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Community and Q&A

AFFORDABLE Low Energy

John Brooks | Posted in Energy Efficiency and Durability on

Forget about Spray Foam
Forget about Conditioned Attics
Forget about Vaulted Ceilings

Provide a Simple(and rigid) Air Control Layer
Add Ventilation
Add a Thermal Control Layer
Add Cladding Structure and Roof Structure
Add Replaceable windows and doors and Sacrificial Claddings

Cladding structure can be as simple as furring strips

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Replies

  1. Doug McEvers | | #1

    John, I think I get the main thrust of your post but I would stop short on vaulted ceilings. The right roof truss design, my favorite (vaulted parallel chord truss) does not add any lumber or roof height to a structure but does add a significant amount of volume without an energy compromise. This type truss gives full insulation to the plate line and when used on a gable end allows the use of what I call "high glass". Windows with the tops beyond the typical 7' height to bring winter sun deep into living areas here in MN. I never do an addition these days without a vault of some type, customers want something beyond the standard 8' ceiling height, if built airtight and highly insulated there is no energy penalty. Also forget about the "stratification" argument, this does not occur in an airtight and well insulated building, the natural convective loop will mix the air and temperatures will be nearly even from floor to ceiling.

  2. Lucas Durand - 7A | | #2

    Doug,
    I agree. I am in NW Ontario and my neighbor has 24" deep parallel chord trusses for a vaulted ceiling with R60. Very nice roof.
    John,
    Located in a very cold and mostly dry climate.
    As a simple and rigid air control layer: T&G exterior grade plywood sheathing caulked and taped as interrior cladding.
    Thermal control layer does not consist of foam, is moisture permeable, wood framed to desired thickness without exterior sheathing of any type.
    WRB is applied over thermal control Layer.
    Furring strips over WRB then Siding.
    What do you think?

  3. Riversong | | #3

    Ah, so. But high ceilings, and particularly cathedral ceilings, disturb the flow of chi and either scatter it or capture it. Very bad Feng Shui!

    Stratification problems are more than just warm air.

  4. John Brooks | | #4

    Lucas,
    Where is the thermal "break" in your wall?
    Is plywood your finish material or just racking board/air barrier?
    Do you plan a service core for the wiring ?
    what about fire control layer?

  5. John Brooks | | #5

    I have sadly come to realize that 95% of My clients are not going to buy a Simple Boxy House
    with a Sensible Roof.
    We are Mericans.....Style, Flair and Emotions trump common sense.

    I propose a construction method that might help overcome the "vanity problem".
    I propose to frame the walls with 2x4
    Install Ceiling joists
    Fully Wrap the walls and the top of the ceiling joists with structural sheathing.
    Complete the air control layer with gaskets and or airstop tape.

    Build the roof above the living enclosure as a Hat
    The roof can be almost any stupid shape that "the client" or the community insists on.
    As long as it actually sheds water away from the living enclosure.

    Mechanical enclosures can pop into the Attic as long as they are wrapped inside the Sheathing/Air Control Layer

    Large quantities of cheap insulation can be installed on the Attic Floor Deck
    More can easily be added in the future.

    The wall thermal control layer could either be outsulation or a thermally broken cavity wall.

  6. John Brooks | | #6

    I also intended to say that mini-warehouse enclosures could pop into the attic also...
    As long as they are wrapped inside the Sheathing Air Barrier Layer

  7. User avatar GBA Editor
    Martin Holladay | | #7

    John,
    You are describing the REMOTE system -- otherwise known as modified PERSIST.
    PERSIST walls + unconditioned attic with deep insulation on the attic floor.

  8. Lucas Durand - 7A | | #8

    John,
    I am very interested in the idea of a vapour-open, rigid, warm side air-barrier of the type apparently not uncommon in European design... but which seems about as popular as sunburn on this side of the pond.

    The thermal break would be in the framing. Personaly, I like the "Modified Larsen Truss" a la Riversong. However, I have been thinking of a variation that would accomodate the use of Roxul batt insulation instead of the dense pack cellulose.
    The plywood would not be the finished surface but seems like it might be a good material for a simple, rigid, durable and continuous air-barrier that does double-duty in providing structure. Too much vapour permience possibly is the issue in my clmate I suppose (~10300 HDD).
    A wiring chase could be provided between the plywood and the finished wall surface. I like this idea since it offers protection to the air-barrier from occupant damage.

    Whenever I mention the use of this type of sheathing on the interior side of an exterior wall I get looks like I have horns coming out of my head. Is this really a dead end road do you think?

    ps.
    http://www.canply.org/english/products/easy_tg/easytgfloor.htm
    http://www.roxul.com/home

  9. Riversong | | #9

    Lucas,

    I kind of like the Riversong Truss, too. And sheathing it internally - on the load-bearing inner frame - would overcome the resistance of some code officials and conventional builders (though, as you suggest, convention would see this as back-assward).

    I don't think you'd have too much vapor permeance for your climate, since exterior grade plywood has a perm of about 0.15-0.2/inch, so 5/8" (the thinnest T&G) would have about 0.3 perm. If anything, that perm rate would be too little to allow drying to the interior, but the exterior could be vapor open and most drying in your climate would be in that direction.

    The problem I see with using T&G plywood as the air barrier is that it still requires a slight expansion gap at the butt ends. And, since 5/8" is a bit of overkill for interior shear bracing, I would suggest using 1/2" CDX square edge (perm 0.4) and taping the seams (as the PH folks do).

    A double-framed or trussed wall with an interior wiring chase can get pretty thick, however, and since drywall is the standard for air barrier materials, I believe that the air-tight drywall system is still a pretty good approach to air sealing. Holes are easy to see and patch.

  10. John Brooks | | #10

    Whenever I mention the use of this type of sheathing on the interior side of an exterior wall I get looks like I have horns coming out of my head. Is this really a dead end road do you think?

    Lucas,
    I have considered the process of structural sheathing interior of framing and concluded that it would not be worthwhile without a wire and plumbing service core....adding extra material,labor and wall thickness.
    The construction sequencing would be difficult as well.

  11. John Brooks | | #11

    John,
    You are describing the REMOTE system -- otherwise known as modified PERSIST.
    PERSIST walls + unconditioned attic with deep insulation on the attic floor.

    Martin,
    What I am proposing is Not exactly the same as PERSIST or REMOTE.
    PERSIST has the pressure boundary at the roofline.
    REMOTE has the pressure boundary at the BOTTOM of the ceiling joists.
    I propose a Structural Sheathing Air Control Layer ABOVE the ceiling joists.
    REMOTE does not allow fixtures or wires above the finish ceiling.
    My proposed detail would allow above ceiling wires and ceiling fixtures.

    I think that the platform provided by the attic deck Sheathing would make roof construction much SAFER and faster ...this should help offset the extra labor of installing the attic floor deck.

    I also propose to Avoid/Minimize the use of Vapor Barrier Membranes and Ginourmous Screws

  12. Riversong | | #12

    John,

    Unless I'm not imagining exactly what you are describing, a problem with building the roof "hat" on top of a sheathed box below is that code requires tension connections between ceiling joists (rafter ties) and rafters, absent a structural ridge or trusses.

    Raising the rafters on to a plate atop the ceiling joists, as is sometimes done to increase eave insulation depth, requires metal tension ties between rafters and joists since the side lapping is eliminated.

    My approach to eliminating (or reducing) ceiling penetrations on the top floor is to use only wall sconces or switched receptacles for area lighting, which also allows a reduction in ceiling height to a more intimate 7½ feet. Then I can use the ADA air barrier with confidence. I am typically left with a masonry chimney and plumbing vent penetration to seal (I bring my radon vent up the 5" thermal gap between exterior wall trusses). Metal-flashing and mortar fire stop around the chimney creates an air barrier and I use a roof boot at the ceiling level for the plumbing vents.

  13. John Brooks | | #13

    Robert,
    I'm not sure if you caught my frustration with trying to convince my clients to accept a simple house shape.
    The house I live in is a simple shape....I like simple.....I can not sell simple.
    My house is Not-So-Big.
    I can not sell Not-So-Big.
    The rafter tie concept that you are talking about is almost never used in custom home construction...at least around here(N.Texas)
    Rafters and Ceiling Joists are just as likely not to be parallel.
    Ridge Beams are structural..and believe me we have lots of Ridge Beams.
    We also have a lot of stiff-back intermediate beams that reinforce the Rafters.

    So you see...my world is a little different than yours.
    I am trying to explore construction methods that would not cost much more than Using Spray Foam....yet would perform far better than a typical Spray foam house.

    I also think that Airtight Drywall works for you because your homes are simple and you are hands-on thru the whole process.

    I am looking for a more user friendly method that would not take a multi page set of construction drawings (or on site coaching)to cover all the details.

  14. John Brooks | | #14

    I am also discussing this concept over at JLC
    http://forums.jlconline.com/forums/showthread.php?p=519341#post519341

  15. John Brooks | | #15

    The photograph on Carl's Blog is just one example of why I think we should avoid including the Attic within the Living Enclosure.
    https://www.greenbuildingadvisor.com/blogs/dept/green-building-curmudgeon/when-will-we-reach-beautiful-simplicity-green-building
    When I first opened his blog ..I thought the photo was meant to illustrate what NOT to do....the opposite of simplicity.
    Granted this example is a retrofit...
    Look at all that surface area of $$$ foam...look at that monster of an HVAC system.
    The roof assembly is probably less than R-30 and there are questions about whether it is Code Legal.
    see Martin's blog
    https://www.greenbuildingadvisor.com/blogs/dept/musings/it-s-ok-skimp-insulation-icynene-says

    Lower pitch Roofs and Architecture that takes advantage of the Roof volume are Not-Quite-So-Bad.
    Unfortunately in North Texas most neighborhood restrictions do not allow low pitch roofs and the public (for the most part) does not buy simple (smart) Architecture.

  16. Doug McEvers | | #16

    I walked through a new home under construction in Houston last February, slab on grade, all of the ductwork in the attic, outside of the thermal boundary I presume. The thing that caught my eye was not one rooftop solar installation of any kind. Blazing heat in the summer and hot water heated by natural gas?

  17. John Brooks | | #17

    Michael Chandler,
    Why do you have an R-40 Wall and an R-30 roof?
    https://www.greenbuildingadvisor.com/homes/nc-home-grabs-five-green-ratings

    I am not only challenging Carl Seville and Michael Chandler to RETHINK.....
    I challenge my own work and my mentor (Jim Sargent)
    https://www.greenbuildingadvisor.com/leed-gold-home-dallas-texas
    Even though this home has a low pitch roof...there is still a lot of surface area of $$$ low R-value Foam and rafter assembly....
    This home has a compact HVAC system(Daikin) that could have been brought down below the Attic Deck...yet it looks like a dumb octopus.
    My personal home is similar except I have a big honkin HVAC and a not-so-dumb octopus in my conditioned attic.

  18. John Brooks | | #18

    OOPS
    Michael,
    I see your wall is R-46

  19. Doug McEvers | | #19

    Brother Brooks,

    What is the energy code for your part of TX for walls. ceiling, foundation and windows. I bet we can put together some details that will make your designs stand out from an energy efficiency perspective. If the public demands high roof lines, take advantage with vaulted trusses, you can even use a vaulted truss to get HVAC equipment in the conditioned space.

    The key to cost effective design is to meld simplicity with complexity and keep costs down. If your homes look similar to others in the neighborhood, but have a more simple roof system, a few less corners, a more favorable surface to volume ratio, the savings can go towards a better building envelope and lower energy bills for the owner.

    My costs per square foot are not the lowest around but I feel I offer the best value, my customers seem to agree and they love to boast about the low energy bills. Offer a premium product at a competitive price with careful planning and management of construction costs and you will distinguish yourself. Give your customers a bit more than they expect, this will take you far.

  20. Riversong | | #20

    John,

    I won't speak for Micheal, but there is a myth that it's more important to insulate the ceiling than the walls, based on the myth that heat rises. Of course, it's only hot air (or other fluids) that rises, and not because it's hot but because it has lower density and floats. But in a tight house where there is little infiltration and little air temperature stratification, the delta-T should be nearly the same at walls and ceiling.

    Ceilings, if they're flat, are the most cost-effective and easiest place to install lots of R-value, but all except the simplest 1-storey houses have more exterior wall area than ceiling area - even with cathedral ceilings. So placing additional R-value in the larger surface areas makes sense, as long as the entire assembly performs well.

  21. John Brooks | | #21

    Robert,
    I agree with what you have just said.(as usual)
    I do not question Michael's High-R wall.
    I just think that the reason he is shackled to the the R-30 ceiling is because of the limitations of spray foam and the conditioned attic.

  22. John Brooks | | #22

    Doug M,
    North Texas code min is:
    R30 or R38 ceiling depending on glazing area
    R13 walls
    Zero for slab insulation

    I would like to hear your ideas about trusses and how you air seal, insulate and ventilate your vaulted trusses.
    But the problem with trusses is that The Custom home buyers ...
    Including almost all of my "green clients" want (insist on) Architectural styles that are Not-So-Truss-Friendly

  23. Doug McEvers | | #23

    John,

    I live in the cold, snowy north and I use a warm side (room side) air barrier, in my case vapor barrier 6 mil or greater. My wall dries to the exterior and I use fiberboard sheathing and housewrap along with the much maligned fiberglass batt.

    Roof assembly is as follows from the room side, 5/8" drywall, 6 mil poly or greater, fiberglass blown insulation R-80 minimum. I use air chutes between each rafter, run the wall sheathing right up to the air chute for wind-wash protection, an energy heel of at least 12" and 1/2" cdx plywood roof sheathing. The eaves are vented and so is the ridge, I want airflow in each rafter space.

    In the hot and humid south it seems you are going to be putting your primary air barrier on the warm side as well, the outside of the wall in your case. I had a customer for a product I sell from Dallas and went through his home several years ago. He used 2 x 6 walls, OSB sheathing and a layer of 1" foam over that. Airtight Drywall was his interior air barrier and as I remember the roof was conventional rafters with blown insulation.

    Do you use a radiant barrier, is it a foil faced roof sheathing?

  24. John Brooks | | #24

    Do you use a radiant barrier, is it a foil faced roof sheathing?

    Most of the projects lately have been open cell spray foam directly on the underside of the roof deck.
    Since there is no air space we do not use foil faced sheathing.
    Of course I am looking at avoiding spray foam in the future.

  25. Riversong | | #25

    John Brook: "I am looking at avoiding spray foam in the future."

    I hear that the future is also looking to avoid spray foam and other petrochemical products. ;-)

  26. John Brooks | | #26

    R.Riversong:"Ah, so. But high ceilings, and particularly cathedral ceilings, disturb the flow of chi and either scatter it or capture it. Very bad Feng Shui!
    Stratification problems are more than just warm air."

    Robert,
    Can you explain the other stratification problems?

  27. John Brooks | | #27

    Robert R.,
    As I move away from sprayfoam.......
    I don't think I can count on most of the contractors around here(N.Texas) to understand Air-Tight-Drywall... or to execute it well enough.
    The other problem I see is that there is no way to test for air tightness until after drywall.

    I think you understand my attic floor deck (Air-Tight-Sheathing) concept.
    Assuming Ceiling Joists 16"oc.
    What type/thickness of structural sheathing would you reccomend ?

  28. John Brooks | | #28

    Riversong:"stratification problems are more than just warm air"

    Perhaps you are talking about MOIST Warm air ?
    The Warmest and "Wetest" air concentrated at the Cold thermal bridge Ridge?

  29. Riversong | | #29

    John,

    I thought I was being clear, but perhaps you thought I was being facetious. Feng Shui (literally "wind & water") is the ancient art and science of the relationship between physical space and the flow of chi, or life energy. Wind and water flow according to natural laws, and that flow can be either destructive or life-supporting.

    Applying those same principles of flow to our built environment is the art of Feng Shui. Doors that open straight into a road or the outside curve of a river can let in too much Yang (masculine) energy at too high a speed. A front door that faces a back door will let energy pass through without staying and leave a space lethargic. Leaving a bathroom door open or a toilet lid up will drain energy from a home.

    Too many interior corners will trap energy and a pointy cathedral ceiling can trap and scatter energy. Sharp corners are aggressive. Long hallways are acceleration lanes. Energy, like wind and water, likes to meander.

    Teepees and cathedrals create a connection between heaven and earth, and domes and octagons are heavenly, but complex multi-roofed dwellings are like teeth on a saw and promote bickering.

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