Long-Span Beam
jackofalltrades777
| Posted in General Questions on
For a 4 car garage, I want to use a glulam beam or steel beam with a 48′ span length from concrete wall to concrete wall installed in a beam pocket. Which would be the least expensive route, glulam or steel beam?
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Peter, the relative costs would depend on several factors, but at that length a steel W-section ("I-beam") would almost certainly be less expensive than engineered wood.
Depending on your clearance, you might want to consider an open steel truss for this span. Trusses are often deeper, but may be cheaper. The steel beams come in two flavors: "regular" I beams, with the usual cross section that looks like a capital "I", and wide flange beams that have wider flanges (surprise! :-) compared to a regular I beam. The "W" in the number denotes a wide flange beam.
An important thing to remember is that a 48 foot beam will be very heavy. Crane-setting heavy. Keep in mind that the numbers in the steel beam designation number, something like "W12x58" mean the following:
"W" denotes "wide flange"
12 means 12" high, but these are like pipe dimensions, so it's actually 12.19" in this particular case.
58 is an important number... 58 means the beam weighs 58 pounds per foot -- so a 48 foot beam of this type would weigh 2,784 pounds. Keep that in mind.
You'll get more stiffness per unit height for steel in most cases, so you can probably use a beam of smaller cross sectional area if using steel compared to wood. I agree with Michael that steel will likely be cheaper for this.
BTW, have the steel fabricator/supplier prime the beam before shipment. This will make it easier to paint, and will protect it so that it doesn't rust during construction. It's usually either cheap or free to have them prime the beam for you.
Bill
Bill, I agree on all counts except that W-sections are so ubiquitous that at least since the early 90s they are considered "regular" I-beams, at least in residential construction. I don't think I've ever seen a traditional I-beam on a jobsite. When used as a beam, W-sections are almost always a more efficient use of material than other steel shapes.
We just set a W12x120, 20' long, and a W18x86, 22' long, on a job. Both were monsters. The flanges on the W12x120 are 1 1/8" thick!
I think I've see a traditional I beam maybe one time on a residential property. Even on commerical jobs (which is what I mostly work with), wide flange beams are very common. It's important when ordering though to specify which you want, since the steel fabricators do NOT assume you to mean a wide flange bema when you place an order.
Wide flange beams have flat flanges on the inside too, regular I beams have beveled inner faces on the flanges that get thicker as they get closer to the web. I think wide flange beams are preferred on residential construction at least in part because you can set wood joists on the flanges with the end of the joist butted against the web of the beam. With a "regular" I beam, that won't work since the sloped flange doesn't provide a flat bearing surface.
Bill
I got to ask how badly do you need/want the 48 foot clear span?
Seems like having a single post in the center would cut the costs by 60%, likely thousands of dollars.
Seems like you would be crazy not to have an engineer design that big a span and they would be in the best position the select the bests option for your situation.
Walta
Peter,
What's it holding up?
I was waiting for someone to ask that.
If it's just a freestanding 4-car garage, say 24x48, I'd run the roofline the long way and use roof trusses. A 24' truss is no big deal at all. Put a post on each side of the four doors and run a 12' glulam over the door to hold that end of trusses, regular stick-built wall on the other end. Almost like a pole barn.
It's an ICF wall garage (6" core) with a polyurethane 6" SIP roof, supported by 3 beams on the long end (48'). Engineer gave the following options:
5.125 x 27 GLB x 48' length = $3,825 per beam
(4) 1.75x24 Microlam 2.0E = PENDING PRICE
Steel Wide Flange Beam W21 x 44 = $2,357 per beam
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Steel is highly conductive of heat. You have to be very careful with the details or those steel beams can undo all of the benefit of SIP's.
My current price for a Versa-Lam 2.1E 1.75x18 is $14.45/LF in NJ. I would have to call my sales guy to get a price for 24", but looking at the smaller sizes, the price increase is about $1 for each additional 1" of depth. So you might be at $80/LF for a 4-ply, which is about the same as the glulam, excluding the cost of the lags and the labor to put it together. Though my recollection is that Microllam's are priced a bit lower than Versa-Lam's. I have not purchased steel in a while, but I will be interested to see how it compares.
I have an unconditioned 35' x 24' 3-car garage and we used 7" x 18" Parallam's placed in concrete pockets. The family room is directly above the garage so we used wood to avoid the conductivity issues DC mentioned.
Your image shows a section of wall between the overhead doors. Is there a reason you can't have support posts at the center? That would greatly reduce the size of the beams needed.
Steel prices are up quite a bit (I've been told about 4x, according to my metal fabricator), but might still be cheaper than engineering wood beams.
Regarding insulation and thermal conductivity, that's not that hard to deal with. Just insulate everything commercial building style -- on the EXTERIOR of the structure. In the case of a steel beam, just be sure the beam doesn't go all the way through the wall so that you can insulate over the ends. It's not usually difficult to design this way as long as you design this way from the beginning.
Bill
So how does a 4 car garage fit into the Green Building world?
I am guessing you do not want trusses because you will have a automotive lift and you need the ceiling height in the center?
Seems to me you could stick frame the roof with high collar ties and skip the beam.
I do commend you for not building a pole barn and after it is built trying desperately to make it be a high performance building.
Walta
Walter, you can't use collar ties to resist horizontal loads. You can use rafter ties, in the bottom third of the rafter span, but if you go higher you will put too much stress on the rafters. I've seen balloon-framed barns with the walls 3-4" out of plumb and 2-3" kinks in the rafters when builders ignore this rule.
No center posts, as the center of the garage will be used for parking of equipment/car so having a supporting post would not work. There will also be car lift. I need at least 12' of center height. The SIP roof peaks at 16' from interior slab. Subtract 2-3 feet for the beam which leaves me at 13-14' of ceiling height at the center.
The SIP roof would come to a point at the ridge beam and the beam would be sitting on the 6" concrete ICF wall with 2 5/8" of rigid foam on both sides. So the beam would be within the thermal envelope of the building. It will be a heated/cooled garage.
I got the steel beam pricing of $2,357 per beam. So that would be the least expensive, so far. Waiting on the Microlam pricing. The steel beam would be 2,200 lbs with a 6.50" flange and .350 thick. One issue with steel is how do you run a SIP roof screw into a steel beam?
The usual way to tie wood to steel beams is to either set joists/rafters on top of the steel, similar to what you do at a foundation wall, set joists/rafters inside the beam on the lower flange, or put a nailer on top of the beam and anchor to that. As long as you treat the steel beam as something solely there to support vertical loads, you can just "set" things on it. That's easier than trying to use the steel to tie rafters together on either side (for example), where you have tensional forces to deal with too. Let the rafters tie to the other rafters, put the steel beam underneath as a sort of load bearing ridge beam, that's probably the easiest way to go.
You should really retain the services of an engineer here, BTW. This isn't a project that should take long to engineer (so not too many billable hours), but it's a large enough project that it really needs an engineer to take care of things like connections between structural members such as what you're asking about here. You may also need some wind bracing depending on your local code requirements.
Bill
I am not suggesting the poster build the roof with the proper engineering, just try to get the poster to get go of his fixation for a Sip building. The market has clearly spoken the SIP thing is so 20 years ago and is non completive model in price of its performance.
Consider making the wall taller and covering it with trusses.
But sometime the heart want what the heart want and so it will be.
Walta
A couple of factors on why I am doing a SIP roof:
1 - Garage wall needs to go way taller to do truss roof and still have room for a car lift inside
2 - Polyurethane SIP is Class A Fire Rated (I live in wildfire area)
3 - SIP roof can be installed in 1 day
4 - SIP roof will give me an "instant" 24" overhang on all sides. No need to frame out 24" soffits and fascia (extra lumber, labor and time)
5 - SIP roof installed in 1 day will let me be insulated & dried-in in just 1 day. Truss roof would require setting trusses, installing OSB sheathing, framing out soffits, fascia, etc. Then spray foaming under roof trusses or wait for ceiling drywall to be installed and then blowing in cellulose. This would take weeks or months in today's building market.
6 - SIP Soffit & SIP roof doesn't require soffit venting. Fire embers are #1 cause of fire starting in wildfires. A vented attic and soffit just introduces embers into structure. Most houses catch on fire from embers entering attic and soffit vents, long before any actual fire encroaches onto the structure.
Building has been engineered as SIP roof and ICF wall.
If what you want is a 48x24 building with 12' interior height and clear span, well insulated, I think you'll be way ahead to build with 2x6 walls and 24' scissor trusses for the roof. Then insulate the hell out of it. Even if you have to go with higher walls to get the interior clearance you need you'll still come out way ahead.
Since you opened the conversation by asking about cost I'm offering this unsolicited advice.
That's exactly what I'd recommend as well, now that I understand the situation better. Parallel chord trusses would also work.
Check with your contractor on the installation labor - the steel will need to have a plate bolted to the steel to nail the framing to or install SIP screws into. TH weld stud or drilling holes in the steel will add cost that the GLB won't have. The micro lams seem to have constructability issues, they will be long & floppy then need to be screwed together. The GLB may be cheaper once labor is accounted for. It seems all solutions need a crane.
Beam size increase with the square of length, so I am thinking a heavy truss front to back between the doors would result in smaller cheaper beams and still no post.
Then a post between the doors would not really be in the way
A pair of posts between the doors would almost certainly be out of the way. 6 feet from each wall you almost could not drive into them
Strange discussion. The initial question is about relative costs, but the contractor is supplying pricing for the OP, so ???
If Peter wants a clear-span garage I don't see much p0int arguing with him about it.
Both the steel and wood-based alternatives have complications in how they will meet the ICF. The steel due to thermal bridging, the others will need the pocket detailed to avoid rot.
If the price isn't too outrageous my own preference from both a build-ability and aesthetic perspective would be the glu-lams.
Looking at the OP's drawings and wishes, I think the simplest design would be to use a single wide flange steel beam for a structural ridge at the roof peak. From there run rafters down to the walls to support the SIP panels, there is no need for the extra two beams in the roof. The garge doors are much shorter span, LVL/LSL/Gluelam would work much better.
The nice part about having a wide flange at the ridge is you can install a nice chain hoist trolley on it which can come in handy for lifting and moving things. Make sure to set the rafters above the wide flange for this.
I know someone that has this exact setup (minus the SIP) in their garage.
I agree with Akos here. One, central beam in the middle would probably be able to do what is needed. It's common to build commercially like this, sometimes with a central beam, heavy trusses coming off perpindicularly to the heavy beam, and then smaller trusses between the heavy trusses to support the roof. Lots of options.
Note that if you run TWO heavy beams near the peak, you could run a small gantry crane between them and have a clear span to run the length of the garage. That might be something to consider.
Bill
I do like this suggestion too, especially because of the added hoist functionality. I am just curious how the rafters are attached to the beam. I have used wide flange beams packed with LVL's to attach floor trusses, but not for the ridge. Is the OP still going to have to pack the beam with LVL's to attach the rafters or can the rafter hangers be welded to the beam? Then steel columns on each end within the conditioned space attached to an insulated footing or an uninsulated footing with a column bearing block?
You attach a wood plate to the top of the wide flange. Bevel 2x lumber to the rafter angle and set it on this plate, the rafters than sit on this tapered section. There is also a Simpson VPA but I find it is more work than beveling.
With ICF, the steel beam would be sitting on the concrete core, so there would still be a layer of rigid insulation on the outside to reduce thermal bridging.
Thanks for the explanation.
ICF is completely inappropriate for this application. The roof can be supported with conventional framing. Concrete is absolutely the most climate-unfriendly building material. It adds nothing to this structure.
DC,
Peter currently lives in a small ICF/SIPs house he recently built. I agree with you, but I think that ship has sailed.
Shocking that the steel is still less given how much it has gone up. I guess if you don't need steel posts, so they don't need to weld on-site, that probably helps.
You almost never need to weld on site. Typical steel arrives to the jobsite entirely prefabricated with all the pieces numbered. The crews just bolt things together like a big kit. Welding and riviting onsite is a thing of the past for the most part.
In the case of columns, what I typically do is spec the columns with bolt plates on the ends, and holes punched in the flange of the beam, or a welded-on bolt plate in the correct location along the beam. The reason to do it one way or the other is usually based on the limitations of the steel fabricator's equipment -- if their punch can't fit into the flange of the beam, then they can't punch holes in it for you :-)
The usual way it works is I design and draw everything (then I have my structural engineer check and seal anything if required), the fabricator then makes all the pieces in their shop, primes them all, then delivers them to the jobsite. The crew at the jobsite then bolts everything together with (usually) A325 grade bolts, using hardware assemblies that I specific (bolt / washer / lockwasher / sometimes a jam nut, etc.) in each bolt location. I typically have the steel fabricator supply all the hardware that I specific on my drawings.
One of the reasons you here steel buildings being advertised as "saving time" is because most of the parts are prefabricated, so the crew on the jobsite has less to do to put things together.
Bill
The 3 beam solution is likely due to the span limits of the 6" SIP roof panels.
Even with big beams, I don't like that design. Sure sure the engineers say it is ok, well they can see what happens with 3 feet of snow on it.
As I mentioned a center truss would significantly reduce the size of the beams, and I can think of no logical setup where a lift would end up between the doors, so a truss, or god forbid a post would simply not get in the way.
Unless you are collector of delivery vans, the most height you need is about 11 feet, and only in the bay with the lift. Since it looks like you have a 9 foot wall, I think scissors trusses would work , since that height is only needed in the center third of the building.
I have a 24x36 that needs a lift and a roof raising, so yeah, I have thought this through a few times. One of my options is 2/3 attic truss, 1/3 scissor, or 1/3 standard roof to make a spot for the lift
>"Even with big beams, I don't like that design. Sure sure the engineers say it is ok, well they can see what happens with 3 feet of snow on it."
If the structure was designed to handle 3 feet of snow load, then the structure will be fine -- nothing will happen. Long beams aren't any more risky or dangerous than short beams as long as they've been properly designed to carry whatever loads are required. The problems only arise when there are problems with the design (undersized beams, etc.). Highway overpasses sometimes have beams of 50 or even 100 feet, and you almost never hear of any failures. The same goes for large bridges over rivers and canyons.
Beams support loads, that's all they do. If the beam is designed to be strong enough for the loads that will be encountered, the structure stays up. It's really just that simple, there is no magic involved. Even a very short beam, if undersized for the load, can fail.
Bill
Yes, engineer stated GLB beams spans of 100+ feet are possible. However, in such spans, if using a wood frame wall. Extra $$ is needed to reinforce the wall to be able to carry that beam/roof load down the wall. With an ICF/concrete wall. It can easily handle such a load without any special reinforcement.
>" It can easily handle such a load without any special reinforcement."
Be careful with assumptions like that. Concentrated point loads such as right under a large beam (the deistributed load of the roof is concentrated on the points that support the beam carrying the distributed load) can be more than you might expect. You may need to embed a column in the wall to support the beam, for example.
The big issue that is often overlooked is that the SOIL under the wall has to be able to support the load too. Soil has an ability to support only a limited number of pounds per unit area, and how much it can handle depends on soil type. If you have a regular wall with a distributed load, this isn't usually an issue, but supporting a concentrated load under a column might require an unusually large footing to distributed the load over a sufficient area of soil to avoid settling issues.
Bill
I appreciate all the input! Lots to read and think over.
Center posts - There is added costs to the center posts (steel posts themselves, must do a footing under them). The post does interfere with parking equipment in the middle between the 2 bays. It's not a huge inconvenience but it does add some.
3 Spanning Beams - The reason it needs 3 beams is the 6" polyurethane roof SIPs need the support.
Why ICF walls? - I am located in a wildfire area and the concrete walls provide a way better fire resistance (4 hours) than wood frame walls (20-60 minutes) would. I also need the sound resistance of concrete (ICF is 8x quieter than a 2x wall) as I will be running a compressor in there. I am also in a high termite area (yes I know they can go into foam but it's not a food source & foam doesn't compromise strength). Of the ICF homes I know, NONE have had termite infestations. Of all the wood frame homes in the area, ALL of them have had termite infestations at one point. It's a constant battle with the termites. Thousands of dollars are spent in termite treatments, re-treatments, slab drilling, etc.
Have you priced it with 24' trusses on 4' centers? It's just a general principle that you run your structural members on the shortest possible span. Running them 48' feet when a 24' span is possible just seems intuitively wrong.
I have not but will get a quote. It's actually a 28' span as the garage depth is 28' from wall to wall. I don't think 4' centers would work with a 30 psf snow load.
Will a scissor truss still give me enough room to fit a 12' car lift and still have enough height that as the garage roof slopes back down to the wall height? In that it won't interfere with a car on a lift in the air? It's not just max height. Once a car is on the lift and up in the air. The roof height has to be tall enough that it won't hit the cars front hood area or back trunk deck lid area.
Any estimated what would a truss roof cost for this 48 x 28 garage?
Curious on any ball park costs for the below:
- Scissor trusses for a 48 x 28 roof
- 1/2" OSB Roof Sheathing
- Frame a 24" Soffit all around the entire roof perimeter
- Insulate roof to R-40 (not possible with scissor truss unless spray foamed?)
Construction costs vary so dramatically by region and other circumstances that you have to price it locally. But generally trusses are the cheapest possible roof, especially for long spans.
R-40 is only ten inches of fluff insulation, that shouldn't be a problem.
Here is a to scale image. It shows the limited ceiling height. With scissor trusses, I don't think I would have the clearance needed.
Above you're talking about a 6" sip and around a 24" beam. So the underside of the beam is 30" from the top of the roof. You should check with a truss designer but 30" clearance with R-40 insulation doesn't seem at all unreasonable for a scissor truss. Certainly parallel chord trusses could do that. Even solid wood rafters on 16" centers.
How far can your SIP's span? If you want to go with SIP's I would put the trusses at the maximum span the SIP's allow, people build pole barns all the time with trusses at 48" and even 96". Or you can go with a more conventional roof, cathedral ceiling, either exterior foam insulation or flash and batt on the interior. There your truss spacing would be dictated by the span your sheathing can support, usually 24".