Count me IN for 2010
homedesign
| Posted in Energy Efficiency and Durability on
I just upgraded to the annual membership.
I would love to see more videos like these “free” ones
https://www.greenbuildingadvisor.com/how-install-rigid-foam-insulation-outside-house
Kudos to Dan Morrison, Gary Bergeron and David Joyce…..Excellent videos
Kudos to Martin for ALL the great blogs
My only other suggestion is to add a more user friendly discussion forum.
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Replies
John,
Thanks! -- for your support, your kind words, and your regular contributions to the forums.
I'll ditto the "more user friendly discussion forum". This one is an anachronism. Old-fashioned has its merits, but it ain't necessarily "green" ;-)
Oh yeah...
And editing of posts would be nice...
I mis-typed "annual."
John,
Okay.
I just watched the "How to Install Rigid Foam Insulation Outside a House" video which you linked to and was amazed to see that he used many of the same techniques that I've incorporated into my modified Larsen Truss system: plywood window boxes, air-sealing caulk at bottom and top plates, air-sealing tape, insect flashing.
Because it's unwise to install siding directly over impermeable foam board, he also used a rainscreen system, though his claim of an additional R-2 for an air space that is open to the outdoors is fallacious. He also loses the small additional R-value of the siding because it's outside of the thermal envelope.
Given that much of the outsulation and strapping installation has to be done from staging (whereas the MLT wall can be built with little to no staging), it appears that the labor and time involved with this outsulation system is probably comparable to the labor and time requried for my MLT envelope.
That would eliminate one common argument against the MLT wall. So it comes down to whether the warm frame benefits of outsulation outweigh the hygric advantages and "greenness" of dense-pack cellulose within a thermally-broken frame and air-tight drywall.
One more difference: the MLT system uses a lapped WRB, while the outsulation approach presented in the video relies on offset foam board joints and tape as the long-term weather barrier.
Robert,
All good points....
There is room for improvement ... and outsulation labor is VERY costly
And I think the high cost of MLT is overstated in "reports"
The performance calculations for MLT are usually understated
The video does show the best outsulation install that I have seen.
Robert,
Surprisingly, building scientist John Straube disagrees with your assessment (which makes intuitive sense) that "his claim of an additional R-2 for an air space that is open to the outdoors is fallacious."
When I wrote my September 2006 article on Tyvek Thermawrap, I looked into the question. Straube told me that "the airflow behind normal [rainscreen] cladding systems does not have much of an effect on R-value. There is not enough airflow behind most cladding systems to significantly reduce R-value."
So, R-1 for a normal 3/4-inch air space, or R-2 if there is a low-e surface facing the air space -- according to Straube.
The report I was thinking of was not exactly MLT but a similar "truss"
http://www.buildingscience.com/documents/reports/RR-0903_High-R_Value_Walls.pdf/view?searchterm=high-r
I believe the Riversong MLT would have tested out better on the software.
They label the truss wall as Overly costly...
Outsulation done well seems Extremely labor intensive(costly) as well.
Robert,
It seems to me that with the addition of an interior layer of formaldehyde-free OSB as a taped air barrier your system would be extremely similar to the typical European "breathable to the outside" wood framed walls. They would typically add 2x2 strapping to the interior of the OSB air barrier creating a wiring chase and then install gwb or plaster on top of the strapping, protecting the air barrier from future penetration.
The advantage of this system seems to be the creation of an easily verifiable air barrier during the framing phase, disadvantage is the extra cost of the OSB and strapping.
Martin,
It would depend, of course, on what kind of "rainscreen". Which is why I've been using the term "drainscreen" for spaced cladding that is not open at bottom and top.
But to get an effective R-value advantage to a lowE facing, there has to be a dead air space. Foil will dramatically reduce the radiant heat transfer to or from the cladding, but foil is highly conductive and will create convection currents in the air if it is not prevented from moving.
It is for that reason that a one-sided foil 3/4" air space (E=0.05) will offer R-3.55 downward (floor), but only R-1.67 upward (ceiling) and R-2.8 horizontal (wall).
Perhaps Straube is assuming some but not too much convection and reducing the ASHRAE R-2.8 standard to R-2?
Jesse,
Formaldehyde-free or not, I would never use OSB inside a thermal envelope. There are too many resins and unknown health and environmental impacts. And it's unnecessary, excessive and eliminates breathing to the inside and the ability of the wall system to be a hygric buffer for the interior.
Perhaps the OSB creates an air barrier that can be inspected during framing. But the air-tight drywall system creates an air barrier that can be permanently inspected and easily repaired, even by the homeowner. With polypans around each electrical outlet and foamed wiring holes in plates, there's no reason for a wiring chase.
In fact, one of my main objections to the PH approach is that it "chases" zero air exchange and then makes it up with a sophisticated HRV/heating system. Tight is more than good enough. There's no reason except obsession to go for hermetically-sealed.
Thank you John, but the credit for the video work goes directly to our associate editor, Rob Wotzak. In fact, today I asked him to take credit for them by putting his name on them somewhere. There are a lot more videos like that coming down the pike too. Rob's been pretty busy.
The credit for such great discussions go to people like you, John. In fact, I think you were the first commenter on the site -- I remember being in Vegas last year launching the site at some trade show booth and seeing your name pop up in the forums. We had been trying to seed it with our buddies to make it look active when you popped up commenting and participating like crazy. None of us knew who you were.
It's going to be a good 2010.
When are you going to write one of your houses?
Dan,
I was looking for the "credits" to see who was responsible for the video.
I just assumed it was you. Congrats to Rob Wotzak and Building America.
I have only designed a handful of Almost-Low-Energy Enclosures.
I hesitate to post my projects because I am rethinking and questioning everything that I have learned. Perhaps I will post my house and write about what I would do different next time.
BTW I think you should give that Riversong guy a raise ;-)
Hi guys. The R2 assessment comes from measured field temperature (hence some assumptions) data and is based on a reflective foil facing with about a 3/4" air space. The R-value would be about half this without a radiant foil. The rate of airflow in most ventilated wall systems (also based on measurements by BSC, U of Waterloo, Penn State, BRANZ) is sufficiently slow that one still gets significant R-value benefit.
Finally, the primary benefit of insulated sheathing, aka "outsulation" (which was a trade name for EIFS so I was at first concerned is that it reduces or eliminates the potential for air leakage condensation, while significantly increasing the drying capacity of framing (esp at critical locations such as rim joists) and any sheathing. Insulating between framing increases the risk of moisture damage: thick walls filled with fiberglass only are at greater risk than normal 2x6 walls.
The highly insulated framed wall can reduce its risk, likely to close that of insulated sheathing by using a very permeable and moisture tolerant exterior sheathing (eg DensGlas, treated fiberboard) and well ventilated cladding (furring strips etc). But still a little riskier.
Hi John Straube,
I am thinking that either outsulation or some method of thermally broken framing is the way to go in my Hot/Mixed/Humid Climate (North Texas)
I really think spray foam is NOT the solution.
The construction method in the video that I referenced looks(to me) like it could work in my climate.
I would suggest to replace the 2x6 OVE wall with a 2x4 Not-So-OVE wall and NO cavity insulation.
Ray Moore has done some PERSIST construction in Austin...
This(video) looks better and less expensive than PERSIST
I also wonder if there is some way to take advantage of All 4 foil layers
Some type of perimeter gasket and spacers between the 2 sheathing layers?
A Four-fer
John Straube,
If you're still on-line here, what kind of "ventilated wall systems" were among those tested for interstitial airflow?
Did they all have a full 3/4" airspace? Were they closed at top, or fully vented botton and top? How much were the vent channels restricted by insect screening? Were these tests performed in a lab or in the field with typical wind and solar radiant conditions? What climatic zones were tested or simulated?
John B.
Thanks for the plug. But if they doubled my salary, I'd still be getting nothing.