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truss question

rktect 1

rktect 1

Gold Member
Joined
Oct 20, 2009
Messages
1,113
Location
Illinois
I've got a truss related question.

We have a (diy) home owner who has a ranch house about 26'x40'. (estimated 40 feet, probably more, not shown on plans) They want to remove an interior wall which seperates two bedrooms at about mid point, 13 feet of the 26 foot length, and put a new wall in about 4 feet over to enlarge one bedroom and create a smaller bathroom for the bedroom.

I asked them to provide information showing that this was not a bearing wall holding up the ceiling that they are removing. Their comment back to me was that the ceiling and roof above is a truss which spans the entire 26 feet at two outside points and that the interior wall is only an interior wall not used for support. The truss will not be changed in any way. They also indicated that the floor joists run the same direction as the ceiling truss and sit on top of a steel beam in the basement. The steeal beam runs perpendicular at mid span or 13 feet. To me this means that the spans are correct for this to be an interior bearing wall as the floor joists certainly sit directly below on top of the steel beam.

Having never used a truss in my entire time as an architect, is this a true statement? The truss is designed to span the overall length in small homes like this?
 
Re: truss question

rktect,

I am not a grammar policeman, but when I hear 26X40 I think of the 26 as width and the 40 as length.

My arithmetic says that is a 1040 SF house. There is a bathroom in that small a house that can give up four feet of floor space?

Trusses can be designed so many ways. If there are bearing points those are usually indicated by red tags by the manufacturer.

26 ft doesn't sound so far a spread for an ordinary clear span truss, but you are right to look for verification.

I think there might be many ways to skin the cat, including more floor supports, but engineering may be needed if it can't be derived by checking span tables etc.
 
Re: truss question

The trusses COULD have been designed to span the entire space with no intermediate bearing necessary.

I would want to see some calcs for whatever wall gets moved and the floor joists below. It is possible that the floor joists may not accommodate the relocated wall-bath, etc.

The issue then becomes not so much the roof, but the floor joists.

mj
 
Re: truss question

Sorry Jim, I guessed at the 40 feet in lenght. It isn't shown and wasn't required for this permit. Probably is longer than that. Might even have a build out either in the front or back increasing the total square footage.

So I would have to ask them to check what? The truss in the attic to see if the truss has been marked with red tags at mid span where the interior wall is at? If no red tag, then give them the ok to move the interior wall?
 
Re: truss question

I agree with the previous posts. Most trusses I have seen in the field are clear span, but not all.

I assume you don't have the truss drawings on file or the original house plans. I myself would not trust red tags. I see a lot of tagging for the location of lateral bracing but not necessarily load-bearing.
 
Re: truss question

Normally trusses are designed as simple spans and an intermediate support for a prefabricated 26'-0" metal plate connected truss would be very uncommon (but possible in an unusual circumstance).

Typically, a truss designed for intermediate support will have diagonals terminating at the support point and a vertical member between the top and bottom chords.
 
Re: truss question

mjesse said:
The trusses COULD have been designed to span the entire space with no intermediate bearing necessary.I would want to see some calcs for whatever wall gets moved and the floor joists below. It is possible that the floor joists may not accommodate the relocated wall-bath, etc.

The issue then becomes not so much the roof, but the floor joists.

mj
Click to expand...
If the wall in question is determined to not be an interior bearing wall, I don't see how adding a new non bearing wall over four feet changes the floor joists. They should have been designed for this span and condition to begin with. In fact the span tables located in the IRC gives a typical SPF #2 2x8 at 16" o.c. a span of 14'-2" for sleeping areas. They are at 13'-0". Yes the bathroom was never considered originally but I do not think that adding the bathtub to the outermost corner (at exterior walls) changes much in the loading. Shouldn't that be a part of the live loads?
 
Re: truss question

TJ,

That is correct, I do not have the old plans on file. This is really a part of our older section of town. The house is probably 30-50 years old, if I had to guess.
 
Re: truss question

RKt

Without seeing the plans, I would have to assume the worst.

I could imagine moving the wall 4' away from the center steel, and dropping a 6' whirlpool tub, double vanity, linen closet, and tile shower on the other side of it.

This would create a BIG problem for 50 y.o. 2x8 joist (more assumption)

Just trying to take all factors, not just the trusses into account.

Where in IL are you? I'm in Lake County.

mj
 
Re: truss question

rk - I tend to agree that the trusses, more than likely, were designed for clear span. As brudgers points out, there are design elements within the individual trusses that could help out. Also, reverse engineering the trusses would not be too difficult. A rep from a fabricator could prepare the needed documentation fairly easily.

mjesse - I would be more concerned with NEW lumber than with old lumber. A 50 year old 2x8 would probably carry as much (or more) than a new 2x10.
 
Re: truss question

We often see "3-point trusses" which is what I call a truss with an intermediate bearing point. However they can be easily identified by peaking in the attic and seeing their design. Worst case, thge homeowner will require an engineer to visit and design it. Best case, the inspector can verify that the trusses are 2-point, or clear span trusses.
 
Re: truss question

26' span is not that far for a designed truss with bearings at the end. You could make the applicant do there work by climbing into the attic to look for: Spacing of the truss, size of lumber used on the webs, T-cord & B-cord, drawing of what the truss looks like, roof pitch, o/s bearing width, lumber grade on all members, species of lumber and the red bearing tag somewhere where your center wall is. If there's no bearing tag, applicant may have made his point. Take the information to a real lumberyard and see if their truss supplier will enter it into their magic box and provide you with the needed info. It's worth a shot! I bet you'll find a truss splice plate at both sides of the bottom cord at 14' too, truss manufacture hates to waste material.
 
Re: truss question

Odds are the proof is in the trusses. The walls below should not be in contact with the the bottom cord of the trusses except by truss clips. That's not to say that it didn't happen but it may answer the question of bearing. Trusses never bear on just the bottom cord, there is always a confluence of webs at the bearing points. So if all the trusses, except the gables, are the same and if the walls below do not line up with webs throughout the structure it's obviously a clear span truss. 26' is an easy span for a truss. I've never seen a red tag on a truss that indicates a bearing point, that must be unique to the East coast or I've been missing it all these years.
 
Re: truss question

vegas paul said:
We often see "3-point trusses" which is what I call a truss with an intermediate bearing point. However they can be easily identified by peaking in the attic and seeing their design. Worst case, thge homeowner will require an engineer to visit and design it. Best case, the inspector can verify that the trusses are 2-point, or clear span trusses.
Click to expand...
Roof trusses are almost always have to be clear span. That is the point of trusses in the first place. The partition walls (interior walls) should not be in contact with the bottom chord to allow for flex of the truss as required - otherwise the friction can add another load condition to the bottom chord of the truss when there is wind loads for example.

There is some basic principles to trusses that should remain. If this is an actual roof trusses.

Edit: I guess tigerloose had pointed out the same points.
 
Re: truss question

30 to 50 years is a large range. 50 years ago there was no Truss Plate Institute (1960), judging these trusses by today's standards is probably not a good idea. There is a good chance that there may be split ring connectors, plywood gussetts, or even field built. 30 years ago truss technology was pretty well evolved, but, not computerized and material-minimized as it is today.

Have the homeowner take some pictures of the trusses and bring them in so you can help direct to the next step which will probably be hiring an engineer.
 
Re: truss question

Rick - you might have misunderstood, I was not saying that non-bearing partition walls are connected to the middle of the truss, I was saying that (in these here parts) we see trusses that are DESIGNED by the truss engineer to bear on 3 BEARING points, including one interior BEARING wall; thus a 3-point truss system. Thiss allows greater design creativity (at a somewhat greater cost) for some of the grander home designs seen here. Very common. Your comment that trusses should be clear span is not applicable, or another way of looking at it is that they ARE clear span, over two spans! (by design).
 
Re: truss question

vegas paul said:
Rick - you might have misunderstood, I was not saying that non-bearing partition walls are connected to the middle of the truss, I was saying that (in these here parts) we see trusses that are DESIGNED by the truss engineer to bear on 3 BEARING points, including one interior BEARING wall; thus a 3-point truss system. Thiss allows greater design creativity (at a somewhat greater cost) for some of the grander home designs seen here. Very common. Your comment that trusses should be clear span is not applicable, or another way of looking at it is that they ARE clear span, over two spans! (by design).
Click to expand...
Ok. Then the interior bearing my not be removed. It is just not an option. Not unless the design calcs are designed sufficient to make the full span by being over-engineered. That is not likely.
 
Re: truss question

Texas Truss

381911124.jpg
 
Re: truss question

And even if some dumba$$ tries to remove the tag the remnants under the nailplate will still be there...
 
Re: truss question

If you look at the webbing you can usually figure out the bearing points. The webbing is either in compression of tension. It will be in compression at the bearing points. Also the walls running perpendicular to the trusses at non-bearing points will have a gap between the top plate and truss. Usually they will use 1 X 4 top plates for these walls.

The best thing to do is to have him have an Engineer look at it.
 
Re: truss question

Batwood said:
Usually they will use 1 X 4 top plates for these walls.
Click to expand...
1X4 top plate??? Never seen that. Where in the code does it allow a 1 X top plate?
 
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