Q&A Forums

attic humidity Post New Topic | Post Reply

Author	Comments
john white Posted: Aug 02, 2009 01:04 AM	attic humidity just got my roof sprayed on friday. I bought two humidity and temp monitors to have an idea of whats going on up there. temp went from 76 this morning in the attic to 90 at the hottest part of the day. right now the humidity is somewhere between 52-55% in the attic, temp is 80. right now inside humidity is 41-46% and inside temp is 72. I understand that the 41-46% is within specs, but I cant find anything on attic humidity. I would think before the foam it was much higher since it was outside air. outside humidity is 83%.
Michael Fusco Posted: Aug 02, 2009 11:23 AM	Your temp should be 7-8 degrees above living space temp. Humidity, at least in my experience, usually runs within 4-5 %. A couple of things may be happening. First, check the a/c. In addition to cooling the house, the A/c is also the de-humidifier. If it is 90 ouside, and the attic is 90, with the inside (living space) temperature is 72, I would suspect there is air infiltration from the outside. If however, it is 105 outside and the a/c is grossly oversized, you may be rinning 5 minutes on, off 10, running 5 etc. That will cause a spike in energy usage, and not very much de-humidifying. Most probable, you have infilatration, but you do need to check both. Most common areas for infilatration: 1. Home is single story and garage is attached. Floor of garage not sprayed, even if garage is insulated, if you open the front doors, this will cause infilatration, expecially if there is an entry hatch. 2. Attic extends over proch, and there is no knee wall between porch and attic. 3. Ridge vent is not sealed. 4. Soffit vents are not sealed 5. Turbines on roof are still open. 6. (and this is my all time favorite)... everything is sprayed except there is a hatch in the garage, which is left open all day (the garage door) and the hatch allows infilatration as it is not sealed in any way. 7. Windows or dormers in attic leaking. Call your applicator, share with him what you are seeing, let him take a look....everyone makes a mistake...maybe he just missed a spot.
john white Posted: Aug 02, 2009 12:30 PM	Most common areas for infilatration: 1. Home is single story and garage is attached. Floor of garage not sprayed, even if garage is insulated, if you open the front doors, this will cause infilatration, expecially if there is an entry hatch. this is correct. the garage floor isnt sprayed or insulated and there is a entry hatch. so I should get him to spray the floor in the garage area? I have some insulaton I could put there but it sounds like it would be best to spray it? whats the best way to handle the hatch? 2. Attic extends over proch, and there is no knee wall between porch and attic. NA 3. Ridge vent is not sealed. these are sealed 4. Soffit vents are not sealed only 1 isnt sealed, they had ran a exhaust fan while doing the job and I let it sit in there for most of the day after the install. the stupid thing is that they didnt realize that the soffit wouldnt allow airflow at the rate the fan blows so the fan was actually pushing back more air than it was pushing out due to restriction. I removed the van from there and put it out of the attic door. I did stuff it with a big clump of foam but I know it isnt sealed properly. they are supposed to do that when they come back. 5. Turbines on roof are still open. NA 6. (and this is my all time favorite)... everything is sprayed except there is a hatch in the garage, which is left open all day (the garage door) and the hatch allows infilatration as it is not sealed in any way. NA 7. Windows or dormers in attic leaking. NA Also, they sprayed all of the rafters but some of them arent quite coated all of the way. it looks like the guy maybe couldnt see when he was spraying and left some pockets. some of them I can still kind of touch the underside of the roof. how much should I jump up and down over this? this is what it looks like right now, I have two different monitors, 1 positioned right near the AC in the attic and 1 towards the middle of the attic. 82 degrees 69% near the AC, 84 degrees 58% near the middle. inside temp is 74 degrees and 41-47% on the humidity. outdoor temp is 86 and humidity is 69% my AC has been sort of short cycling today, since it is slightly cooler outside. my thermostat seems to be acting up a little. It wants to kick on 1 degree over setpoint. plus the thermostat is in a bad spot. its within like 5 feet of the return, but also behind a desk. I believe I am going to get a wireless one and sit it more towards the middle of the livingroom away from the return. one other thing, I know the ducts have some leaks in the attic. if this thing is short cycling how much will that effect the humidity in the attic?
jimcoler I have over 10 years of experience specifying and installing open and closed cell spray foam. I've sold my business but I'm still selling for the new owners and consulting on large and custom specific jobs. I've expanded my knowledge into t Posted: Aug 02, 2009 01:10 PM	I would get the guys to finish the job and seal up the rest of the attic. If there are spot which appear to be not sprayed or under sprayed, have them touch it up. Once the job is "finished" then I would say it should be fair to start measuring the temp and RH. Jim Coler
john white Posted: Aug 02, 2009 06:10 PM	attic temp is up to 94. I put one of the humidity monitors in the middle of the carport area and the humidity didnt really change much. it was around 60%. still around 70% on the AC end. I went feel around and there are alot of cavities putting out a good bit of heat. my AC and ducts are still condensating a good bit. AC is holding 73 degrees but seems to be running for much longer periods since the sun came out.
mason Posted: Aug 02, 2009 08:36 PM	I just got to my computer and see that some others have been providing some good advice. The best advice comes from Jimc. Have the contractors finish the job. Make sure the vents are sealed and the foam is sprayed to at least 1/4 inch of the specified amount Everywhere. The garage if not insulated will seriously affect heat transfer into your house. I know, the worst room in my home is the office space over my uninsulated garage. It is at least 3-4 degrees colder or hotter than the rest of the house just from the garage space below me. You may find that your AC units are over engineered after the foam has been sprayed and do not run as much. This will increase humidity in the house somewhat. The AC units have to run in order for them to take moisture out of the air.
john white Posted: Aug 02, 2009 09:54 PM	what is a considered an optimum cycle time for the AC? here is an example from this afternoon when it was in the 90's in the attic. on 41 minutes off 18 minutes on 34 minutes off 21 minutes
mason Posted: Aug 03, 2009 07:56 AM	I don't know the optimum run times on AC units, but I do know they should be running more often than they are off. Ask a HVAC engineer who you trust to provide the answers. For example, a year after spraying foam into my basement and attic, I replaced my furnace and AC. I downsized by AC unit from a 2.5 ton to a 2 ton unit and dcreased the BTUs of my furnace by 3500. The result, additonal energy savings of around 5-10% (achieved 20% initially with the initial foam application) and reduced my humidity in the basement by 10% in the summer during the most humid days and increased the humidity in the winter by 15% in the driest coldest days of the winter. I have my thermostat set around 72 degrees F and my whole house stays within 1-2 degrees of that temperature at all times The AC runs most of the time. Note: humidity ranging between 35 to 55% in a building is considered the sweet spot for comfort and to prevent moisture deterioration. Even humidity around 60% may be ok if you have moisture tolerant materials and the dew point is not achieved within the building assembly.
john white Posted: Aug 03, 2009 04:33 PM	I spoke with the sales guy and he is going to have someone come out and touch up the spots that they missed. when I enquired about spraying the floor of the attic above the garage he said that he would do it but he doesnt normally do it on existing homes because it isnt cost efficient. he claimed that unless there was a 15 degree differential between the attic temp and the garage temp the heat wouldnt pass thru. He also said that 60-70 humidity was acceptable for our climate. another thing that I thought about was that my dryer vent is exhausted in the garage area, so some of that humid air from the dryer may be making its way into the attic thru the hatch, since the hatch isnt sealed. it seems like most of my humidity is coming from the air conditioner. like I said, I still have some condensation forming on the plenum, the drain line, and on some of the ducts. I think I am going to get a AC guy to come check the unit and make sure that the freon level is correct because I read if it is slightly low it affects the air conditioners ability to remove humidity.
mason Posted: Aug 03, 2009 05:04 PM	I treat the garage as any other outside space. If the ceiling of your garage is the floor of the attic then it will affect the temperature. I live in Northern Virginia and my garage is typically with a few degrees of the outside temperature and has the same humidity. So I would think unless this garage is significantly different, the same would apply and the part that connects to the attic space should be insulated. What is the difference from insulating the knee walls? PS the dryer should be vented outside not into your garage.
john white Posted: Aug 03, 2009 08:19 PM	I agree with you mason. in my limited knowledge it seems like the hot air is going to travel to meet the cool air, regardless of how much differential there is. there should be a significant difference anyway. Im not really seeing that difference. I believe my problem stems from those areas ont he rafters that are not covered, some areas that are not blown on as thick as they should have been, and also the attic roof above the garage not being sprayed. I also got in the attic and checked the thickness. there are alot of areas that are not within .5" of what was supposed to be sprayed. I chose this company because the sales guy seemed knowledgeable, or at least much more knowledgeable than the other companies that I spoke with in the area. They have been around a long time. maybe I just got a bad crew. It seems so hard to get someone to do things right these days, so it doesnt surprise me. couple that with my bad luck and I am sure this will never ever work out for me!
jimcoler I have over 10 years of experience specifying and installing open and closed cell spray foam. I've sold my business but I'm still selling for the new owners and consulting on large and custom specific jobs. I've expanded my knowledge into t Posted: Aug 05, 2009 10:58 PM	Mason's right - you need to vent the dryer outside - not in the garage! This just adds a high level of moisture to the garage which will try to work it's way into the attic as it's not "air sealed" between the two. Your contractor may be right about the cost effectiveness of a 15F temp differece if he's looking at just the thermal transfer factors, but we all know that standard construction is not air tight and air will still pass through from the garage into attic. Now, think about when you start your car in the morning. All of those exhaust fumes in heated air rise up to the garage ceiling and try to get into the attic. If there's an opening, they'll work their way into this space. Now, you have a semi sealed attic with nasty exhaust fumes (including carbon monoxide) in your attic space. They cool down and carbon monoxide is heavier than air so it drops and tries to leach into your home's living space. You NEED to air seal the garage to attic space so you might as well insulate it. Besides that, if your car catches fire in the garage (we've had a few this year already) do you want it taking the house with it because the flames and smoke run through the attic? I think the dryer is a good start at where the moiosture is coming from. You need to think in terms of what is higher humidity and and lower humidity. It sounds like your AC system may be working fine if you have condensation on the outside of the ducts. You just have too much moisture in the air surrounding these ducts. If the attic is still connected to outside, then it can be coming partially from here. If you have a damp basement or crawlspace this might contribute. The dryer is a definite contributor. So, find the sources of moisture and control them. On another note, you can increase the humidity taken out of the air by decreasing the fan speed if you have a furnace which allows for this adjustment. The longer the system runs with a cooler "A" coil, the more moisture it will draw out of the air. The huge energy losses come primarily from short runs and the massive start up loads on the compressor. A fast fan with a very cool "A" coil will tell the thermostat to stop before it has a chance to cool the objects in the room. Some thermostats also have RH settings on them which will kick the unit on to dry the air as necessary using a humidistat. Get it sealed up right and let's see how it works from there before you start throwing stones at all of your contractors. Jim Coler
john white Posted: Aug 06, 2009 09:04 AM	the funny thing about the dryer vent.... I put the humidity monitor in the space above the garage and the humidity is lower than on the backside fo the house where the AC is. my house is L shaped. the very top of the L is where the AC is. the garage is the _ in the L. It seems like if the humidity were coming from the garage it would be higher in the area by the garage. I also had a AC duct that was leaking pretty bad that I found. Im not sure if the condensation that forms kind of feeds the cycle of the humidity in the air or not. regardless the humidity % seems to stay between 50-60% now. attic temp is still up there during the day, up around 95-100 degrees. The insulation guy is supposed to be back tomorrow to correct the spots that are missing insulation and I will see about getting him to spray the garage.
john white Posted: Aug 06, 2009 10:24 AM	I spoke with the sales guy again and he swears up and down that spraying the garage floor isnt going to help on the temp in the attic. he also said that 95-100 degrees during the hottest part of the day is about the best you would get in the attic temp on a retrofit. he said that maybe on average you could get the temp in the 80's, but down here in our climate he said it would reach 95-100 during the hottest part of the day.
jimcoler I have over 10 years of experience specifying and installing open and closed cell spray foam. I've sold my business but I'm still selling for the new owners and consulting on large and custom specific jobs. I've expanded my knowledge into t Posted: Aug 06, 2009 10:37 AM	The dryer is exhausting "hot and humid" air from the dryer. This hot air is going to rise to the top of your garage and head for the attic. If you have leaks in the attic, this will create a stack effect which draws the humidity into the attic. Once the attic is sealed including all soffit vents, ridge vents and gable vents, and there communication of air to the garage is minimized, you should see a difference. The temps stated seem high based on a good install of a sealed attic. I would expect this with leakage to outside but a much more comparable temp to inside temps, especially with ductwork in the attic space. Again, if you control the source of the moisture, you should control the condensation issues. Condensation occurs when warm moist air comes in contact with a cold surface which is below the dewpoint. The more moisture you have in the air, the more potential for condensation. Jim Coler
Greg Pruitt Posted: Aug 20, 2010 07:10 AM	I have been in the business for 6 years, garages must be either separated with a false wall, or both the roof deck and the floor/ceiling of the garage must be sprayed. It is considered a hot wall. Your temperatures in the attic in a properly sprayed home will be between 3-10 degrees of the inside in a hot climate. Cannot comment on cold climates. I am in Texas.
Greg Pruitt Posted: Aug 20, 2010 07:10 AM	I have been in the business for 6 years, garages must be either separated with a false wall, or both the roof deck and the floor/ceiling of the garage must be sprayed. It is considered a hot wall. Your temperatures in the attic in a properly sprayed home will be between 3-10 degrees of the inside in a hot climate. Cannot comment on cold climates. I am in Texas.
mason Posted: Aug 20, 2010 05:02 PM	I lived in South Texas for 7 years with summer time temperatures averaging over a hundred degrees and humidity averaging 80% daily. Spraying the underside of the attic roof deck kept the attic humidity within 5 % of the inside and the temperature within 6-8 degrees of the interior temperature. If you are not getting those results, there is air infiltration from the outside that is messing up your results or you are not exhausting moist air to the outside as you should. Find the air leaks, seal them, insulate the garage and exhaust your vents to the outside (not into the garage) and you should be OK
john white Posted: Aug 20, 2010 05:55 PM	just to update this, I had the guy come back and touch up and also had them spray the area above the garage to seal that off. I just went see what the temp and humidity was up there in the attic its 89 degrees with 61% humidity in the house its 73 degrees with 43% humidity whats the optimum humidity for indoors? It seems like I am hotter at 73 degrees than I should be. the foam has definitely helped. before I couldnt get my indoor temp below 78 degrees on a hot summer day. also, I was having condensation problems on my ducts and plenum before the foam, but now everything is back to normal. oh and my vents from the bathrooms and kitchen are ducted outside.