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Community and Q&A

Insulating ceiling during winter construction?

Nick Hall | Posted in General Questions on

Our house is currently at the stage where they are about to start interior framing. Unfortunately this means that there is a giant hole in the envelope (the ceiling!) and they are wanting to run temporary heat as it is quite cold (a typical daytime temperature this time of year is about 15F). Of course you can pump a lot of heat into a structure and not have it get too warm when you have no ceiling and a vented attic.

So my builder and I were discussing options for partially insulating the ceiling so that it would be warmer with much less heat used. My calculations show that even if we do R-10 ceiling insulation temporarily until after framing/drywall, we’d be able to get the building warm enough without using nearly as much heat.

As for context, we are planning R-60 cellulose ceilling, vented attic, airtight drywall method for the ceiling.

My builder’s idea was to staple insulation mesh netting to the trusses and then blow in a layer of perhaps 3-4″ of cellulose so that it would provide a decent insulation layer but not be so thick that it would be difficult for the plumbers to do their vent stacks (then we would have to blow in the rest of the cellulose after the ceiling drywall is on, so there would be an additional trip charge for the cellulose truck).

My question regarding this method is that it would seem to me like 3-4″ of cellulose would provide very little in terms of an air barrier, so there would be lots of air going up into the attic, which would not only take away heat, but moisture. This time of year the daytime temperature is about 15F and the dew point is around 10F — somewhere around 80% relative humidity usually. I know new concrete releases a lot of moisture so my guess is that the humidity of the heated interior (at perhaps 40-50F) would get high enough to get above a 15F dew point and then condense near the top of the cellulose insulation as air escapes up to the attic. So the cellulose would likely get damp all winter, and probably also make the bottom of the trusses damp as well. But the outside temperatures will be well below freezing until after the ceiling drywall is on (and we have an air barrier), so will this wetness in such cold temperatures cause a problem (mainly I’m thinking about mold)?

The other methods I have brainstormed are:

Instead of using the mesh netting, use a smart vapor barrier like Certainteed Membrain, and blow 3-4″ cellulose on top of that. This could provide a decent air barrier, but I don’t see data indicating it is designed to bear weight.

Sheet the bottom of the trusses with OSB, tape the seams with Siga Wigluv and then we have our air barrier and can build a service chase between that and the drywall. This would allow us to blow the insulation on top without worries as the air would be sealed and provide the benefits of a service cavity and probably better air sealing. Negatives are cost and loss of a couple inches headroom.

Has anyone done any of these methods or have any thoughts to share about them or winter construction (other than wait until summer!)? I greatly appreciate it, thanks!

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Replies

  1. David Meiland | | #1

    Why do they want to start heating now? Seems to me that they should push through, finish the rough-in, install the insulation and drywall, and then start heating (and possibly dehumidifying).

    If you do anything now that adds to the cost, who pays for it?

  2. Nick Hall | | #2

    Main reason for the heat is the difficulty of framing at 15F or colder, especially since certain tasks are difficult with gloves on.

  3. David Meiland | | #3

    Obviously I don't know the house plans, but if you have flat ceilings and an attic, and you can hang the drywall ceiling now, you can retain some heat that way without doing much of anything that isn't really needed later. You'd have to give some thought as to how to handle partition top plates and ceiling boxes for electrical, but maybe it would be a worthwhile improvement.

    Or... buy the guys heated vests. They can use those on future jobs too.

  4. Stephen Sheehy | | #4

    A good reason for insulating now is to avoid using those nasty kerosene or propane heaters that are loud, stink and produce nasty levels of CO.

    Obviously, productivity and quality go up when workers are comfortable, don't need gloves and breathe clean air.

    My new house was insulated about this time last year. We're in Maine and had a lot of sub-zero weather. Since the only ceiling penetration was a single plumbing stack, it was easy to insulate the (vented) ceiling space. We stapled our air-barrier membrane to the underside of the trusses. Then nailed 1x4 strapping, then hung drywall. Then fully insulated with cellulose from above, through a hole left in one of the gable ends. We were able to heat the house for the rest of the winter with a single 5000 watt electric heater.

    How you handle things depends on how much work, if any, needs to get done in the unconditioned space above the ceiling. Most of our house had high, sloped ceilings with no penetrations for lights, etc. But we used a flat 8' ceiling along the north side with a conditioned utility space above that allowed placement of plumbing and wiring, hrv ducts, etc. Kitchen, bathrooms and mechanical room were all on the north side.

  5. Nick Hall | | #5

    Thanks David. I thought about doing it that way as well as that would work fine in theory, but it seems like a lot of people are negative about doing the ceiling drywall before framing:

    http://greenbuildingtalk.com/Forums/tabid/53/aff/16/aft/77548/afv/topic/Default.aspx

    https://www.greenbuildingadvisor.com/community/forum/general-questions/17954/airtight-drywall-approach

    Sounds like it gives problems for the electrical so I'm not sure it would be workable without more considerable effort. Interesting idea though as it has advantages in other respects.

  6. Nick Hall | | #6

    Thanks Stephen. Can I ask you what air-barrier membrane did you use -- apparently it supports the weight of the cellulose fine? We would have a few more plumbing penetrations than you but that would probably be workable. The entire ceiling plane is flat. With your approach, do the electrical wires run in the space created by the strapping, between the drywall and the membrane? I remember I've read that strapping is common in the northeast but here it is never done that I've heard of, but doesn't seem to be a big deal to do.

  7. Stephen Sheehy | | #7

    Nick-We used Siga Majpel, but the insulation is really held up by the strapping and drywall. We were concerned that if we dumped 2 feet of cellulose on top of the membrane, we'd strip the staples and compromise the air sealing and maybe blow the membrane out entirely. It was easy to insulate from the hole in the gable end and fill the hole later.

    Because we had the utility space above the ceiling on the entire north side of the house, we didn't need to put any wires or pipes in the space between the drywall and the membrane. All the lights in the sloped ceiling spaces are wall mounted or Tech Lighting Kable system lights. Because the utility space is conditioned, we could install the much-maligned but cheap and useful recessed cans in the kitchen and bathrooms without worrying about air sealing them.

    If your situation is different, you could create a chase for wires by strapping with 2x4s instead of 1x4s.

    It was easy to drywall the entire underside of the roof trusses all at once and then install interior partitions since the entire roof load is carried by the trusses.

    Here's a photo showing what it looked like before the drywall went up.

  8. David Meiland | | #8

    Stephen, are your partition top plates under the drywall and not directly connected to the truss bottom chords?

    edit to add, I know northeasterners strap their ceilings, but I've never once done it in 30 years and don't see the point, especially with trusses. Doesn't the strapping create air pockets between the cellulose and the drywall?

  9. Stephen Sheehy | | #9

    David- that's right.

  10. Charlie Sullivan | | #10

    Perhaps use the mesh plus a small amount of cellulose as your builder suggests, but them put in a temporary sheet of poly under the mesh as an air barrier, and rip it out just before the drywall goes in?

  11. Joe Suhrada | | #11

    Put up taped OSB and make a chase underneath with 2x4 strapping to run wires, boxes, etc. put your r60 cellulose up there with no worry. No Membrain, no net, etc.

  12. Joe Suhrada | | #12

    How many sheets of OSB are you taking vs. cost of Membrain, time to air seal the boxes. Also you get a stiffer bottom chord all across with the OSB. You can use cheaper tape other than Siga and also duct mastic since no one will see the ugliness of it. I think it is a superior system, and as long as your inspector doesn't mind, go for it. You only lose 2" headroom.

  13. Aj Builder, Upstate NY Zone 6a | | #13

    Another example of a home being constructed with lack of regard to when.

    People, please give some thought to when you construct in the future.

    As to working inside in an unheated space, that is not the worst issue, trying to roof a home is for me the worst of it. Shingles don't seal down, roofs are more dangerous to work on with snow, ice... etc..

    As to cold inside work, we just have a small radiant heater on top of a propane cylinder, warm up by it once in awhile while starting the day, and once working we end up being warm or too warm and peeling off layers.

    Best though to get homes framed up and insulated by Columbus Day.

  14. Joe Suhrada | | #14

    Yes, AJ, but banks, architects, building departments, sub contractors and Mother Nature are not always accordance with that good plan. Once the first shots of battle are fired off, all plans of war become useless. I am sure you know well this song and dance. And once you get to Hell, keep going as Churchill explained. Then there is no backing up.

  15. Joe Suhrada | | #15

    Besides, he WAS framed up by Columbus Day. Columbus Day, 2016!!!!

  16. Joe Suhrada | | #16

    Nick, I was thinking about this a bit as I will be in similar pickle soon. I wonder if you have a source for reclaimed foam. Polyiso, in particular? I was thinking you could use it for your ceiling and do the strapping under it. If you get an inch it is about 6R value inside like that I think. Later, when you insulate, you can put your cellulose up there. It is not very vapor permeable so your cellulose must dry upwards and out through vented ridge. Correct me if I am wrong in calling for this use (Dana or Martin) ... Around here, I can get a great deal on this kind of foam product. With firring strips underneath, I also have a handy wire chase and I bet if I get the foam faced in this instance, facing down towards the sheet rock, there is even a little more added insulation benefit with that air gap.

  17. Expert Member
    Malcolm Taylor | | #17

    Joe, Ceilings are typically strapped once the interior walls are in place. If you do it before then it's worth remembering that you won't be able to use pre-cut studs or standard truss clips to secure the top plates.

  18. Nick Hall | | #18

    Interesting ideas. I've not heard of sheeting the ceiling with polyiso and strapping under that. I guess I'm willing to try some less common ideas but not something that I can't find that anyone has done before :-) Right now I'm leaning towards doing nothing (just framing the interior walls like normal and having to deal with the cold) or doing the OSB service chase idea. I'd like to avoid making it too complicated. And yes, it would have been nice to be at this stage several months ago but delays happen unfortunately and there's not really anything that can be done but keep going at this point. At least the roof is on! I really appreciate all the ideas that keep coming. Thanks.

  19. Joe Suhrada | | #19

    Good point, Malcolm. More cutting. But a better job. I wonder if taped polyiso one inch would be a better solution than the OSB? About the same price for materials and you get the R value and non permeability of the foam... Dana?

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