I am building a house in Montauk NY. It will be a shingled house in a very exposed location. It is 2×6 wall construction, 16″ on center. My builder was planning on blowing the walls and rafter bays with Icynene. On the exterior walls he then typically puts a layer of 1/2″ plywood under the drywall. He builds a very solid structure (anthony power beams for all headers) but this results, i think in significant thermal bridging. I have been looking into foam insulation (either exterior or interior) to provide a thermal break. Then I read about the Mooney Wall.
The house is about 5200 square feet. Heating system will be propane powered radiant on all levels (basement, first floor, second floor).
Does anyone foresee any issues with using the Mooney Wall construction but instead of dens pak using icynene? I realize that the cavities would be 7″ of foam, but it seems like all of the headers and studs would be covered by at least 1.5″ of foam and the furring would dramatically decrease thermal bridging.
Also, wondering what you think best practices will be on the attic? Again, roof rafters are 2×12, and the builder was planning on filling the bays with icynene. Anything more i could do? I was thinking adding 1-2″ of XPS. But then it seemed i would have to drywall over it…the expense of covering the rafters might not be worth it.
I think the basement will be 2″ of XPS covered in drywall.
Thanks for all of your help. I have spent hours reading through all of the posts!
IGS
Edited 1/19/2009 3:48 pm ET by IanSmith
Replies
I think that approach would be a whole lot more expensive than simply buying SIP's.
Not only that but SIP's would be at least 200% stronger than a mooney wall.
One problem would be cost.
Another is that the cross grid of furring horizontally would interfere with spraying the foam in place.
You would be better off using cellulose than icy for roughly the same R-value and infiltration control.
If you want spray insulation for the benefits it provides, you want polyurethene foam which provides nearly twice the R-value. It stiffens up a wall and no need for plywood under the SR, and it is a VB.
In a 5.5" wall at starting R7-7.2 degrading to R6.5 to 6.8, you can get an R38 wall.
For concern about thermal bridging, I install the foil facedppolyisoanurate foam ( Thermax) sheets to the studs and then 3/4" strapping to furr out horizontally for SR attachment. If you used that at 1" over cellulose in the 5.5" cavities, you get about R26.
Help me out here - I am trying to imagine why he uses the plywood on the interior?
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Frenchy - the problem with SIPs is that the house is already 95% framed.Piffin - for the Thermax, what direction do you have the aluminum surface face? as far as open cell vs closed cell, i was thinking open cell foam would be adequate given given the 5.5" cavity (R19-20). Closed cell, i think, is a lot more expensive. The biggest heat loss area would then be the thermally bridged studs. I have concern about cellulose given the super high humidity out here...the fog just rolls in and permeates everything.One of the high end architects in East Hampton started speccing 3/4" plywood on all interior surfaces (including interior walls, ceilings, etc.) . Provides added structural stiffening (although they also put 3/4" on the exterior, all glued and screwed") and noise control. . The builder worked on one of those houses (one of the $1000/foot jobs) and liked the end result - although he only installs it on exterior walls. Also in high wind areas makes the house quieter.Redford: he did insulate the exterior of the foundation using the Marflex Shockwave rubber insulation / drainage board system. 1" is about R-9 (including concrete foundation)IGSEdited 1/19/2009 12:55 pm ET by IanSmith
Edited 1/19/2009 3:47 pm ET by IanSmith
I am one of those who too prefers to place a 3/4" sheet of plywood under the drywall or whatever the wall covering is. I was not aware of anyone else that did that so this is nice to hear. It really does help cut down the noise and the structure definitely imparts a feeling of increased stability in the event of inclement weather.
Edited 1/19/2009 8:35 pm by Pebble
Pebble: Re: 3/4" plywood under the sheetrock...There are only a few builders and architects that specify it out here. It was certainly a new concept for me, but I have a friend who did it, and i don't know whether it is psychological or not but it seemed to make a difference.
Edited 1/19/2009 4:13 pm ET by IanSmith
Our finish carp used to work for a builder in the 70's in AZ I think that sheathed the interior walls then drywall. In fact I think they may have had plaster walls.
There have been numberous reports here at BT of the icy absorbing moisture from the air and holding it like a sponge, so if you have a reason to fear using cellulose, you have more reason to fear the Icynene. Moisture control is another whole issue.I am on an island and we have humidity to deal with. I use Chopped fibregla BIBsystem mostly. Not quite as high an R-value but for practical purposes the same.I place the Thermax with foil facing into the house. It requires air space in front of it to benefit from the radiant surface in addition to the actual R-value. I am in a heating climate. I'd re-think in a cooling climate and put it on the exterior of the house.
But the strapping over foil inside gives me that space.I have used OSB on interior under the SR on older structures to stiffen it up, replacing the thickness of the plaster lathe with the OSB, then SR over. Had the added benefit of being able to hang art anyplace without a stud finder or special wall hangers.I was imagining that since your wall is 2x6 framing, that it might be 24" OC and that was the reason for the interior sheathing. You sometimes get a wavy surface with the larger layout. That and harder to find nailing for trim at baseboard and crown.
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I should also point out that polyurethene foam stiffens up a frame and makes a house very quiet. With good windows, you literally cannot hear traffic or storm winds outside a couple places I have built that way. That is worth taking into consideration.
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cousin..... what is the name of the architect in east hampton?
i know a couple in that area
as far as the mooney goes.... the primary thing to me is having a well thought out strategy for the whole system....
the Mooney wall replaced our old "energy wall"
which was 2x4 w/ dens-pak.... then borate treated 1" eps then horizontal 1x3 furring
your wall system sounds ok.... but in an open attic i would be looking for an r-60 with loose blow celluloseMike Hussein Smith Rhode Island : Design / Build / Repair / Restore
Mike: The architect that does the super high end stuff is Francis Fleetwood. I am working with yet another cousin of ours, Rob Smith from Hollenbeck & Smith.When you say "open attic" I am assuming you mean unfinished with no wall partitions? We are looking to have an unvented attic. The wind can blow sideways and upwards in Montauk and I would prefer to seal the structure. We will also have air handlers in the attic for A/C. So i thought that spraying the rafters was best bet.For me for the walls, it seems the debate is whether to do a Mooney-type wall w/Foam or to layer 1" XPS over the studs, then add plywood and drywall on top of that.As far as open vs. closed, we have not yet bid them out, so i don't really know the upcharge. I have not heard the issues of significant issues with open cell foam and moisture. Although most builders in Montauk are using open cell foam with good result.
Ian, perhaps another cousin?
See if Hollenbeck knows an architect in Toledo-Paul Hollenbeck?
thanks.........might be pauls son perhaps. Paul's probably 60 or so.
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Frank Hollenbeck is retired as he is about 76 years old. the office is run by Rob Smith.
Thank you, must be a popular name in the architect trade...........well, at least two of them.A Great Place for Information, Comraderie, and a Sucker Punch.
Remodeling Contractor just outside the Glass City.
http://www.quittintime.com/
"I place the Thermax with foil facing into the house."I wouldn't think that the OP's location, being at times very humid and hot and at other times quite cold, would be appropriate for a layer containing foil anywhere in the wall. Foil will absolutely prevent diffusion of moisture in either direction. Most of the building science stuff we see here and elsewhere advocates providing drying potential in either direction, except in the coldest climates.
That is a point to consider - also with the closed cell foam - but I won't argue it one way or another without full knowledge of the whole package for HVAC, venting, siding detailing, etc. I know I can make it work fine here, and this is not a whole lot different climate. 6-7000 degree days, on the water, and humid in summer.
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One problem would be cost.
He's building a 5200 square foot house in Montauk. I don't think cost is an issue:-)
Yup, but he is concerned about the cost upcharge from icy to closed cell.I think the cost is relatively close when viewed as a "per R-value" comparison rather than per inch.
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If not SIPs, I'd go with a continuous layer of Thermax on the inside as described by Piffen. Also, given the choice, I'd probably insulate the exterior of the foundation, rather than the inside. 1/2" plywood on the interior is curious, does he say why he does this?
The walls they prefabbed for the last This Old House were (I think)
2" foam board on outside. Spray foam. Interior plywood then a 2x3 open stud bay in which they ran all utilities and the sheetrock.
I can see alot of advantages of this method one being absolutely no openings in the exterior wall save for the windows and doors.
I did a similar wall recently but as follows from the outside in, 1/2" OSB, 2x6 frame with R-21 FG batts, 2" of T-max, then a 2x4 interior wall (also w/FG). All the wiring and most of the plumbing ran within the inboard 2x4 wall. The only penetrations through the 2x6 wall were vent ducts and an occasional wire for an exterior outlet.
Sounds like if you go Mooney you will increase your wall thickness by an inch. That will affect your window and door jamb thicknesses. Not a big dea if you plan ahead for it.
It looks like you are going to be spending a lot of money on a nice house. I would give Building Science a call and have them review the plans for the best insulation system. They could easily recommend a different system on different exterior walls because of the Home's orientation.
Interesting. I had thought of doing that, but wasn't sure they did that type of consulting work. I will definately give them a call. Thx.
Back in the 60's my shoemaking mentor built his house with 3/8 ply intetior then 1/2 SR. One of his daughter's date was drunk and took a shot at him with a fist. Howard ducked then he drove said boy friend to the ER for a cast on his arm. HMMM
Sounds like over kill but sure makes sense
I think you're going to have to figure out a cost vs. benefit equation for several of the suggestions listed here. Another scheme would be to just use the 2x6 studs with aerogel strips to minimize the thermal bridging. They have self adhesive peel off strips and although they are expensive they go up quick.