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need hole in concrete for HVAC-how to support floor joists?


hammerash's Avatar
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10-01-08, 10:15 PM   #1  
need hole in concrete for HVAC-how to support floor joists?

put an addtion on and need to enlarge a hole in foundation from about 24" wide to about 48" wide. this is end supporting joists and roof, BUT on first floor there is sliding glass door right above and therefore a header is distributing the weight around the current opening. I have a 4x6 seal plate. the original house had a span of about 11'. they essentially put ledger board to side of seal plate and attached joists for the addition. the total span is 23'6". I need to enlarge the opening in foundation to about 48". This opening will be under the door header. the door will in fact be removed later on and a larger header (LVL) will be placed to widen the opening. so I am looking at having to support 3 joists (if looking at them as being continuous over the seal plate, which I believe is correct way to view this) I can not get piece of angle iron in there. I was thinking of putting another 4x6 under seal plate and putting angle iron under this (like used when put brick over window). then putting 2 2x6's on each end as jacks. does this sound reasonable? in the old house, this is kitchen and there isn't anything located near this area as it is walkway into the dining room in new addtion. there will be cabinets at the other end of the joists. so not really much in way of dead load.

 
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OhioDraft's Avatar
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10-03-08, 06:10 AM   #2  
i'll have a go at this one, but your description is a little unclear. below is the way i understand it...



is the proposed beam picking up only floor load because of the door above? do you have enough room for this sort of a construction, as in fnd. wall depth? regardless, i wouldn't trust a few inches of unreinforced concrete to hold anything at all. the hole in the concrete will have to be cut right up the sill and the sill then supported with something. the trib of each floor span will determine exactly what that will need to be (if i am correct that there is only floor load above this opening). and with a total span of 23'6" and an assumed 11'9" trib (half of total span) @ 40 psf DL+LL your looking at (2) 2x6's for that beam. the calcs also support (3) 2x4's but i would definitely be hesitant to do that.

TGIF

 
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10-03-08, 11:45 AM   #3  
your drawing is close. There is a 4x6 sill plate (4 high by 6 wide) sitting on 6" of concrete and the old joists are hung from side of it (inside crawl space). they put a ledger onto this sill plate on outside and then hung new joists onto the ledger. you are right about the door above-the opening in concrete will be completely within the door header so I would only be carrying floor load with a total span of 23' 6".

now your drawing shows the new proposed 2x sitting on the concrete. that would be very hard to notch out the concrete like this. I was going to put another 4x6 underneath of the sill plate and then put an angle iron around this 4x6 and then use two 2x6 jacks on each end. if you are saying that 2 2x6's or 3 2x4's underneath the original sill is enough, then I probably wouldn't need the angle iron as a 4high x 6wide should be at least as strong as 3 2x4's? but angle iron is not that expensive so probably just use it. see drawing below. I guess I actually would be carrying 4 joists since I need at least a 48" wide opening (3 joist cavities=4 joists) and then need some space to get the 4 jacks in (6") for total of 54"


 
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10-03-08, 12:40 PM   #4  
ah i see. the joist set up is a little odd. anyways, if you want to use the 6"wideX4"deep beam, I calc'd a glulam at that size that will be more than sufficient, unless your installing a hot tub directly above or you live on the san andreas fault line. just dont substitute that for a piece of solid lumber, its not the same strength as laminated beams (obviously).

make sure your 2x6's get good, flat bearing on the wall below the beam. the angle seems unnecessary but better safe that sorry. good luck

 
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10-03-08, 02:53 PM   #5  
can you direct me to a manufacturers web site for the glulam? I can't seem to find any with those dimensions. Tried louisiana pacific, georgia pacific. didn't see anything that was only 4" deep. most where at least 7" or more. I will try calling a lumber supply and see what they have or can get.

 
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10-03-08, 04:38 PM   #6  
found this

http://www.ilevel.com/roofs/r_ParallamPSL_beams.aspx

click on the specifiers guide. Looks like a 1.3E timberstrand LSL, 3 1/2" wide x 5 1/2" deep would be good for a 4'8" opening on a depth of 24' (mine was 23'6")(page 6-floor one story). only need 1 1/2" bearing at each end. am I reading this right?

I had planned on using regular lumber 4x6 and the angle iron. the angle would have been 1/4" thick and 6" wide x 4" high. I did not do calculations since I don't know where there are tables for steel angle like this. THe steel would be nice cause I can readily get it near me. I may have problems getting the glulam or the timberstrand.

 
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10-04-08, 01:37 PM   #7  
if the glulam is not easily accessible, the solid lumber with the angle you suggest would be fine, in fact it would be more like overkill as it seems. But the lumber would not be sufficient by itself. i would still use (2) 2x6's at each bearing just for good measure.

 
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