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Mike's passive solar greenhouse design/build  RSS feed

 
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Ok, another design question.  My North wall/roof construction will likely consist of the curved trusses, then a layer of pine boards, then a piece of black visqueen plastic, then 4" of strofoam (1" sheets to conform to the curve), then horizontal purlins, then metal roofing.

I was talking to a building guy and he reminded me that styrofoam is not that great on the environment.  I'm not sure how bad but he suggested rock wool insulation panels instead.  All my searches for rock wool sheets find something marketed as more of a sound proofing material.  Rock wool bats are available but I'm hoping to use a sheet product to allow for the somewhat simple design laid out above.  I'm not sure if I'd need some sort of waterproof membrane (housewrap) outside the rock wool to protect it?  

I could make batts work if I put the pine on the inside of the trusses, visqueen between the pine and the trusses, then the batts between the trusses, then purlins outside the trusses, then the roofing.  I'd have more thermal bridging and installing the stuff would all be overhead from inside, vs just laying the materials on from the outside.

Anyone with experience with rock wool panels or insulation who can comment?  Thanks!
 
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Sorry for the late reply.  I found another modeling package called RC_BuildingSimulator which I am trying to set up to model the passive solar DWG greenhouse mentioned before.  I have it working, but I am not sure that I have set it up correctly.  Is there anyone with thermodynamics background that is willing to help set up an initial model?  As a note, one of the researchers will be sending me some performance data to validate the model with.  With a little work I am hoping that we can validate the model and then optimize various parameters against site specific data.
 
Mike Jay
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Ebo and Gordon and anyone else who's interested in the data collection and analysis part of this project.  I started a new thread to talk about those sorts of things over here.  Thanks!
 
Mike Jay
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Ok team, we've entered the construction phase!  I laid out the location of the greenhouse and started digging.  While I realized I was on a bit of a slope, it ended up being more of a drop than I realized.  

My original plan was to dig down enough on the low side to get the footing just hidden underground.  Then on the uphill side I'd have about one cement block buried.  Now that I got the water level set up I see that I'd have at least 2 blocks underground and I'd be digging about a 3' deep trench.

So my new plan (tell me if I'm crazy) is to do a step footing.  I'll have it rise up 8" (or 16" if it works out better) to avoid digging too deep.  I believe I should continue the lower elevation under the step for maybe 2' so that the footing is twice as tall as it steps up.  I'll locate the step the correct distance from the corner so a whole number of blocks will fit on the lower level.  When I do that, will the cement in the upper part of the form push down and out the lower level or is it stiff enough to not pour out the bottom?

First pic is of the removed topsoil.  Second is where I dug down to the same level as the low end of the building in strategic spots for the level.  I shouldn't have dug that deepest hole but I hadn't thought of the step option yet.  So I'll fill it back in and tamp it as I go.

Plan is then to form up the footings with wooden stakes and 2x8s to make a 12" wide by 8" high footing.  I'll also put two 1/2" rebar in the footing with extra rebar by the steps.

I've never done footings or concrete work so even if I sound like I know what I'm doing, I don't
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Perimeter dug
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Level spots excavated
 
Mike Jay
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More work has happened.  I dug out for the footings with two 8" steps.  I formed it up per instructions from a few knowledgeable friends.  Luckily one of them had a builder's level which is a tripod mounted level with a scope on it.  That was brilliant for setting the tops of the forms.  

Measuring for the location of the steps in the footing was a bit tricky.  I had to remember to account for one missing grout line and the overlap of the upper block past the step.  I think I did it correctly.  I bent the 1/2" rebar by eye using a long piece of steel conduit.

Saturday was the big pour.  3.5 cubic yards of concrete and 3 friends (two were experienced, thank God).  It was stressful but we got it done.  Stripped off the forms yesterday.  Tomorrow the cement blocks arrive and I get to learn how to lay block.  Luckily a gentleman in our homesteading club is a retired mason and will show me how to do it  Or maybe he'll show the missus and I can be the mason tender.

I also changed the floor plan to be a rectangle (no silly corner angle).  Driving around it will be harder but I can handle it...
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We have a footing!
 
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Yay Mike!! That's awesome!! Setting block isn't hard, just heavy. Keep it straight (make sure you have good tight strings to do so) and that's really most of it.
Keep it up! You rock!!
Keep showing us pictures!
Pearl
 
Mike Jay
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Thanks Pearl!  I'm sure it's something I can handle and they'll be structurally sound.  I'm just hoping it also looks halfway decent as well.  
 
Ebo David
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@Mike, you might want to take a look at BlueMax and similar elastomerics <https://www.youtube.com/watch?v=i7F3C4MsQwE>.  You can actually use it to both glue the joints together before filling with cement, and also keep the moisture on the respective sides of the walls.  I would not leave it with just the elastomeric, BUT it would be a nice way to lay them out.

Best of success!!!
 
Mike Jay
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Thanks Ebo, I've seen another product (Surface Bonding Cement) to cover the faces of the blocks to skip the mortaring step.  I worry about a couple things with those systems which is why I'll go with the proven mortar method (and learn a good skill).

  • Blocks aren't perfect and have little bumps that don't let them sit perfectly flat.  I'm guessing that leads to little shims or knocking off all the bits that interfere.
  • My building is 20' by 40' which is a nice even number of blocks (with the 3/8" mortar joint).
  • The steps in the footing are 8" to account for a 7.625" tall block and a 3/8" mortar joint.

  • While they very well may work, I think I'll stick with the tried-and-true.
     
    Ebo David
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    Understand, and agree.  Personally I will likely use mortar of the joints, finish flush and use an elastomeric on the surfaces.

    Forgot to add, pour a solid cell every corner and at least every 4', plus continuous bond beams on the shed.  On the greenhouse, use SIPs with engineered trusses.
     
    Mike Jay
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    Yup, each rebar in the photo is 4' apart and that cell will be filled.  I'll also do the corners and maybe throw some spare rebar in them if I have it laying around.
     
    Ebo David
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    Did you decide not to place any insulation underground, or will you install that later?
     
    Mike Jay
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    We'll install that later.  I didn't want to mess with forming up around the insulation.  I found a cool fiberglass insulation panel but it only works for vertical foundation insulation. It's called Warm-N-Dri.  Now I'm down to trying to source Rockwool sheets (not batts) or extruded polystyrene for the footing insulation.
     
    Mike Jay
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    I found a localish place that sells rockwool board (not bats) at a good price with reasonably delivery.  They recommended against using it in a skirt arrangement though.  So I guess I'll use extruded polystyrene for below grade.  

    Cement blocks arrived today.  13,000 lbs worth.  Glad I had them delivered
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    Mike Jay
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    A retired mason friend of mine came by to teach me how to lay block.  I'm glad it's just for a greenhouse.  We did 26 block with one bag of mortar.  Then it got too hot so I'm waiting till late afternoon to go at it again.  
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    Ebo David
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    Glad you have some help.  It is amazing what you can get done with just one extra pair of hands.  THen when you add another mind and a decade+ experience life gets good...
     
    Mike Jay
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    Man, this heat has been a real drag.  The week prior to the 4th of July was spent laying block.  We worked from 5-9 AM and 6-9 PM to avoid the worst of it.  But it's done and looks halfway decent.  I was the "mason" and the missus was the helper.  It would've really sucked to do by myself.  The two door spots are raised up a few inches from grade.  The downhill one is the summer entrance and will be wheelbarrowable.  The uphill one was in an area of more slope so there will be a step down when you enter.  That will be the year-round entrance with an exterior door that opens into a small vestibule.

    This week I got a bunch of cement bags and filled the cores where the rebar came up.  I also filled the four corner cores.  We filled in the cores below each truss position with rubble and set the post bases in about 8" of cement.

    I'm pleasantly surprised with the amount of mass that the masonry provides.  The footing is about 3.5 cubic yards which Dr. Google says would weigh about 13,000 lbs.  The blocks weighed about 9,400 lbs and the core filling cement was another 1,500 for a total of 24,000 lbs.  Awesome!  I'm really glad I had the blocks and ready mix delivered

    Starting soon I'll be assembling a pair of test trusses (screws but no glue) to see how they fit, how sturdy they feel and get the angle cuts for the ends figured out.  Then I'll disassemble them and use each piece as templates for the remaining trusses.

    Now for the next construction question...  How should I protect the trusses and ridge board from the elements (humidity and sun through glazing)?  

    My initial idea was Thompson's water seal to soak into the wood and then apply a clear varnish over so I can see the wood grain.  But I called Thompson's and varnish won't stick to it since it's parafin based.  They suggested only paint will stick to it.  It's weird that one will stick and the other won't.  I'd love something natural but I want this to last for at least 40 years with as little maintenance work as possible (since I'm lazy).  And I don't want to be brushing on nasty stuff over my perennial plants.  On the North trusses I'm fine with white paint but I'd love to see the wood grain on the South wall.  At this point I'm thinking I'll give up and use Thompson's with a white paint on everything.  I'm open to ideas!
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    Masonry work is done!!!
     
    Pearl Sutton
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    Awesome work Mike!! YAY!!  Told you block ain't hard to do, just heavy. Very heavy.
    That looks excellent!

    I have lost track of what you are making your trusses out of, can you remind us? Wood, but what type, what wood, what format (solid board, plywood, etc) I'm wondering it you can seal your top edges different than your visible areas...
     
    Mike Jay
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    Aww shucks, thanks Pearl!

    The trusses are a combination of chunks of new 2x6 from the big box (likely pine/spruce/fir) and long strips of LVL beam which is also a pine/spruce/fir in glued together plies.  Just like plywood except all the plies go in the same direction for strength.  The assembly will be glued and screwed together.  Hopefully my template trusses will be done today or tomorrow so I can show it off.

    I could seal the top edge with something different if needed.  I was planning on putting some tape on the top edge that is against the poly glazing for additional protection.  I'm currently thinking of using foil duct tape.  Unless the little corners/crinkles it generates when bending around the curve would cause sharp spots to tear the poly.  
     
    Pearl Sutton
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    Do you mean the foil tape that is like tinfoil that you peel off the paper backing? That's not too sharp, if you are using a decent poly, are you using film or panels? Film will have problems with a LOT of things, and tape wouldn't help it much. Panels won't be cut by tape, but probably don't need it either.

    A thought, and it may be a bad one, if I were doing it, I think I'd seal the top edge of the trusses with something like wet/dry roofing tar, to be sure the wood stayed dry, and it's not sharp. There are types that stay soft set (one of those I'd put a strip of poly on to keep it from being sticky) and some that dry harder (a bit of fabric on them applied when wet would keep them from being sharp.)  I have no idea if you would consider that appropriate at all, but it is something that would definitely permanently waterproof that top edge, and be controllable, so you could make the visible edges pretty.
     
    Mike Jay
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    Yes, I was talking about the beefy tin foil tape that is what you're supposed to use on ducts (vs the "duct tape" they sell in large quantities at Home Depot which should not be used on ducts).

    I am planning on the 6mil greenhouse poly film for the glazing.  If I was using double wall poly panels I wouldn't be worried at all.  My main concern is condensation between the poly and the wood leading to rot on the wood.  So your idea of a roofing tar (or equivalent) is a good one.  I'll have to think of some other, possibly more natural, options along those lines.  Foil tape is expensive so this would be neat.  Thanks!!!
     
    Pearl Sutton
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    Yeah, I know it's not natural at all. I was trying to think of something that can trowel on to the top edges only that is a serious seal. My other thoughts that fit that category were just as unnatural: liquid flashing, silicone, etc. Wonder if you can put something into plaster that makes it really waterproof? Egg whites maybe? Bet someone has done that! Worth looking it up...

    Heh, now my head has off gone into foods that are waterproof, toffee! Peanut brittle with no peanuts!  :D "What did you glaze your trusses with?" "Maple syrup, makes it smell nice in here too!" I'm sitting here giggling....
     
    Ebo David
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    I would suggest looking at the plans they publish for the Deep Winter Greenhouse at U. Minnesota's Extension https://extension.umn.edu/growing-systems/deep-winter-greenhouses.  The plans have details near the end how they handle the foundation/framing interface and other important features.  I would give you the link, but last I checked you have to register to get the plans from them, but they are free and the info is really good.

    I'll write more later -- just found some more termite damage in the house renovation...
     
    Ebo David
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    Oh, almost forgot...  If you really want to boost the mass and also deal with several types of issues you might think of filling the open cells with dirt or something (just as a thermal mass), and then pour a short bond beam around the entire perimeter http://imiweb.org/02-410-0142-u-block-cmu-bond-beams/.  It will strengthen the structure and give you more thermal mass cheaply.    Just a thought...
     
    Mike Jay
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    Thanks Ebo, I think I have that publication (Cold Climate Greenhouse Resource - 8.6 Mb).  I just scanned through it and the details were not to specific.  I was looking in the chapters just before the long series of actual examples.  Maybe you have a different publication?

    I talked to the paint guy at Menards this afternoon.  He suggested the best coating options would be a spar marine varnish for anywhere I want the best UV protection and the wood to show through, and an acrylic opaque white deck stain for anywhere I want a reflective surface on the wood.  He said Cabot was the brand to go with (of their options).  He didn't think either would flake as they age.  I'll keep researching but that's where my head is at the moment.

    Yes, a bond beam would have really added some strength but it's too late for that.  I think the rebar from the footing up through the wall should be enough.  I will try to fill them with something.  Hopefully I get a reason to dig up some sand and dump it in the North ones.  The South ones may get filled with soil so I can put a head of lettuce in each one :)
     
    Ebo David
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    that is a nice resource, but not what I was referring to.  I dug around and found the construction documents request page:

     https://umn.qualtrics.com/jfe/form/SV_5574TT1OwksqS57

    If you wanted to still install a bond been, I do not think it is to late.  You could probably form one up for say 4"around the top.

    Oh, one thing -- if you fill the cells with dirt, have something separate the dirt from any wood just in case termites or something gets in them.  You should be able to easily cap the dirt filled cells with a little concrete to make sure.

    BTW, this all looks great, and I wish you the best of success!
     
    Mike Jay
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    Thanks Ebo, I just downloaded that and scanned through it.  Some details are unavoidably different due to the building shape but some were awesome.  Especially the specification for "elastomeric paint" on all the wood.  I looked that stuff up and it looks pretty awesome.  So we might have a new candidate for the wood coating.  And the details for around the sill were very helpful.  Thanks!

    Since I have the post bases embedded in the stem wall already, I can't add a bond beam on top  

    Anywhere I put dirt in the cores I'm sure it wouldn't be in contact with the wood.  That would probably be just along the South wall.  E/W/N walls would ideally be sand (given local resources), possibly capped with cement as you suggest.  

    Termites?  What are they?

    Edit, apparently they are little bugs that we don't have up here.  
     
    Mike Jay
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    Ok, I assembled the first two trusses with screws (no glue yet) to see how they look and feel and how they would join at the peak of the roof.  I learned a lot and I'm not quite sure how I'll do it fast enough with wet glue.

    I used 10" 2x6 blocks for the normal spacers and then 16" ones at the bottom and 24" ones at the top (due to more material that would be cut off for the ridge board).  One issue is that the LVL strips bend around the blocks to make the curve.  The blocks aren't curved.  So there are small gaps where they don't meet up flush.  I'm not going to make curved 2x6 blocks cuz that would be a real pain.

    Does anyone have any idea if construction adhesive would be a good choice for the glue?  I was planning on standard wood glue but construction adhesive might fill those gaps a bit better.  But does it hold up to long term loads?

    For this mock-up I just used two 3.5" screws per side per block.  The finished trusses were quite beefy to my slight surprise and pleasure.  I laid the pair on the foundation to see how they overlap at the top.  They pretty much look like what I expected.  I'll cut the tops and bottoms tomorrow so if anyone has feedback on the end details, please let me know asap.

    First picture is of the two trusses laying on the end of the stem wall.  Basically just shows how they look once assembled.

    Second picture is a closeup of a block.  You might be able to see the gaps where the curvy wood meets the non-curvy blocks.

    Third picture is of the overlap at the peak.

    Fourth picture is of the overlap with a 2x8 scrap for reference.  I think I could use a 2x10, 2x6 or whatever for the ridge.  The red and blue lines are my proposed end cuts.  Is there a better way?
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    Looks really great!  How are you forming your trusses?  Are you using some sort of template/form to get the bend correct?
     
    Ebo David
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    Mike.   Regarding the cuts for the ridge beam, are you going to have the truss overlap at the meet or but-joint so they are in the same plane?

    If they overlap at the top, then have the blue line make a left angle under the ridge beam like the red line does.  That way you have wood supporting under both sides.

    If you intend them to meet inline, I would split the difference of the angle cut so that they meet in the middle of the beam, and also cut some plywood gusset plates -- so that you make sure the joints go *nowhere*.

    Also one way to rough out a curve is to flip over a belt sander and use the flat to grind quick curves (both concave and convex).  It does not have to be perfect.  In fact I am not sure you *need it, but I would ask someone that has more experience with building trusses.
     
    Mike Jay
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    Hi Phil, I made a template in the driveway and then moved it to the wall of my wood shop (so I could work standing up).  I'll take a pic next time I'm out there.

    Hi Ebo, the trusses will meet up in the same plane.  I was originally thinking of doing what I think you're saying (per the picture below).  But then the left truss won't have anything to bear against for the bottom inch which made me worry a bit.  I could do plywood gussets but they'd interfere with the moveable insulation that I'll use later on.  I'm planning on just toenail screwing thru the ridge board into the trusses in a few spots to hold them securely.

    Good point on the belt sander, that would be pretty easy.  I even have a stationary mount belt sander which would make it even easier.....
    DSC04507s2.jpg
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    Mike Jay
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    Phil Gardener wrote:How are you forming your trusses?  Are you using some sort of template/form to get the bend correct?



    Here's the pics of the template.  Now that I've made a few, having it flat on sawhorses would be nice.  Then the pieces would be more likely to stay flat to one another.  Oh well, this takes up less space.
    DSC04508s.jpg
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    Phil Gardener
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    Nice looking set-up!  Thanks for sharing the pictures; I'm looking forward to seeing the finished product!
     
    Mike Jay
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    Thanks Phil, me too

    I hope I didn't mess up today.  The missus and I made 6 trusses and the first was just gluing up the sample.  I had bent and clamped that piece by piece to the form.  The rest we glued it all up and clamped as we added the 2x6 blocks.  It went much faster but when we took them out of the form they sprung back a bit more than the original.  Maybe 1/2 to 1" at both ends.  Hopefully it won't be noticeable in the final product.

    I used construction adhesive for the glue which worked out nicely.  It stays wet while I'm dinking around with clamps and screws until I get the whole thing glued.  After making one truss we'd set it aside and build the next.  When that was done, the squeeze out from the prior one was set up enough that a putty knife removed the excess neatly.

    Hopefully we'll have the trusses built and varnished by Monday when I have some help coming to erect them.
     
    Ebo David
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    Mike, your truss frame is inspiring ;-)  I am surprised that the trusses are not coming out flat with that setup, but maybe I do not understand the comment.  

    I look forward to follow your progress.
     
    Mike Jay
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    Hey Ebo, I meant that the 2x6 and the LVL strips are a pain to keep aligned as I clamp and screw them.  It's easy for one to slide sideways 1/16th" relative to the other if I'm not careful.  The trusses overall are quite flat.  While I expected them to be strong in the intended load directions, I'm pleasantly surprised at how stiff they are.  Once erected I was thinking I'd have to have several purlins going across the trusses to keep them at 4' on center.  They are so much less floppy that I think I'll be able to get away with only one purlin.  Plus some diagonals for structural bracing.
     
    Ebo David
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    Mike, if i am following you correctly you should be able to correct that by clamping the pieces in two planes -- if you clamp the piece from the wall sticking out, you can force the rib to lay flat against the jig, and the other one parallel to the wall to pull the two ribs and the spacer block against it.
     
    Mike Jay
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    True, I could pinch them between a few scrap boards to keep them aligned.  But then it would flatten out the squeezed out glue and make it harder to remove...  And it would take a bit longer with the glue setting up.  But it would work.

    I did pull out the oscillating spindle sander with the belt attachment to round off the 2x6's.  That worked nicely, thanks for the idea!
    DSC04510s.jpg
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    Ebo David
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    Mike, you are welcome.  I am glad it helped.

    As for the flattening the glue problem... On thing that could be done, but it will be tedious to set up, is to use use screws or bolts as stops.   The basic idea is that you have something which adjusts the heights of different pieces in the assembly so that the only parts touching the truss pieces are the screw heads.  THe problem is how to adjust the head heights.  Probably a better way is to take one of the assembled beams, mark out where the glue joints go, carve/route a glue channel,m and then wax everything up so that glue drippings do not stick so easily.  That way you have flat pieces parts and no smushed glue berries.
     
    Mike Jay
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    Whew, what a week it's been.  We assembled the trusses early last week.  I helped a buddy cut up a bunch of pine on his sawmill and took it to a kiln to dry (for the E/W/N walls).  I laid out two trusses to test fit them and scribed the intersection at the top (while laying flat).  Then I cut all the ends of all the trusses to match.  We stained them with two coats of white stain.  A family member arrived Sunday to help and we finished the staining, got some scaffolding from a friend and started putting up the trusses.

    Scaffolding is worth it's weight in gold.  Or at least silver.  Couldn't've done this project without it.  Getting the ridge and the first few sets of trusses in place was a bit tricky and took three of us.  Once that was done, the rest really went pretty nicely.  Everything fit!

    The first picture is of the trusses laid out after getting stained.  The shallow radius trusses for the North wall are on the right and are fairly identical.  The more curvy trusses for the South wall are on the left.  They aren't as identical   The ends of the trusses line up very well but the belly varies by up to 1-1/2".  So we put them in order from best to worst to keep the variability truss-to-truss to a minimum.

    The second picture is of us getting the first four trusses in place.  We used a temporary support clamped to the scaffolding to hold the ridge in the approximate location while putting the first pair together.  Then the second pair dictated the correct location of the ridge and the saddle was retired for a while.

    The third picture is after we did all we could reach from the first scaffold position.  The scaffolding had wheels which is highly recommended.  Boy, that's a tall greenhouse...

    The fourth picture is a closeup of how the trusses intersect at the top.  The left (North) truss kind of wraps around underneath and also bears against the South truss.  This really helped during construction because the ridge would kind of sit on that seat.

    The fifth picture is of the "post bases" at the bottom that the trusses sit on.  They are designed for 4x4's so I made 1" spacers.  They're beveled to shed any water that lands on them.

    And the last picture was taken before we put the last truss pair in place.  Since then we added another brace to the ground at the other end of the building.

    All in all I'm very happy.  I had some wonderful help and loaner scaffolding that made the whole thing possible.  The top of the ridge is 16'-1.5" above the top of the block wall (4.9 meters).  So an 18' tree could live in this greenhouse.  It's a bit taller than I expected in my mind but it matches the drawings so I can't complain.  I'm really glad I was nit picky when locating the 2x6 spacers for the trusses.  Having them all line up really looks neat as you move around in the greenhouse.  I'm also glad I put as much space between those spacers because the shadows they cast is punctuated by a lot of light.

    I just have to decide what I'm telling the neighbors when they ask.  I'm thinking of saying I'm starting a church...
    DSC04522s.jpg
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    Trusses ready to go
    DSC04532s.jpg
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    First few trusses are up
    DSC04540s.jpg
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    Three are done
    DSC04544s.jpg
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    Close up of top
    DSC04552s.jpg
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    Close up of bottom
    DSC04561s.jpg
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    Mostly done!!!
     
    I agree. Here's the link: https://richsoil.com/wood-heat.jsp
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