Calling ALL engineers (shade-tree included)

[Dennis McCullen]

I've just changed designs for my new shop from a raised-center aisle (monitor) building, and I'm now working on the feasibility of a "clerestory" design. That's a fancy word for two simple shed roofs that meet at different heights. I have a small camper to account for, so the left side (from the front) of the building is intended to be the higher side and partially open rear wall and mostly open front wall. Yes, more a carport. Looking from the front of the building, you see a 12 ft outer wall on the left rising 2/12 for 20 ft, so it is 15 ft 4 inches at the top. Drop down about three ft and you have the highest point of the wood shop sloping to the right for 22 ft also at a 2/12 pitch, reaching 8 ft 8 in at the outer wall. The ?? deal with the shop building. I want a simple shed roof, with the rafters exposed to stretch the 23 ft. The front to rear dimension is 30 ft and those front and rear walls will be built of 2x6 (16"0c). I'd like to have only one post in the middle of the shop to support a beam spanning the 30 ft (minus 11" bearing front and rear wall). I feel sure 2x8 rafters meeting atop the beam with a 2 ft lap would hold up a plywood sheathed roof deck, stripped with 2x4 and sheet metal covered. Getting to ?1) I've searched extensively and keep coming up with LVLs being nail-laminated for a 3.5" thick beam to support everything in the construction world. Since I'll be placing a post at 15 ft, has anyone seen these placed end to end? I can build a large post and cradle the two ends of the LVLs that sit in the middle of the shop. The roof would be bearing on this at mid-point and I see no limit on what size post I can build (nail laminated and glued) to accommodate the LVLs in the middle of the shop. I know that a 30 ft long LVL that is 3-1/2" thick would be preferable, but not possible for me to haul or install w/o lifting equipment. I'm instead looking at 4 15 ft LVLs.q2) If I install a roll-up door in the front wall of the shop, how much of a wall (how much distance to the high corner) do I need before I can install the door. I'm hoping that a 2 ft distance of a 2x6 wall is enough so the door can be a 10 ft door. OK - go see a civil engineer, but if any of you have this type of experience, it''l inform me what questions to be prepared for. Thanks.

[Lee Schierer]

Most LVL suppliers will review your design and advise as to what LVL size you need to accomplish the desired task.

My work shop has two 1-3/4 x 12" LVL's glued and bolted together spanning 18' 8" in my shop so I wouldn't think a 15' span would be a problem assuming the LVL is sized for the expected load. These LVL's were supplied in a 20' length.

[Brett Bobo]

Hi Dennis,
A picture is worth a thousand words here but as Lee suggested, your local engineered lumber supplier will typically design these for you. With that being said, yes, either dimensional or engineered lumber are typically run end to end with the use of a saddle connection. Simpson, as an example, sells them and they also carry an architectural line of connectors for exposed concepts like this. Unless you're looking at the 1 3/4" wide material based to simplify handling and erection, 3 1/2" wide material is readily available, as are other widths such as 5 1/4", 7", etc. Also, there are several variations of engineered lumber under other names such as PSL, LSL, Glulam, etc.

Regarding your second question, I believe you're referring to the header depth above the garage door. A 2' depth is substantial so you should have many options but there are several other variables that need to be known. For example, what is your facade above the header? With brick, there are deflection limitations that need to be accounted for in the design but I'd prefer a conservative design on the header size as too often headers have visible deflection over the years.

As you may already know, try to maintain your rafter spans under 24' as the availability of longer dimensional lumber is harder to find and of course, priced accordingly. Even still, you're likely looking at 2x12s. Otherwise, purlins and struts will be required to brace the roof system, which means more beams below. Similarly, while rafters in this A frame type configuration with equivalent pitches on both sides can theoretically be self-supporting, typically the ridge beam is designed to carry the roof load. Since the span of the ridge beam sounds to be considerable, a substantial engineered ridge beam may be required or the use of the beams below you're asking about, if applicable.

You might consider engineered roof trusses to avoid the primary issue you're concerned about, open floor space, and this would also considerably help offset the costs of larger member sizes for rafters, ridge beam, beams, and columns.

Having said this, it's imperative this system be engineered for your specific scenario, location, design loads, local code, etc. Even though I'm a structural engineer and this is straight forward, I'd be doing you a disservice to attempt to give you specific sizes without knowing many other variables. This is something an engineered lumber supplier or truss supplier does day and and day out and would be the best option going forward once you have a plan finalized.

Good luck and be sure to post pictures of the finished shop-it should be a great space!

[Jason Roehl]

Not to rain on your parade, but you really need to talk to someone locally with plans in hand. You don't mention your location--potential snow load? Potential wind loads (hurricane area)? What about local building codes?

Personally, I believe when it comes to the structure of a building, a few hundred extra bucks and a few extra hours of labor for more/larger lumber is well worth it in the long run. Remember that building codes, for the most part, are the MINIMUM allowed, not necessarily sufficient for a sturdy building that one can be proud of. Just yesterday, we had a nice little storm come through, with straight-line winds and tornadoes nearby. My house was built in 1974, and we barely noticed any creaking of the house in the 50+ MPH winds. I've been in plenty of newer houses that groan and creak in winds of 25-30 MPH winds.

There's nothing like a little rocking in the wind to weaken all the connecting joints...

[Steve Rozmiarek]

In my new woodshop, I added clerestory windows to a heavily modified existing structure. You lost me on as to what you are trying to do, but I will say the windows are worth the effort. If you are asking about a beam to support a 23 foot span, it's not necessary if there can be two supporting walls. (don't you potentially have three?) 23 foot can be free spanned, with appropriate wall construction and heavier rafters.

[Jim Andrew]

Steve, would be nice if you would post some pics of the way you modified your building adding the clerestory windows. The building Dennis is describing seems to have 2 different height walls to create an offset to make a space for the windows. There is a building built a few miles from here designed that way, it creates natural light for the north half of the building. Of course, the north half has to have a sloped ceiling. They put a flat ceiling in the south half. Seems you could get the same look by just building one side of the building with longer rafters. Your windows would not be centered in the building though. The 2/12 pitch roof would be better if it were raised to a 4 or 5/12, as a steeper roof is stronger.

[Steve Rozmiarek]

Jim, I'm trying to do this from my phone, so the results may be a little goofy. I only have a few pics here, none great, but will post a couple. The windows are not obvious in them, they were taken in the dark, but you can get the idea. The windows are above the stairs. Note, the framing looks goofy in the pics. It's mainly because new furring over old studs look strange in pics.

275304

Something tells me that didn't work...

https://lh4.googleusercontent.com/-mj7KwH3lpmU/UnWP8-9GSyI/AAAAAAAAC8U/Bv55vxFef_Q/w1044-h164-no/20131004_200021.jpg

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https://lh4.googleusercontent.com/-3SGbIta7MvA/UnWQbh1in4I/AAAAAAAAC9M/iE-aXWrCct8/w286-h508-no/20131004_200210.jpg

[Steve Rozmiarek]

Ok, explanations of the pics in the previous post. It was an old house, basically L shape, 14 rooms. It now has 1 room and a basement, so extensive framing had to be done. My wife and I basically built another roof under the rafters, everything was 2x4, so I wanted more insulation and more strength. I wanted open ceilings to the bottoms of the rafters, but I like the exposed ties, so no beams were used. We scissor truss constructed the part with the balcony. The other part, the one with the stairs to the basement, is where the clerestory windows are. The pics are taken in the dark, so they don't show up, and the pics were not taken to show the windows, so they may not help. Gives an idea of what we have now though.

The construction of that roof had to span about 30 feet, so I used 2x12 rafters, and fairly simple framing to accomplish. I'll take a pic of it better in the next day or so. As an aside, it now has all the electrical, and some insulation. Hoping to be putting up drywall by Christmas!

[Brett Bobo]

Hi Steve,
The perimeter framing at the exterior walls is interesting as there appears to be a "beam" carrying the rafters with a top plate(s) underneath. Do you possibly have a close-up photo of this detail? Maybe this is the goofy framing you were referring to so is there a furring strip on the face of the studs and top plate?

[Jim Andrew]

Steve, thanks for posting the pics, looks like you went to lots of work. Had another thought for Dennis new shop, Have to think of how they build Morton buildings. What I'm thinking is the way they use heavy trusses, and then space them from 8 to 12' oc. If Dennis built his building with heavy trusses, designed for his clerestory roof, the trusses could be spaced far apart enough to install the clerestory windows between the trusses, using horizontal purlins between the trusses. The local building officials here require manufactured trusses, but I have a book from midwest plan services that shows how to build your own glued trusses, which you could do if they were allowed.

[Dennis McCullen]

Thanks for the participation, everyone and I did mislead w/o pictures, so here is a pic of the basic plan. I got indications that it loaded but , if not, I'll try again. First off the clerestory design will not let light directly into the shop b/c the carport will be the beneficiary with the higher roof - that's where height is needed to park a small camper. However, there will be a few windows high in the adjacent shop wall to glean SOME of the light, though indirectly, from the carport side. The beam in question will be front to rear, 30 ft long, and supported by one built up (nail lam) post in the middle. On its ends the beam will rest atop 2x6 stud walls that will be completely sheathed with plywood, except for the numerous door and window openings. The 30 ft beam is intended to support the midpoint of the 22 ft span, which will be 2x8 rafters 12 ft long, 24" oc and overlapped atop the beam. No ceiling joists for now, but using 2x8s with hopes of being a little on the strong side in case I ever want to add a frame work for some insulation. Atop the 2x8 rafters, I'll have a layer of plywood. probably 5/8", then roofing felt and radiant barrier bubble wrap. I intend to strip this with 2x4s laid flat for a surface to screw on metal roofing and to provide the needed air space above the foil so it can do it's reflective thing on radiant heat.

[Dennis McCullen]

I am not sure if it is indicated on this drawing, but the 22 ft wide shop part is then 30 ft deep, front to rear. That is the length of beam I want to put up, or rather two 15 ft beams end to end, married on a post in the very middle (both ways) of the shop. I can live with one post and actually embrace it as a place to lower electricity and dust collection utilities (avoid crossing the floor) for the table saw and jointer that will occupy the floor there. Lesser used machines, e.g. drill press, band saw, will stay on the perimeter. Again, sorry not to be more thorough the 1st go round, and I have contacted a local lumber yard that will size the beam for me. I am still curious about whether some of you may have built up such a beam from laminated veneer lumber and how you may have handled the slope of the rafters sitting atop the beam. I feel I can carefully dado out a couple of 2x6s at the proper angle, getting progressively deeper over the 3-1/2" width of the beam. It would be flush one inch from an edge and 5/8" deep an inch from the other edge. This would give me an angled top plate for the beam, and would correspond to the angle of the rafters crossing it. That should give me a nailing surface for the rafters sitting flush with the top plate. This may not add to strength of the beam but would facilitate attachment to it. I have only seen referenced that when having a manufacturer size a beam, you should ask for specific instructions on attachment, at the ends of the beam where it rest atop and between framing members, and for framing members supported by the beam. In my case, I'm also interested in attaching one 15 ft length of 1-3/4" LVL to it's identical counterpart. Bolt size, spacing pattern, construction adhesive, etc. One respondent mentioned a saddle for the top of the post where I can marry the two 15 ft lengths to each other end to end (over a post) after I've laminated the two 1-3/4" LVLs together to form a 3-1/2" thick beam. From what I've read, the loading I am expecting from above would be fine sitting atop tripled 2x12s. - I mentioned the roof make up and what sits on the beam and one very good question was snow load. I live in southeast Louisiana and most years have none to deal with, That said, just a few years ago we had 8" of snow. It was gone in 3 days but that is still a consideration, even though that's the most I've seen here in 62 years of living. I am in hurricane country and built a house that has only shaken a little once. Hurricane Katrina produced increasing winds up to and hold 105 mph for a few hours. LET'S NOT DO THAT AGAIN, PLEASE! I will get some pro advice on the beam size and would appreciate comments on attachment methods for similar beams. I'll definitely look up saddles to marry the two beams end to end and I'm strongly considering having a massive post base built at a welding shop for the one post centered in the workshop. I want my post to be rigid and have little to no sway horizontally. With a couple of braces at 45 degrees the post to beam should add to the strength and not depend on the end gable walls. Thanks for sharing your experiences, sawmillers!

[Brett Bobo]

The 30 ft beam is intended to support the midpoint of the 22 ft span, which will be 2x8 rafters 12 ft long, 24" oc and overlapped atop the beam


I am still curious about whether some of you may have built up such a beam from laminated veneer lumber and how you may have handled the slope of the rafters sitting atop the beam. I feel I can carefully dado out a couple of 2x6s at the proper angle, getting progressively deeper over the 3-1/2" width of the beam. It would be flush one inch from an edge and 5/8" deep an inch from the other edge. This would give me an angled top plate for the beam, and would correspond to the angle of the rafters crossing it. That should give me a nailing surface for the rafters sitting flush with the top plate.

From these comments, I understand you to say that you plan to run the 2x8 long over the top of the beam, i.e. a ridge beam, and install a beveled, continuous top plate along the length of the ridge beam to provide full bearing for the rafters. If so, you're over-complicating the installation as it's simpler, without comprising either the integrity of the ridge beam or the rafters. The rafters would frame directly into the side of the ridge beam, build a pony wall on top of the ridge beam, and install another ridge beam on top of the pony wall (basically just a nailer) for the rafters making up the higher roof.

If the ridge beam is designed to run the full 30' length of the shop, then there's no need to install the lower beams at the ceiling level. Of course, this assumes the rafters are designed for the clear spans to the ridge beam. This would provide you with the most open-space possible. Otherwise, if the ridge beam needs to be supported along it's length, then only one beam at the ceiling level would be required in either direction, depending on the strut (bracing) locations and orientation. In other words, the adjacent beam isn't required as long as it's not supporting the ridge beam.

For the structural fastening of the rafters to the ridge beam for the lower roof, take a look at this mechanical connector:

http://www.strongtie.com/products/connectors/LRU.asp?source=sslumbcat

I would suggest spending time looking through their catalog and they also provide the saddle connections I mentioned earlier. Keep in mind too that the big box stores do carry most of the commonly used Simpson products.

For the structural fastening of laminating two LVL's together, the manufacturer specifically indicates this in their technical data. So, it'll vary slightly depending on which manufacturer you decide to go with but more than likely it'll be a Weyerhauser product.

Hope that helps,
Brett

[Dennis McCullen]

Brett, thanks for hanging with me here. I just saw a building being framed using exactly the method you describe and I'm afraid I did not supply enough info to differentiate my situation from that. I do not know if you saw the attachment from me a couple of posts ago, but please take a look at that and realize the shop is only the right half of the pic at the bottom. It is shown as 22 ft wide whereas the left side is a carport 20 ft wide. Both halves will be 30 ft deep, but let's just consider the shop for now. Just to the right of that 9 ft door and just beneath the sloping rafters is where the intended beam runs from the front of the shop to the rear. Halfway of it's length is a post. Rather than end those 2x8 rafters into the sides of the beam on a miter cut, I intend to overlap them on top of the beam. There are no horizontal bottom chords, i.e. ceing joists. I have plenty of ceiling height at this point (10 ft min) so sacrificing a ft for the beam still gives me a clearance beneath it of 9 ft. This roof is a simple shed roof sloping from L to R in the pic, spanning 22 ft. I've used joist hangers in the past in special situations, but I'd prefer loading on the top of the beam and lapping the rafters, nailing them together for that foot. For the immediate future, there will be no lowered ceiling in the building. When you look up, you will see the plywood sheathing that is nailed down atop the rafters. I'm using a foil radiant barrier outside of the plywood and stripping that for an air space (to let the foil do it's reflective thing). A sheet metal roof will then be attached to the stripping (2 x 4 on the flat). With the design being a simple shed roof, not a gable, I do not see where the "ridge beam" or "pony wall" fit in, but like I said, I'm not being entirely clear as I try to communicate the design. Most all of us have built sheds with one wall higher than another to provide a slope on the roof. The rafters of that shed provide the tension connection that keep the walls from pushing outward. This is what I'm doing, just on a larger scale. Dennis

[Dennis McCullen]

Hey Brett, "If so, you're over-complicating the installation as it's simpler, without comprising either the integrity of the ridge beam or the rafters. The rafters would frame directly into the side of the ridge beam, build a pony wall on top of the ridge beam, and install another ridge beam on top of the pony wall (basically just a nailer) for the rafters making up the higher roof." This is where I've mislead you. The beam is just to the right of the door on the right half of the building. Disregard the left half, the carport. I now see what you mean about a ridge beam and pony wall and that would be applicable for the left or West wall of the shop. Thanks, Dennis

[Brett Bobo]

Hi Dennis,
No worries, I'm having a hard time following your intended plan as I previously thought you were modifying the entire roof (both the shop and carport) based on the drawing you provided. I'm not sure what happens with the left side of the roof but I'll focus on the right side only. A revised sketch would be very helpful.

Why don't you just install rafters that are designed to clear span to the middle of the shop, i.e. the 22' length? This would eliminate your other framing concerns.
I'll hold off on further comments as maybe this will solve the issue. If not, we'll re-group and go again.:D

[Dennis McCullen]

Hi Dennis,
No worries, I'm having a hard time following your intended plan as I previously thought you were modifying the entire roof (both the shop and carport) based on the drawing you provided. I'm not sure what happens with the left side of the roof but I'll focus on the right side only. A revised sketch would be very helpful.

Why don't you just install rafters that are designed to clear span to the middle of the shop, i.e. the 22' length? This would eliminate your other framing concerns.
I'll hold off on further comments as maybe this will solve the issue. If not, we'll re-group and go again.:D THe full length rafters is a great idea but I usually work alone (Bayou Self Construction Co.) and I believe a clearspan for 22 ft would involve engineered roof trusses. The weight is one factor then there's the bottom chord at 8-9 ft, then there's the idea of me putting some windows in the top of the tall wall to glean some light from the carport side's clerestory windows and lastly, I want to put in an exhaust duct in the tallest part of the room just beneath the rafters to remove heat and filter the air of the saw dust I hope to create. Just completely ignore the left side (tall side) on the drawing; it's a carport and will be built separately. Picture the right side with a simple shed roof and the inside not having a ceiling, just rafters that run from 8 ft on the right to 11'8" on the left. The beam in the middle of the rise lowers the clearance some 14" because the rafters sit on top of it rather than run into rafter hangers on the sides of it. That still leaves 8'8" clearance under the beam. The left side rafters then rise from 9'10" to 11'8". I'm hoping this help to move heat away from man and material down at shop level. I'll put another sketch up in a bit after I've had a chance to wake up and get stirring.

[Brett Bobo]

Even at a 22' span, you can still use dimensional lumber if sized accordingly, i.e. 2x12s. Typically, the maximum, readily available lengths of dimensional lumber are 24', keeping in mind the actual length based on a shallow pitch of 2/12. Also, keep in mind that there are other engineered material options, still stick framed, for longer spans of roof systems, without compromising on ceiling height. In other words, there is no need for trusses in this situation, other than preference.

Considering you're a one man wrecking crew, I'd try to avoid the beam concept (and associated bracing, columns, base plates, etc) all together as you'll need either equipment or several helpers for the installation. I think you'll still need a helper, regardless, even from a safety standpoint. Also, I still don't know what the existing framing is at the center of the building (or how much of the building is new vs. existing) but at least for the shop space side, you can maximize your spacing without interruptions from framing in the floor space or directly above.

[Steve Rozmiarek]

All, sorry I haven't gotten better pics up yet, they are on the list though. I went in for "routine outpatient" surgery last Tuesday, and just got home. As soon as I can use the scaffolding without the little wife freaking out, I'll get them posted.

[Dennis McCullen]

All, sorry I haven't gotten better pics up yet, they are on the list though. I went in for "routine outpatient" surgery last Tuesday, and just got home. As soon as I can use the scaffolding without the little wife freaking out, I'll get them posted.
For a speedy recovery and don't do anything you wouldn't do if she were watching!

[Steve Rozmiarek]

Hey, I got to the woodshop without feeling like I was going to pass out finally!

Dennis, I think Brett has given you better advice than I can. I'm just a complete shadetree hack, so I overbuild, and do it in a more complicated way than the pros. I see you were worried about horsing the lumber around yourself if you free spanned the roof. I did with the rafters on the top roof, they are 22' 2x12's, and I did it myself. In fact, my little wife and myself have done everything from demo to where it is today. You can horse the 22' 2x12's around, but it requires a plan. You work alone, its no more complicated than the other stuff you have to plan for, just more airbourne.

As you can see in the pics, I couldn't retrofit a beam into the old house, so I have to use cross ties. A beam would make the roof a lot cleaner, but not an option in my situation. Where you can use a beam, I would. I'd also use full span rafters for sure.

You can also see something I'd change on my pony wall. I framed it for structural, without thinking the window finishing all the way through. I have to trim a spacer block now, and furr out the windows so the wood siding that will be the finished surface inside will come out right. Could have planned that better. FYI, the windows are all flange mount, and the building has 1 1/2" of sheeting minimum. More framing goofyness, the temp double doors visible in the second photo are just part of the old structure I hinged in place so I could get a table saw into the building using the forklift. I will build doors for them after I move in. They are 9' tall and 6' wide, for scale.
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