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View MrRon's profile

Wood Truss Detail

by MrRon
posted 01-10-2013 10:16 PM


20 replies so far

View RonKl's profile

RonKl

7 posts in 634 days


#1 posted 01-10-2013 11:15 PM

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

View teejk's profile

teejk

1215 posts in 1343 days


#2 posted 01-10-2013 11:44 PM

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

1256 posts in 731 days


#3 posted 01-11-2013 12:16 AM

+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?

View kdc68's profile

kdc68

1980 posts in 935 days


#4 posted 01-11-2013 12:43 AM

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

543 posts in 732 days


#5 posted 01-11-2013 01:06 AM

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"

View Grandpa's profile

Grandpa

3136 posts in 1334 days


#6 posted 01-11-2013 01:14 AM

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

View REO's profile

REO

614 posts in 732 days


#7 posted 01-11-2013 01:25 AM

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.

View John Ormsby's profile

John Ormsby

1280 posts in 2395 days


#8 posted 01-11-2013 01:32 AM

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

View MrRon's profile

MrRon

2837 posts in 1902 days


#9 posted 01-11-2013 09:37 PM

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

1980 posts in 935 days


#10 posted 01-11-2013 09:44 PM

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

View kdc68's profile

kdc68

1980 posts in 935 days


#11 posted 01-12-2013 12:30 AM

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 1502 days


#12 posted 01-12-2013 03:15 AM

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

View Grandpa's profile

Grandpa

3136 posts in 1334 days


#13 posted 01-12-2013 04:32 AM

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.

View MrRon's profile

MrRon

2837 posts in 1902 days


#14 posted 01-12-2013 08:28 PM

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

View REO's profile

REO

614 posts in 732 days


#15 posted 01-12-2013 09:49 PM

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.

View joeyinsouthaustin's profile

joeyinsouthaustin

1256 posts in 731 days


#16 posted 01-13-2013 02:24 AM

The foam air chutes. create a space between spun, or sprayed insulation, and the deck. Allowing circulation between the soffit vents and the ridge vent.

-- Who is John Galt?

View Grandpa's profile

Grandpa

3136 posts in 1334 days


#17 posted 01-13-2013 02:41 AM

Yes as Joey stated. They have ribs that stand them off from the decking and leaving chute for air to travel through to get above the insulation. It also keep insulation from filling the attic. Air chute is probably a regional thing. You can build them or buy them. Some people use wood strips to hold thin plywood off the decking. The foam kind are stapled to the bottom side of the decking. If you make them you need to be able to nail them to the side of the rafters. They are great devices.

View joeyinsouthaustin's profile

joeyinsouthaustin

1256 posts in 731 days


#18 posted 01-13-2013 03:49 PM

tried to get this last night. here is a pic, one of many varieties.

-- Who is John Galt?

View MrRon's profile

MrRon

2837 posts in 1902 days


#19 posted 01-13-2013 06:20 PM

Thanks. I wasn’t familiar with the term “air chute”. I’ve used them before when I was building my shop. The trusses I want to build are 3/12 slope and 24’ span. I’m using the “Fink truss” which is good for a 26’ span using 2×4’s. Gusset plates will be 1/2” plywood. The truss press is a good idea. I may go that way.

View teejk's profile

teejk

1215 posts in 1343 days


#20 posted 01-13-2013 06:55 PM

and as long as we’re talking about trusses…whoever built my first house must have goofed and had to replicate one on site…easy enough since the factory trusses were there to use as a template. using plywood, glue and roofing nails created little “pockets” that the yellow jackets (those nasty ones) loved!

I set out to replace the 16’ garage door one warm autumn day only to see them flying everywhere. Waited for night time and a few cans of Raid later, I bet I got at least a 1,000 of them on a single 22’ truss. Point is, if you are making your own, fill those pockets with foam or something if bugs are a problem.

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