How to calculate max unsupported span of trusses?

The Coastal Craftsman · Nov 20, 2009

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 :sad:

Cheers guys

ARI001 · Nov 20, 2009

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

Kent Whitten · Nov 20, 2009

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.

The Coastal Craftsman · Nov 22, 2009

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?

The Coastal Craftsman · Nov 21, 2009

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.

Framer53 · Nov 22, 2009

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

The Coastal Craftsman · Nov 22, 2009

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. :thumbsup:

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!

Kent Whitten · Nov 22, 2009

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.

The Coastal Craftsman · Nov 22, 2009

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 · Nov 22, 2009

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.

The Coastal Craftsman · Nov 23, 2009

KennMacMoragh said:
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.

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 · Nov 23, 2009

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

RobertCDF · Nov 23, 2009

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.

JT Wood · Nov 23, 2009

RobertCDF said:
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.

x2.

Johnston · Nov 25, 2009

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.

How to calculate max unsupported span of trusses?

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