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davemax21 | Posted in General Questions on

While I was on the subject originally regarding adding central air to my gas furnace, someone was talking about humidity levels in the winter and how dry you feel at home.
I just realized and was told that whole house humidifiers only work/operate anyway, when the furnace is actually running. Makes sense.
in my opinion, and having a hydrometer to prove it, whole house humidifiers are a waste of money, period.
My humidity levels do move much at all.. house is dry, very dry. The only thing that helps is a portable humidifier, large enough for the room you are in, that has the ability to run constantly.

Seriously, my humidifier on my furnace, operates, I see the water, etc… it’s set properly, but yes, there is no enough running time to add any moisture to the air in the home.
and the hydrometer proves it.
Just some thoughts on this ..

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  1. davemax21 | | #1

    Meant, "My humidity levels do NOT move at all".

  2. GBA Editor
    Martin Holladay | | #2

    The way to raise the indoor humidity level in winter in a house with dry indoor air is to seal air leaks in the home's thermal envelope. It's the air leakage that is keeping your indoor air so dry.

    -- Martin Holladay

  3. davemax21 | | #3

    I'd like to believe that but the air outside is pushing 90 plus % humidity.

  4. WisJim | | #4

    What temperature is that "humid" outside air? I suspect it is colder outside so that when that air leaks into the house and is heated, the amount of moisture is so small that it doesn't increase the inside "relative" humidity. Cold air doesn't carry much moisture, so high relative humidity in cold air isn't really much actual air borne moisture.

  5. davemax21 | | #5

    Got it.
    I didn't know that, I just look at my indoor- outdoor thermometer/hydrometer and it might be over 90% humidity outside, I assume it's very moist air.

  6. mpg9999 | | #6

    90% relative humidity at 32 degrees would be around 20% relative humidity at 72 degrees, so not very moist air at all.

  7. GBA Editor
    Martin Holladay | | #7

    Michael is right: cold outdoor air can't hold much moisture. For more information on this issue, see How to Use the Psychrometric Chart.

    -- Martin Holladay

  8. Dana1 | | #8

    Think "dew point", not "relative humidity". Dew point is a measure of the absolute humidity of the air, independent of it's temperature.

    Any time it's below ~38F outside the outside air is guaranteed to be drier than the low end of the human health & comfort end (~30% RH @ 68F), and the outdoor dew point is often below 38F even when the outdoor air temp is warmer than that.

    Over-ventilating the house with that air is the problem, air sealing to prevent unintended ventilation (= infiltration) & controlled ventilation are the solution, and it works in all climate zones.

  9. davemax21 | | #9

    with that, and maybe not related, are soffit vents a must? or optional, in a cape cod style attic?
    I was told with the slant part of the roof approaching the knee walls, venting the soffits may not make sense because the rafters in that area could be so small , 2x4 or 2x6, that to insulate , those areas would be packed too tight with insulation to allow any air flow anyway. I mean, it's such a small attic up there, in the cape cods, and there are 2 gable vents.. was just originally concerned with the ice damming.

  10. GBA Editor
    Martin Holladay | | #10

    Q. "Are soffit vents a must or optional in a Cape Cod style attic?"

    A. The answer depends on whether you are designing the sloped ceiling sections to be vented assemblies or unvented assemblies. Whether these sloped ceilings are vented or unvented, the sections definitely need to be insulated.

    These two articles will explain all of the different ways to insulate sloped ceilings:

    How to Build an Insulated Cathedral Ceiling

    Insulating a Cape Cod House

    -- Martin Holladay

  11. davemax21 | | #11

    thank you. they attic is vented.

  12. davemax21 | | #12

    I don't have mold or moisture issues in the attic, just trying to prevent the damming.
    I've had 2 reputable insulation companies, and a contractor/home builder for over 30 years who has done work on my home, and all see to agree that the soffit vents may not be needed. Just removing the mess that's up there. Which is needed because the ceilings are all being replaced,. then air sealing , new ceilings, they all seem to state packing the tight slanted areas with insulation (but still putting in the baffles, and then probably blow in cellulose.
    Ps. the ceilings are just very old, cracked, uneven, and one room has misplaced blocks, etc... nice to get a clean look. The ceiling replacement will be total, down to the closets as well.

  13. GBA Editor
    Martin Holladay | | #13

    If you eliminate the ventilation channels from your sloped ceilings, make sure that you adopt one of the insulation strategies that work for unvented assemblies (either rigid foam above the roof sheathing, or closed-cell spray foam on the underside of the roof sheathing).

    It is a code violation to install an air-permeable insulation like fiberglass, cellulose, or mineral wool between rafters unless either (a) there is a ventilation channel between the top of the insulation and the underside of the roof sheathing, or (b) there is a layer of rigid foam above the roof sheathing, or (c) there is a layer of spray-foam insulation on the underside of the roof sheathing.

    Here are links to two articles that discuss solutions to ice dams:

    Prevent Ice Dams With Air Sealing and Insulation

    Ice Dam Basics

    -- Martin Holladay

  14. user-2310254 | | #14

    Dave. Where are you located?

  15. davemax21 | | #15

    Located in Syracuse.NY

    so baffles can be used to accomplish a space between the roof sheathing and insulation in the slopes, correct? even though there may not be any soffit vents, as long as there is a space between the two, insulation and sheathing, that accomplishes ventilation? so packing the sloped areas, as long as they're not packed completely?

    Per the article Martin, I'm surprised he states "gable vents are not needed".

  16. davemax21 | | #16

    I have to google these terms as I go along. so I see what is the roof sheathing. and you can't have insulation packed right up against the sheathing, unless it's the board or foam. I also see some good diagrams of the cape cods with the baffles in those tight areas, then insulation packed. good visuals and great to understand it.

  17. GBA Editor
    Martin Holladay | | #17

    Soffit vents + a ridge vent is the best type of attic (or cathedral ceiling) ventilation. Gable vents are no longer recommended (although they may work fine for an attic).

    Q. "So baffles can be used to accomplish a space between the roof sheathing and insulation in the slopes, correct?"

    A. Yes. More information here: Site-Built Ventilation Baffles for Roofs.

    Q. "Even though there may not be any soffit vents, as long as there is a space between the two, insulation and sheathing, that accomplishes ventilation?"

    A. No. If you decide to create a vented roof assembly, the soffit vents are required. You need soffit vents; a ventilation channel created by baffles; and a ridge vent.

    Q. "So packing the sloped areas, as long as they're not packed completely?"

    A. You can install insulation in the sloped areas, as long as you follow the guidelines in the article I linked to: How to Build an Insulated Cathedral Ceiling. Did you read the article yet?

    With the type of insulation materials that many people install (fiberglass, cellulose, or mineral wool), you must have a ventilation channel between the top of the insulation and the underside of the roof sheathing. The volume between the ventilation baffle and the ceiling can be packed with insulation, as long as the insulation isn't packed so tightly that it bends the baffle or impinges on the ventilation channel.

    -- Martin Holladay

  18. davemax21 | | #18

    Thanks again. I currently have a ridge vent and 2 gable vents at the ends.
    But I think my ultimate question has been, do I need soffit vents? If I don't have soffit vents, and not using sprayfoam, what can I do in the sloped areas?

  19. GBA Editor
    Martin Holladay | | #19

    You can either (a) retrofit soffit vents -- if you don't know how to do it, consult a builder -- or you can (b) create an unvented sloped roof assembly with rigid foam above the sheathing, or spray foam below the sheathing.

    Once again, I'm going to urge you to read the article I linked to: How to Build an Insulated Cathedral Ceiling.

    I think it makes more sense for you to take the time to read the article rather than to ask a series questions that are covered in that article.

    -- Martin Holladay

  20. davemax21 | | #20

    I looked at the article and have a better understanding of this;, but of course I focus on this part of the article;

    " Can I use dense-packed cellulose as the only insulation for an unvented roof assembly?

    In a word, no — the code explicitly forbids this method. Cellulose can only be used in an unvented roof assembly if there is an adequate layer of rigid foam above the roof sheathing or an adequate layer of closed-cell spray foam under the roof sheathing. Cellulose alone won't work.

    However, in some areas of the country, especially in the Northeast, insulation contractors have been dense-packing unvented rafter bays with cellulose for years. Because the method has deep roots in New England, many building inspectors accept such installations."

  21. davemax21 | | #21

    I guess when the ceilings are down, it won't be that difficult to get it sprayed then.
    closed cell?

  22. davemax21 | | #22

    Final observation. if I have soffit vents put in, it would have to be for every bay? can't just add a few ?
    and if there were vents, I would use the baffles, to allow air flow, but could then pack insulation up against it.. as long as the baffles are not squeezed against the sheathing.

  23. davemax21 | | #23

    Ok, so my insulation guy just emailed me a diagram of my type of house and it's a 1 1/2 story cape.
    The end of my roof doesn't go all the way down level with the floor of the upstairs, the roof line is not as steep a typical cape cod.. there are no knee walls, there are closets at both ends of each bedroom.
    When you walk in the closets, the ceiling slants down but you still have a height of 4 feet at the exterior walls. I am thinking this would be easier to work with when starting to insulate.

  24. davemax21 | | #24

    I attached a very similar type roof line , just the room over the porch, my house doesn't have the second roof line. It just goes straight back to the other side of the house. Other side is identical.

  25. GBA Editor
    Martin Holladay | | #25

    Even if your roof shape is similar to the house in the photo, the same rules apply.

    If you're using a fluffy insulation, you need to vent the rafter bays. That means every rafter bay, not just every other rafter bay. And that means you'll need soffit vents and a ridge vent.

    If you can't accomplish this type of venting, you need to install rigid foam above the roof sheathing, or closed-cell spray foam below the roof sheathing. Details are spelled out in the articles I linked to.

    -- Martin Holladay

  26. davemax21 | | #26

    I understand.
    if the rigid foam is above the sheathing, does that mean the shingles are on the foam board? I'm confused with that.
    PS, what do you call that style of house I attached?

  27. GBA Editor
    Martin Holladay | | #27

    The house you describe is called a "story and a half."

    Here is a link to an article that tells you how to install rigid foam insulation on the exterior side of the roof sheathing: How to Install Rigid Foam On Top of Roof Sheathing.

  28. davemax21 | | #28


  29. Expert Member
    Dana Dorsett | | #29

    Syracuse NY is in US climate zone 5A. In that climate zone only 40% of the total R needs to be above-deck foam or closed cell under the roof deck. Given the high environmental cost of most closed cell spray foam as well as some types of rigid-board, the greenest solution is to use recliamed roofing foam (from commercial building demolition) above the roof deck, with open cell foam or fiber insulation under the roof deck.

    If you have 2x6 rafters you can get R23 rock wool under the roof deck, at which point 4" of 2lb density fiber faced roofing polyiso ~(R22-R23, labeled-R, but R20-ish performance from a dew-point control perspective). That would put you well over the 40% needed to keep the roof deck dry, and a center-cavity ~R45-ish. Even though code-min is R49, since the R20+ over the roof deck is not thermally bridged by rafters it will actually outperform R49 between rafters or joists, and the assembly would still meet code-min on a U-factor basis (< U0.026 ) after adding in the R-value of all layers (including air films), and calculating the thermal bridging losses.

    This sort of material is often cheaper than batts on an square feet x R basis. These folks in Oneonta are selling 3" roofing iso (about R16) for $20/sheet:

    That works out to 63 cents per square foot, (/16=) 4 cents per R-foot^2. That doesn't include the cost of a half-inch OSB nailer deck on which to attach the roofing or the screws requjired for attaching the nailer deck to the structural deck, but it's still dirt cheap, about 1/3 the cost of virgin stock 3" polyiso, and about 1/10,000 the environmental cost per R of new closed cell polyurethane using HFC blowing agents.

    There are others:

  30. davemax21 | | #30

    Can I ask about insulating the walls of the house as well? Because the walls are so on even with decades of paint and all the wallpaper and some small cracks at the top from years of settling, I plan on having the interior walls removed whatever is in there taken out, insulated then new smooth drywall. There is no lathe and plaster . No housewrap or anything house was built in 1920 was wood sided then covered with vinyl. If I can afford it. Would spray foaming be the best solution? Or is batt OK?
    I was told that air sealing is more important, but still needs insulation. I heard batting can get moist in the walls,
    What would be best?

  31. user-2310254 | | #31


    Do the walls have sheathing? If so, what kind?

  32. davemax21 | | #32

    When you say sheathing? Plywood? The house was built with plywood. I actually just read an old article here where plastic sheeting, vapor or air barrier is not necessarily needed. That that could work, but closed cell foam it might be better.

  33. GBA Editor
    Martin Holladay | | #33

    Spray foam insulation is one option among many. But here's my advice: find a reputable general contractor you trust. It's going to be hard for you to get up to speed fast enough to figure this job out on your own.

    Over the course of the answers in this thread, you've learned a lot. You've learned for the first time that cold outdoor air doesn't hold as much moisture as warm indoor air. You've learned for the first time that ventilation channels for cathedral ceilings require soffit vents.

    You've told us that you have had to Google the words used in the answers provided in this thread. (It's admirable, by the way, that you are doing this Googling.) You've learned for the first time that when a cathedral ceiling is vented, the ventilation has to be in every bay, not just some of the bays. And you've asked what Steve means by "sheathing."

    It's great that you've learned so much. But there is still a lot more to learn. You'll find it easier to hire a reputable general contractor.

    -- Martin Holladay

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