Went to a customer’s house to try and locate the source of water coming thru the light fixtures. Hse was built in 1988 and has two stories with three distinct roofs, asphalt shingles,overhang in the back only, built shed style( roof slopes from the front of the hse to the back, maybe a 5 pitch.) Inside the ceilings go all the way up, no attic or accessible space. Punched thru the ceiling and found rigid foam board covered by batt insulation, above that a 4-6″ space then the underside of the roof. Found the underside of the decking all wet and the batt insulation soggy. I am thinking that the roof is just a series of 2×8/10? laid from front to back so each space between the rafters is in effect separate cavity. No way to get into these spaces and no way to remove the insulation unless either the roof or the ceiling are removed.
I am thinking of putting 4″ round soffit plugs in each cavity both front and back to allow air to flow thru the space and hopefully dry out any wet insulation and eliminate the problem.
Any thoughts on how to solve this problem would be welcome
Replies
Can lights in the ceiling? When older style cans leak warm moist air through the holes in them, it will condense on any cold surface, such as your roof deck. Sealed cans at least don't leak air, but sometimes with the space above cold enough, condensation will collect on the inside of the can.
I'm assuming you're installing these vents outside.
A great place for Information, Comraderie, and a sucker punch.
Remodeling Contractor just outside the Glass City.
Quittin' Time
I'd check the interior humidity first.
It's winter and cold air doesn't carry a whole lot of moisture, when it's warmed up it carries even less. The moisture is coming from somewhere and I doubt it's outside.
The moisture is definitely coming from condensation. That is the only explaination why the entire underside of the deck is wet.
The dew point inside my house in normally around 45-50F in the cold winter months here in MA. If the roof is zero at night that is a lot of water vapor to condense out. Just look how much comes off a cold one in the Summer in a matter of minutes!! Now consider the fact that the house is sitting there 24/7 slowly adding drops every minute.
Every shower, cooking, and breathing adds water vapor to the indoor air.
I have to ask the same questions, again.
If the house had this problem when it was built then 18 years of condensate as you have described would have rotted out the roof/ceiling system.
Your description seems to indicate that this has only recently begun, or you would have described the tearout in much harsher terms....rotten, nasty, blackened, moldy, etc.
If it is truely recent, then there is an event that occurred to add more water vapor than normal to the house's past history and its reaction is to drip water from the ceiling. Changing to a sealed can light may only force the water vapor to move to a less obvious point of condensation.
Seventy degree, 35% RH interior air has a dew point of 40 deg. If the RH of the house in a cold climate is too high then condensation is probable. Your profile does not tell us the climatological region that you live in..such info could change points of view.
.........Iron Helix
i didn't have the original question IH.
Ooooops.......sorry!
............................................Iron Helix
Thanks for everyone's input. According to the homeowner the house, which is a rental, has had moisture problems for awhile (not sure how long but the owner states "awhile", many repairs to the ceilings, new roof three yrs ago). One problem was that a bathroom fan went directly into a cavity between the rafters
(since removed), and a ceiling can light is notorious for leaking water during a cold snap
( RI area) but the ceilings are stained in many locations. I checked only one area of the roof ( thru access in a small closet in the middle of the house) and found condensation. I will need to find access to the other cavities and see if they are wet. There are 6 soffit vents both front and back but my thinking is because of the design of the roof these vents can only ventilate the area between the rafters in which they are installed. Maybe the problem is only in the one area where the can is in the ceiling
You are getting good advise from IH & MA and questions have been asked you need to know the answers to before you will resolve the problem. As well you need to address the ventilation of each cavity between the roof joists. The necessary minimum venting required below the roof deck is a function of rafter length and slope. As an example a 5/12 slope with an eave to peak distance between 16 & 33 feet with an air tight vapor barrier and insulation assembly with minimal air leakage requires an unrestricted airway of 2inches. This airway also requires 3.6 square inches of (unrestricted) intake and 4.5 sq. in. of outlet per foot of free open area for each side of the roof. With additional light cans and other heat and moisture loss requires even more ventilation. In regards to the new roof if an ice & watershield was used as an underlay this adds to your problem as no water vapor can escape through the roofing. You need to open a couple of these cavities to find the extent of the problem as was earlier discussed you may have a much bigger headache inside the cavity.
"dew point inside my house in normally around 45-50F in the cold winter months "
If your inside air temp is 70, at a DP of 45 you would have an RH of 49%. At DP of 50 and 70 IAT, RH is 58%. That's too humid for reasonable comfort during the winter for most people. Are you sure about those numbers or did you just make them up while you were typing?
I read the RH periodically from instruments and then do the simple conversion, as you might have, with a psychometric (spell?) chart.
The higher humidity makes it feel warmer than it is.
I've never heard that level is uncomfortable. Do you have a reference where I could find information like that? That would be very handy to have on hand.
Thanks,
Stu
"..higher humidity makes it feel warmer than it is.."
Higher humidity (relative humidity) during the heating season, typically creates a feeling of less warm rather than more warmth, all other factors being the same. ASHRAE Fundamentals, Chapter 8 covers this in great detail. The Trane Air Conditioning Manual, in continuous publication since around 1905, also covers this fairly well.
This has been my personal observation as well. IF you have control over the RH in your home (via a humidifier on your furnace for example), try an experiment. Lower the humidity to 30 - 35% for a week, then raise it to 50% and see how you feel. Keep the temperature constant.
Higher RH levels will make you feel less comfortable in the cooling season, i.e. "it's not the heat, it's the humidity", but the opposite is true in the winter. Moist air has more capacity to absorb (and transfer in general) heat than dry air. It has more mass. Since the air inside conditioned spaces is typically 30 degrees cooler than the human body this is a significant source of heat loss (others being respiration, radiation, and perspiration).
There is a recommended range for relative humidity that has more to do with health than comfort. The range is from 20% to 60% for most general occupancies. Specifc use area, like operating rooms and clean rooms have specific requirements that are more stringent. Below 30% people start to get dry eyes and sinuses, static electricity becomes problematic, wood floors and furnitures becomes dry and brittle, and certain spores grow more efficiently. Above 50% condensation on glass (except for very good windows), and as I mentioned above, higher air temperatures are required for the same level of comfort, more energy required, and another set of spores prefer these conditions to grow.
Listen to you! Really have your "s" together on the ASHRAE book.
I'll have to try the experiment when I might be home long enough to notice.
That is seriously worth understanding. Can you recommend a text or link where there is a reletively easy to understand explaination?
thanks,
Stu
It's my job. Is there an "easy to understand" reference for this stuff? There probably is, but you'll have to Google and sort. The enginerd texts and lessons learned from "dead" men are not easy understand or come by, respectively. These are my two primary sources. A great deal of information and opinion has been published on this matter (psychrometrics) and there is some very valid and differing opinions as to how specific humidity levels apply to health, indoor air qaulity, mold control and comfort. By no means is there a "right" answer to humidity questions.
There a few online sources, ES Magazine, HPAC Engineering and ASHRAE all have wesites.
"..and cold air doesn't carry a whole lot of moisture, when it's warmed up it carries even less.."
I think I know what you meant to say, but what you said is the opposite of reality. Heating air does not change the amount of moisture it "carries".
Where do you think all that water is coming from?
Apparently the leak is a recent developement...what has changed about the house envelope?
Stopped up gas appliance vent, or a plugged dryer vent, or a ventless heater, spa/jacuzzi, aquarium or lots of potted plants??
Do the windows sweat? What is the relative interior humidity?
Find the source first.................Iron Helix
When the fiberglass insulation gets wet it rarely ever dries out. This could be contributing to other problems as it would be an additional source of moisture.
"..fiberglass insulation .... would be an additional source of moisture."
You'll have to explain how fiberglass insulation can be a source of moisture. I seen a lot a fg bashing on this site by those that prefer other means to insulate, but this is the first I heard that fg insulation can create moisture. Wow! You learn something new every day. Maybe we could replace humidifiers with insulation.
If the fiberglass is getting wet from another source it will hold that moisture. The fiberglass can stay wet long after whatever is causing the moisture problem to subside. That is what I meant by an additional source of moisture.
In our previous flood damaged home I found insulation in cavities as wet as the day of the flood, six months later. This was my own observation.
I understand what you meant, but the insulation is not a "source" of moisture. A source would be a leak or a flood or moist air being brought into the space for ventilation or due to leakage. It, in your example, holds moisture quite well , and makes a good reservoir.
I was just being sarcastic.