floor joist supports

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  #1  
Old 04-29-09, 06:21 PM
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floor joist supports



I've "inherited" this project & will need some help deciding what the best techniques would be to complete various parts of this job. In this case the question is about the floor joists & the support of these floor joists. They're on 24" centers & are 2 X 8's (maybe 2 X 10's, I'll have to check). I never really liked the X brace type of under-floor supports, preferring instead to use (in this case) 2 X 8's (or 2 X 10's) cut to 22 1/2" & place them 1 1/2" offset to nail them in. What's actually better? How far apart should the supports be from the wall & from each other?

Thanx!
 
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Old 04-29-09, 07:31 PM
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How long are those joists, 16' ? How much weight is going to be or the floor when the structure is done? It looks like you need I beams with columns.
 
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Old 04-29-09, 08:29 PM
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Originally Posted by Pulpo View Post
How long are those joists, 16' ? How much weight is going to be or the floor when the structure is done? It looks like you need I beams with columns.
That's a 36' span. The floor portion in the center is just under 20' wide at that point & the full 36' wide where the stairs & dormer will be. I don't have the spec's handy but it's supposed to exceed whatever the standard deflection/deviation is for that type of distance. Something like 1/16" per inch at so many thousand pounds load I think is something I read in the paperwork.
 
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Old 04-29-09, 09:35 PM
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Those calculations are beyond my scope but even the 20' section seems like a long way to go without something under it. I found something on Google but chances are you're already beyond their examples. Start around page 48.

Carpenter's Calculations Manual - Google Book Search
 
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Old 04-29-09, 11:36 PM
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You need to follow the engineering specifications that came with the attic trusses. I would suggest solid blocking at each side of the attic floor ends, to act as fire stop. While you have this group of attic trusses installed, it is a good time to think ahead. Put a brace on the attic floor in the middle, back to the gable foundation wall nailing each trust on layout. (Rat run) Lay your extension ladder up against the bottom of the floor trusses at a normal climbing angle, anchor the bottom of the ladder and the top. Push your plywood up the ladder the helper, and set the first sheet 1/2 inch away from the upright wall studs. Nail that one in place. Tack the others, to make a temporary floor. Send up your 2x4's, if needed for ceiling bracing above the attic ceiling at this time. Send up your plywood sheathing for the roof, also. Then set another group of trusses, brace them off, and load them.

Do not cut any of these engineered attic trusses. Inform the owner of the live load they are rated at as listed in the engineering documents. Look for any special bracing in the truss webs, above the ceiling, or at the gables, running horizontally midway up the gable. You may also need 2x4 blocking at the peak, two or three trusses back from the gable for the diagonal bracing. The Inspector will look for these also.

Floor bridging or blocking, only distributes a concentrated load. It does nothing to strengthen a floor against a uniform load. It may not be required at all.

The architects' and builders ... - Google Book Search

Be safe, G
 
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Old 04-30-09, 05:35 PM
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Hmmmm, I don't seem to be getting the e-mail notifications of answers to this...

Thanks for the advice, but I don't fully understand it. I'm the homeowner in question, the contractor is no longer in the picture. To help make up for that huge loss I need to do as much labor myself as possible, if for no other reason than to protect what's there from further degradation. I thought the floor blocking/bracing & wings for the gambrel roof (another post in this forum) would be simple enough for me to do. I'm perfectly capable, but I don't have the knowledge of the best way to do it or the proper way (how far apart, how far from the edge, etc.). I know at some point I'll have to hire another pro to pick up where I left off, but I was hoping to do some of the simpler, but more labor intensive, jobs first until I get funding to continue.

So, blocking is OK & possibly better than bracing? How far apart? How far from the wall should it start? My basement uses bracing with blocking under a 1/2 wall. I'll have to pop out some ceiling tiles to see how far apart it is, as I assume similar distances would apply here, right?

I have several other questions but decided to start with what I thought would be the simple ones. Apparenty it's not so simple after all?
 
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Old 04-30-09, 06:52 PM
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You mentioned some paperwork in your first post. Do you have a set of drawings? If you have the drawings, can you post the part in question? If not, do you have $200 for an architect to look at it for an hour & tell you what to do?
 
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Old 04-30-09, 08:17 PM
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Originally Posted by Pulpo View Post
You mentioned some paperwork in your first post. Do you have a set of drawings? If you have the drawings, can you post the part in question? If not, do you have $200 for an architect to look at it for an hour & tell you what to do?
I've got the drawings from the truss manufacturer for the trusses, I'll take a look after work tonight. The rest was to be built on-site & if there were any proper plans on paper for that the contractor kept them. There isn't much to this building that would require more than that though, so I doubt he had more than a hand-written plan with the dimensions. Once the pre-fabbed trusses were up the dormer end-walls (site-built, in the forground, up-side-down in the picture) were to be placed in position & then the dormer roof & side-walls framed, then the wings, bracing/blocking, & steel roof, windows & doors. Then the loft floor & stairs & its done. I'd be surprised if he had more than notes to go by. Architect? I was thinking of a rough carpenter, but maybe I should consider somebody like that too.
 
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Old 04-30-09, 08:52 PM
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Just go to the Building Department and get a copy of the plans, drawings, ect. Of course if this is permitted, no problem. If not, you need help. I would have someone that knows what they are doing check on the framer, flat worker, electrition, etc. Perhaps hire a consulting Contractor to give you direction. This is an involved project.
Be safe, G
 
  #10  
Old 04-30-09, 09:58 PM
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I think GBR had a good idea in the post earlier.. (not that the last post just now wasnt good.. lol)

Its a good idea to lay up some plywood for the floor as you go .. if you try and crossbrace too many floor joists now, you could get some drift just from cutting differences.. the joists wont all be nice and parallel anymore. You could do it with rechecking each joist at the 4ft (end of plywood) portions tho.. but just the idea of being able to slide a sheet up the ladder and turn it without banging into other trusses etc is nice.

One thing to check though.. is the structure square as-is ? If you can, measure the distance from where the existing truss meets the corner of the foundation wall, to where the last truss would meet in the same fashion.. across the whole structure, in an X. If the structure isnt reasonably square, the you have to have a plan of 'splitting' the difference across all the trusses.

I wonder if you can find another carpenter that might allow you to do some of the smaller jobs, alot of them dont like the idea .. there's legal issues, but also it can become a whole 'what if we did this way and that to make it cheaper", or "can you show me how to do this", etc. They like to just look at the job, get an idea, get the parts, get it done, and get paid.
 
  #11  
Old 05-01-09, 07:25 AM
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The most important thing at the moment is the support of that floor. I don't see any other way except columns but if you don't have all the drawings, an architect can confirm or deny that in less than an hour.
 
  #12  
Old 05-01-09, 03:44 PM
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That's supposed to be a clear span under the floor, no columns, & the fact that they're just 2 X 6" had me concerned as well. I looked over the truss info today & after I got through all the disclaimers & bi-lingual stuff I actually found info on the various methods of blocking or bracing that they suggest. I'm confused about the live load, snow load, & I think dead load figures though for the floor area. I'm also confused by these spec's; A 40 psf dead load seems awful low for a storage area. There's also a spec for a 10 psf live load on the floor. I assume psf means pounds per square foot, so if that's the case this floor is rated to be a ceiling, not a floor. I'm wondering now if this contractor was worse than I thought & the trusses are a total loss, as I cannot accept those numbers for an office/storage area loft if they actually mean what I think they do.

After typing all this a light went on in my head; call the manufacturer! I was able to get ahold of them, & although they confirm that these trusses are fine for my application, they're actually working with me to try to figure it all out. As I was typign this they called back to inform me that the loads I mentioned above are for the area outside of the floor area, the spec for the actual usable part of the loft is 85 psf live load. They also explained about the blocking (not needed if the 3/4" tongue & goove floor is used) & perlins, & even how to scab on the wings. I was even assured that I could call with questions at any time. I had no idea their customer service would be so helpful a year after the sale.

Thank you for the advice, I never would have thought to call them (I thought they just sold the parts to my contractor, I didn't realize that they actually designed them just fo rmy job) without coming here. I'm sure I'll be back with different questions later though!
 
  #13  
Old 05-01-09, 06:00 PM
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I'm glad to hear that their customer service is that good & it's good to know that the tongue & groove elininates the need for blocking.
 
  #14  
Old 05-01-09, 10:14 PM
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I forgot to add that they sent me to this site for more info: SBCA - Structural Building Components Association It's the Wood Truss Council of America site.
 
 

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