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Cold climate hat.

Lucas Durand - 7A | Posted in Energy Efficiency and Durability on

I have asked Martin to post a wall/roof detail that is intended to separate the thermal and air control layers of the roof from the weather shedding layers. I see several possible advantages:
1. As the insulation is encapsulated on six sides, I wonder if this will yield better thermal performance by reducing convection?
2. As the roof deck is separated from the thermal control layer, unwanted solar heat gain in summer is reduced.
3. Adaptable. The depth of the drop-ceiling can be varied for more or less insulation.
4. Ease of construction. Framing proceeds almost as normal platform construction but the upper floor walls are framed 2′ or so higher than the desired ceiling height. Trusses are installed and roofing proceeds. Exterior wall trusses, drop ceiling and insulation are then installed under the cover of the roof.

I’m wondering what people’s general impressions are?
Also wondering about the best method for blowing loose-fill cellulose into the drop-ceiling? Installation should be through board sheathing under the ceiling so as not to disrupt the TYPAR membrane under the trusses.
Options I’ve come up with so far:
1. Leaving openings in the board sheathing (barely large enough) for a person to fit their torso through, then closing up the openings as you go.
2. Sheathing the ceiling and blowing cellulose as you go. Finishing by blowing through holes in the sheathing.

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Replies

  1. John Brooks | | #1

    Lucas,
    I picked up the Hat analogy from Peter Pfeiffer
    I think this is a good track
    A house can "wear" a hat (the roof structure & roof cladding)
    and a coat (the cladding structure & cladding)

  2. John Brooks | | #2

    we should be able to shed/change the cladings as they wear out

  3. GBA Editor
    Martin Holladay | | #3

    Lucas Durand:

  4. Lucas Durand - 7A | | #4

    we should be able to shed/change the cladings as they wear out

    Yes, that is another advantage. I like repairability - so rare these days.
    Did Dr. Joe say a roof is just a wall lying on it's side? This makes sense and if true it seems to me that the roof cladding should be more like a sloped rainscreen than an integral part of the thermal/air control layer.

  5. John Brooks | | #5

    Lucas,
    One of my favorite European Videos shows the roof concept you are talking about ..
    I will dig it up

  6. John Brooks | | #6

    Starting around minute 2:05
    https://www.youtube.com/watch?v=wBQHBr7zn0M&feature=related
    looks much like a rain screen "tilted"...eh?

  7. John Brooks | | #7

    Lucas,
    Back to your detail
    I find it very interesting
    thanks for sharing it and sticking your neck out

  8. Lucas Durand | | #8

    No worries John. You like half-baked ideas, eh? ;-)

  9. John Brooks | | #9

    Lucas,
    You realize that you are going to have to split your freeware royalties with Robert

  10. Riversong | | #10

    Of course a hat and coat perform different functions because of their orientation.

    Did Dr. Joe say a roof is just a wall lying on it's side?

    Unfortunately, he did, and this has led to much misunderstanding from my perspective.

    In 1991, Ned Nisson wrote an article for JLC called Hot Debate Over Hot Roofs in which he said:

    Not Just a Slanting Wall

    If walls don’t need ventilation, then why should roofs? To make the point more graphic, draw a sketch of an exterior wall section. Is the wall ventilated? Of course not. Now rotate the drawing 45 degrees and, presto, it’s an insulated cathedral ceiling. Since it’s the same component, why should it now need ventilation simply because it is tilted? I’ve seen lecturers use this technique to convince whole rooms full of builders that cathedral ceilings shouldn’t need ventilation any more than vertical walls.

    While convincing, this demonstration is flawed in that it overlooks several fundamental differences between walls and roofs, such as snow loading, sun exposure and, perhaps most important, air leakage from the occupied space below.

    But I love the breatheability of this system: all rough-sawn sheathings, no plywood except in the gussets (but that could be 1x as well), the continuous WRB on the outside and the continuous VB/air barrier on the inside (not that I like poly VB except in such extreme climates). If the attic were also ventilated, this would be a near-perfect design, as that would limit solar gain and allow drying of all materials in the Hat should there be incidental leakage or condensation.

    My only criticism of this "half-baked" idea is that the inside and outside finishes leave a bit to be desired. Typer-covered boards and poly-covered boards are just not that attractive. Perhaps some siding and drywall would improve the aesthetic. And you've got to close off that bird's nest ledge on the top of the wall. ;-)

  11. Lucas Durand | | #11

    Lucas,
    You realize that you are going to have to split your freeware royalties with Robert

    Wiki-building anyone?

  12. Lucas Durand | | #12

    My only criticism of this "half-baked" idea is that the inside and outside finishes leave a bit to be desired. Typer-covered boards and poly-covered boards are just not that attractive.

    What do you mean Robert? Faded "Tyvek cladding" is back-woods chic where I live ;-)
    I'm not into granite counter-tops but I guess I should spring for some soffit and facia at least.

    What do you think about my approach to blowing cellulose in that space? How do you think you might do loose fill in that space?

  13. Garth Sproule | | #13

    Robert
    You said that you love the "breatheability of this system". It is completely lined with poly on the inside the way I read it. I would vote for ADA instead of poly.

    Lucas
    Nice!! Thinking inside the box again ; -) Your exterior wall would work well with the ThermoMass as well. As to insulating, why couldn't it be blown in through holes in the Tyvek from the attic space?
    BTW, I hope you get a nail gun for Xmas...your gonna need it!

  14. Anonymous | | #14

    Lucas, nice graphic... ideas

    diagonal steel bracing, and then just clad exterior with one layer of wood, like a novelty siding shiplap.

    Then on inside brace the same if needed and just use Typar under T&G or drywall which ever is preferred for finish.

    On the roof, plywood as it is a pretty good use of a tree. Does anyone have the green data on plywood?

  15. Garth Sproule | | #15

    Lucas
    Just thought of another bonus with your idea. It should eliminate the "truss uplift" problem as both top and bottom chords of the truss "see" the same RH. But...this same differential movement due to RH may cause some problems with your walls? Your upper floor window boxes may get jacked up in the winter...

  16. Riversong | | #16

    Faded "Tyvek cladding" is back-woods chic where I live

    Wow! Pretty upscale. It's tarpaper palaces around here.

    You said that you love the "breatheability of this system". It is completely lined with poly on the inside the way I read it. I would vote for ADA instead of poly.

    Actually, I was referring to the natural board sheathing. But the exposed interior poly will quickly become full of picture hanger holes and tears from indoor knife fighting and whatnot. ;-)

    I'm not convinced that poly is necessary in a 10,000 HDD climate if the indoor RH is low in winter. Maybe in John Klingel's 14,000 HDD clime in Fairbanks with low winter RH outdoors.

    Does anyone have the green data on plywood?

    I don't think there's anything "green" about plywood, other than it's more durable than OSB.

    While, theoretically, ½" CDX can substitute for 1" rough-sawn boards and thus save forest materials, I believe that most plywood is still peeled from large-diameter old-growth trees and then processed in huge factories with lots of energy inputs and formaldehyde-based resins and then shipped half way across the continent. Maybe it was a bit greener when they used oxblood as a glue (though I doubt the oxen would have agreed).

  17. Riversong | | #17

    What do you think about my approach to blowing cellulose in that space? How do you think you might do loose fill in that space?

    Options I've come up with so far:
    1. Leaving openings in the board sheathing (barely large enough) for a person to fit their torso through, then closing up the openings as you go.
    2. Sheathing the ceiling and blowing cellulose as you go. Finishing by blowing through holes in the sheathing.

    I don't think I'd want to crawl around in that confined space while making a cellulose blizzard and pumping it in from below as you sheathed would make a horrible mess on the floor below.

    I think the only reasonable option is to blow it through the Typar and then seal the seams or holes. But I'm not convinced that the Typar will offer any advantage there and may create a liability. Cellulose is famous for preventing internal convection (just a few inches over fiberglass attic batts will stop most air flow). And the Typar would contain a puddle if the roof leaked or condensed. I'd rather see sloped Typar under the roof decking as a secondary weather barrier and drainage plane and let the attic ventilation air keep the cellulose dry.

    1. As the insulation is encapsulated on six sides, I wonder if this will yield better thermal performance by reducing convection?

    I doubt it. See above.

    2. As the roof deck is separated from the thermal control layer, unwanted solar heat gain in summer is reduced.

    The best way to reduce summer solar gain is with a reflective roofing and attic ventilation. Additional insulation will only slow the rate of heat transfer, which is still directly proportional to the delta-T between attic and ceiling.

    3. Adaptable. The depth of the drop-ceiling can be varied for more or less insulation.

    Yes, this eliminates the need for high-heeled trusses, but it may make the studs so long that 2x4s will not be allowed.

    4. Ease of construction. Framing proceeds almost as normal platform construction but the upper floor walls are framed 2' or so higher than the desired ceiling height. Trusses are installed and roofing proceeds. Exterior wall trusses, drop ceiling and insulation are then installed under the cover of the roof.

    I agree that the sequence seems straightforward.

  18. Lucas Durand | | #18

    Thanks for the comments everyone.
    I should have indicated on the drawing that claddings (interior and exterior) have been omited in the drawing.
    Though faded "Tyvek cladding" is hip with some people in my area, I think I will go the distance and install facia and soffit (to close off the birds nest ledge), possibly fiber cement siding (no rainscreen) and... haven't decided what over the exposed foundation.
    On the interior side, I'm not excited about the extra man-hours and materials involved with furring-out the wall with 2x3s (for wiring and protecting my precious air barrier) but I haven't yet ruled it out either. ADA is all but out with me since drywall will be a contract job and all contractors I've spoken with think ADA stands for "American Dental Association". Drywall against the poly surface is still on the table but doesn't excite me either (my air barrier!)...

  19. Lucas Durand | | #19

    I think the only reasonable option is to blow it through the Typar and then seal the seams or holes.

    I guess I'll have to rethink this.
    My first concern was that there wouldn't be much to walk on and work off of over the Typar. I could always put some scaffold planks between the truss members though.
    My second concern was that I would drop something heavy (like my body) through the Typar. I better just be careful.
    If I were to blow cellulose down through the Typar, I wonder if it would be possible to reach dense pack densities? What if I used two layers of Typar? I imagine this would leave the Typar all puffed up like a marshmallow but would it hold? In this case I'm using the Typar more like a permeable membrane to restrain the insulation rather than a simple WRB.

  20. Lucas Durand | | #20

    I'm not convinced that poly is necessary in a 10,000 HDD climate if the indoor RH is low in winter. Maybe in John Klingel's 14,000 HDD clime in Fairbanks with low winter RH outdoors.

    I think you are right Robert. However, there is no convincing people of that here. One would have to illegaly build a structure without "vapour barrier" then after 20 years invite some inspectors to disect the building. Even then they'd probably shrug, tell me I was lucky then fine me and make me put up a VB.
    I should take another look at that product "Membrane".

  21. Lucas Durand | | #21

    But...this same differential movement due to RH may cause some problems with your walls? Your upper floor window boxes may get jacked up in the winter...

    I didn't think of this... Dimensional lumber mostly swells across the grain. Could this realy be an issue?

  22. Riversong | | #22

    One would have to illegaly build a structure

    I think that living as an outlaw is the only reasonable and responsible way to live today.

    "The people cannot delegate to government the power to do anything which would be unlawful for them to do themselves." ... whenever the Legislators endeavor to take away, and destroy the Property of the People, or to reduce them to Slavery under Arbitrary Power, they put themselves into a state of War with the People, who are thereupon absolved from any farther Obedience, and are left to the common Refuge, which God hath provided for all Men, against Force and Violence.

    Whensoever therefore the Legislative shall transgress this fundamental Rule of Society, and either by Ambition, Fear, Folly or Corruption, endeavor to grasp themselves, or put into the hands of any other an Absolute Power over the Lives, Liberties, and Estates of the People; By this breach of Trust they forfeit the Power the People had put into their hands, for quite contrary ends, and it devolves to the People, who have a Right to resume their original Liberty."

    - John Locke (1632-1704) English philosopher and political theorist. Considered the ideological progenitor of the American Revolution and who, by far, was the non-biblical writer most often quoted by the Founding Fathers of the USA. -- Source: Second Treatise on Civil Government

  23. GBA Editor
    Martin Holladay | | #23

    From Lucas Durand:
    This sketch is the rest of the envelope that goes under my earlier "hat" sketch. Commentary is welcome.

  24. John Brooks | | #24

    My gut reaction is that it is looking less affordable and more labor intensive.
    I wonder how much rough sawn 1x6 costs per sf? compared to plywood?

  25. GBA Editor
    Martin Holladay | | #25

    John,
    Here in Vermont, every time I've priced rough-sawn boards, they've been cheaper than plywood. However, they are more labor-intensive to install.

  26. Lucas Durand | | #26

    it is looking less affordable and more labor intensive

    Board sheathing is more labour intensive than plywood... but there is no rainscreen to worry about... The truss wall uses less lumber than a traditional double wall, but may take a little longer to build... then again maybe not...
    Framing the service cavities does not excite me...

    I wonder how much rough sawn 1x6 costs per sf? compared to plywood?

    This might be a regional thing, but rough-sawn is quite cheap in NW Ontario. Cheaper than KD lumber. Many people in my area have their own backyard mills.
    I will determine the cost difference between RS and plywood.

  27. John Brooks | | #27

    The roughly less than plywood answer is good enough.
    I wonder how you are going to detail the poly at the partiion walls?
    In Plan and Section.
    Are you building this like a big open barn and then building the partitions after the poly?

  28. Lucas Durand - 7A | | #28

    Are you building this like a big open barn and then building the partitions after the poly?

    That is the plan. The trusses only have to span 32'. Poly will be installed on the walls and ceiling before framing the partion walls. A strip of poly will have to be installed over the top plate of the lower wall before the joists go in. That strip will have to be wide enough that it can be wrapped up the exterior face of the rim joist and under the bottom plate of the upper wall.

  29. Lucas Durand - 7A | | #29

    John, what do you think of that service cavity? I'm not excited about it but it seems to be the best of the available options...
    Do you think there is potential to do some architecturaly interesting things with this service cavity? I was thinking that the cavity could be framed to look like columns or inset shelving or other interesting features...

  30. Riversong | | #30

    I disagree that rough sawn sheathing is necessarily more labor intensive than plywood. Moving boards if far easier than moving plywood, especially up to a roof, they don't become a sail when the wind catches them, they are much easier to cut and can be cut in place, they are easier to nail if nailing by hand (which probably no one does anymore), they offer better traction and can be installed with occasional skips on a roof to create a ladder (and then filled in on the way down). Diagonal boards require a bit more careful measuring and cutting, but a jig can be set up that makes this easy.

    As for your envelope system, it is quite a bit resource-intensive and requires the equivalent of three frame walls. And you'll have to think through the assembly sequence - braced walls are typically framed on the deck with exterior sheathing to square and brace, and then raised in place with "hinge" nails to secure it to the deck. How do you plan to frame, raise and interiorly sheath the load-bearing walls?

  31. Riversong | | #31

    And then there is the issue which Roger Woodbury raises on his "Which is the Right Direction?" thread about the perception of loss of usable square footage with very thick walls.

    I argued that this is a misperception, but unfortunately it's the way most people think and our housing market and building industry encourages.

  32. Lucas Durand | | #32

    How do you plan to frame, raise and interiorly sheath the load-bearing walls?

    I plan to frame the stud walls upside-down so to speak - with the top plate towards the edge of the floor deck. I'll sheath and square the walls on the deck - probably in 16' sections - then tip the wall upright and "walk" it into position where it can be plumbed and braced.
    Pain-in-the-ass... probably. Maybe not-so-bad once you get a system going...

  33. Lucas Durand | | #33

    On the subject of board sheathing, I actualy find it easier to square the wall using the first board than fiddle with plywood.
    I agree with you Robert that plywood is more awkward to work with.

  34. Garth Sproule 7B | | #34

    Lookin good! How do you address shear bracing for walls and roof? Does horizontal board sheathing meet approval??

  35. Lucas Durand | | #35

    And then there is the issue which Roger Woodbury raises on his "Which is the Right Direction?" thread about the perception of loss of usable square footage with very thick walls.

    As drawn these are thick walls to be sure... From exterior sheathing to interior drywall is 15.5"... Still not as thick as straw-bale.
    Personally, I am not too concerned about the perception of loss of square footage. I will build one house in my life and it will be to my specs and it will never be for sale.
    I feel that I am getting close to an ideal set of specs in this sketch... I just wish I could find a somewhat better solution than the service cavity... but without penetrating to the poly ACL.

  36. John Brooks | | #36

    Lucas,
    My only thought about the service core is that maybe you could have a wainscot.
    I was able to avoid almost all light switches in my exterior walls.
    I only had a few outlets in the exterior walls.
    I wonder if you could also use a few "floor outlets"

    You have probably read Dan Kolbert's JCL article ... but just in case
    careful how you detail inswing doors in exterior walls.

  37. Lucas Durand | | #37

    Thank you for your comments John.
    A few "toe-stubbers" are preferable to all that extra material.

  38. Lucas Durand | | #38

    Thanks Garth.
    To answer your question, the structural sheathing (which is to the interior) will have to be on the diagonal for shear bracing.
    The roof will be a hip roof. Because of the truss layout for a hip roof, lateral bracing is not really an issue. The larger full-span trusses are laterally braced by perpendicular triangular trusses at each end. For this reason and the better overhang all around, I've gone away from the simple gable roof I started with.
    I've been thinking lately that I might save some material by sheathing the exterior of the wall and the roof by putting the boards on the diagonal and then nailing them on 8" centres. Better yet, space the boards 1.5" apart using some scrap 2x2. If the boards are installed on the diagonal, then there should still be plenty of material to nail/screw into for siding and roofing...

  39. Riversong | | #39

    Lucas,

    Speaking of walking sheathed walls around the deck and not wanting to injure your ACL...

    The only significant injury I've sustained in 30 years of building was when I (and several others) carried a sheathed 8' tall wall from one side of the deck to the other. It was awkward and I ended up tearing (not the ACL - anterior cruciate ligament, that is) but the cartilage in my right knee.

    I needed surgery and, having no health or disability insurance (it was a community project and I made sure that all the volunteers on the job were covered by worker's comp), I had to beg for free health care. I had 30% of the cartilage removed from my knee and was told that, once gone, it would never grow back.

    Then I came across an article about how they were regenerating cartilage in the knees of thoroughbred race horses with glucosamine and chondroitin and got some at my local health food store. No sooner was I off crutches and a cane then I put on a mountaineering backpack and climbed Mt Katahdin - just to prove I could.

    So carrying walls is not something I would choose to do again (perhaps you can raise it and then board it?) and I don't like Dr. Joe's ACL - nothing wrong with "air barrrier", which is far more a barrier than what passes for vapor barriers (aka retarders) today.

  40. Riversong | | #40

    But these are best the best cold climate hats: http://images.sabob.com/products/images/1/Columbia_Siwwy_Wabbit_Hat.jpeg

  41. Lucas Durand - 7A | | #41

    Robert, that first line deserves a drumroll ;-)
    You're right though. I am at an age where inatention to posture and seemingly minor misteps result in not-so-minor after-effects.

  42. Lucas Durand - 7A | | #42

    I also have a hat just like that.

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