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Advice on Attic Venting/Insulating

Post in 'The Green Room' started by Clarkbug, Jan 1, 2013.

  1. Clarkbug

    Clarkbug Minister of Fire

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    Looking for some advice from those familiar with old homes and attic ventilation. Gonna be a long post, so you might wanna grab a beverage of your choice first....

    My wife and I bought an old farm house a few years back, blissfully ignorant of many things (specifically, not realizing that having TWO oil tanks in the basement, with another buried outside, is NOT a good sign) Anyway, its a circa 1880 Foursquare Italianite, with two separate additions tacked on to the back of it. Im looking for input on the main part (the square) of the house.

    The house was vacant (but maintained) for a few years before we bought it. During that time a microburst storm hit the area, and the hail destroyed what had been a nice slate roof. The guy that owned the house put a new asphalt shingle roof on, but has not added any venting.

    During our home inspection, we found a bat colony in the attic, so the entire attic was vacuumed out, along with what was there for rockwool insulation, and about 6" of cellulose was blown in there once the bats were moved out.

    Im now in the process of working on renovating one of the upstairs rooms that originally had a plaster ceiling. Due to leaks/bats/whatever, much of the ceiling is in poor shape. My thought was to pull down the plaster, leave the lath, and put up new T&G. Here is where my brain started working, and where I need some input.

    I realized that the attic wasnt vented previously (other than two 4x4 holes in the soffit) because of the slate roof, and gaps in the boards. Its a hip roof with a flat portion on the top, so no real good access to put in a ridge vent, and no gable to add a vent there. So Im now at a crossroads as to how to proceed with my ceiling plan. I can either:

    1. Spray foam the roof deck/rafters in the attic. This moves my envelope to the roof deck, and makes it so that I dont have to do anything else up there. I know this will probably be expensive, and I worry since its a "new" building product compared to others that have been around. I worry about trapping moisture if there is a roof leak, and if someone will curse my name when they go to work on the roof years from now.

    2. Start a LOT of projects at once. Add a continuous soffit vent and static vents to the roof, or something like a solar attic fan, and blow more cellulose into the attic. The issue is that I dont have an effective air seal, so I would have to add rigid foam board with taped seams underneath the T&G panels. This should provide an air seal, and additional R value. The benefit is that a cold roof is a proven system, and nothing will be permanently done to the structure. The down side is that its a lot of work to get rolling, and I would want to get the venting in place before I work any more on my ceiling.

    Sorry for the crazy long post and lots of random information, but Im just looking for some help/insight on this issue. It seems like everything I read doesnt fit my unique situation....

    Thank you in advance!

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  2. woodgeek

    woodgeek Minister of Fire

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    If the floor of the attic is not airsealed to the finished part of the house, you need to either do that first or foam the decking overhead. Most of the moisture in an attic that needs to be removed from venting leaks from the conditioned space below.
  3. Clarkbug

    Clarkbug Minister of Fire

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    Agreed, and thats why Im sort of in a quandary right now. It wasnt an issue before due to no one living here, and currently we arent living on the second floor while we work on it, so there isnt a significant amount of moisture headed up there. But I want to get it fixed right, and thats why Im not sure of what to do here....
  4. woodgeek

    woodgeek Minister of Fire

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    Sealing the attic floor is usually more cost effective, and removes much of the need for ventilation if done correctly. This assumes there are no mechanicals or ducts up there...and that you don't want additional living space. Getting a foam quote might help you decide!

    As for how to vent, I will leave that to those with more roof expertise, sounds like you are looking at 'hat' vents near the top and separate soffit vents. Cosmetics might be an issue in a historic house. Powered systems are usually overkill for ventilation, and in un-airsealed attics can **increase** energy usage by sucking conditioned air out of the house.
  5. Clarkbug

    Clarkbug Minister of Fire

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    No mechanicals in the attic. I do want to wire up some J-boxes to put a ceiling fan in,and I would do that ahead of blowing more insulation. No need for more living space up there, and I dont think we want to use it for storage. Right now I just want the bats to stay out of it. Sealing the floor might be difficult, just given the amount of cellulose thats up there now. Ugh. I guess I could find out about spray foaming the ceiling plane instead of the roof sheathing, but that still doesnt help the venting issue.

    Agreed, the powered system is probably overkill, but I just dont know enough about venting a hip roof to know better....
  6. Highbeam

    Highbeam Minister of Fire

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    What we do here is install a continuous ridge vent. You walk along the ridge with a circular saw cutting off the sheathing about 2" on either side of the ridge. Then add a corrugated plastic spaced thing and then roof on top of that. I much prefer the ridge vent to the turtles.
  7. Clarkbug

    Clarkbug Minister of Fire

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    The problem is that I dont have a ridge, I have a hip roof. So I have four little ridges, and a flat spot on the top of it. I see that they make a ridge vent rated for hip roofs, but that seems like it would be a bad idea...
  8. Highbeam

    Highbeam Minister of Fire

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    There's hip roofs and then there's hip roofs. Only with a square house do your hips result in a lack of ridge. That is a problem and the limited amount of ridge vent would not be worth the trouble. Then again, any venting out the top is harder with a "tepee" style house. The good news is that you are supposed to overvent at the soffit to provide a positive pressure in the attic to minimize the sucking of conditioned air out of the home.

    Time for a huge cupola!
  9. semipro

    semipro Minister of Fire

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    If your attic could be used for storage or living area I'd strongly lean towards option 1.

    It sounds like you're going to have a lot to do on your old house. It might be best to get this done soon and by a pro just so you can move on to other projects.

    Given that I've been working on my old house for the last 10 years and trying to do everything myself that's what I'd recommend.
  10. Clarkbug

    Clarkbug Minister of Fire

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    Thanks for the input all.

    Yeah, its a square alright, at least for most of it before the addition runs into it.

    The attic really cant be used for living area, and I guess it could be storage if I felt like putting a proper hatch in it. Right now its a real pain to get up there, and I wouldnt want to store a dang thing in there.

    Definitely considering a pro for it, especially if we go spray foam. Its just that I either need a pro to put in soffit vents and some other type of vent near the peak, or I need a pro to spray foam things, and I dont know which one I need.
  11. sloeffle

    sloeffle Member

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    I think your best bet is option 1. It is definitely the most expensive option but I think it will be allot less work in the long run and you will end up happier. If you do end up foaming the bottom of the roof though that space needs to become conditioned.

    The guy who foamed my house said they have a had allot of good luck foaming the bottom of roofs on old farm houses in my area. You will probably want to go with close cell foam since their is a possibility of the foam coming in contact with water.

    Scott
  12. Clarkbug

    Clarkbug Minister of Fire

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    I guess where Im torn is that Im part old house lover, part building scientist, and part homeowner that has to pay for all this stuff.

    The cost of the spray foam hasnt scared me yet (I havent seen the price, so I may eat these words), as much as its relatively permanent nature. Its a "new" building product, and I dont know how my old house will interact with it. I know that some stuff thats more energy efficient is also bad for the longevity of my house. (Like insulating my fieldstone walls in the basement). I just would like to know the pros/cons from someone "in the know" who isnt selling one product or the other.

    The idea of spray foam is great, but I do worry about what happens when the roof leaks or a tree branch crashes through the sheathing. Then what happens? How do you fix that?

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