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Cooling Equipment Ambient, Attic Rafter Insulation. Need Advice!

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MarkC
MarkC Member Posts: 18
Hello. Knowing this site has many helpful users who typically provide thoughtful technical analysis/information on a given situation, I’m hoping I can get the same for below question! Thx in advance and sorry for the lengthy text.

The previous owner of my home installed 1” or so (aged?) rock wool batting between 6” roof rafters in an unfinished and unconditioned walk-up attic stopping about 12-18” before reaching the ridge beam - and covered those areas with Masonite (the house does not have eave/soffit vents). From the 12-18” stop point to beneath the ridge beam, the two pitched sides of the roof are spanned horizontally with the same materials creating a sort of ‘chamber’ where all the rafter bay ends tie into. Finally, fixed louvered vents were added at each of the two gable ends where the ridge beam ‘heat chamber’ spans between. Contributing to ventilation, the attic was originally constructed with two 2x3 gable-end windows which are now fitted with casement windows of the same size.

However, these materials were not well installed and in some cases falling down after many years. So I began to remove it under the assumption that all of this was incorrectly installed with heat loss in mind and that insulation/barrier above the attic floor would provide no heat loss benefit.

However, I did not realize until after I began removal when I could see how everything was laid out (described above) that the purpose of all this was probably intended for reducing heat gain rather than heat loss.

About 12 years ago, and well after all of the insulation was installed, I added central cooling to the house. The second floor air handler and ducts (insulated) are also located in the attic.

So the primary question is do I leave all insulation in place or remove? Some input thoughts/questions to this are:

1. Does it sound like the materials in/on the rafters provide benefit? Similarly, is it correct that above provides no heat loss benefit?...and that a focus on the attic floor and sealing leaks is where the effort should be. Same for heat gain?
2. I’ve never seen insulation in unfinished attic roof rafters, unless the attic is a conditioned living space. Agree?
3. Assuming the attic temp is lower with these materials in place, are there practical benefits for a cooling system? If so, are those benefits small or large? At which temp are cooling ducts, air handler, line set negatively affected by their ambient temp?
4. Could the rafter materials elevate the temp of roof shingles, shortening life?

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 23,318
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    Two questions to which I do not see a clear answer above. First, are there eave vents? And second, does the insulation between rafters have a clear space between it and the roof above, or is it jammed up against the roof?

    If there is a clear space between the insulation and the roof, and there are eave vents, the stuff was put in with at least some thought, though not, perhaps, as well as it might have been -- and the combination will work both to keep the roof cooler than it otherwise would be and to keep the loft space under it quite a bit cooler than it other wise would be. All that in the summer time.

    In the winter time -- heating season -- the loft space will be warmer than otherwise, from heat being conducted (or leaked!) up through the attic floor, but the insulation in the roof will reduce heat loss through the roof. That said, an inch of insulation which I think is what you said isn't going to help much.

    Most folks do insulate the attic floor and let the loft go cold. Some, however, insulate the roof -- particularly if it is to be used for storage, or if there is mechanical equipment and the like up there. Since the attic floor has less area than the roof, it takes less insulation to get the same effect by putting it in the floor. But not that much less.

    You're comment on insulation on rafters in an unfinished space -- about half the main place I care for is done that way. The other half isn't, and I wish it were.

    On the cooling ducts. The cooler you can keep the space where they are located the better. To that extent, the rafter insulation will be very helpful.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • MarkC
    MarkC Member Posts: 18
    edited July 2018
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    Hi Jamie, Thx for your response.

    No, there are no eave vents. And yes, the insulation is about 1" thick in a 6" deep rafter bay (dimensional lumber)
  • Zman
    Zman Member Posts: 7,569
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    I like the detail you describe. I think someone gave it thought and it does help with radiant heat gain from the roof.
    If you can get your hands on an IR camera, I would live to see how the temp looks with and without on a sunny day.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • MarkC
    MarkC Member Posts: 18
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    Hi Zman,

    Thx for your thoughts on the radiant heat gain.

    Unfortunately, no immediate access to an IR camera.
  • Rich_49
    Rich_49 Member Posts: 2,766
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    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    732-751-1560
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
    CanuckerGordy
  • MarkC
    MarkC Member Posts: 18
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    Hi Rich,

    Thx for the vid. Interesting stuff!
  • Rich_49
    Rich_49 Member Posts: 2,766
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    Hope it helped
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    732-751-1560
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
  • GBart
    GBart Member Posts: 746
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    Honestly your best go-to for home insulation Q&A etc etc is this guy

    https://www.energyvanguard.com/
    MarkC
  • GBart
    GBart Member Posts: 746
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    That site can help you plan a redo with better, modern materials, generally if you have equipment in the attic it works better in a protected/insulated environment.

    The catch is where the home is located, down south there's a way to do it and in the NE another, because up here you want heat gain in the winter, at least some.

    Most experts now all agree that any standard insulation is nothing more than a filter, it does nothing for infiltration but helps with slowing heat movement. A big factor is thermal bridges which for example could be any 2x4 or 2x6 that touches the in and out, heat will transfer along that bridge and move. Most are pushing foam because it seals and really cuts thermal movement.

    This company has a lot of info and videos, etc. Unfortunately there are a lot of options out there and you need to pick the right one for the home and where it is located.

    https://www.reflectixinc.com/
    MarkC
  • Rich_49
    Rich_49 Member Posts: 2,766
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    Here is the owner of Energy Vanguard ( Allison Bailes ) discussing Reflectix . Pay no attention to their videos and stick with the professionals , most Reflectix guys are just like so many salesmen , full of diaper batter . https://www.energyvanguard.com/blog/29497/The-Foil-Faced-Bubble-Wrap-Sham-Understanding-Radiant-Barriers
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    732-751-1560
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
    GBart
  • GBart
    GBart Member Posts: 746
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    Rich said:

    Here is the owner of Energy Vanguard ( Allison Bailes ) discussing Reflectix . Pay no attention to their videos and stick with the professionals , most Reflectix guys are just like so many salesmen , full of diaper batter . https://www.energyvanguard.com/blog/29497/The-Foil-Faced-Bubble-Wrap-Sham-Understanding-Radiant-Barriers

    Thanks for that, I haven't been able to decide how I felt about Reflectix especially when installed directly to roof deck, I also know that many of the new types of underlayment for roofing doesn't like that at all. This is the Green Building Advisor article he referred to, good reading as well.

    http://www.greenbuildingadvisor.com/blogs/dept/qa-spotlight/bubble-wrap-duct-insulation-good-idea
  • GBart
    GBart Member Posts: 746
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    This is also a great article, I like the end where he explains : Does radiant heat pass through insulation like radio waves?
    Another scare tactic employed by some marketers of radiant barriers is the idea that conventional insulation materials — sometimes called “mass insulation” — allow radiant heat to pass right through them. Scam artists have been known to warn builders that “mass insulation is transparent to radiant heat.” The implication is that a layer of aluminum foil is necessary to prevent radiant heat from traveling like radio waves right through a deep layer of cellulose.

    In fact, most mass insulation products do a good job of stopping radiant heat flow. Radiant heat easily travels through air (for example, from a wood stove to nearby skin) or a vacuum (for example, from the sun to the earth). But radiant energy can’t travel through a solid material.

    If the sun is shining on a concrete patio, for example, the heat travels to the soil below by conduction, not radiation. Here’s what happens: the concrete is first warmed by the sun (by radiation), and then the warm concrete gives off some of its heat to the ground below (by conduction). There is no radiant heat transfer from the sun to the soil.

    When radiant heat hits one side of a deep layer of insulation, only a tiny percentage of that heat is “shine-through” radiation that manages to miss all of the fibers in the insulation blanket and emerge unscathed on the other side.

    The fact that heat flows through a layer of insulation doesn’t mean that the insulation isn’t working. By definition, insulation slows down heat flow; it doesn’t stop it. Heat will always flow from hot to cold. The more insulation, however, the slower the rate of heat flow.


    http://www.greenbuildingadvisor.com/blogs/dept/musings/understanding-r-value
  • GBart
    GBart Member Posts: 746
    edited August 2018
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    So I found a set of pics with thermal imaging, this is what will be in the pic, a duct with surface mounted bubble wrap and a run with fiberglass insulation with a reflective shield


  • GBart
    GBart Member Posts: 746
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    and this is the heat moving, look at the heat intensity of the bubble wrapped trunk with no air gap, wow


  • nibs
    nibs Member Posts: 511
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    Mark, suggest you goggle "warm roof", what you describe falls into the category of warm roof construction, which is a newish trend in North America. The problem with putting insulation directly against the outside of the structure is that if not done correctly you run the risk of trapping warm moist air against the wood and encouraging rot. My flat roof built 4 years ago has the insulation directly under the plywood skin, and is very carefully build in a way that allows no air to enter or leave the insulated area, the eves which are not insulated are vented. Check that no air can move under the insulation or through the insulation and you should be fine.
  • MarkC
    MarkC Member Posts: 18
    edited August 2018
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    Nibs, thx. I’ll check it out. However, these materials were installed well before I owned the house (at least 17 yrs) so I suspect the warm roof you’re describing is probably a much more recent method. Maybe this install was way ahead of its time...but I doubt it.

    As far as ensuring moisture entrapment doesn’t occur, assessing that sounds like a tall order in both measurement and execution for someone like myself who doesn’t do this type of thing on a regular basis. What I can say is the eves are not vented. Outside of that, the envelope of this roof and attic (built 1924) on a carefully measured, scientific scale is probably of the ‘Swiss cheese’ magnitude!