of poor ventillation and lack of vapor barriers is likely the problem.
Creating a more conventional attic would probably be one solution to the problem. The best configuration is eave vents and ridge vents, though the muffin style vents near the ridge is a reasonable replacement for the ridge vents. Gable end vents usually aren't very effective. The usual rule of thumb is one square inch of ventillation (divided between eave and ridge) for each square foot of roof.
The new ceiling should have a vapor barrier and be carefully sealed to prevent any air leakage up into the attic (eg, around pipe openings, through stud cavities exposed by drop ceilings, etc). And of course an appropriate amount of insulation.
There are other solutions, such as a "hot roof". Others can explain them.
Dan;
Thanks for the response. I will check more air conditions before making any changes. The roof was replaced a couple years ago but there was small mold problem before that time so there may not be an association. The original roofing was wood shakes and the replacement is composite shingles which may have resulted in a tighter roof. Taken with the window and door changes it could all have contributed to an increase in the problem size.
In addition the crawl space has some moisture from the ground water in the winter months particularly as our summers are mostly dry. There was also a water leak which caused water buildup in an air duct in the crawl space where mold could have grown and been blown back into the air.
I would first address the moisture issue in the crawlspace before considering ventilation. Damp foundations can pump more moisture into a house than almost any other source. There is no downside to drying out the foundation.
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I doubt that the window change caused this. It had probably begun the day after it was finished and you moved in, but has only now gotten your notice as it getss worse.
I presume you have a cathedral cieling which is the most common place for condensation problems
San Jose`, is that a nice warm climate? Humid? dry? airconditioned most of the time?
What kind of insulation do you have?
Is there a vapour barier? Where?
Crawl space? Is it dry?
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Piffin;
Thanks for the response.
I don't have the answers to your questions but will investigate further. From other responses I think there are some tests that will be useful and I will open the ceiling to find out the type of insulation and if there is any moisture barrier material.
Check out the average temps for San Jose. I didn't know a temperature range from summer to winter could be that nice.
http://www.weather.com/outlook/homeandgarden/home/wxclimatology/monthly/graph/USCA0993?from=36hr_bottomnav_home
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A comp roof is definitely tighter--a shake roof over skip sheathing breathes really well. The fact that the mold is around the light fixture suggests that moisture is taking advantage of that hole in the ceiling to get inside the ceiling/roof assembly, where it is condensing.
First, are you sure it is mold?
Is it blackish stripes that tend to follow the joists?
If so, it might be soot if you burn a lot of candles.
If it is mold, it is possibly a moisture problem from the crawl, basement or slab.
Mold results from high moisture levels: find the source of the moisture and eliminate it
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Yeah, that's a good point. Blackish deposits, especially at cooler spots on the ceiling such as ceiling joists, are often due to candle or fireplace smoke.Mold will visibly "grow" in small fairly distinct dots that grow larger over time. Smoke will cause darkening that's uniform over a small area (when examining a few square inches up close).Dampen a Q-tip with FRESH chlorine bleach and touch it to one of the spots. (Be careful to not drip on carpet, etc.) Mold will instantly turn white, but smoke will not be significantly affected.
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Good info above. Here is a couple of ideas on a completely different vein... Are the moisture pointloads within the house proper ventilated? In other words, are there kitchen and bathroom exhaust fans that are vented to the exterior?
Like Piffin's Q about a possibly damp crawl space, I'm wondering about the indoor moisture sources.
Sounds like your roof design may not be the best but I'm guessing it might be less of an issue since you don't have the large indoor/outdoor temperature differentials that people, say, in New England, have to deal with. I'm also guessing that the outdoor relative humidity tends to be pretty moderate in your climate.
Does this black stuff tend to occur more during the winter or summer?