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Forum topic by MrRon posted 588 days ago 1557 views 0 times favorited 20 replies Add to Favorites Watch
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MrRon

2788 posts in 1869 days


588 days ago

The following sketch shows the end of a roof truss that is joined by “Simpson strong-tie” plates. I don’t know how the ends of the wood are cut. I want the top chord to extend out 12” for an eaves, but that would mean the bottom chord would taper down to the top plate and not leave enough support.


20 replies so far

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RonKl

7 posts in 601 days


#1 posted 588 days ago

Be very careful about modifying the truss in any way. Truss designs are sealed, legal documents and altering them would probably void any insurance claim for damage that might not even be directly related to the change. Many moons ago I ran a small truss plant for about 1-1/2 years and am very familiar with the legalities involved. Building inspectors are all over ANY alterations made during construction and would shoot down any permit application that involved a truss change, no matter how minor, without a sealed engineering drawing to back it up. Trusses with “tails” for eaves are designed at the beginning stage of their construction in the truss plant.

One suggestion is to install secondary rafter extensions with tapered ends to match the roof slope between the trusses, fastening them at the exterior and center bearing wall top plates. A simple 2X4 is enough – there’s negligible load. Then run another of appropriate length under the roof deck attached to the extension. A return to a ledger on the side of the house sturdies up the unit and provides a soffet. Fastening to the underside of the roof deck shouldn’t be a big deal since, I presume, there’ll be a new roof installed to cover the eave.

-- RonKl - New Jersey

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teejk

1208 posts in 1310 days


#2 posted 588 days ago

ronK…we built a house a few years ago utilizing a lot of different trusses (cathedral, attic, standard etc.)...for the inspector on the “structure” phase we had engineering plans stapled everywhere (even though he had the full prints already). Trusses save a lot of $$$ (2×4 or 2×6 using short sticks) but the inspectors are on high alert and look at them very carefully…

View joeyinsouthaustin's profile

joeyinsouthaustin

1245 posts in 698 days


#3 posted 588 days ago

+1 Ron. Have done this several times. You can also sister on to the side of the truss and extend out in plane with the top chord

-- Who is John Galt?

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kdc68

1956 posts in 903 days


#4 posted 588 days ago

MrRonjoeyinsouthaustin RonKl are absolutely correct. Do not modify the truss. Find the pitch of the roof and plumb cut the extension accordingly and sister them in

-- Measure "at least" twice and cut once

View bbc557ci's profile

bbc557ci

541 posts in 700 days


#5 posted 588 days ago

Is the roof system going to be over a heated/living area? If so, and if you get much snow accumulation in your area, be sure the truss design and or modifications are such that there is adequate roof/attic ventellation. Just a thought ;o)

-- Bill, central NY...no where near the "big apple"

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Grandpa

3075 posts in 1301 days


#6 posted 588 days ago

Ditto what those guys said. They are right on track. Never modify a truss. I find them all the time as a home inspector.

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REO

596 posts in 700 days


#7 posted 588 days ago

the support is carried through the truss plate to the top chord. If ypou want to extend the truss for an uverhang just nail or “sister” the tail to the side. even the truss design software doesent tak the outboard load into account for 12” ohang. 24” does change the numbers foir reactions on the truss.

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John Ormsby

1278 posts in 2363 days


#8 posted 588 days ago

Like others have stated already, Never cut into a truss. Cut 4’ 3” long extensions and nail them to the sides of the trusses. Plumb cut the ends before install or afterwards. No big deal to do. i usually make sure there is plenty of strength on any extension tails being added to trusses. A 3 to 1 ratio seems to work very well. So, for a 1 foot tail multiplied by 3 and you have 4’ long pieces. Add a bit more for the small extra lumb cut and you can get by with a 4’ 3” board. An 8’ long 2×4 cut at the proper diagonal in the middle and then flipped will net you 2 extensions with no waste.

-- Oldworld, Fair Oaks, Ca

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MrRon

2788 posts in 1869 days


#9 posted 587 days ago

I should have mentioned that I wanted to make the trusses, not buy them ready made. The detail I was following in a construction book, shows a mending plate covering the bottom chord, but doesn’t indicate how the top chord meets the bottom chord. I will be using plywood gussets on both sides of each connection with glue and nails.

Sketch added 5 minutes ago.

View kdc68's profile

kdc68

1956 posts in 903 days


#10 posted 587 days ago

The bottom chord has a scarf cut and the top chord rests on the angle. The roof pitch has two angles. A plumb cut and a scarf cut. The two angles add to 90 degrees. Example : 4 -12 pitch – plumb is 71.6 and scarf is 18.4

-- Measure "at least" twice and cut once

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kdc68

1956 posts in 903 days


#11 posted 587 days ago

Response to your sketch. The gusset size is really depends on the pitch, but I would size it covering as much of the top chord as possible. Your gusset could be cut in a trianglular shape matcing the pitch, if you are making your own gussets. Sorry for the crude drawing

-- Measure "at least" twice and cut once

View IrreverentJack's profile

IrreverentJack

724 posts in 1469 days


#12 posted 587 days ago

You need to take into account insulation space needed for the ceiling carried over the walls (plates) if the trusses are to be used in a living space. -Jack

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Grandpa

3075 posts in 1301 days


#13 posted 587 days ago

Like kdc68 said make the joint tight then glue and plywood with ringskank nails. Still the same…don’t cut any part of it. The integrity of the truss is compromised if you make it or a factory makes the truss. Install foam air chutes or make your own if you prefer.

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MrRon

2788 posts in 1869 days


#14 posted 586 days ago

Excuse my ignorance, but what are foam air chutes? Do you mean the plastic foam device that provides for air circulation at the eaves?

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REO

596 posts in 700 days


#15 posted 586 days ago

what are the dimensions of the truss you want to build? it is best to make the bottom chord end cut match the pitch of the top chord for the truss plate design. depending on the span the plywood gussets can transfer the load with a gap without difficulty. in most cases trusses have to be built and certified by a licensed company. I got by building 48’ clear span trusses for a roof that was torn off in a tornado and the city passed them without certification. I made my own truss press and have built many trusses for uninspected remodels and buildings.

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