[GSBN] [nbne] no Timber frame for Alberta house
Derek Roff
derek at unm.edu
Sun Sep 18 14:54:04 UTC 2011
I agree that a timber frame structure is not the only choice, and not the stiffest, most wind-resisting choice, but I think it is a reasonable alternative, depending on local conditions and resources. If the plan starts with strawbale, choosing to combine bales with a timber frame is probably most common in Vermont and neighboring states, because timber is so much more available. Timber frames are much rarer in the western US, because timber is scarcer. I suspect that timber isn't abundant in Alberta, but if there is a local, affordable source, timber frame could be a good choice. I'm not a fan of notching bales at every post, but the strawbale perimeter can be inside or outside the primary support posts. This simplifies air leakage questions, and adds some new issues, as is true of every building choice. And if we look back in history to a similar climate, all the early Nebraska strawbale buildings had no posts, no supporting structure beyond the bales, and little wood outside of the roof itself.
I had intended to mention in my previous post, that picking strawbale, piers, or any other specific design element, as a way of significantly reducing costs, is likely to bring disappointment. Building a good quality custom home on a specific site doesn't allow for major cost savings at the structural level. Interior elements, fixtures, and appliances are a big part of the total cost. Windows, flooring and roofing choices are largely independent of the envelope choices. Big savings are only available if the owner/builder considers their work time as unpaid labor. In that case, some building methods fit the owner/builder's skill set better, and/or are more amateur-friendly.
I aslo agree with Sarah that the ground will be warmer than the air in Alberta's winter. But that doesn't make the ground near the surface a source of heat. Maybe I don't understand this use of "earth coupling". While Alberta probably has a lot of local variation, I suspect that in many places, the frost line is at 5 to 8 feet in depth. Even going deeper than that, or using a shallow frost-protected foundation design, the earth under the building is still going to be well below the desired indoor air temperatures. Hence, any earth coupling is going to be a heat sink and an energy loss for the house. Are you suggesting that insulation under the floor will not be necessary/prudent in an "earth coupled" design? I'd like to learn more about what the Intertribal Council on Utility Policy and Laura Bartels have done, but I am skeptical that a building over a crawlspace decreases insulation problems in this climate.
I'd like to hear more from Rob Tom, about how he would insulate under the floor and address moisture questions in the stone plinth design that he mentioned. Also, please tell us more about the amount of excavation required, if any, before beginning construction of the plinth.
Derelict
Derek Roff
On Sep 17, 2011, at 12:43 AM, Robert Riversong wrote:
> Thank you Sarah. I was tempted to make some similar comments about wind shear resistance, plaster joints and ground coupling, but - as one on this list who does not use timber frames and straw bale walls - I was reluctant to stir the pot (not like me, is that?).
>
> Timber frames are wonderful for the aesthetic and craft, but they are costly and can be wasteful of forest resources (if they require a secondary frame for thermal cavity or to support wall claddings). Timber frames are not nearly as well braced for lateral shear as even a conventional 2x6 house with plywood sheathing. Straw bale infill is a far better alternative than SIPS, but vulnerable to the air and moisture leakage problems at the many frame interruptions. And putting the whole enchillada up on piers in a cold climate makes little sense (unless, perhaps, there is no water supply or the house is in a flood plain!) since the ground is always warmer than the average winter air temperature.
>
> I think the natural building community relies heavily on timber frames with straw infill for reasons that can be counterproductive to thermal efficiency, durability and affordability. Hybrid frames, as Sarah suggests, can be a good compromise.
>
> - Robert
>
> --- On Fri, 9/16/11, sarahkh at lightlink.com <sarahkh at lightlink.com> wrote:
>
> From: sarahkh at lightlink.com <sarahkh at lightlink.com>
> Subject: [nbne] no Timber frame for Alberta house
> To: Derek.Rof.nbne at lists.riseup.net, "Global Straw Building Network" <GSBN at sustainablesources.com>, "Mark Piepkorn" <duckchow at potkettleblack.com>, GSBN at greenbuilder.com, "Alex Wilson" <alex at atwilson.com>
> Date: Friday, September 16, 2011, 10:26 PM
>
> I want to respond to Alex's assumption that a rugged timber frame is a "must"
> for dealing with the Chinook winds.
> Timber frames are not all that stiff. The bracing of a frame -- a few short
> braces per wall -- is far less extensive than the
> bracing of a stud wall by diagonal board sheathing, let alone plywood. And
> as timbers dry and shrink, some of the braces will
> become less tight than they were at raising day. The old timber framed barn
> I used to live in creaked in the wind. I once had
> a conversation with Bruce King about timber frame and straw bale, and he agreed
> that the plastered bale wall is stiffer than the
> frame, and provides the bracing for the building if it is strong enough.
>
> I would conclude then that if a house is going to be slammed by powerful winds,
> the more uninterrupted expanses of plaster
> on inside and outsides of the walls, the better. As we discussed at our winter
> meeting, timbers break up the plaster walls
> quite a lot, requiring all kinds of fussing around with air fins, caulks, gaskets,
> and the like. These would also be potential air
> leakage points, made more significant by the strong winds pushing and pulling
> air around the house. I'd go with a hybrid
> approach, with roof structure held up by door and window framing and a minimum
> of additional members inside the bale walls
> (a la Clark Sanders, and others), and posts and beams in the middle of the house
> helping to hold up the roof or ceiling.
> Timber ledgers fastened to exterior walls could catch the ends of timber joists,
> if those are part of the design. This approach
> ought to be cheaper as well.
>
> I would also want to see a strong and well-cured plaster on the walls, and supported
> on the foundation. This would be the
> key to the house's wind resistance, in my mind. Supporting it on the foundation
> means the house would be best off with a
> continuous foundation at the base of the walls.
>
> I'm not an engineer, so other strategies might suffice, but I believe this approach
> would be the strongest and most reliable
> over time.
>
> Tying the house to the ground structurally would not only tend to make it stronger,
> but also help make it able to weather
> periods of no heat without freezing. This was a key design criterion of the
> Buffalo House project in South Dakota, organized
> by the Intertribal Council on Utility Policy and Laura Bartels. The HUD houses
> built by the Tribal Housing Authority on the
> Rosebud Lakota reservation were generally built on piers AND badly insulated.
> They cost a fortune to heat in the Great Plains
> winters, and when people were not there paying for heat, the pipes froze.
> So the Buffalo House is a model project to show
> that a HUD-style size and shape can be built with straw bales over a crawlspace,
> with passive solar consideration in the
> window design. Not only is it intended to be heated for much less cost, but
> it is supposed to demonstrate "passive
> survivability" i.e. not freeze when someone isn't home. Even if a homeowner
> intends not to stop paying the heating bills in
> the winter, this model suggests that there is a thermal advantage to putting
> a house on the ground, and it is designed for a
> similar climate to Alberta. (Intertribal COUP has a website for those interested.)
>
>
> Thanks,
> Sarah Highland
>
>
>
> >
> >
> >A majority of the strawbale houses, built to the Passiv Haus standard, that>
> I visited in Europe a couple of years ago, were
> built on piers. They had >massive insulation in the floors as well as the walls,
> usually with strawba>les in the floor. All of
> these houses had free air space between the groun>d and the top of the piers.
> I asked whether this was a contradiction with
> >the goal of maximum energy conservation. The reply was that the moisture r>isk
> created by blocking air flow is a serious
> consideration, and sufficient> insulation takes care of the energy loss problem.
>
> >
> >Although Canada's maritime provinces don't have the extreme weather of Albe>rta,
> I believe that many of the SB houses
> there are built on piers. Kim Th>ompson (sp?) may be able to tell us.
> >
> >Derelict
> >Derek Roff
> >
> >On Sep 15, 2011, at 12:54 PM, ejgeorge at riseup.net wrote:
> >
> >> Hey Mark & Alex,
> >>
> >> That's what we did for our house. Pier foundations with posts sitting on
> >the piers but the floor cantilevers out a bit to
> hold the bale walls (we we>nt with a full wrap instead of infill for less thermal
> bridging and improve>d airtightness). The
> entire floor cavity (including cantilever) is insulate>d with blown cellulose.
> We then stacked stone underneath for a faux stone
> f>oundation to 1) cut wind from blowing underneath and 2) aesthetics.
> >>
> >> You can see some of the details in photos on Aaron's website:
> >> http://www.tugleywood.com/
> >> (under photos, under Dennis-George House)
> >>
> >> It certainly was the quickest and cheapest option, but has some cons too,>
> including all the general cons of uninsulated
> crawlspaces such as critters> and convective heat loss under the floor (though
> I have to say, the dry-la>id stone around the
> perimeter did a surprising job cutting that down).
> >>
> >> Also, I don't think it's as sturdy as a full foundation would be - e.g. i>f
> someone really slams a door or the washing
> machine gets unbalanced on the> spin cycle, you can feel the whole house vibrate
> for a second. That could >be partially due
> to the height of our piers (only 16" or so on one side of >the house but 3 1/2'
> or so on the other as the grade slopes down).
> This mig>ht be more significant when considering your cousin's wind extremes.
> We're >somewhat exposed on a plateau and
> get some good winds, but nothing near the> extent he'll be dealing with!
> >>
> >> Feel free to contact Aaron & I if you have more questions or want more de>tails.
>
> >>
> >>
> >> ej
> >>
> >> ej George, CSBA
> >>
> >>
> >>
> >> Quoting "Mark Piepkorn" <duckchow at potkettleblack.com>:
> >>
> >>> Hi folks,
> >>>
> >>> A question or two from Alex Wilson, who some of you know. If you don't,
> >see
> >>> http://www2.buildinggreen.com/about/people/alexwilson
> >>>
> >>> I attempted to write a brief synopsis here of his contributions to impro>ving
> the built environment starting way back
> before "green" was a word that> went with "building," and failed utterly. Suffice
> it to say that he's more> than earned our most
> thorough and considered responses. Please be sure to >CC him at alex at atwilson.com
>
> >>>
> >>>> My cousin Allyn is considering building a timber-frame/straw-bale house>
> on a piece of land he owns in Alberta,
> Canada. It is land adjoining his si>ster's ranch in the foothills of the Rockies
> of southwestern Alberta. He wa>nts to build it
> really cheaply and was thinking that he might save money by> avoiding a full
> perimeter foundation--and going with piers or
> something li>ke that. But I don't see how he would support the straw-bale walls
> in this >case.
> >>>>
> >>>> Any thoughts on that? Have you ever heard of someone doing that?
> >>>>
> >>>> Any resources I might recommend to him on building a low-cost timber-fr>ame/straw-bale
> home? Or any really neat
> designs you've seen?
> >>>>
> >>>> The Chinook winds there are wicked, so I think a rugged timber frame is>
> an absolute must with straw-bale. Right near
> the ranch, they've recorded a> _full week_ where the steady wind _never dropped
> below 60 mph_ and a full >hour where the
> steady wind never dropped below 100 mph!
> >>>>
> >>>> My cousin Lucy (Allyn's sister, who owns the ranch), with her then-husb>and,
> built a timber-frame with in-fill straw-
> bale walls maybe 25 years ago,> and as far as I know it's working great. The
> bale walls are a huge benefit> in sound
> deadening. With the very strong Chinook winds in the spring, the >constant noise
> of the wind can drive people crazy--literally.
> The suicide r>ate goes up in that region, apparently, when it's really windy
> and people s>peculate that noise is the main
> factor.
> >>>>
> >>>> Thanks for any thoughts and suggestions you can share.
> >>>>
> >>>> Hope you are well.
> >>>>
> >>>> Cheers,
> >>>>
> >>>> -Alex
> >>>>
> >>>> 39 Leonard Road
> >>>> Dummerston, VT 05301
> >>>> /On sabbatical from BuildingGreen, Inc. through November, 2011/
> >>>> 802-257-0019 (H)
> >>>> 802-579-4858 (C)
> >>>> www.atwilson.com <http://www.atwilson.com>
> >>>> Twitter: http://twitter.com/atwilson
> >>>>
> >>>> /"Anyone who believes exponential growth can go on forever in a finite
> >world is either a madman or an economist."
> Kenneth Boulding, circa 1980/
> >>>
> >>>
> >>> Strawbale on piers is doable. It's a reasonable choice for budget-minded>
> owner-builders, especially if they have big
> wood for the floor sills as a >readily available local commodity. The thing
> with that scheme is dealing wi>th the floor
> insulation.
> >>>
> >>> It's easy enough to calc spans using common charts based on estimated we>ight.
> Considering his local soil qualities may
> be important.
> >>>
> >>> I think the best owner-builder designs are the simplest ones. Keep it si>mple
> and well thought through. Don't wanna be
> building some fancy folly for> years to come; get it over with and get on with
> life. He might enjoy looki>ng around
> www.balewatch.com
> >>>
> >>> With your permission I'd like to forward the pertinent parts of your not>e
> to a small email list populated with a raft of
> strawbale hotshots.
> >>>
> >>> I hope the sabbatical is doing wonders.
> >>>
> >>>
> >>> Mark
> >>>
> >>>
> >>
> >>
> >>
> >> - - - - -
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> >
> >Derek Roff
> >derek at unm.edu
> >
> >
> >
> >
> >
> >
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