What Size Beam?

[Chainsaw_Willie]

If the wall isn't load bearing couldn't you design the trolley frame to just lift the load instead of holding the house up? IE three pieces of steel 1 horizontal and two vertical.

Or you could just rip the wall out and buy a engine hoist.

Not an engineer but if the rafters don't have any diagonals coming off of them then they are probably just there so when a load is applied to the roof the walls don't bow out. IE they are in tension?

Well, this is what I'm trying to figure out - how much load does the wall bear and how to calculate it? Each rafter that runs from one side to the other is actually two pieces of wood that overlap slightly in the middle (they look like 2"x8"x12'), and the wall down the middle holds them up where they overlap.

So what I gather from all this hemming and hawing is that the calculations to figure out what size beam to put in are so complicated that no mere mortal can figure them out without an engineering degree... Huh.

Attached is a rough top-down view of what I'm dealing with as far as walls and the orientation and overlap of the rafters. If there is no cross bracing from the roof to the rafters then is it safe to say the rafters are merely providing tension to keep the walls from bowing out? If that's true, then what keeps the front & back walls from bowing in a structure where the rafters are one piece and there is no wall in the middle?

[Yanos]

If you are really persistent on engineering this yourself you need to at least figure out the truss construction to determine if the the interior wall is load bearing. Member dimensions (length, configuration, type (2x8...etc.), connection). Once you determine the trusses are meant for clear span, well, then it's easy, you just need to determine the load of the trolley, hoist and load rating plus some measure of safety. If not clear span, well it's slightly more complicated. Local requirements regarding loads (dead, live; seismic, wind, snow, etc.) will need to be included in the calcs. And lets ignore foundation construction for now.

The simple answer would be to find the original stamping engineering (may have to ask the architect) and pay him the couple of hours to give you a proper edmucated answer. Can you calc and solve this issue yourself??? Sure. The question is what level of confidence will you have in the result, even with the help of anonymous mags...

Take it for what its worth from a civil guy (non-vertical) who is half in the bag, I'd at least seek outside counsel to verify my results.

[BCMtnHound]

Just anecdotal. Old house from the 50's I rented had a garage exactly the dims and such as your pic. Double doors and no interior supporting walls. Never peeked into the enclosed roof structure, but it held the Oct '06 dump of 1m until melt in Apr.

Hoists are sweet. Pics upon completion plz.

[BigDaddy]

I use a local engineer who charges by the beam. It's usually $150 and he does it while I wait.

Even though I sort of know how to do it, it is money well spent. Your's is a pretty simple problem, so I wouldn't imagine it costing much more than $200 or so.

Another thought is to go to your local lumber yard. They sometimes have people who will calculate it for you. They'll let you know what info to provide. Is this for the Firebird (or Trans Am) workshop?

[Foggy_Goggles]

In your picture, the central line is the wall you are wanting to replace correct?

Your sure that the roof construction is rafters, not trusses?

Does this wall go all the way to the ridge, beam if rafters?

I guess I'm not understanding the existing construction, a picture would go a long way. How is an interior wall supporting rafters? It might be supporting the ridge beam (are their posts coming down from the peak of the roof onto this wall?) or the bottom chord of a truss.

Are you getting a permit? If not do you care that in the future when you sell the property it may be obvious that that you did non-permitted work? If yes, the building department will either require a engineered set of plans or may do the engineering for you (they will in my country). If no, draw up some basic plans and give them to the place where you buy your steel, they may be able to do some engineering for you.

I understand where all the engineers are coming from. You actually may end up saving $ by bringing one of them in on the project. What ends up happening often when you self engineer is that the additional costs for your safety factor (more expensive materials, more intricate design details, wasted labor) cost more than having an enginerd say "do it like this".

That said, find the right engineer with a get it done attitude. Too many of them have little real world construction experience and have some overly complex retarded ideas. Still getting over trying to explain to one of these losers that you really can't easily replace a 20" X 30' cantilevered log that buried 8' inside the house.

[RootSkier]

What foggy said. No offense, but if you are calling ceiling joists "rafters," you may need design assistance.

[userA]

these dentists are telling you to seek professional help will.
b

[bushman]

Engineers smengineers, just do it, thats what I do and sometimes it turns out pretty good.

[::: :::]

And lets ignore foundation construction for now.

actually, new footings under new posts are pretty much required


and this is a good suggestion for a lead on engineering. if they don't have a detailer on staff or on consult, they'll at least know someone to get you going.

give them to the place where you buy your steel, they may be able to do some engineering for you.

i'm guessing you can get an engineering solution for $400 or so
it will give you peace of mind and a good parts list with instructions for how to install everything correctly and to code
(if nothing else, it will help resale down the road to have properly engineered structure on the property)

[::: :::]

If there is no cross bracing from the roof to the rafters then is it safe to say the rafters are merely providing tension to keep the walls from bowing out?

potentially...are the horizontal members holding any attic space/storage? are they continuous? or lapped? what size are they?
can you draw the section of the roof? ie what the framing looks like from the side with sizes shown and spacing dimensions?
what are the exterior walls made of? 2x4's 16" on center? do they have plywood on the exterior under the cladding?
when was this structure built?

If that's true, then what keeps the front & back walls from bowing in a structure where the rafters are one piece and there is no wall in the middle?

the plywood on the roof creates a diaphragm that stiffens the structure in the long direction, as do the parallel walls along the exterior (and maybe this new beam), and blocking between them, and down to the slab which, if there's no footing, probably has at least a thickened edge

[RootSkier]

the plywood on the roof creates a diaphragm that stiffens the structure in the long direction, as do the parallel walls along the exterior (and maybe this new beam), and blocking between them, and down to the slab which, if there's no footing, probably has at least a thickened edge

This is wrong. Usually, and it sounds like the case in willie's garage, the walls are roof are held together by the CEILING JOISTS. Vaulted roofs require a structural ridge, which means the ridge is usually substantially larger and there is a more significant connection at the ridge/rafter connection.

[RootSkier]

If that's true, then what keeps the front & back walls from bowing in a structure where the rafters are one piece and there is no wall in the middle?

A structural ridge.

[::: :::]

This is wrong. Usually, and it sounds like the case in willie's garage, the walls are roof are held together by the CEILING JOISTS. Vaulted roofs require a structural ridge, which means the ridge is usually substantially larger and there is a more significant connection at the ridge/rafter connection.

you're right...i misread it and thought he was asking about the direction perpendicular to the joists

sorry will!

[Chainsaw_Willie]

Dang, this is a lot harder to explain than I thought. Okay, I'll revisit this after I'm fully moved in and can take some pics.

But, the roof is basically a pyramid shape like in the picture I posted. There are "rafters" or whatever they're called running parallel to the front and back walls of the structure that are each two pieces of wood that overlap at the central wall, as in the drawing I posted. I don't think there are any joists because there is no bracing to the roof structure from these rafters.

I'm calling them "rafters" but maybe that's the wrong terminology...

Anyway, I'll get some pictures later and yes, my Firebird will be living in here.

[Tippster]

Wife is a remodeler who does all the drawings for her shit and then gets a stamp. Her answer is "it depends. Get a local Structural Engineer on it." Basically she is echoing the other voices of reason in this thread. Talk to a pro.

[GoldMember]

Willie, I am an engineer and am going to tell you; get an engineer. You have more than just sizing a beam to deal with. You'll need column supports at each end, footers under the columns, size dependent on your local soil, and some determination if the end connections on the beam need to be 'fixed' connections to the columns if the wall is a shear wall. Get someone to come out, take a look at what you have, and help you with your decisions. BTW, doesn't matter if you use steel or wood, you still have the same concerns.

[userA]

these are dentists not engineers but congrats on the upgrade.
b

Willie, I am an engineer and am going to tell you; get an engineer. You have more than just sizing a beam to deal with. You'll need column supports at each end, footers under the columns, size dependent on your local soil, and some determination if the end connections on the beam need to be 'fixed' connections to the columns if the wall is a shear wall. Get someone to come out, take a look at what you have, and help you with your decisions. BTW, doesn't matter if you use steel or wood, you still have the same concerns.

i was wrong will, appears to be an engineer in the house.
b

[east or bust]

i was wrong will, appears to be an engineer in the house.
b

Make that two.

OP, you really need someone on site to answer your questions. We can speculate all we want but like GM said there are a lot more factors that come into play than one would think.

[EarlyWood]

So what I gather from all this hemming and hawing is that the calculations to figure out what size beam to put in are so complicated that no mere mortal can figure them out without an engineering degree... Huh.

like your attitude.. :-))

I've been googling this and reading what I can find but that shit's confusing and most of it seems to have to do with supporting a floor, not a roof structure.

you're not supporting the roof structure in sizing this beam... pay attention to the shit about supporting a floor


I haven't sized steel in like forever so am not going there with you.

good luck
:-))

[farmer]

Engineers smengineers, just do it, thats what I do and sometimes it turns out pretty good.

As an old prof once said, "Anyone can build a bridge; over and over again until it stops falling down, or once for 100x what it should cost by over-designing everything. But a good engineer can build it once, in the cheapest way possible.

[GeezerSteve]

As others have noted, you'll need a structural PE stamp to get a permit for this

[Beaver]

I spanned a 16'8" span in a house with a steel I beam once. It was on the main floor with one floor above so I had to consider the live load (floor with people walking on it) and the roof load (covered in snow) to figure the steel size. It ended up being a 102pound/foot wideflange 8" I beam. I had to get tongues welded to the ends to keep it from rolling and attach it to the posts it sat on. I also had to bolt a piece of 2x8 to the bottom. The 2x8 was required so that in the event of a fire it held up longer.

I only used a steel beam to keep from losing head height. If you used wood you could cut the rafters and attach them to the beam with joist hangers but then you wouldn't have the rolly thing.

I suspect that the addition of the rolly thing is going to kill you for beam size.

I'd talk to an engineer.

[EarlyWood]

If you used wood you could cut the rafters and attach them to the beam with joist hangers but then you wouldn't have the rolly thing.

Listen..these horizontals... are not fucking rafters
call em ceiling joists, call em tie beams....they are NOT fucking rafters

you got that willi et al....don't come back here calling those fuckers rafters again

[skiballs]

I don't know whether to laugh or cry at this thread.
An engineer for a 20'x20' garage, really?
OP find a carpenter that knows what he's doing ( not so easy these days ).
20 or so 2x6's and that wall is gone. Get a rolling engine hoist, done.

[RootSkier]

20 or so 2x6's and that wall is gone. Get a rolling engine hoist, done.

What exactly would you do with 20 2X6s? Cobble together some retard-strength beam with some PL200 and a few strips of framing nails?