How To Calculate Max Unsupported Span Of Trusses?

BCConstruction

Hey guys. What do i need to know to calculate the max unsupported span of a truss. Just bought a house and wife wants a wall knocked down.

The lower chords are resting on a wall in one half of the house and on the other half of the house they span the whole width with no support! I cant tell if the wall not being there is from new or was done after it was built! They are same trusses along the length of the house also. This is going to decide if i have to replace a wall or can remove one so marriage could be in trouble depnding on answer

Cheers guys

ARI001

Trusses are engineered so you need to get an engineer to sign off on it unless you happen to have the original plans and specifications on hand. You also need to get a permit as it is required to remove any wall regardless of whether it is bearing or not. Now for the information you are actually after:
dimensions, species, and grade of wood used to construct the trusses.
Roof loading
ground snow load for your area.
deflection limitations
truss spacing

KentWhitten

Trusses usually bear only on outside walls. Not very often is there any load bearing in mid span. You still need to get the truss engineer out to look at it and someone to sign off.

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Salmon Falls Cabinetry

BCConstruction

Cheers guys. I will get some more details next time im at the place. should be tommorow.

Framerman perhaps this is why there is a wall missing in half the house and not the other. Always though some load had to be taken by internal walls. So its good to know the house is gonna be ok if i leave it how it is.

BCConstruction

Framerman you got any more info about getting a engineer out to take a look at this wall that needs removeing. I have never had to do this so im curious to know how i go about getting one? I have spoken to some contractors and they said they have never bothered when doing what im doing but i dont wanna take any chances. Plus it cant be that expensive can it?

KentWhitten

Famous last words.

I want to say that it should be fine, but those too are famous last words. I cannot guarantee that your situation is good to go. I'm just saying that in general, trusses are designed to span from outside wall to outside wall.

Take a camera into the attic and take pictures of the trusses in question. If they are a standard Fink truss (w-shape)



or a Howe truss



then it should be perfectly safe. These will be your most common truss designs. I would guess that you have Fink trusses.

The final call is on your part. If they look any different than those two pictures, then absolutely get someone out to look at it. If it's a Fink or Howe, then like I said, it should be good to go.

BTW, make sure it is a truss. Rafters and ceiling joists are a different ball game.

Post those pictures.

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If you correct your mind, the rest of your life will fall into place ~Lao Tzu

Custom Cabinetry - Portland, Cape Elizabeth, Scarborough, Kennebunkport, Yarmouth, Falmouth, Cumberland, Ogunquit, Maine

Salmon Falls Cabinetry

BCConstruction

Yeah i bet it's more than i am thinking. always is. heres the pics of the trusses.

Framer53

Look like pretty standard truses.
Should be good to go!

BCConstruction

Cheers guys. The area of wall that she wants out is only going to leave 2-3 trusses without the wall under them so im not removing the whole length of support. Im just no truss expert so want to double check my options.

Also whats the deal with all that white stuff over areas of the ply? Their aint been no leaks but it the first time i ever seen ply go like that in a loft!

KentWhitten

You're all set to go, those are simple span trusses. No interior bearing needed.

The white stuff I hope is not mold. That would be a ventilation problem most likely and need attention ASAP. Check your eave vents to see if they're blocked.

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If you correct your mind, the rest of your life will fall into place ~Lao Tzu

Custom Cabinetry - Portland, Cape Elizabeth, Scarborough, Kennebunkport, Yarmouth, Falmouth, Cumberland, Ogunquit, Maine

Salmon Falls Cabinetry

BCConstruction

I aint been up there and had a great looked around yet but seems to have very good ventilation with the 2 vents on each gable end. Hopefully it's not mould. it smells better up there than in the house lol

KennMacMoragh

Isn't this a framing topic?

I don't think there is such a thing as an interior load bearing wall under roof trusses, is there? I have never heard of one. There are interior shear walls under roof trusses, that's the only thing you would have to watch out for. It's real unlikely the wall you want to tear out is going to be a shear wall though.

BCConstruction

I def aint a expert but i thought shear walls used plywood or diagonal braces? These walls just have upright 2x4's with drywall!

macatawacab

Sheer walls are a whole other topic that gets involved. for instance a sheer wall can be gyp over 2x with the right screw pattern and layout.

go with framerman's recommendation

KennMacMoragh

O.k, then that's not a shear wall

RobertCDF

There are such things as load bearing interior walls with trusses. I have set many a girder atop a load bearing interior load bearing wall. I have also set many girders on point load posts in interior walls that someone might be in for a surprise if they think they could take out the wall.

In this case it is not an issue however.

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hughjazz

x2.

Kycym

It'll be more expensive if you guess wrong.

If the framing contractors that you know can't steer you to an engineer or an architect, go to the building department in your municipality and ask them to give you names. They will usually give you a couple of names of ones they are familiar with. If all that fails, use the phone book, if there still is one, or just Google "Structural Engineers" for your area.

It'll cost you $150 +/- for the site visit. Maybe $250 to give you an opinion. It'll cost much more if you guess wrong.

KentWhitten

The answer I gave him is not a guess. He's removing an inside wall that has nothing to do with those trusses. That was free.

__________________
If you correct your mind, the rest of your life will fall into place ~Lao Tzu

Custom Cabinetry - Portland, Cape Elizabeth, Scarborough, Kennebunkport, Yarmouth, Falmouth, Cumberland, Ogunquit, Maine

Salmon Falls Cabinetry

Johnston

Not sure when the house was built but if built correctly.....

If the unknown support wall runs parrallel with the floor joist you could look for a pier/ beam or some support in the crawl space. Should be one if the wall is load bearing and parrallel with floor joist.

With that said your truss design is made so that the weight is carried to the outside walls... Your interior wall is not load bearing. Although your truss/trusses will settle slightly after you remove this wall just from the roof load. Keep that in mind when you finish your rock.