New roof construction

I have to admit that most of my experience with odd construction is very limited, at best. My degree is in electrical engineering, by trade, I'm really an embedded software engineer, and I minored in mechanical engineering - specifically the physics of sound in average building materials. A lot of the materials these guys talk about on this forum have me baffled. I'd like to find a manual on some of this stuff that lays out some of the densities, absorption coefficients, and so on. The truth is, I think I have a pretty good handle on what I want, in a theoretical perspective. But piecing together a practical structure is not something I'm as good at. This is a great website. Sometimes, I'm afraid I'm stepping on someone's toes if I start debating on a subject. Just so you know (i.e. in case I start arguing with you on something :wink: ) I'm really not so full of myself. I do my learning through debating! Let me tell you about what I've a mind to do, as I see you are quite gifted in the construction area. Just something I'm considering.... Instead of hanging a heavy ceiling and adding dense walls and supporting floor, I've considered building an entire "cage" framework, suspended within the main tracking room on steel I-beams and columns. Here's the reasoning: 1) The walls are very tall - the gables peaking at 2 1/2 stories. This is an old building and the foundations are not really very wide or deep in these older buildings. Adding so much weight to a building this size is like creating a miniature black hole in Indianapolis (people will feel gravitated toward me)! 2) Add the weight of the roof to the weight of the walls they sit upon, and we have even more possible trouble. 3) With 3 large beams suspended across from one end to the other (one that goes right over the triangles, but under the roof, and two just along the bottom edges, sitting on columns that are buried 10-15 ft underground, this makes a very sturdy support. Of course, holes will have to be cut in the floor on the main tracking room at all 4 corners, as in the middle of the gable walls, to support these beams. 4) Some extra large (or a large number) of isolators could be used to hang an inside steel framework, on which the floor, walls, and ceilingwould be built and well insulated all the way around - that is, as long as the isolators on which the room rests are truly doing their jobs. The cool thing about this is the ease at which the rest of construction would be, once the skeleton is complete. The downside is trusting those hangers with all the weight and stress, to be able to also serve as true isolators. ??

Eric, near as I can tell by your drawing, those massive triangles are a physical part of your exterior leaf and so shouldn't be impinging on your inner space (unless I'm not seeing this right) - your drawing looks to me like you're planning an outer mass leaf outside the springs/kinetics units, then an inner one suspended on the isolators - however, it looks to me like those massive triangles will be partly inside your INNER leaf, and as such will be one hell of a flanking path - yes, no, WTF??!? Steve

Hello gents....Steve, I was thinking the same thing. It actually occured to me that there is no way to include the truss's in room. To TRULY isolate a room within a room configuration, the new ceiling would have to be BELOW the joist chord of the truss. No? Well, thats my .02 anyway. Looks like it may be one of those.."can't have your cake and eat it too" scenarios. I know this though, a STEEL STRUCTURAL FRAME, 32'x60'x 2 stories tall, is some BIG $$$$$$$$$ :shock: :lol: Eric, I thought you had mentioned there are columns supporting these trusses. IF you are concerned about transferring the load from the framing above the suspended ceiling, to the walls, how bout the trusses themselves? If it were me, I'd investigate the footing for these columns, and maybe have an structural engineer look at these loads, via small steel "I" beams bolted between each truss. Then suspend a new ceiling BELOW the bottom chord FROM THE "I" beams. That would transfer the load to the trusses/columns/footing. Even if you had to dig out for another steel column/increased size footing, it sure would be cheaper than a complete steel frame. Holy moly, I can't even begin to comprehend how you would build that within the existing structure. :shock: fitZ

however, it looks to me like those massive triangles will be partly inside your INNER leaf, and as such will be one hell of a flanking path - yes, no, WTF??!?

Yes, Steve, you hit it on the 3rd note, there! That was, in fact, my biggest complaint. I really don't want to have to give up that extra space. Yes, fitZ, I DO want my cake and eat it, too! After all, what good is a !@%& cake if you can't eat it?! (Sigh) It's crap, isn't it? C'mon, man, I'm not giving up. I KNOW there's a way. (Help us out here, God!) As far as the steel cage structure, The I-Beam columns would rise out of the floor along each corner, just inches inside the original walls. One column would support a beam that would go along the 50' length to the next column on the other end. The other side of the room would hold the other pair. The third pair would be down the middle, through the tops of the triangles. Whether this structure touches any of the building or not makes no diference, you see, because these bad boys would only serve to hold the massive weight of the interior room. The isolators would then hang from these, on which a lighter frame would be built with many "ribs" supporting a steel grate floor. The floor would support everything built on top of it. Yes, possibly more expense than its worth, but worth the 20 minute fantasy freak show (it's fun to pretend). I'd have to see what the real deal will cost, for sure. A good group of steel workers could probably whip that out in a day. But I'd have to look into the cost before seriously considering it. But back to the real issue, Steve. I share this concern of yours. A shunt from outside to inside. Here's the real problem: If I try to remove those triangles, the ENTIRE building WILL collapse. I know it. Those buggars are not only holding up the roof; they hold the walls in place! But I really can't stand to give up the cathedral ceiling. In fact, if that were the ultimate answer, ..... I'm gonna have to sell this place! I won't do without the extra height! Hmph! (....arms crossed and lower lip protruding)

(....arms crossed and lower lip protruding)

:lol: At least you have a sense of humor. fitZ

What about furring out the massive triangles where they enter the acoustic space, adding RC to the furring, insulating, and boxing that portion of the triangles in with double layer of gypsum? If you put a damped, isolated mass leaf around the exposed portions of those beasts, it will kill most of the sound trying to impinge on the beams, so there won't be near as much sound reaching the beams to attempt flanking - I know it wouldn't look quite the same; maybe the last layer could be rough-sawn siding for a more rustic look; the box-in panels would obviously have to be caulked well, just like boxing in an AC duct... Steve

Where the upper beams meet the lower, a custom clamp was made to cinch the two together. Where the two shorter beams meet at the top, another cinch clamp was made and a giant bolt fitted through, straight down the center and also through the lower beam. The bolt is about 14 ft long, 1 3/8" diameter. It is fitted underneath with a nut which is tightened, making the triangle a lone, stiff structure, all on its own.

Hello Eric, just out of curiosity, could you describe the "cinch clamp" that ties the rafter beams to the joist beam, right above the wall. I've tried to imagine what they used to keep the pitched beams from collapsing outward. The only things I could think of were either a steel gusset, or bolts through the two beams, joinery of some kind or a combination of things. No matter what, this must be a STRONG joint. I've always been interested in old timber joinery. I have a book on timber joinery techniques that were used in cathedrals of Europe. :shock: Holy Moly. Those carpenters must have had nerves of steel :lol: I also saw a book on a SYSTEM of joints and assemblies used to design and build the "government" buildings in China going back to the pre Christian era. Talk about skilled carpenters. Absolutely amazing what they could do without a skill saw and nails. Ha! fitZ :)

Steve. I like your idea. Now that you mention it, the rough beams that are presently in place have facades of finished wood attached across the bottoms. I could certainly remove them, box the beams in, then do ..... something.... (putting those facades back on may not make much sense, if I box appropriately, meaning the added width and height would be quite emphasized.... the facades would look kinda like stripes down the middle! But that's an idea worth considering. "Cinch clamps": When I went back up there for another look last week, I noticed I drew the clamps wrong. In reality, the lower beam is notched, the upper beams are inserted and bolted, and some metal ties are inserted into the sides, I believe, just for stability. At the very top, the beams are shaved to a blunt, flat top, and an 8"x 4" block of wood, about a foot long, is set across the top for the bolt to go through, sort of acting like a big washer. I didn't bother changing the drawing, since it didn't seem worth the effort. I'm kinda lazy that way. Okay, so I box in the beams. If you notice in the drawing, the drop ceiling and the upper triangle beams are sort of wanting the same space. I'm guessing the best attack is to merely bend the ceiling surface around underneath each beam when I get to it. (?) Ya thinksies? It'll be kinda messy, or so it seems. Might be a good opportunity to create a bit more diffusion in the room, though. There's about 12.5 ft between each beam.

After re-thinking things, I have decided to make the roof merely that: a simple roof - not a sound barrier, as there seems to be no efficient method available to make it a barrier with today's technology - unless your pockets are very deep. Actually, this doesn't rearrange much from the drawing I already included on page 2, since the drywall barrier is still kinda where I want it. But 3/4" tongue and groove decking on the roof - what's the point? Anyone see any advantaged to that? I think it should remain open at the upper and lower extremes for ventilation purposes.

Yeah, two separate mass leaves, air/insulation between, weather cover over 'em, rock 'n roll... Steve