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lamella roof structure - any cookbooks/resources?

Early in plans to add small addition to the shop. Picture a shed roof off one end. Now instead of a flat angle, change the picture to a 1/2 bowstring arch roof. Peak butts the existing structure, curving down to eave aprox. 20' span. Survyors were here last week, size depends on their final report and drawing of the lot line.

(Ignore the roofing, this is about structure. I have installed rubber roofs in the past including on the back side of this same barn 10 years ago and am happy with that product)

I could design truss with arched top.
But lamella seems to offer possible efficiencies for open ceiling, insulation, and perhaps even ease of construction for one person crew (me).

Anyone built one?
Any quick design resources/cookbooks?

wooden lamella roof - Google Search

smt
 
If you can design it I would say DOIT. I on the other hand am just going with 20" rafters on 12/2 pitch for my small (20 X 24) addition mostly for time consideration.

NO¢
 
Early in plans to add small addition to the shop. Picture a shed roof off one end. Now instead of a flat angle, change the picture to a 1/2 bowstring arch roof. Peak butts the existing structure, curving down to eave aprox. 20' span. Survyors were here last week, size depends on their final report and drawing of the lot line.

(Ignore the roofing, this is about structure. I have installed rubber roofs in the past including on the back side of this same barn 10 years ago and am happy with that product)

I could design truss with arched top.
But lamella seems to offer possible efficiencies for open ceiling, insulation, and perhaps even ease of construction for one person crew (me).

Anyone built one?
Any quick design resources/cookbooks?

wooden lamella roof - Google Search

smt

I like it, but what a pita to build! what kind of fixture would you use to accurately cut all that wood?
 
^^^ Yeah, like he said.
Looks stunning, easy to put up with one guy because the elements are pretty short, but you've got possibly compound miters at each end, with maybe an arch on the top, that is skew, not 'normal' to the side of the beam. Might be easier just to build it 'rectilinear' and shim.
I've always thought that your basic welded-up truss used for concrete-decked (or flat roof) commercial construction would be the way to go. Machine required for placement, but pretty convenient from a layout, HVAC/electrical, and future-use standpoint.

Curved linear trusses would probably be quicker. Laminate the top out of thinner stuff for EZ construction. Good luck with the building inspector.

Chip
 
Looks lovely, for sure. But I see no advantage in terms of strength, material economy, ease of erection, or any other, unless perhaps long rafters are unavailable and you have to do it all with short pieces. Even then, I'd make glulam beams out of them before I considered all that mitering.
 
I can calculate & generate the geometry, but haven't a clue how to approach it for loads and sizing.

"ideally" (for my situation) the lamellas (lamellae?) would consist of (nominal) 8' arc segments, and 4' cross/longways segments. The "ideal practical efficient" structure would not have the 45° crossings of the best load bearing type. Instead, the arcs would be in the direction of normal rafters, and the cross pieces would be long-ways to the outside wall.

on a 56' radius for my site, (20' span, 56' radius arc) the 8' elements could be pattern sawed out of 2 x 12's to yield a 9-1/2" deep curve. matched with 2 x 10 cross pieces, this would yield cells of nominal 2' wide x 4' high. My plan would be to skin the bottom, drop in a 3-1/2" and 5-1/2" batt of rockwool, and skin the top for the rubber membrane.

So in a sense, I am looking to make a lamella framed, stress skinned roof.

But again, no idea how to approach any guesstimates on load bearing capacity to show the county. They are pretty laisse faire for Ag1 structures, but I am sure they would need to see something documented with good references or engineers stamp.

There is one more aspect of this site that makes the lamella structure interesting - the actual site is a triangle. Taking things to the extreme, the lamella iterations make it relatively easy to put a conical roof on a triangular structure, and use the entire area of the remaining lot.

For those who would say triangular spaces are not useful, that is the opposite of my experience with woodworking machinery. Most of my machines need to be "aimed" for a 16' outfeed. But since this is typically a one or two man shop, they can all be "aimed" at the same point while being physically arrayed over a much wider span. My current shop practically has internally arranged triangles of trhough-feed patterns in the way the machines are arrayed.

I don't want to complicate things too much, but it seems that a stress-skinned lamella framed roof could very likely be efficient considering all factors; and to me personally it offers a more interesting or "pleasing" space to work in and exterior presentation.

That calculus may change if the section needs to be deeper than the 10.5" depth imagined, though. (9.5" deep framing elements cut from common 2 x 12's, skinned both sides with 1/2" nominal OSB. (Or inside with 1/2" and top decking 5/8"). I can change (diminish) the radius somewhat to increase the load capacity, but need to keep the arc from getting too high on the adjacent building against which it leans. At some point, the curve will end higher than the back section of the existing building, and more wall structure & weatherization would need to be included above the existing building. OTOH, as the arc height increases over most of the space, i could drop the outer wall to, say, 9' or even 8' if it made the load capacity better.

smt
 
I like it, but what a pita to build! what kind of fixture would you use to accurately cut all that wood?

A significant part of my business over the years has been production of accurate, curved pieces of wood for site installation. That is not a factor. especially for pieces only 8' or so long.

The actual span would not exceed 25', I have made very precise patterns almost that large at times. so making a quick, accurate one to use for aligning the elements as they are erected is practically trivial.

Back to where to begin for loads?

smt
 
Some years ago I built a greenhouse,12x20, using curved arches.
This structure was made entirely of cheap 1x4 material, and was amazingly strong. ( last time I drove by the old place it was still in use 25 years later)
I had bought some drawings from some one in New England, who advertised them as temporary boat building sheds.
The book had lots of info on layout and sizing IIRC.

As an aside, last year when I built my pole shed, I asked at the town building office about self built trusses. They said they would accept them, but I would have to build one and proof it to demonstrate the design.
I'll have a dig through the piles and see if I can find it.

Pete
 
Yeah, I momentarily forgot who I was responding to. :)

One way to address the joinery would be to make your own interlocking criss-cross glue-lam, with alternating continuous-length plys sandwiching slightly shorter spacer segments... and make the whole roof at once. (Or nearly so.)

Maybe do it at ground-level, and hoist/jack into place when complete. And just to further the challenge, get numbers from the building dept. and demonstrate you meet them with the real thing instead of a model. Risky approach, to be sure... Covering it all up with a bottom panel would be a sin, though.

Chip
 
Early in plans to add small addition to the shop. Picture a shed roof off one end. Now instead of a flat angle, change the picture to a 1/2 bowstring arch roof. Peak butts the existing structure, curving down to eave aprox. 20' span. Survyors were here last week, size depends on their final report and drawing of the lot line.

(Ignore the roofing, this is about structure. I have installed rubber roofs in the past including on the back side of this same barn 10 years ago and am happy with that product)

I could design truss with arched top.
But lamella seems to offer possible efficiencies for open ceiling, insulation, and perhaps even ease of construction for one person crew (me).

Anyone built one?
Any quick design resources/cookbooks?

wooden lamella roof - Google Search

smt

Geoffrey de Havilland & his team built many "similar" structures. With wings on them, yet.

There might be more info out there on stress calculations for those that can be adapted than is easily found for static shelters.

It would be interesting to see how the economics compare to Quonset structures, but... I don't see those as practical atop a wall. Floor or buried footers and such are ordinarily the functional substitute for a lower 'tension' member the arch otherwise needs, so one would want rods or cable and turnbuckles - wiping out the gain if at wall-top level, no?

Dutch-labelled "Gambrel" roof might be less-costly, labour-wise, give "almost" as much gain in clear interior space, no?

Those are common enough, even on pre-fab gardening/storage sheds as well as haylofts for rather larger barns.

Until you brought this option to the fore, MY plan was to simply utilize a stock shed, "boot" the base of the walls two feet, frame for better doors. Foam panel board plus "Reflectix" mylar & bubble insulation. Minimalist DIY input that way.

2CW
 
I do not understand the conenction to the existing structure. it looks like a valley to hold water would be formed. never a good idea to rely on the waterproofing instead of gravity to help.
Frank Loyd Wright, Not sure if all his roofs leaked or just the non-standard ones.
Bill D
 
In shape, though not "plan A" structure, it is 1/2 a bowstring. No valleys whatsoever.

Picture a shed roof off one end. Now instead of a flat angle, change the picture to a 1/2 bowstring arch roof. Peak butts the existing structure, curving down to eave aprox. 20' span

Just like a straight shed roof, the existing building (&/or additional structure build onto it) support the peak end.

I'll note once again that among the factors that suggested the lamella construction, is a tapered lot. I may or may not decide (largely based on cost & on surveyor's final drawings of actual dimensions) to build a tapered building. But "if" the roof structure can be built for that span as I have outlined from 2 x 12 dimension lumber, it is practically the simplest method to cover and insulate a tapered building in that size range. All the parts (both parts) are the same, but at one end the last piece is cut shorter in each rank.

smt
 
In shape, though not "plan A" structure, it is 1/2 a bowstring. No valleys whatsoever.



Just like a straight shed roof, the existing building (&/or additional structure build onto it) support the peak end.

smt

IF.. and I know not... that existing structure can stand side loads at right-angles to the long-axis, THEN a half Quonset with corrugated Armco actually COULD work for you.

Not as pretty, no. Ugly, even. Except as to BFBI functionality, of course.

Cheap and fast erection, too.

FWIW-not-much-dept? I'd wonder "somewhat" about the same loads with a HALF lamina, or a HALF Gambrel anyway.

"Back in the day" the "flying" buttress, external, wasn't invented until more than one Cathedral stone or lead roof had toppled its side-walls with deadly effect.

4CW
 
I would suggest asking over at eng-tips.com

IIRC I saw this type contruction in an old book from
the wood products lab in wisc.

Load calcs's ?

I'll put my guess as analyzing the extreme fibers, and then
working that onto a dome calculation.
There still is going be allot of assumptions, and
"Kentucky Windage" to make a safe structure.

To the others wondering "why calculate ?"
Because N.Y. state has a uniform building code, and
snow loading is a large concern.

Stephen, how much snow you get there ?
Nearby Jamestown, NY code is 65 lbs, you may be similar.

I was told by an engineer, that roughly (and it a very rough
estimate) 60 lbs of snow is about 3' deep, and we routinely
get that around here.
 
Doug - Snow load is my biggest concern - we get some real wet ones lately. I have not seen 3' since the year we moved up here (winter of '93 and that was mostly dry snow) but i don't think things will get better with the current climate.

Have to admit, I was considering 50lbs (I think code locally is 40) but willing to go higher. Right now there is not enough understanding on my part to know if the proposed structure would be in the ball park. If it won't support 40, I might as well abandon the idea and go with truss due to expense. If it will, it could be cost effective and probably tweaked (arc radius) and framing details to get more.

But other than the "imagineering" while working 10+ hr days in Maryland, this is only day 2 for starting to consider real parameters. I'm still working on other things, and waiting for the surveryors' report tomorrow. It they say I only have 18 ft, it dramatically improves the load options, though not my space intentions :(

smt
 
I love the visuals, and from what I've read online, it seems inexpensive and relatively easy to do. Stephen, have you ever actually seen one of these, or did you discover it online?

Reminds me of the geodesic domes so popular in the 60's, znd I suppose works on similar principles. But this ain't the 60's anymore, and if you need to get governmental approval I'd imagine you need to find an engineer or professorial type stick their name on your plans. Someone with the right letters after their name.

Thinking maybe you could contact a school of architecture (Cornell? for a referral, or maybe even get someone there interested in participating in the adventure.
 
waiting for the surveryors' report tomorrow. It they say I only have 18 ft, it dramatically improves the load options, though not my space intentions :(

Similar challenge here. Point two-one acre lot, and already has an "annex" built-out that needed a variance, previous owner.

OTOH.. I PREFER to do the ruder sort of my sawdust-making open-air, favourable weather. Which we have a lot of, actually.

Crank-out AWNINGS, of the sort sold for Airstream "land yachts" are - at least HERE - legal even when intruding deeply into the set-back space.

Tilt-up sidewall "door" panels that become a quasi roof, showery rain - or at least sun shades - I have NOT looked into. Those would probably be OK as well with my current neighbors, so long as not left open permanently, anyway.
 
SMT:

Since the original patent for these is German most of the references available are in that language. The only design info I've seen is in Salvadori's book:

Structural Design in Architecture
Mario G. Salvadori; Matthys Levy
ISBN 10: 013853473X / ISBN 13: 9780138534738
(1981, Second Edition)

This type of structure is massively statically indeterminate, but Salvadori simplifies it to make it more tractable. There's an example of engineering a lamella roof on pg 416-420. Math is pretty straightforward (algebra not calculus).

Note that as the arch radius flattens the horizontal thrust goes up very quickly - you may need horizontal ties at the spring line to accommodate these forces.

The snow load is stipulated by the building code. Call the local building official to get that value.

This design would be a great advert for your shop's capabilities.

Regards,

DB
 
To get the maximum strength out of a structure like that you would have to skin it on both top and bottom, thus making the lamellae not visible. Maybe you don't need maximum strength. But if you do, laminated beams would make more sense to me.
 
Richard -

I saw one and took a picture that has been on my desk for years. But can't recall on which travels or where it was seen. I went in expecting trusses, and my jaw dropped. You probably know that round-top ag and light industrial buildings are practically part of the vernacular up here in upstate NY. Mostly bowstring truss, though. Same on the west coast, and bigger!

I did see Tillamook, and it was inspirational, though again not lamella.

Tillamook hangar - Google Search

smt
 








 
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