Building a house addition and have a question on floor truss supprot.

[ustmd]

The house will sit about 4' back from the original house. That will give me more outside room in front of the garage and I can avoid moving the electric meter. I am going to strip off the siding which will expose the side of the original house floor joist truss which I can attach a 2x12 board and use truss hangers. I can't rest the new joist on the original foundation since the trusses go in a different direction or I would do that. Having a step up is an idea. That would give me a higher ceiling in the garage, but I would have to think about that.

I may be misunderstanding, but I would be real careful about the "step up idea". Essentially, you would be putting 50% of the load of the addition on the one floor joist that is in the existing house I find it highly unlikely the joist is rated for the load

 

[M E Cook]

you could also after using the 2x12 ldger build a 2x4 wall next to the bricks to support the floor joist then you can insulate and finish the wall to your liking would not add alot of cost but would look good too

 

[marchanna]

I may be misunderstanding, but I would be real careful about the "step up idea". Essentially, you would be putting 50% of the load of the addition on the one floor joist that is in the existing house I find it highly unlikely the joist is rated for the load

It would be supported directly by the exterior load-bearing wall. It wouldn’t be sitting on a span.

 

[WVBill]

What's your plan for the back wall of the addition? It's going to need to be engineered as a retaining wall for the backfilled slope.

 

[BuilderML]

DO NOT !!! mix conventional lumber with engineered floor joist. If you do end up going the way of using a ledger you should use an 11 7/8" LVL as your ledger with your floor joist. I won't comment on how to attach the ledger as a previous poster said the details matter and are alittle beyond TBN board. Again do not mix your materials. Also i know that 12" TJI clear span your roughly 20' floor but you will have tremendous bounce in your floor. I strongly urge you to go 12" 0.C.. Do as you wish but keep in mind your not talking many more joist. Your 20' span is right at the max. allowed
Good luck with your project

 

[EddieWalker]

Keep it simple. Pour your concrete floor with a footing to support a wall along the side of the house. Then build a stick frame wall to support your joists. This allows you to run electrical through the wall, insulate the wall and connect the studs to the existing house with metal brackets, or wood blocking on it's edge against the existing masonry wall.

 

[TimberHole]

That's a good comment on the bounce. Just because joists are structurall sound does not mean they will be comfortable. We see this issue with steel floors in commercial buildings..

 

[Cord]

The code has a provision in it for empirical ledger designs. For v2015, look in table R507.2. The table is for wood decks and you are over the limit, however you won't have a snow load so I'd be comfortable using the 16-18' column for a 20' span. Of course, all of this would need to be run past your building inspector, but it's a reasonable request.

The next option is to use joist hangers which are readily available and easily installed. Make sure you use the correct nails. No, you don't just use a 10d or 16d nail or drywall screws. The manufacture's cut sheets will tell you what nail is supposed to be used in each hole shape.

Also, for a 20' span, you can use an engineered joist for half the cost of a floor truss. The joists will be a stocked item vs a couple week lead for the trusses. See what brand your lumber yard stocks and refer to the empirical tables that they will publish for your joist depth and spacing.

What bothers me a bit with your existing home is the brick which is flush with the siding. This means there is a cantilever at the second floor. If the existing floor structure is parallel to the wall then there won't be much holding the existing rim joist on. I highly doubt this joist will take the load you are planning to put on it. If this turns out to be true, you might be better off framing a new stud wall to support the floor joists.

 

[Stimw]

No one has ask, what kind of construction is the existing garage wall?
Is it concrete block with brick exterior or wood frame with exterior brick?

 

[Johnkn]

Looking at the side wall it is all brick/block construction. You can see the (likely) 12" cinder not concrete block below grade transitioning to brick backed by (probably 4") block.