Air-tight drywall and netted cellulose
Western Massachusetts / Climate Zone 5
The rough framing is complete on a double-walled house I am working on, and the insulators will be in to net and install dense pack cellulose next week. Our intent is to caulk or gasket the drywall to the framing at all exterior walls. I met with the drywall contractor this morning, who had never done the air-tight drywall approach. I explained the concept and these were his questions:
1. Is sealing the drywall to the studs necessary when we have netting on all the exterior walls under the drywall. Won’t this act as a type of gasket?
2. Is sealing the drywall to the studs necessary when we are installing blueboard and plaster skim coating the entire house?
3. Is non-paper faced drywall necessary in the finished basement if using blueboard? (The basement 2 x 4 walls are insulated with cellulose and 2″ rigid insulation in front of the foundation wall). The foundation has perimeter drains and spray waterproofing.
Thanks for any advice and Happy New Year!
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Replies
The air-permeable netting won't act as an air-barrier gasket, though it will make it more difficult to get a good caulk seal between drywall and framing (which is one of the reasons I always do a closed-wall cellulose install - the others being better density and easier drywall installation).
But the drywall caulking is necessary only to complete the air-barrier assembly between bottom and top plates which must have already been caulked or gasketed to the framing layers below and above. The drywall caulking is only the final element of ADA. And air-tight or flanged electrical boxes are also necessary, as is sealing the drywall to door and window rough opening boxes (which should also have been caulked to the framing and at the box corners).
If the basement is dry and moisture-controlled, including subslab VB, then there's no need for paperless DW. That's for high-moisture areas like bathrooms and damp basements. But always best to keep the DW a little up off the slab.
Robert - thanks for the response.
All framing has been caulked and air sealed as per the details provided on this site. In addition, all electrical boxes are installed in airtight polypans. Window and door openings have plywood bucks and will be spray foamed to door and window jambs. Closed wall cellulose is not an option so we either caulk or provide continuous foam tape at wall and opening perimeters.
Basement slab has a vapor barrier, 4" XPS, Walls to top of footing 2" XPS and framed walls as mentioned. Footing to foundation wall has a capillary break. We have a high watertable, but precautions have been taken for waterproofing, from grade to cast in place water stops. That being said, I feel comfortable with blueboard at basement walls.
In addition I would encourage you to seal the interior wall top plates to the drywall.
I personally prefer gaskets rather than glue on the top plates, less chance of the drywall slipping during install and wiping the glue off the plate, but I'm sure there are potential problems with gaskets as well.
Also your drywallers may be up to speed on truss up-lift but I always remind them anyway not to fasten the ceiling drywall to the trusses within 18" of any interior walls.
Michael - no trusses here. My concern has to do with caulk and/or gaskets with the cellulose netting. Have you any experience with the two in combination?
I would think that gaskets are ruled out by the netting, since they won't seal to the framing, while caulk will penetrate the netting. Tremco is the standard for ADA, but OSI has a Greenseries water-based acoustic sealant which I've never tried.
Why?
I admit that I do not know much about densepack cellulose.
Why do most people seem to use the netting... which seems sooooo labor intensive?
John,
The cellulose installer is sending two laborers to install the cellulose netting next Wednesday. They will start blowing the walls on Thursday. The GC is tacking up floor/ceiling netting prior to strapping.
The drywall contractor will either have to leave a strip of board out of the middle of an eight foot wall (two four foot sheets) or poke holes in each bay and over door and window heads and sills. Then patch all holes.
The drywall labor cost far outweighs the labors netting costs.
Jon, can you point to... or link to the exact details you are talking about?
Jon,
Are you using the strapping because of the netting?
Or is this standard procedure?
Hey Jon,
how about posting some photos?
How is the strapping going work with sealing the drywall to the top and bottom plates?
Strapping is installed for several reasons. Framing lumber is not always exact and nominal lumber dimensions vary from engineered lumber. Strapping allows you to shim or level the ceiling plane. Also, with a netted ceiling, the dense packed cellulose will bulge below the bottom of the joists. Strapping will hold the netting in place. In this project, the garage ceiling drywall will be installed prior to the cellulose because it works with drywall sheets and the garage ceiling is framed with TJI's which create a pretty flat plane.
The details I am talking about are standard cold climate bottom, window opening, top of wall air sealing details for a wood framed wall with shingle siding.
Send me your email and I will forward a link to photos.
While on this topic, if you leave a gap in the middle of the sheet rock wall, do you dense pack UP first, or down first? Is there any point in having the gap near the top, say a foot wide, then packing your way up? This would be coupled w/ leaving the sheet rock off the ceiling so you had a bit of head room (single story, flat ceiling w/ trusses). After you put the lid sheet rock on, you could then finish the wall. My thinking here is two-fold (though it may be askew, too): For one, dense packing bottom-up seems easier, and secondly, if the gap is not packed real tight because of awkwardness of finishing it, it won't matter if it settles a tad because there will be plenty of cellulose above it. That said, would it even be possible to squeeze in and dense pack a one-story house via the attic? Thanks. klingel
How about posting the photo link here? Or, you can now post photos in these threads with the attachment feature.
In my experience, the mid-wall space adds very little to the cost of either hanging or finishing the drywall.
John,
You work with gravity, filling the bottom of the wall first and then from the top plate down - but this is for a double wall that is capped at each storey so there is something in each direction to blow against. If the frame is open from sill to rafters, then filling from above - bottom up - works as long as there is easy access at the eaves because of a steep roof angle and a "high heeled" connection to the wall.
But I wouldn't leave a strip of the drywall open near the ceiling, as that creates another seam to finish. Generally, walls are hung horizontally - after the ceiling - with the first sheet tight to the ceiling and the second below that, with a horizontal factory edge seam in the middle of the wall. So leaving a wider middle-of-the-wall seam with two factory tapered edges, filling it with thinner drywall and then taping that wide joint and filling it flat, is little more work than finishing the simple joint.
Care must be taken, however, around the switchboxes that are typically at the 4' height and might end up in this wide joint. Better, perhaps, to change the switch height a bit to keep it outside the joint, particularly with polypans.
The open band in the drywall must be backed with mesh or fabric to contain the cellulose but allow air to escape. Then it's a simple matter to get good density and maneuver the blower hose down and up.
If the walls are 8' tall, then this center slot technique allows cutting off the tapered edge at the ceiling or floor or both. This makes a cleaner wall/ceiling joint and a flatter surface for baseboard trim attachment.
Robert: OK, and thanks. I have always (just a couple of houses) hung the sheet rock vertically, just so we did not have two 1/2" thick sheets butted against each other. It made more sense to us to have the thin, tapered joints together, oriented vertically. I realize that having a gap at the top will generate some agony and perhaps lead to sheet rock wastage, but I was more concerned about getting the walls packed properly. I will surely try to pack from the attic, and I guess I could just as easily dense pack from the outside. Leaving soffits out, for head room, and butting plywood against plywood when the gap is filled in would not be an issue at all. I guess I'll just have to see which way allows the process or occur w/out a gross PITA factor. j
John,
I've always seen drywall hung horizontally on residential walls, because with vertical orientation the edges can easily run off the stud centers with only 3/4" of wood to catch the fasteners on each sheet. And the center joint can be taped and finished from the floor, while vertical joints require ladders, staging or stilts.
In commercial applications, on metal studs, the drywall is often hung vertically, and I've hung it vertically on my rough-sawn full 2" wide studs. I've also hung it parallel to ceiling joists from wall to wall with no butt joints, which makes a beautifully flat ceiling even without strapping. But this, also, was with full-dimension lumber.
Just one more advantage of rough-sawn framing.
Thanks Jon Wyman
This is a good thread
and Kudos for including your location AND Climate zone!
I never really understood the 4 ft high convention for switches.
I promote 3 ft high because it is more ergonomic and age friendly.
Think about doorknobs... 3 ft high or 4 ft high?
Speaking of switches(and outlets)
since we are talking about exterior walls here
When I was designing my house ... I was able to eliminate switches in the exterior walls and greatly reduce the number of outlets by re-spacing the outlets in the partition walls
John,
This sounds a very useful approach to simplifying ADA installation.
Do you have more details, tips and traps you'd care to share?
The point about aging-in-place features is well made, also.
Timmy,
my personal home was a spray foam project.
When I get this Alternate Airtightness stuff figured out...
I WILL abandon Spray Foam.
I think I will start another thread and mention some strategies that I used on my house.
And the age friendly comment includes children.
Jon,
I understand that you may not want to publish the link to your photo sharing page.
how about posting one or two photos here?
John B,
I had missed the subtlety concerning children. Where did you find switches that turned themselves off automatically? :-)
Speaking of the Mooney wall
http://www.builditsolar.com/Projects/Conservation/MooneyWall/MooneyWall.htm
Two things about the system that puzzle me.
1. The mesh seems labor intensive ...
Why not use a technique more like Robert's?
2. I may be wrong..
but it looks like there is NO attention to airtightness?
I once asked Mike Smith about the airtightness of his houses
at the time he had NEVER done a blower door test.
Jon,
I understand that you are strapping the ceiling.
Are you also strapping the walls?
The photos that I have seen with netting on the walls were what I would call labor intensive.
It have seen 2 methods.
One method (Mike Smith/Mooney) would glue the netting.
The Other method (Dan Kolbert) would side staple the netting and used a gazzilion staples.
The intention seems to be to avoid the bulging you were speaking of.
Another possibility - if your schedule is flexible:
Why can't you hang the drywall on the walls, leave it off the ceiling, then blow it from the joist bay---in the gap between the two walls? Eventually you have to bring the cellulose into the joist bay, but you could do that after you got the walls completely filled, right? You could install blocking and/or ceiling drywall, then insulate the bays in a second step. You might have to do that anyway . . .
This approach would be similar to Robert's truss wall (where he has blown the entire two-story wall section from the attic), but it would be for a house that has continuous top plates joining the two stud walls---or for a design that uses the subflooring to tie the two stud walls together.
Thoughts?
Actually, I've never blown two storeys from the attic - only one at a time. And that works for me because I do the drywall and the cellulose myself. So I can hang the first floor ceilings and walls, blow from the second floor, then hang the second floor ceiling and walls and fill from the attic, then blow the attic on my way out the "hayloft" gable door.
As for electrical boxes, it's impossible to avoid exterior wall receptacles and meet the every-twelve-feet requirement (and kitchen counter receptacles) unless you install floor outlets.
"...electrical boxes...every-twelve-feet requirement..." I could never survive w/ an outlet every 12'. I think every 6' is pretty sparse.
my point about spacing the outlets is that you can reduce the number in the exterior wall
Not eliminate them
by placing the outlets near the corner of the partiion walls.
the total number of outlets is not reduced .. but the number in the exterior wall is.
I think we've chased Jon Wyman away.
Another thread about electric outlets?
No, you haven't chased me away, I have just been away from a computer.
John, the walls aren't strapped, only the ceilings. The walls are double framed. With an eight foot high wall that would typically use two sheets of drywall set horizontally, it seems counterproductive to cut one sheet short to allow for blowing in cellulose after installing wall board. Add to that the conflict with switch locations and the netted approach is our choice. When netting, the installers use high speed upholstery staplers and fasten 1/2" into the side of wall studs to prevent the netted cellulose from bulging past the face of the studs.
A link to the project images can be found here;
http://web.me.com/jmwyman/RiceResidence/Welcome.html
Daniel - It really wouldn't work to have the ceiling drywall unsupported at the edges by the wall drywall and hanging the wall drywall 5/8" down from the ceilings and trying to slip the ceilings in later would be a real pain.
Timmy - as to switches that turn themselves off automatically I've gotten to the point with my 12 year old daughter that I'm installing motion sensor switches on the bathroom lights. Seems like she habitually lights up five lights in her bathroom when she does her "look" before school every morning and I have to remind her to go back and turn them off. I'm also thinking seriously about installing a Lutron lighting control system with the visor control so we can just kill the lights from the car as we head out in the morning.
Robert - the gaskets we use are 1" strips of sill seal attached to the lower top plate usually after the ceiling drywall is hung. perhaps not as good as the examples you site but in combination with the header wrap detail we use, a strip of black poly or tyvek running through the wall between the top plate and uppermost top plate, it's a very workable solution and the interference of the spun-bond poly-olefin scrim netting doesn't seem like much to me. but would probably show up in a blower door test if we really wanted to quantify it.
The attached photo is from an older job where we used the header wrap and sill seal ADA with batt insulation, as you know we've switched to Spider micro-filament fiberglass blown in behind a scrim in the walls with spray foam in our roofs so we don't use the ADA now that we have un-vented roofs.