Venting/Insulation for attic


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Old 01-01-10, 01:37 PM
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Venting/Insulation for attic

I've got a 1960's ranch with low pitch hip roof in Northern Indiana and this fall I covered all my wood soffits with vented aluminum. When I did this I removed the hand full of small vents and cut significantly larger sections out to improve venting. Now that it's cold I'm having condensation buildup on the interior of the ceilings around all my exterior walls. It's worse on the west wall, as you'd expect with the prevailing wind, but even where it's not wet, it's starting to grow mildew. I just checked my attic and I have little insulation throughout most of the area (a few inches of loose fiberglass) and none above the last 10-20 inches around the perimeter.

Today I'm in the process of pushing insulation as best I can out into the perimeter of the ceiling. I put in the vent baffles when I did the soffits knowing I'd eventually add attic insulation so I shouldn't hurt the ventilation. I then intend to come back and blow in several inches of celulose.

If I get the insulation to cover as best as possible, will I eliminate the condensation problem? Or did I possible overdo it with the vents?

Thanks for any advice.
 
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Old 01-01-10, 03:09 PM
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Glad you stopped by. It's always nice to catch someone going the wrong way and get them turned around, it makes me feel good and will make you feel a whole lot better.

More vents if anything. You did not put in too many. Add up all of your vent area (use a reduction for the perforated covering), soffit and where ever above, I assume ridge or roof vents (I hope). A typical venting guide is one square foot of vent area (combined upper and lower) for every 150 square feet of attic space and you must have upper AND lower.

But here is the catch. The number above ASSUMES a well sealed home. If it leaks a lot of air/moisture into the attic, that number will not be enough. The solution is to increase venting as you have done, and to reduce the air leakage into the attic, WHICH IS WHERE THAT MOISTURE IS COMING FROM. Other sources to check are bath and kitchen fans must be vented to the outside.

Here is a guide, a bit slow loading, but worth the wait. It will detail some of the air leak issues.
http://www.efficiencyvermont.com/ste...ide_062507.pdf
Most leaks are easiest to seal before the new insulation goes in. The good part about air sealing is it will not only eliminate your moisture problem, but significantly reduce your heating costs. And it is considered the most cost effective upgrade you can do.

Have a look and see what you think. I have some shorted lists that simply point to holes for wiring, plumbing and a host of others, but where you are dealing with adding more insulation in the future the whole guide is good.

Also, if you choose to blow in cellulose insulation, properly done, it will stop a lot of the leakage you can't find.

Bud
 
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Old 01-01-10, 09:25 PM
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Bud9051 -

Thanks for the reply! I went through the pdf you attached and there are a few things I'm going to check (light fixtures and can lights, bathroom vents, cold air return vents, and a small crack or two in the ceiling dry wall).

But I'm a still not sure about the moisture I'm seeing on the ceilings. It only shows up around the perimeter of the house and is the most pronounced on the west end of the house. It is in a pattern that is consistent with the way the ceiling joists run. Basically the moisture shows up between the joists but not where the joist is, or much less where the joist is anyways. I did a few things today to test my theories. I checked the top surface of the ceiling drywall (atic side) adjacent to where it's wet on the bottom and it wasn't wet. It was VERY cold in the attic (10-20 deg F today), and I could tell there was significant air coming through the new vents (new eave vents and a ridge vent that installed about 10 yrs ago with new roof) but the top of the ceilings did not seem wet. I also put a fan in the bedroom on the west end and pointed it at the ceiling where the moisture was. It dried up relatively quickly (30 mins - 1 hr I think, I wasn't watching but it was dry when I checked it later) and seemed completely dry. If the moisture was coming from the top, I would think it would be soaked through the drywall and take much longer to dry.

We keep our house set at 71 F and based on the humidity meter we have it is in the low 40% relative humidity.

It seems to me the ceiling is getting so cold around the outside wall and there is enough moisture in the room air that water is condensing on the bottom (room) side of the drywall around the perimeter. Does this sound conceivable?

And to finish, my experiment with the insulation doesn't seem to have solved the problem. It may have improved it, but not completely fixed it. I spent a few hours on my belly stuffing batt insulation out in between the ceiling joists earlier today. I got about half the house done and started on the west end. We had dinner plans so I turned off the fan in the room and when we returned tonight at 10pm, the moisuture was forming againg. I can't tell if it's better yet; I will have to wait till morning and see the size of the spots.

If it doesn't fix it, I've got some ideas to go along with sealing gaps and adding more insulation. First is to buy some rigid insulation board (pink board) and cut blocks of it and slide them out onto the perimeter of the ceiling. This will be easier to ensure I get the insulation all the way out over the ceiling and will block air from penetrating down to the drywall. The second idea is to remove the soffit, at least on west end for starters, and access the edges of the ceiling from the outside. I can then try a couple different ways to insulate the ceiling from the cold attic air.

Sorry for the lengthy reply, but I'm desperate! I want to make sure we don't have any long term damage.

One more note - this is all new since I did the soffits and ADDED venting. We've been here 10 years and haven't seen this before and the insulation or areas moisture could pass to attic hasn't changed the entire time.

Thanks!!
 
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Old 01-02-10, 12:21 AM
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It seems to me the ceiling is getting so cold around the outside wall and there is enough moisture in the room air that water is condensing on the bottom (room) side of the drywall around the perimeter. Does this sound conceivable?

You are correct. I was addressing condensation in the attic, and guess I missed that it is on the drywall ceilings inside. Step two is to improve the attic insulation AND shield it from the incoming air. The wind washing effect will render fiberglass insulation totally ineffective. Air goes right through it. That same link will show baffles that both prevent new insulation from blocking the venting and protect the ends of the insulation.

A quick fix might be some 3 1/2" or 6", which ever fits best, fiberglass with the Kraft facing, folded double and with the fold stuffed out into the eave. For stuffing insulation into the eaves, I build a 12" "T" on the end of a 1x3. With unfaced I add a row of 2" nails and a triangle of sheet metal on the bottom. Nails help hold while pushing the insulation into place and the sheet metal helps the tool slide out. Where your pieces would be folded in half you might not need the nails, but maybe some metal on top if needed. But the Kraft should be the correct width and will block incoming air. Say a 4' piece folded in half. The rest of the insulation should be unfaced.

The 40 % RH at 71 degrees will condense moisture at about 45 degrees. When you run the fan, you are warming as well as drying the ceiling. As a reference, a closed wall cavity, with no air blowing in, with 6" R=19 insulation will have a wall temp about 2 degrees below inside air. So it doesn't take a ton of insulation to do the job, as long as it is protected from the air flow.

I think you've got it. Eventually you will want to take that attic up to R=50 or so. I like a raised center walkway, maybe two 2x6's on edge with some osb on top. That allows some insulation underneath and gives you a place to get up there if service is ever needed. When the attic is fully insulated, it becomes hard to use it for much else.

Back to bed to see if I can fall asleep now .
Bud
 
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Old 01-02-10, 05:48 AM
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A quick update.

While the moisture is back, it is significantly less this morning. And the outside temp is colder this morning and the wind is stronger. So, your last post and my self-diagnosis has me confident I'm on the right track. Unfortunately, I think I need to redo a lot of what I did yesterday and make sure the air is blocked.

I'll give more updates as I make progress.

Thanks for the advice.

Brad
 
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Old 01-03-10, 06:13 AM
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Saturday's update -

A LONG COLD day!!

I started by removing the aluminum soffiting (than goodness I used screws and hadn't put on the facia pcs yet!!). I started on the west end. Once I got the soffiting removed and cut away a few spots of the original plywood eaves, I had access to the outside ends of the ceiling/ceiling joist/rafters. I started with the area I had crammed insulation into from the inside yesterday. First I added insulation (just tore of pcs from an unfaced roll of R-11) from the outside in all the bays that didn't get filled out fully from the previous day's work. I then cut 14.5" X ~8" pcs of pink foam brd (R3) and placed them vertically between each rafter. The piece fully covered from one rafter to the next, up to the underside of the roof and down over the sheathing of the exterior wall (inside the eave). Where there were vent baffle shoots, I cut around them. Then to ensure no air passage into the attic (except through the vents baffles), I used some expandable spray foam around the edges of each pc of pink board.
I was able to complete all of the west end and significant portions of the south and north sides. The outside temp was down to low single digits last night and (drum roll) the ceiling in the west bedroom is DRY!!.
I've got to wrap things up today by finishing the pink board on the remainder of the house and *hopefully* have time to put the soffit pcs back up. It will be cold again!!

Thanks!!

Maybe I'll even have some time to watch some football today!! Thank goodness for a DVR!!
 
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Old 01-03-10, 08:30 AM
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The only thing I caught in your last description is that it doesn't sound like you used baffles in every rafter bay. At this point, cold outside, not sure if you want to go back and add them. Might wait and see how what you have works. The risk would be the roof deck above the unvented bays getting warm enough to cause snow melt and ice, or not venting well enough to promote condensation. But the total venting you have should be better than it was. Just may want to consider the addition before it does get buttoned all the way up.

Otherwise, sounds like you have the issue under control and a good understanding of the problem.

Enjoy,
Bud
 
 

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