Need help figuring out barn extension

petebert · Jul 29, 2017

I want to extend the sloped sides of my barn. I've built all sorts of stuff, just nothing quite like this so I don't know the best way to put it together. If I could get some design ideas or a picture of how it should go together, I can build it no problem. Also let me know if my terminology for any of the parts is incorrect.

The gutters/bottom of soffit sit around 12' above the ground. I want to take that down to around 7'. What I'm not sure about is how to tie into the existing structure. I'm going to post some pictures below to show the existing structure. Let's start with the fascia board, that's probably just nailed into the rafters. So that's not weight bearing at all right? Could I put some hangers onto them and make them weight bearing. Then just hang the rafters for the new roof on the opposite side? Or will I need to take the fascia board off and rest the new rafters onto the same beam that the existing ones are resting on. The existing rafters are notched and resting on the beams, also nailed in but I'm not exactly sure how they're nailed in, they're in a tough spot to get a good look at. All the boards are 2x12's, I know some of you guys know the pine span tables pretty well so let me know if I need to double up any of the beams let me know. This will be in SE Michigan so the concern is snow load and if the new roof adds weight to the exisiting roof.

buckeyefarmer · Jul 29, 2017

Take fascia off, put new rafters so top is same as old truss top. End of new rafter against wall of building with a new header under it for load support. New header bolted to existing barn posts. Or maybe you can use hangers from existing barn header for new rafters, if right size.
Im planning to do the same soon.

buckeyefarmer · Jul 29, 2017

And dont hang anything but a gutter from the fascia.

petebert · Jul 30, 2017

Could I notch the new rafters, set them on the existing header and then nail the new rafters to the existing rafters?

buckeyefarmer · Jul 30, 2017

Only if the new rafters are supported from bottom also. Notching at the top end of rafter, so it hangs from the notch takes away from load capacity. You can notch at bottom end of a rafter without losing capacity if notch bears to the bottom of the rafter.
Are your existing headers bolted, or just nailed to the poles? From picture i didnt see a bolt.

Streetcar · Jul 30, 2017

By extending the roof, you are increasing loads on the existing post and headers. You need to verify that the existing materials and connections are satisfactory for the increased loads.
Never attach structural members to fascia

radioman · Jul 30, 2017

here is my 2 cents -- i wouldnt cut your new rafters and make it fit inside of the truss carriers you already have. the new rafters would have to be cut down so thin it would be the weak point of your roof. I would take your fascia off and cut the siding off 12 inches or so down from under fascia and add another 2x12 outside of your post below it so the top of new rafters would line up to the old roof ( be sure to add room to slip the new metal roof under the old or if asphalt, the osb matches exactly at the old roof osb.. keep in mind - you have 2 truss carriers to your old roof, i would use simpson lags screws (kind for ledger support) and screw the new 2x12 to the post since you will only have one for new roof and there would be no birdmouth on new rafters. for each new rafter it would be tied to the new 2x12 below it and nailed to each old rafter at the top.

EddieWalker · Jul 30, 2017

HOLD ON!!!! Do not notch your new rafters or try to put them on top of your existing beams. The notch will ruin all integrity in the rafter!!!!!

Remove the fascia board. Attach a ledger board to the outside wall of your building so it's tight under your existing rafters. Bolts are always the best for attaching a ledger board, but the new style of lag bolts are pretty good too. Just be sure you get the ones rated for a structural load. They are also called structural screws. Be sure that the word "structural" is on there!!! Some of them are just fancy, extra long screws that do not have any load rating. This will be the support to carry the weight of your new rafters.

Then attach your rafters to the side of your existing rafters with the weight of the new rafter resting on the ledger board. To secure the rafter to the ledger board, use metal brackets with proper fasteners. Simpson has several to chose from. The nails they sell work, but can be a pain to install. They have structural screws that cost more, but are real easy to install.

KennyG · Jul 30, 2017

Not wanting to start a fight, but I'm going to question Eddie on this one (always a dangerous move). Rafters are most stressed in middle where the bending loads are greatest. At the ends the load is purely compression where wood, like most materials is very strong. We notch rafters all the time on the bottom end (birds mouth). If I were doing this I would go the ledger board approach but I wouldn't object to notching the rafter if someone wanted to go that way (within reason of course).

buckeyefarmer · Jul 30, 2017

See post 5

buckeyefarmer · Jul 30, 2017

See post 5

petebert · Jul 30, 2017

I'm getting confused here, any pictures of these options? As far as the siding/wall. I'm removing all of the siding. Once the extension is built it will be part of the open area inside the barn. There's a 6x6 post spaced every 10-12 feet. There's 2x4 girts between them for the siding to attach to but those aren't needed for any structural integrity right? The header boards provide all the structural support needed right?

As far as notching them, the existing ones are notched, why couldn't the new ones be notched too ? That being said I'd prefer to not have the extra workload of doing that.

As far as adding a new ledger board or new header. What's confusing me there is I had planned on making the new roof be one continuous roof with the existing roof. So wouldn't the rafter have to line up with each other. So when I picture this in my head the new ledger/header can't be lower than the existing one. On the other hand, if I build a 2nd roof a few inches below the existing I wont have to remove my existing gutters or soffits. And this sounds like a super easy build to me, attach a ledger, use some hangers and your good.

EddieWalker · Jul 30, 2017

KennyG said:
Not wanting to start a fight, but I'm going to question Eddie on this one (always a dangerous move). Rafters are most stressed in middle where the bending loads are greatest. At the ends the load is purely compression where wood, like most materials is very strong. We notch rafters all the time on the bottom end (birds mouth). If I were doing this I would go the ledger board approach but I wouldn't object to notching the rafter if someone wanted to go that way (within reason of course).

When notching the birds-mouth at the bottom of the rafter, you are going from the full width of the board on the strong side, and carrying it over the top plate, or beam. When you go the other direction, and notch the birds-mouth at the top, you have made the thickness of the board what you cut it. To add to the board now being thinner, it is also tremendously weaker due to the tendency to crack at the birds-mouth cut.

buckeyefarmer · Jul 30, 2017

Like this.

buckeyefarmer · Jul 30, 2017

bottom cut, full board still supports weight.

top cut, uncut part of board supports all weight, cut half part, if unsupported, carries no weight.

buckeyefarmer · Jul 30, 2017

The way i showed keeps the same roofline as existing. The new outside rafter is lower because your existing rafters are notched.

petebert · Jul 30, 2017

Thanks, that helps a lot. The forum seems to be messing up today so I double posted. Was a little tricky but I got the pictures to come through.

petebert · Jul 30, 2017

So let's talk about the option of adding a 2nd roof instead of it being a continuous roof.

Pros - I don't have to disassemble my soffit, fascia and gutters which are all still nice and tight and in good shape.

Cons - I lose 1' of height and in snow country this is important for maintaining slope rate. I'm far enough south in Michigan that I can use a 4/12 pitch. So starting height of 11', end height of 7', 12' wide extension and I have a 4/12 pitch. Although this means no overhang at all. This is a livestock barn and the extension is going to be a sheep barn. The sheep don't care how tall it is but I figure I can get away with 7' tall at the end to still be able to maneuver comfortably as a human and could even get a compact tractor into the door.

From the ground to the bottom of my soffit is 11'6". So as I sit here and do the math. I first have to take off a few inches for a flashing, I'll have to check the span tables but lets say 2x12 rafters, I'd really end up at only 6' tall at the end. Now knock off a couple inches for a door frame and it's not much of an opening.

Looks like I can use 2x8's for a 12' span with 16" spacing.

Cord · Jul 31, 2017

You just put all the shed roof load in shear on the beam spanning between the posts. You also doubled the load on that member without any consideration of it's bearing capacity.