Questions about wood i-beams

[JSUPreston]

My shop is a 20'x20' cement block building with a basic shed roof that slopes down about 6" or so over its run from front to back.

The rafters are approximately 12' long 2x8 and overlap approx. 1/2 way. Under those rafters are a set of four 10' 2x8 sandwiched together to support the rafters, with a butt joint in the dead center of the shop. To support the sandwiched 2x8 butt joint, there is a column of 4 4x4 posts. (I'll try to post pics later...at work right now)

The column is killing me. Even when I had the BT3100, I could barely walk around it because of the column. I can't crosscut a large piece of wood easily, no matter where I put a table saw.

I was thinking of a couple of options to remove the column. One is to somehow strengthen the 2x8 butt joint with steel plates and carraige bolts and hope that holds.

Another would be to somehow put a couple of 20' 2x8 in place of the current 2x8s. Don't know how I would fit it in, unless I came in through the outside. Pics will explain better. I'm afraid that the 20' span would be too much and would cause the 2x8s to split.

The other options I can come up with are to replace the sandwiched 2x8s with a wood i-beam, or to sandwich a wood i-beam up next to the existing rafters. I'm not too concerned with how it would look, but I want to make sure the roof will hold up, especially since it was redone in late '06 or early '07.

What are y'all's thoughts on this? Also, does anyone have a clue as to how much a 20' 8" thick wood i-beam would cost?

Thanks!

[Tequila]

I was thinking of a couple of options to remove the column. One is to somehow strengthen the 2x8 butt joint with steel plates and carraige bolts and hope that holds.

It will sag, and you won't be happy with the results.

Another would be to somehow put a couple of 20' 2x8 in place of the current 2x8s. Don't know how I would fit it in, unless I came in through the outside. Pics will explain better. I'm afraid that the 20' span would be too much and would cause the 2x8s to split.

It probably won't split, but it will sag, and you won't be happy with the results.

The other options I can come up with are to replace the sandwiched 2x8s with a wood i-beam, or to sandwich a wood i-beam up next to the existing rafters. I'm not too concerned with how it would look, but I want to make sure the roof will hold up, especially since it was redone in late '06 or early '07

What are y'all's thoughts on this? Also, does anyone have a clue as to how much a 20' 8" thick wood i-beam would cost?

You're on your way to the right answer, but not quite there yet. An I beam would be just as strong as the existing 2x8 sandwich, but not stronger unless it's bigger. And you need something stronger to go across the 20' span.

I'd suggest looking into replacing the wood with a steel I beam. That's the typical option around here for garages - post in the middle, or steel beam to support the rafters. You'll be able to span the 20' easily without having to put in four trees worth of lumber.

[Uncle Cracker]

Hate to bring doom and gloom, but I gotta issue a word of caution: A beam of that nature would have to be engineered to that specific function, accounting for everything from load to size to climate to humidity to construction materials. You can't just size it based on the space you have. Even if it can take the weight, there may be a sagging problem. You also need to consider that all the weight borne by the column will now be split between the two end walls. Are they up to the task? You may need to consider a large timber, or even a steel I-beam. No way you will simply be able to reinforce the existing butt joint. You will need a permit and an inspection, and the building department is going to wanna see the math, just like they would a truss system. To do otherwise is to risk a denial of claim from your insurance carrier if there is a problem, not to mention the fines for lack of permit. There is much more here than meets the eye, and the whole thing needs to be thought out very carefully, or you will be wearing a roof for a hat.

[Garasaki]

Yeah you are definately flirting with disaster here. Structural members are not slapped in haphazardly because someone felt like putting em in there, they are placed where they are to perform a specific task and their size is generally choosen to perform that task, and absolutely nothing more.

The column is holding your house up (not just the roof - your roof falls down, it brings the walls with it). Please think about that statement for a little while before you start trying to remove without having someone qualified look at your situation.

FYI the strength of a beam is more closely related to it's "depth" or "height" then how wide it is. As such, adding more 2x8's is not your solution here.

[jackellis]

Engineered lumber (I-joists and laminated beams) might work as well as steel at lower cost, but I agree that you need get help from an engineer.

Not exactly the same situation as yours but one of our neighbors decided to replace their roof with a ceramic tile product that looks a bit like wood shakes. Trouble is, they didn't consider the added weight. Some months after they finished their DIY roofing job, they noticed places where the trusses were sagging. I'm pretty sure strengthening the roof from inside the attic was not much fun.

[iceman61]

Uncle Cracker & Garasaki are exactly right. Also if you go with a steel beam you will be looking at an S-beam. It has more depth than width thus will handle more load, but then you may be sacrificing head room. Your options will most likely be: S-beam, a couple of 14" glue-lams nailed together. You do have the option of sandwiching 2 boards on either side of a steel plate like you were thinking but for that span you're probably looking at 2x12's & 1/4" plate. I just built a shop with a 24' span & the 14" glue lams were specified & have installed the wood/steel sandwich beam in a customer's house. Both engineer specs I want to add.

You do need to run all of this by an engineer & he will tell you EXACTLY what you need because he will have to do calculations on all the loads. he will figure in loads you probably wouldn't even think about. (snow, wind, etc)

Heads up: check with some of the larger scale material suppliers in your area. Some of them have an licensed engineer in the building that will gladly do the calculations for you if you give them all the specs & let you know all of your options. Take pictures to him or her also so there is no misunderstandings.

[Garasaki]

That reminds me.

Any changes you make must meet building code, which will include the different loads mentioned above that are not necessarily obvious.

If you makes changes, and they don't meet code, and your house falls down, insurance won't cover anything.

[Pappy]

I am thinking down the road of using wood beams to add a second floor to my shop building. I talked to Bison Products here in town and was told it would take at least 14" beams at 16"on center to support the load I want.

[pelligrini]

A steel beam would probably be the most expensive, but you could also put a rolling shop hoist on it if a need arises.

[JSUPreston]

In my case, the shop is totally isolated from the house, so danger to the house in nil. The thickest beam I could probably go with that would intersect the rafters at their overlap is 10", maybe 12". Any more than that, and I'll finish scalping myself.

I was hoping that some sort of i-beam might work, be it wood or steel. However, I don't think I want building inspectors and structural engineers crawling all over the property. Our house was built when our 'hood was in the country, and I'd be willing to bet that we are out of code (yet apparently safe) on a lot of stuff. For example, up until 3 years ago, we had a grey water line emptying into a garden.

I think the block walls would handle the load, but I would have to bring in an engineer to be sure.

Looks like I will just have to deal with the column, until I can run across a spare $10k or so to build a new shop. Just out of curiosity, how much would one of the wood and/or steel i-beams be? I couldn't find a price using the web.

Thanks for all the valuable input! You guys are incredible with the amount of knowledge you have.

[Uncle Cracker]

Just out of curiosity, how much would one of the wood and/or steel i-beams be? I couldn't find a price using the web.

I don't think you will find a price on the web. Look instead to a truss company for the wooden beam, and to a company that sells (or demolishes) prefab metal buildings for the steel beam.

[jackellis]

ust out of curiosity, how much would one of the wood and/or steel i-beams be? I couldn't find a price using the web.

Expensive. I've been told that a steel moment frame for a three story, 900 square foot house, which prevents racking in high winds or an earthquake, costs on the order of $5-7k in California. Even adjusting for the California premium, you're still looking at a lot of money for a steel beam, labor not included.

[Garasaki]

I'm not sure that's really apples to apples.

Not only because of the california premium, but because of the radically different design parameters included. Said moment beam would have A LOT more load, I think, then this dudes garage beam.

Really the only way to know how much it will cost is get ahold of someone to come bid it for you.

[Tequila]

Really the only way to know how much it will cost is get ahold of someone to come bid it for you.

Good advice, since the price of the beam itself is going to be a fraction of what it will cost to get it on site. And installing it is going to be a whole other can of worms, since you need to put in temporary supports to hold the roof up while you remove the old 2x8's. And you'll need some equipment brought in to lift a beam that heavy into place.

You really need to get in touch with someone who can come out and give you suggestions and pricing in person. You're just spinning your wheels asking what parts will cost.

[LarryG]

Guys, c'mon. A roof on a 20x20 shop building isn't exactly rocket science. So, setting all the Chicken Little stuff aside for a moment ...

Preston, I called our structural engineer and relayed the specifics in your OP to him. Before I go any farther, I must caution you -- despite that I said above -- that the information that follows should be considered PRELIMINARY and you would still be well advised to have a structural engineer look at your building. This is especially true with respect to the way the new roof beam (however it is done) bears on your existing concrete block walls.

Here are three options for you:

1. Onto each side of your existing (4) 2x8 beam, bolt on (1) 1-3/4" W x 14" D LVL (Laminated Veneer Lumber) beam. That is, you will need two such LVLs, one per side.

2. If the 14" depth is a problem (which you indicated it might be), you can instead add (2) 1-3/4" x 11-1/4" LVLs onto each side of the existing beam. IOW, for this approach, you'll need four LVLs, two per side.

3. If you want to replace the wood beam entirely, you would need a W8x15 steel beam.

For the LVLs, you should be able to call a good lumber yard (but probably not Lowe's or HD) and get a price. For the steel beam, just call a steel fab shop and tell them you need a W8x15 that is 20' long and they should be able to give you a price.

IMO, and also that of our engineer, either of the two LVL solutions are the way to go, because you're talking about two to four pieces of store-bought lumber, some thru-bolts, and half a Saturday of your time.

But again, the way the beam bears on the block wall is important. The depths of the various beams wouldn't change, but the ends do have to have adequate bearing area and be properly anchored. If bearing the beam ends on the wall was a problem, you could rest them on new wood columns that are hard up against the walls. Several options within each option ... which is why you need to get someone local to look at the problem before you actually do anything.