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Beam sizing ??

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Forum topic by honeydonot posted 08-18-2013 11:57 AM 1108 views 0 times favorited 15 replies Add to Favorites Watch
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honeydonot

4 posts in 1203 days


08-18-2013 11:57 AM

I am looking to build out the bottom 8’ of the top floor of our cabin.
This is the front of the cabin, that is 2 stories of open vault space (16’ 9” high).
The build out will be 3’ deep x 19’ 7” wide.
I need to size a beam to span the 19’ 7” opening.

The roof of the cabin is supported by 4-3”x12” laminated (spruce or pine beams) 1 on each exterior side wall, and 2 spaced at 8’ centers (so cabin is 24’ wide). The beams are 27’ 4” between the front and back supporting exterior walls. The front has a 36” overhang, also supported on the same beams.
The exterior roof is a laminated asphalt shingle, likely on 3/4” plywood or OSB.
Although it is cold in Alberta, Canada, we don’t get a real heavy wet snow. I would think a snow load rating of 20-30 lb/sf would the maximum.
I have attached a couple pictures of the interior side of the front pf the cabin(sorry the picture quality is poor).
The 8’ height being removed, is about 7” down from the bottom of the upper windows. Assuming the height of the beam will need to be greater than 7” (unless it is made of steel), we will have to live with a noticeable beam, that will encroach down into the new opening.
I was figuring on either a 3.5”x12” LVL or 2 sistered 1.8”x12” LVL beams.
Does someone have the means to calculate the actual required beam size?

Thank you for reading the wordy post.


15 replies so far

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NoLongerHere

893 posts in 2135 days


#1 posted 08-18-2013 01:14 PM

I can’t visualize what you are doing 100%. need more info. Are you building a 3 ft. “display” platform above the doors? inside or outside? what is it? Will there be a railing?

You can do a scaled drawing with all the info and give it to the beam company and they will size it for you.

19.7” is not that long really. If your existing floor joist are 2×8s or 10s and your worried about a beam sticking down, consider installing two of the same size with a 1/4” flitch beam…. but check all loads and codes to be sure. (disregard if exposed on the exterior.)

I hope this helps a little.

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firefighterontheside

13435 posts in 1316 days


#2 posted 08-18-2013 01:25 PM

By flitch do you mean a piece of steel the same length and width sandwiched between 2 2*10 and bolted together.

-- Bill M. "People change, walnut doesn't" by Gene.

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NoLongerHere

893 posts in 2135 days


#3 posted 08-18-2013 02:38 PM

yep

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honeydonot

4 posts in 1203 days


#4 posted 08-18-2013 05:00 PM

Thanks for your replies. I will try to explain better.
The span that I am trying to determine the beam size for, is for the new opening that I will be creating in the exterior wall of the cabin. If you look at my pictures, I will essentially be removing the 4 lower windows, and need to support the roof on the front side of the cabin.
I hope that makes it clearer. If there is more info required, please advise.
As far as the LVL guys go here (Alberta, Canada); when I last had to purchase a LVL beam for the last wall removal I did (wall removal on interior of house), the lumber yard engineers would only comment on engineered floor joists, not dimensional lumber or LVL beams.
Thanks again

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MrRon

3926 posts in 2703 days


#5 posted 08-18-2013 05:07 PM

Since this is an interior installation, snow loading doesn’t enter into the picture. Here are some examples:
For sleeping rooms and attics; 30PSF live,10PSF dead load; a 2×12 str sel spruce/pine/fir, 21’-6”, 16" spacing; 23'-7" @12" spacing. These are from the "Visual Handbook od Building and Remodeling" by Charlie Wing. Canadian codes quoted.
All rooms except sleeping rooms and attics: 40PSF, live; 10PSF dead load; a 2x12 str sel spruce/pine/fir, 21'-6"@12" spacing; 19'-6"
16” spacing.
Hope this helps.

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honeydonot

4 posts in 1203 days


#6 posted 08-18-2013 05:21 PM

The beam will be an interior beam. The only place snow load would play into this, is that it is supporting the top part of the exterior wall, which is supporting the 2-3”x12” finger-jointed laminated beams in the picture(s), which are supporting the exterior roof. There are no living quarters above support beam, only exterior wall and roof, so I was figuring on a 20-30 PSF snow, and a dead load. I believe a typical roof dead load is 10 PSF, also supporting the upper part of the “window wall”, so 15 PSF
I don’t see where any joist spans play into this??
Thanks for your reply, let me know if I am explaining the job adequately.

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NoLongerHere

893 posts in 2135 days


#7 posted 08-18-2013 05:43 PM

man, I was in left field taken a whiz when they handed out the plans… what happened.

much better explanation. never mind my first reply…NFC

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REO

889 posts in 1533 days


#8 posted 08-18-2013 05:47 PM

a hand sketch of the existing and projected floor plans would help. two elevation drawings would help as well. these will give a complete concept of what you want to do. include a few reference dimensions.

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Woodendeavor

276 posts in 2066 days


#9 posted 08-18-2013 10:34 PM

I believe I understand what you are doing and don’t think it is possible. The space between windows 1 and 2 and between window 3 and 4 are point loads carrying the beams in the ceiling and were designed to carry the roof load with no deflection. That being said any beam you put in there will have deflection in it and will not support the roof as it was designed. My only advice would be to find doors that match the rough openings of the windows otherwise I would suggest you talk to a structural engineer

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firefighterontheside

13435 posts in 1316 days


#10 posted 08-19-2013 01:01 AM

I think you may be able to get by with one post in the middle. Like woodendeavor said, the columns in between the windows transfer the roof load all the way down to the foundation. Either way there is not going to be a table to tell you what you might use. An engineer would have to calculate the load and then determine what is needed to span the distance. In the process you would have to put up several temporary columns to support the roof timbers.

-- Bill M. "People change, walnut doesn't" by Gene.

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NoLongerHere

893 posts in 2135 days


#11 posted 08-20-2013 12:44 PM

let me try again.
So what you are saying is you want to build a 3 ft x 20 ft. addition with a flat roof attached between the windows and the existing 4 windows removed to create a 19 ft. cased or drywall opening. Right?

The flat roof is going to be problematic and a little odd, it will be “squatty” and obvious it’s an addition.

What if – you took the whole wall, floor to vaulted ceiling and moved it to the end of the beams? You could extend the roof to recreate the overhang, even add to the end of the beams if you wanted.

one last idea – Install an all glass four seasons sun room and make four cased openings where the windows were, no beam work required.

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crank49

3980 posts in 2430 days


#12 posted 08-20-2013 05:59 PM

To meet code we have to design to a 35 lb snow load in Tennessee and the biggest snow I ever saw here in the last 60 years was 18”. I can’t believe you would only need 25 to 30 lbs in Alberta.

I once spent a few days in Edmonton in the winter. Cold and dark pretty well sums up my first impression. There was not a lot of snow then, but it sure felt like the potential was there.

-- Michael: Hillary has a long list of accomplishments, though most DAs would refer to them as felonies.

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honeydonot

4 posts in 1203 days


#13 posted 08-21-2013 03:28 AM

Thanks reedwood, your suggestion about moving the whole wall out to the end of the beams, was a plan b, but there are a few other complications or compromises that are too great.
Like woodendeavor suggested, I will need to talk to a structural engineer, to see if this is even possible, then I will address beam size if it is possible.
Thank you for all of your input.

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NoLongerHere

893 posts in 2135 days


#14 posted 08-21-2013 02:20 PM

Any chance you can leave the two side windows and just have a 8-9 ft. cased opening?

That would leave the supporting structure under the two side beams untouched and you could install a new shorter header over the two center openings.

My guess. it would still have to have steel in it, maybe even steel columns/cripples and a beefed up floor. That’s a lot of weight in the center, but it’s definitely do able and ten times easier than removing all four windows.

I’m still wondering how you’re gong to frame the flat roof, add pitch, flash to window trim and waterproof, insulate and add recessed cans in such a small space. That’s why I was suggesting the aluminum framed sun room. It seems like it would be perfect for this application.

BTW – Did you check to see if your HVAC can handle this added sq. ft.? You might have to extend or add floor vents too.

I enjoy brain storming projects like yours…. thanks for listening.

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REO

889 posts in 1533 days


#15 posted 08-21-2013 02:54 PM

as has been mentioned before there are existing point loads. if you want to move the point to the center then you will have to tear up the floor and put town a new footer or be sure the under laying wall can take the focused load. nothing can be derived fro the pictures and the description given. it is certainly possible to determine a beam that will do what has been asked but better info needs to be provided.

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