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Topic:   Ventilation Issue - 2102 visits (1 today, 6 this week)

Dennis Robitaille
Member


Posts: 354
From:Saugus, MA
Registered: Jan 2003

posted December 04, 2005 04:39 PM            

I received an e-mail from a MA homeowner who has a ventilation issue.

This is what he sent after I asked him some questions.

"It's a ranch on a slab that I added a second floor to with pull down attic stairs, the attic is sheet rocked and heated.
On the attic floor R25 was used on the knee walls R19 and on the attic ceiling R25 and there is a window on each gable wall
Soffit vents are perforated vinyl and cobra ridge vents also Styrofoam baffles were used at soffits and along roof sheathing where insulation contact
All bathrooms are vented to the out side on top of roof with 70 cfm vent fans. 2 to three shower are done per day in master and 3 to 6 in kids bath, I just put all vents on timers.
No humidifiers are being used.
No plants.
2 large dogs German Shepard's and one pint size.
5 people live in the house and always seem to have aleast one more all the time.
The house is a slab with forced hot water heat.
On the floor and the second floor humidity seems to be around 65 to 70% seems high to me but why?
I installed a power attic ventilator with a humidistat that seems to be helping but I think it pulls more air from the ridge vents than anything else.
I've caulked foamed and sealed everything I can think of and taken advice from everyone and tried everything. everyone tells me its air moving to the attic and or poor attic ventilation I don't know what else to do, it seems that one side of the attic is worse which I think north eat to east side.
The roof sheathing on this side is discolored and not on the other side, even the gable end get frost on them as well as al the nails, it starts there first.
The house is a colonial style with an 8 pitch roof using trust construction the attic floor is 1/2 inch plywood and the walls 5' up are sheet rocked the 4' along the roof truss and then 8' flat along the ceiling and then the same back to the floor if that makes sense. so you end up with a finished attic wide by 36' long with a 7' ceiling height 8' across the top ceiling and 4' along the 45 degree slopes.

Lou Collier
Member


Posts: 71
From:Richmond,VA
Registered: Feb 2005

posted December 04, 2005 05:50 PM         

Dennis,

My first thought is that moisture is migrating up from the slab. I will often find moisture or frost on the roof sheathing (or nail tips) in houses on crawl spaces that have no vapor barrier.

In one house that had a vapor barrier, there was a leak in the crawl space at the front wall. This was the only area in the attic with frost on the sheating and nail tips.

As you know, warm air holds more moisture than cold air. One possibility is that the moisture is rising from the slab, the warm interior of the house absorbs this moisture, and condensation forms in the attic as this interior air (which is warm and moist)escapes into the attic.

How old is the house? It may have no poly beneath the slab. How is the drainage around the house? Does it have gutters and downspout extensions? Is all surface water directed away from the house?

Does the range hood exhaust to the exterior?

Just my thoughts...

Jerry Peck
Member




Posts: 7866
From:Pembroke Pines, FL
Registered: Feb 2003

posted December 04, 2005 06:39 PM            

If you read what he has, I don't see how he can have it, for one thing, how can he drywall the attic with trusses?

How can he have R-25 under the attic floor? And why only R-19 on the knee walls?

I suspect that he has sealed and foamed everything up, and had little to no ventilation to start with, and his exhaust fans and attic fan are depressurizing the hose, which is drawing the moisture up through the slab from the soil, up through the second floor (nice open air flow stairway, no doubt), then through the second floor ceiling and into the drywalled attic, where the attic fan exhausts it to the outdoors (in doing so, the entire house is depressurized, so even more moist air is coming in from outside where ever it can.

Does the slab have a moisture barrier under it? Was it installed properly? (Most are not, at least not the ones I've seen, although they are getting better the last few years.)

This is one for Caoimhín Connell, are you out there Caoimhín?

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Jerry Peck
South Florida

Dennis Robitaille
Member


Posts: 354
From:Saugus, MA
Registered: Jan 2003

posted December 04, 2005 07:02 PM            

Jerry,

Pretty much my thoughts. I sent him another e-mail asking about the attic setup.

Dennis

Phillip Stojanik
Member


Posts: 864
From:Houston, Texas
Registered: Aug 2002

posted December 04, 2005 07:34 PM            

While there may well be moisture coming up through the slab, there is actually a large amount of moisture being introduced just by the day to day activities of the occupants in that house full of people and pets. It also sounds like the homeowner may be creating some of his own problem with the construction and ventilation techniques he has used.

Typically in a cold climates, humidity indoors is control/mitigated by the amount of cold air coming into the structure from outside. Once that cold air is heated to the comfort level indoors, the RH is very low even if the RH of the cold air was very high to begin with. If the house is sealed too tightly, then there is not enough cold air coming in to dilute the moist air that is accumulating indoors because of all of the typical and anticipated mechanisms.

You might send the homeowner this link in an email. Reading this document may help him sort out some of his mistakes and he may be able to get a better handle on the problem.
http://eesc.orst.edu/agcomwebfile/edmat/EC1437.pdf

Lou Collier
Member


Posts: 71
From:Richmond,VA
Registered: Feb 2005

posted December 04, 2005 08:32 PM         

Philip,

You are absolutely correct in stating that if outside air is being drawn into the house in a cold climate, it will actually dry the air inside the structure. So I don't see that as a problem--at least during the winter months.

Jerry,

Not sure what you mean about the insulation. With a typical attic truss, it would be no problem to get R-25 in the floor. In this climate, we only put R-13 in the kneewalls. R-19 should be plenty for New England. I really don't think this is an insulation problem.

I am presuming that what we are calling the attic is now a finished and heated living space. I may be confused?

[This message has been edited by Lou Collier (edited December 04, 2005).]

Jerry Peck
Member




Posts: 7866
From:Pembroke Pines, FL
Registered: Feb 2003

posted December 05, 2005 04:50 AM            

Lou,

"With a typical attic truss, it would be no problem to get R-25 in the floor."

Maybe I'm mis-reading it or assuming too much, but if the attic is drywalled, the attic floor would be covered with plywood or OSB, turning the attic into a bonus room like room (the walls and ceiling are already drywalled too), which makes the ceiling of the "attic" now the area which should have the R-25, right?

------------------
Jerry Peck
South Florida

Lou Collier
Member


Posts: 71
From:Richmond,VA
Registered: Feb 2005

posted December 05, 2005 05:05 AM         

Here is the third line down of the homeowner's email:

"On the attic floor R25 was used on the knee walls R19 and on the attic ceiling R25"

So my assumption is that this was a space left unfinished by the builder, and the floor of the space was insulated by the builder during construction as this space was unfinished and unheated--a true attic.

The homeowner finished it off later. This is common practice around here. In fact, many builders put the drywall stacked in the unfinished attic to make it easy to later finish the space.

I hope that is not confusing--don't have time to rewrite it to make it clear. I think maybe we are both making many assumptions!

Anyway, I don't think the insulation is the problem.

Jerry Peck
Member




Posts: 7866
From:Pembroke Pines, FL
Registered: Feb 2003

posted December 05, 2005 05:21 AM            

"The homeowner finished it off later. This is common practice around here. In fact, many builders put the drywall stacked in the unfinished attic to make it easy to later finish the space."

Okay, but back to my other question - How can you do that in a truss attic? You would have truss webs, verticals, and diagonals running everywhere, right?

------------------
Jerry Peck
South Florida

Lou Collier
Member


Posts: 71
From:Richmond,VA
Registered: Feb 2005

posted December 05, 2005 06:22 AM         

Click for photo (2479 Bytes)

It's called an attic truss.
http://www.cwc.ca/products/trusses/shapes.php

Jerry Peck
Member




Posts: 7866
From:Pembroke Pines, FL
Registered: Feb 2003

posted December 05, 2005 06:32 AM            

Looks like it must take a pretty good slope roof for that to give adequate height inside, and a good width to give much width to the roof.

Never see those down here.

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Jerry Peck
South Florida

Lou Collier
Member


Posts: 71
From:Richmond,VA
Registered: Feb 2005

posted December 05, 2005 02:40 PM         

The use of attic trusses is very common here in the new "McMansions". Many of the roofs have slopes from 9:12 to 12:12.

Click for photo (60987 Bytes)

Click for photo (15119 Bytes)

Susan Cieslewicz
Member



Posts: 1603
From:Lake Villa, Il
Registered: Sep 2002

posted December 05, 2005 07:49 PM            

It probably sounds off the wall, but what about the laundry area? These areas can produce a large amount of moisture....

Is the dryer vent terminating to the exterior properly?

Just a thought.
Sue

Richard Shaffer
New Member


Posts: 6
From:Marblehead, Ma.
Registered: Nov 2005

posted December 06, 2005 09:37 AM            

Very confusing,obvious ventilation problem.How many vapor barriers are there?Also, can't have gable end and ridge vents together, one will effect the other.

Ken Bates
Member


Posts: 181
From:Boston Massachusetts
Registered: Jan 2005

posted December 06, 2005 09:47 AM            

Is the "forced hot water heat" using baseboard convectors or tubing embedded in the slab.

They do take a lot of showers. If it's in floor radiant ask the owner to shut off the boiler water supply and monitor the pressure guage for a pressure drop.

Also, Cobra is not the most efficient ridge vent.
http://www.BostonHomeinspector.com
http://www.Aceinspect.com

Terry Beck
Member


Posts: 24
From:Hamilton, Montana
Registered: Aug 2005

posted December 06, 2005 09:58 AM            

Several good points have already been raised; especially the artical posted by Phillip, "Home Moisture Problems". Couple of small points to add:
Customer mentioned Cobra ridge vents - there are baffeled and unbaffeled ridge vents. Studies show unbaffeled ridge vents really do little good. Apparently Cobra makes two baffeled types, the Cobra II, and a Snow country version. The regular Cobra rolled vent is not.
Also, the cutomer says he caulked and sealed the attic. There are several good articles at www.energystar.gov including http://www.energystar.gov/ia/home_improvement/home_sealing/DIY_COLOR_100_dpi.pdf
that may point out some air leaks he missed.
Also - what type of heating system is in this home? Heating systems can contribute a lot of moisture. So do fish aquariums. Also, how big is this house? With that many people and showers a day creating 70% RH in living areas, maybe he just needs better interior ventilation, a bigger house, or a dehumidifier (See Van-EE).
I am still curious what other ideas are out there.

James A. Weyenberg
New Member


Posts: 1
From:Neenah, Wi.
Registered: Aug 2004

posted December 18, 2005 12:06 PM            

Dennis,
With 70% humidity (rain forest conditions) and that amount of exhaust venting (providing it is being used properly) One might look to severe negative pressure creating furnace and water heater exhaust backup. Gas creates very large amounts of water vapor that could be the source of the moisture. Not to mention the CO back up with it. Check it out and warn the owner about CO.

Thom Walker
Member


Posts: 26
From:Corpus Christi, Texas
Registered: Jul 2001

posted December 18, 2005 03:46 PM            

Hello Dennis,
It's been a while since I lived in Yankee land. I'm still here spying to see if I can figure out how to bring the warm weather North so I can live closer to the Grand kids, since their parents don't have enough sense to move here.

I will assume that your home owner has been monitoring his boiler pressure and the replenishment rate of the water.
Additionally, I have to assume that he is monitoring the performances of the pressure release valves at the radiators.

It's unclear to me how long the problem has been ongoing. Is this his first winter? Did he have any problems in the summer?

As you know, pinpointing the cause can be really expensive if the panic button is pushed too early. Maybe the following questions will help the process of discovery.

Are both floors (all finished areas) being heated equally? Is the heat supply adeqaute for the space intended? If a door separates the two floors, try leaving it open for a few days and see if it makes a difference.

Were the the pipes behind the knee walls and between the floors insulated before the insulation went in and the drywall went up?

Are the windows in the gables single pane? If so, that inside plastic storm window stuff worked great in one house I lived in.

Is the drainage around the house good and are there any trees, etc possibly blocking the ventillation on the North (NE) side where he sees the worst area?

Is he certain that he left ventilation routes from the soffit vents to the ridge vent when he finished off that room?

Finally, I would suggest tat the power fan with the ridge vent is a bad idea. I believe it could be keeping the ridge vent from functioning.

Have a great Christmas.

------------------
The only thing in life that can't be taken away is your integrity.That you have to give away.

Thom

Mike Schulz
Member


Posts: 342
From:Fuquay Varina, NC
Registered: Jan 2003

posted December 19, 2005 02:00 PM            

I personally like a ridge vent and a attic fan. My reasoning is this. I have been in many attics that where 140+ that has soffit and ridge vent. I believe you can never have to much ventilation in an attic. Not around here anyway. When the thermostat on the fan is not satisfied to come on the ridge vent works. When the fan comes on it draws air from the soffit. by creating a vaccum. Yes it will pull air from the ridge vent but if it has enough CFM it will also draw from every where else. Plus air movement from the fan will help moisture from passing into the attic from collecting.
My opinion and I am sticking to it!
Mike

Michael Greenwalt
Member


Posts: 16
From:Milford KS
Registered: Sep 2005

posted December 20, 2005 06:43 AM            

One other small thing to consider, does the homeowner use "vent-less" heating anywhere in the house. They can put up to a gallon of water per hour into the home during use. And two of them, (like I saw last week) make the home a sort of sauna!