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|10-23-2013, 12:47 AM||#1|
Join Date: Oct 2013
Posts: 2Rewards Points: 10
Could use some help with garage ceiling.
Hi, everyone. Hoping I'm not beating a dead horse here, but I've lost a few nights sleep over this so I thought I'd join and ask.
I have an outbuilding that came with my (very old) house. It's a simple block building with gable roof, asphalt shingles, traditionally framed roof with the following specs:
12' 7" wide appx.
42" rise in roof appx from top plate to bottom of ridge
=> ~6.7/12 pitch
Walls (and thus ceiling) are about 88" high.
The roof is framed with 2x4's for the ceiling joists/rafter ties as well as the rafters, and has a single top plate made out of 2x. Collar ties are 1x and it has a 1x6 ridge board. Rafters are 16" apart. OSB/shingle skin.
I need the maximum amount of headroom. I'm 6'4" and need to be able to press a loaded barbell overhead without a second thought about it hitting anything. This includes olympic lifts like the snatch and jerk. I'd also like to be able to do box jumps, pullups, etc. As-is, I need at least a foot more, but I'd like as much as I can get.
I'm not sure if I can get away with less here because there's no snow load really - I'm in the deep south. Given that it's effectively a shed with no snow load, but a "serious" roof, can I just move the joists up the rafters halfway?
If that won't work, I'm guessing I need to go the beam route (unless there are other ideas with structural purlins or something better) in which case I was told I'd need two 14" LVLs to span the 24 feet. Do these have to go to the floor or can they sit on the gable walls/top plate? 4x4 post or 6x6 needed?
There are no birdsmouths on the rafters - can I just nail up a wooden wedge on the top plate in this case?
I'm happy to take some pics tomorrow as well if needed. Unfortunately, money is VERY tight and I want to strike while the air is cold since I've found a ton of dead brown recluses in there. If I can get away without a beam and moving the rafter ties up halfway, I'm in. I know most places say 1/3 up the rafter but a) it's a shed pretty much and b) no snow here. That is, not sure if that advice is overkill for my situation or not.
Last edited by myrongaines; 10-23-2013 at 12:50 AM.
|10-23-2013, 01:29 AM||#2|
Join Date: Apr 2012
Location: Fairhaven, Massachusetts
Posts: 2,914Rewards Points: 2,106
Welcome to the Forum!
rafter ties are located within the lower 1/3 of the rafter. the downside to using a raised rafter tie is it reduces the load capacity of your rafters. if at the maximum 1/3 above the top of the wall this reduces the rafter's strength 67%. See Table R802.5 (at bottom) http://publicecodes.cyberregs.com/icod/irc
when your rafter ties are at the top of the wall as is common with ceiling joists and a flat ceiling you are able to take 100% of the load capacity of your rafters.
not knowing what species of wood your rafters are I think you'll see from the span tables that by reducing their capacity 67% they may not handle to the roof load.
a structural ridge beam is another means to eliminate rafter ties and provide a structurally sounds roof. you must transfer the beam loads down to the ground. your existing structure would have to be evaluated if you simply wanted to post the beam down to the existing block wall, which also involves the foundation.
the simple way is to install a column under each end of the beam down to a foundation capable of supporting these loads.
each end of the beam would be supporting over 2,000 lbs., and as much as 2,500 lbs depending on your live load requirements. if your existing block wall and foundation are capable of handling this point load you'd be ok. It is nearly impossible to evaluate a structure over an internet forum, you need a set of knowledgeable eyes on site.
now if it's just a shed and you are not concerned about the outcome you could always do as you suggest and see what happens.
I'd recommend getting the aid of someone local such as an experienced builder or building designer, or even a professional engineer.
"You get what you pay for, and sometimes free costs more!"
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|10-25-2013, 06:49 PM||#3|
Join Date: Jun 2009
Location: atl & hilton head
Posts: 4,341Rewards Points: 4,264
so forget the clean 'n' jerk & just do bench press's now go grab some sleep once lost, its never regain'd
|10-26-2013, 01:31 PM||#4|
Join Date: Oct 2013
Posts: 2Rewards Points: 10
I tore more out of the building, got 2/3 of the ceiling down, and all the workbench areas etc. cleared out.
Looks like part of the foundation has settled in the corner, so I'll have to mudjack that up at some point before proceeding, but:
I've settled pretty much on running 2 14" LVL beams across the 24' span and putting them up in the ridge. I suppose I need to know now how to actually retrofit the beam(s) in. If I want to leave the roof intact, how does one fasten the beam to the rafters? Must I notch/birdsmouth the rafters, or can I stick it up in the ridge and fasten another way? I don't have birdsmouths on the wall plate either, so I figure I'll need to put wedges and simpson ties on there, too.
From there, I'll do it as follows:
Frame a garage door with 4x4 or 6x6 fence posts, and a *****in' header on the gable end. Then put the beam down to that (with another post on the header)
Just run a beam inside the wall on the other end if I must to a point load and maybe frame around that wall and use that area for hanging barbells etc to make good use of it.
Seems to be the most affordable route, no? Unfortunately since I'm getting into strongman style training overhead work is of prime importance.
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