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Beam sizing for span??? Want to cut a 12' hole in my log wall :)

Started by Piston, October 02, 2017, 04:55:27 AM

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Piston

I'm trying to use the "toolbox" calculator to figure out how much I can "open up" a 3 season enclosed addition or not.  https://forestryforum.com/members/donp/beamclc06b.htm

I have a room in my log home that is directly opposite my central fireplace, it's about 10' deep by 12' wide, and is basically a 'sitting room'.  I call it my whiskey room.  (although it doubles as a 'coffee room' on nice mornings) ;D  However, it's uninsulated and closed off from the main house, separated by a homemade (also uninsulated) dutch style door.  So it isn't exactly 4 season friendly!  The whiskey room is conventionally framed with 2x4, not logs like the house.

Here is a photo.... The room I want to open up is the door on the left


(Just remembered why I don't post many photos on this site!  I tried uploading more they are all failing, hopefully you get the point  ;D)


I want to open this room up, so instead of it being a separate space, it's part of the main living area, sort of like an "el" I suppose???  So ideally, I'd take a chainsaw to the walls and put a 12' opening in, which is the width of the room, but...I know it's not that easy  :D

First problem of course, is that it needs to be fully insulated, there are a LOT of other logistics involved but I'll try to stay on track.  Aside from that, I need to figure out what size/type of beam I can put there that will support the 12' span.  This is where I'm having an issue... I don't know how to figure out what the "total load" or "dead load" is for my roof, that will be setting on top of this 9' span. 

The walls are 8x8 logs.  The top log will stay, and will be the support.  (Actually the top logs are smaller sections that wouldn't make the span, so I'd have to replace them with one solid length beam)

I had a pretty good handle on basic structural understanding and loads back when I was addicted to reading timberframing books, but that information seems to have been misplaced and is no longer in storage within my brain cells.   :)

In addition to opening up the floor plan some more, and getting a bit of extra usable space, I'm hoping that this would allow a fair amount of extra light in the house, as it is extremely dark in here all the time. 

-Matt
"What the Lion is to the Cat the Mastiff is to the Dog, the noblest of the family; he stands alone, and all others sink before him. His courage does not exceed his temper and generosity, and in attachment he equals the kindest of his race."

Don P

look down from above and accumulate the loads first.
describe the roof. I see a heavy timber truss, is it structural or decorative... is it in the opening?
Is there a structural ridgebeam with common rafters sloping down to the log wall with another shed roof from the whiskey room landing somewhere on that?

then quantify... what is the log roof span (building width/2), the whiskey room depth, where those rafters land, and the local snow load.

Roger Nair

Piston, this could be a tricky kind of build.  My list of concerns beyond Don P's would be:

1.  The wall to be removed is 2 x4 and where the beam needs to be placed is in an area of convergence of different planes of roof and ceiling from the rooms on both sides.  Ideally, the beam should fit into the 3 1/2 inch space left by the removed studs.

2.  The choice of beam could be one of a number of manufactured lumber beams, flitch plate core build up or even sawn lumber.

3.  The available height is a problem and could limit the beam options.

4.  The state of the foundation to accept a significant point load must be determined.

Good luck.
An optimist believes this is the best of all possible worlds, the pessimist fears that the optimist is correct.--James Branch Cabell

Piston

Quote from: Don P on October 02, 2017, 07:31:51 AM
look down from above and accumulate the loads first.
describe the roof. I see a heavy timber truss, is it structural or decorative... is it in the opening?
Is there a structural ridgebeam with common rafters sloping down to the log wall with another shed roof from the whiskey room landing somewhere on that?

then quantify... what is the log roof span (building width/2), the whiskey room depth, where those rafters land, and the local snow load.

I was able to get this photo to upload, it's not great, but shows a better view of the wall portion I'd like to remove.


The trusses are decorations, not load bearing.

The roof rafters are 2x12 and slope down to set onto the log wall that your looking at in the picture above.  The house is a saltbox style and this is the "long" side of the roof.  The span from the ridge beam down to where the rafters rest on the wall is approximately 22'.  It is a metal roof, and my snow load is 90 lbs/ft. 


It's a little hard to tell in the photo, but just above the door there, you see the last 'seem' between the logs, then the T&G pine starts up the ceiling.  Those beams you see are sitting on the log wall, I have not taken the pine down to see exactly how they are set there. 


I was able to "snippet" a photo of a photo (can't get it to upload to this forum) of the house.  This is how the outside of the room sits in relation to the house.


The room is 10' deep. 
-Matt
"What the Lion is to the Cat the Mastiff is to the Dog, the noblest of the family; he stands alone, and all others sink before him. His courage does not exceed his temper and generosity, and in attachment he equals the kindest of his race."

Piston

Quote from: Roger Nair on October 02, 2017, 09:56:19 AM
Piston, this could be a tricky kind of build.  My list of concerns beyond Don P's would be:

1.  The wall to be removed is 2 x4 and where the beam needs to be placed is in an area of convergence of different planes of roof and ceiling from the rooms on both sides.  Ideally, the beam should fit into the 3 1/2 inch space left by the removed studs.

2.  The choice of beam could be one of a number of manufactured lumber beams, flitch plate core build up or even sawn lumber.

3.  The available height is a problem and could limit the beam options.

4.  The state of the foundation to accept a significant point load must be determined.

Good luck.

Thanks for the reply Roger. 
The Whiskey Room itself is conventionally framed with 2x4, however the log wall that it attaches to, the one that you see in the second photo posted, is all 8" log construction. 
The height could be an issue, however as long as the beam stays above the current door header height, I think I'd be okay with it. 
-Matt
"What the Lion is to the Cat the Mastiff is to the Dog, the noblest of the family; he stands alone, and all others sink before him. His courage does not exceed his temper and generosity, and in attachment he equals the kindest of his race."

Roger Nair

An optimist believes this is the best of all possible worlds, the pessimist fears that the optimist is correct.--James Branch Cabell

Don P

Cool. the whiskey room roof is bearing on the red entry door wall and the opposite wall across from that not on the main roof. It looks like the chimney shields the whiskey room valleys somewhat.
I think that "span" of 22' is the length of the rafter not the horizontal measure from wall line to ridge. I'm calling it 16'... a 32' wide building?

It wouldn't hurt to design around carrying the entire 12x 16' of area, it looks like that is 50 pound per square foot country, check that. 12'x16' x 60psf (50 live + 10 psf dead load)=11520 lbs on a 144" span

I would go to an LVL for this, so manual design value entry;
https://forestryforum.com/members/donp/beamclcNDS2.htm
load 11520
span 144
width3.5
depth 11.875
Fb 2800
E 2.0
Fv 280

I'd actually try to sneak a third ply in there for a 5.25" depth
you are point loading the ends of the log wall at the cutouts. I would stand vertical posts under the beam so they bear the load rather than the log wall. As per Roger's comment, look under the floor, harden that up and make sure the foundation and footings can handle an additional 3 tons under each post... trace that load path from the roof to the footings.

The vertical posts can work to brace the cut wall. If you plow a dado into the face of the post that will butt up to the log wall say 1-3/4 deep x 2" wide and tenon the ends of the logs to slip into that groove the post will help stabilize the log wall.

Piston

Wow, thanks Don!

Your correct about the span, 16' (I did give you length of rafter 22' as you suspected)  ;D

Because of where I am on the mountain, my snow load is 90lbs per sq. foot. Is that what you were referring to as the 50lb live load?

Also, I could go up to 7.5" wide on the LVL if that adds a lot more strength, since that would equal the depth of my log wall that it will be sitting on?

I will plan on posts at each end with the notch/tenon cutout as recommended.

Roger,
The foundation underneath this wall is an 8" concrete wall sitting on the main footer under that.  I'd imagine this should be sufficient but could use some reassurance  ;D


Thanks again, very helpful.
-Matt
"What the Lion is to the Cat the Mastiff is to the Dog, the noblest of the family; he stands alone, and all others sink before him. His courage does not exceed his temper and generosity, and in attachment he equals the kindest of his race."

Don P

tell more about the top end of the rafter, and the shed dormer to the rear. Is there a beam with several posts under the ridge, or a wall, or a level ceiling...what is holding that end of the rafters up?

The lvl's come 1-3/4" thick so 4 plies would be 7" wide on the calc, 90+10= 100 psf load on 192 sf =19200 lbs. I get a pass. This is into engineer territory. with engineered components that is part of the service of the sale. Draw out and dimension everything, take pics of everything we are talking about. Take that to the beam supplier and ask for them to specify the beam.

It would take pretty extensive roof work but you could open a vaulted whiskey room roof into the main roof plane for maximum light.


ChugiakTinkerer

Piston, the snow load that Don mentions may be after taking into account the pitch and metal roof.  For most roofs, the snow load is less than the ground load, but there are numerous factors that go into calculating a roof snow load.  The IRC avoids that by just using the ground snow load and requiring you to build for that.  But if you can get an engineer's assistance, you may be able to arrive at a design load that is under 50 psf.

The magic formula is in the publication by the American Society of Civil Engineers, ASCE 7 - Minimum Design Loads for Buildings and Other Structures.  In addition to the factors above, the ASCE 7 looks at building use, heating and insulation regime, and the prevailing wind and tree cover around the building.  It's complicated and unique to every structure, but it's within accepted engineering practice and will give you a realistic estimate of the loads your roof is holding.  It may be worth consulting with a local engineer to see what you're dealing with.
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