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Open attic windows for last-resort ventilation?

Posted by wavy_glass (My Page) on
Wed, Dec 23, 09 at 14:14

Hi all,

I paid too little attention to the section on attic ventilation in our inspection report before buying our 1928 farm house in Wisconsin. The inspector wrote, clear as day: INADEQUATE VENTILATION. I'm fairly sure that there are no gable or soffit vents, but these weren't mentioned either way in the inspection report.

I hope to be having an energy audit very soon (in next month or two) to give me a comprehensive sense of what needs to be done.

My question for now is: should I leave the two windows on either side of the attic open to ensure that the attic is cold enough to prevent ice dams? I realize that the ventilation may be uneven and/or remain inadquate. But is it still worth doing until the auditor gives me his/her opinion on the situation?

Thanks for any and all thoughts!

Follow-Up Postings:

RE: Open attic windows for last-resort ventilation?

This is not an uncommon problem in old houses who have previously had a slate roof because they, for the most part has natural ventilation. Did yours, do you know? We have a few really up-on-it people here about such things. Hoping they contribute. It's my understanding that adequate insulation in your attic will go a long way toward preventing ice dams, because it's the heat escaping from your living areas up into the attic what melts the snow. Even if you don't have wall insulation, you should try to get some down in your attic.

We had an energy audit done about fifteen years ago. One of the best things to lead us to good decisions on saving energy and also being comfortable. But, to be honest, he didn't even touch on things like ice damming.

RE: Open attic windows for last-resort ventilation?

The primary purpose of attic ventilation is to allow excessive moisture to escape from the attic rather than for the purpose of cooling the attic (there are more effective ways to cool an attic). A vapor retarder membrane/paint at the top floor ceiling will reduce the need for ventilation quite a bit. Ridge and soffit vents will reduce the amount of ventilation needed as well. This should be stipulated in the local building code.

It is highly unlikely that you will need much attic ventilation in the winter in Wisconsin unless a bathroom exhaust terminates in the attic (or at an eave next to a soffit vent) which, of course, should not be the case. Windows can meet the code requirement for ventilation but can allow snow to enter in the winter defeating the purpose of the ventilation unless there is a well designed louver system. In warm humid climates excessive ventilation can allow moisture to enter the attic space and defeat the primary purpose of ventilation.

If you want to save energy cost and avoid leaks from ice dams, add insulation to the attic floor or the roof rafters and apply Ice & Water Shield to the roof eave under the roofing. A true "cold roof" will also reduce the chance of ice dams but such a design requires a double layer of roof sheathing with a substantial air space between them not just a ventilated attic.

RE: Open attic windows for last-resort ventilation?

I completely agree with everything macv wrote. If there's no history of ice dams or apparent interior damage from them, there's no reason to think they will suddenly begin happening. Ice dam formation is influenced by many factors: orientation to the sun, snow amounts, outside temperature, etc., etc. Not to cast aspersions on whoever did your home inspection, but just looking and seeing no vents doesn't necessarily mean INADEQUATE VENTILATION. The two gable end windows may have been providing enough ventilation ever since 1928.

If you really want to do something in the interim before the energy audit, you can buy adjustable window inserts with small louvred openings and screens at most big hardware stores. They fit under the bottom window sash and are only about 5-6 inches in height. One in each window would provide an exit for any moisture that might find its way into the attic.

Here's a totally unsolicited, but entirely free opinion: Be cautious and skeptical about any recommendations from the energy audit. Fine old houses need understanding and care. Too many things done in the name of energy savings can do a lot of damage very quickly and/or waste a lot of money. Replacement windows are a prime example of the latter.

RE: Open attic windows for last-resort ventilation?

Many many thanks for your responses.

One concern is that I don't know what the history of ice dams might be. The house's longtime neighbor, who is himself a builder, has a smaller and newer home that's fully insulated and has tremendous problems with ice dams. He says our house hasn't had problems. Instead--and that's the way he put it: "instead"--it gets these huge icicles on the back side. But aren't icicles evidence of the sort of thaw and refreezing that I should be concerned about? I just don't know.

Before we bought the house it was complete rewired head to toe to remove old knob and tube, and they reblew the attic with loose insulation that is at code (for a house of its age) at R-38 (I believe).

And yet, with its being 33 degrees today, I'm hearing drips while i'm inside the house. "Are those INSIDE the wall?" I think to my terrified self. I'm also seeing the thaw render the cedar shake totally soaked.

It's my hope that all this is new-old-home-owner nerves. And I thank you all for your suggestions and solidarity.

One more thing: our old "Wavy_Glass" windows are staying put, no matter what the energy auditor says. :)

p.s. mainegrower

P.S. Mainegrower, I'm originally from Maine. Although if you're a grower, you're probably up North, whereas I'm from down south. Yes, yes, I know: you probably think I should just say in that case that I'm from New Hampshire. :)


Here's a pic I just snapped. Does this portend anything bad in my future? Should I knock down the icicles and start raking my roof?

Here is a link that might be useful: Worry?

RE: Open attic windows for last-resort ventilation?

Doesn't look that bad to me. (But, then, I'm in the banana belt of Canada.)

they reblew the attic with loose insulation that is at code (for a house of its age) at R-38 (I believe).

But that doesn't mean they made any attempt to seal the attic from air leakage from the house.

RE: Open attic windows for last-resort ventilation?

The ice dam history is now pretty much irrelevant because of the addition of the insulation. Doesn't mean dams are more or less likely, just that the dynamic of roof, attic, etc.have changed. It's a little hard to tell from the picture's perspective, but what I see is ice primarily forming in and behind the gutters. This is always an issue in cold climates. Gutters provide a ledge which causes water to accumulate and back up in the form of ice. When the sun hits the gutter - especially an aluminum one - it heats up, melts some ice which then refreezes when the sun no longer shines on it. You can see icicles in the picture which have formed behind the gutter and are now attached to the wall.

Icicles can indicate danger from ice dams, but not always. They do indicate freezing and thawing but if there is a good width of flashing and/or ice and water shield under the shingles, water will not penetrate the roof deck and enter the interior. Very wide eave overhangs accomplish the same thing and are common in old houses in cold, snowy climates. I had icicles from eave to ground last winter on the east facing roof, but no leaks at all thanks to eave width and ice and water shield on the roof deck.(BTW, if I were a professional builder like your neighbor, I think I would want to keep my problems with ice dams a secret!)

The only somewhat ominous thing is the dripping sound. See if you can determine if it is outside or within the walls. Usually though, if water is getting inside the walls there is no sound because the water is absorbed by the wall insulation. Don't break off the icicles - too easy to damage the shingles or gutter. Roof raking can do the same thing if you're not very careful and it's really hard work that usually winds up dumping a load of snow on the raker.

I am in mid coastal Maine - still not New Hampshire or Massachusetts but both are creeping ever northward. It is perfectly natural to feel anxiety about a new old house, but chances are everything is fine. Have a wonderful Christmas.

PS: Knob and tube wiring, if it's in good shape, is actually safer than modern wiring because the current and ground are far apart from each other.

RE: Open attic windows for last-resort ventilation?

Knob & tube wiring consists of two wires with no ground wire and usually both wires are fused. It is true that they are better insulated and spaced than modern wiring so the system is pretty safe from fire but it is not possible to protect people against shocks from electrical leaks at equipment and appliances. The K&T wiring is only legal if you make no modifications to the circuit. Even a minor renovation or the addition of a new appliance or outlet would require replacement of the circuit.

RE: Open attic windows for last-resort ventilation?

Macv is right; I should have written that the hot wire and neutral wire are widely spaced. There is no ground wire and it is therefore impossible to ground appliances and other electrical devices up to modern standards. That said, however, K&T wiring is still safer than modern wiring if it is in good condition, has not been modified and has not had insulation piled on top of it. Added insulation can prevent heat from dissipating around the wires - perhaps this is the reason your wiring was replaced.

RE: Open attic windows for last-resort ventilation?

Thanks mainegrower and macv. The K&T wiring was replaced at our request. The inspector said he couldn't be sure of the quality of the ground in the sockets, so we had a master electrician come in. They found the K&T, and we made a total rewire a condition of sale. The seller acquiesced.

Maingrower, I believe the drip is in fact on the outside of the house. One reason I believe I *can* hear is that we do not have insulation in the walls. As a pre-WWII house, my understanding is that this is normal.

I suppose I will just try to get through the winter with fingers crossed that ice damming won't be a problem. The energy auditor does a full inspection of ventilation, including ventilation of the bathroom fan, etc., so I'm hoping he can give me a sense of whether the attic is safe from moisture and heat from conditioned living area. The attic access is a standard door from the second floor hallway, and the gap below the door is large. I have added weather stripping to the door and wedged a tube of foam under the door (I took the foam tube out of one of those ridiculous double draft stopper products). That seems to be cutting the air loss up into the attic considerably. I'm planning to tack a water heater blanket to the door on the attic side for extra insulation, unless someone around objects... :)

All, I really do appreciate the encouragement and advice for this new old-home owner. It's great to have comrades, even if they are digital.

Thanks again.

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