Residential timber truss repair

[hsad]

Hi all,

I'm having to repair a residential timber truss. All the plates at the roof peak have let go and the entire roof is currently shored up. Does anyone have insight on good repair methods? plywood plates with bolts? nails? Anyone have experience with these fixes.

 

[jimstructures]

hsad,

Did the joint connections fail or are the beams themselves compromised, say from moisture or chrushing of wood fibers? We need to know more about how the failure is proceeding. A sketch would also help, both plan view and elevation of the truss.

Jim

 

[hsad]

The members seem to be okay, the plates have very large and shallow teeth that seem to have worked their way out over the service of the roof. When the plates slipped the truss fell onto the stud wall.

I've included a couple pics.I don't have my notebook on me but i believe it spans approx 28' and it is a howe truss.

 

[hsad]

picture

 

[Ron]

bring everything back into alignment and add nails to the plates to correct the separation (assuming no plate deformation has occurred)

 

[dik]

The TPI requires that the gap between the truss and plate does not exceed the thickness of a business card as a guide. Allowable value due to gap varies: 1/32 - 100%, 1/16 - 60%, 3/32 - 40%, >3/32 - 0%. I will check to see if they can be refastened. You may not get enough nails in to provide equivalent attachment. There is little additional capacity and the plate size is minimised.

Having said all that, it is probably best that you use new plywood gusset plates with nails and LePage Premium PL Premium adhesive.

Dik

 

[dik]

See sections 3.7 to 3.9 of the standard

Dik

 

[XR250]

They probably worked their way loose from decades of thermal and moisture cycles. I would go back with 1/2 plywood on both faces without plates as dik suggested. The loads on gussets at the peak are not usually huge.

 

[oldestguy]

I've made several trusses with plywood gussets. I used ring shank nails and let them go on to the other side, just for better grip. I'd go to the WEB site for the US Forest Products Lab in Madison, WI. for some info. When I built mine they had many guides for how to do this with plywood gussets.. Doing like Ron says with re-using the plates may work, but who furnishes short ring shank nails and then all that hand work? No way. Assuming you will use a nail gun, I'd rip off the metal first and use plywood, otherwise plenty of problems with the plates in the way there. I'd also be prepared to replace a bunch of joints if one is bad, many may also be ready to go.

 

[oldestguy]

OG again: The more I think about this, perhaps cut plywood gussets large enough to by-pass the metal plates, use three clamps to snug the plywood to the members, drive the nails, missing the plates. If you want to design the numbers of nails, nice, but I'd duplicate or increase the nails according to the number of indents on the plates.

 

[dik]

I've made several trusses with plywood gussets.

Same here... a lot of Hudson Bay northern stores were constructed using nailed trusses with plywood gussets. Stelco (I think) made hardened truss gusset nails back 45 or so years ago. When I first started engineering we used to draw the truss member forces right on the truss drawing; it was referred to as a Cremona diagram. It's how I started early in engineering.

CMHC used to have nailed truss plans for roof framing.

Dik

 

[dik]

Was there any sort of warranty on this? How old? if new, has the truss supplier been given an opportunity to come up with a repair?

As for repair:
Determine the loads in the web members and connect for full load to gusset.
Determine the resultant force for the web members in the direction of the chord member.
Connect the gusset to the chord member for this force.
Get yourself a beer... you worked hard for it...

Dik

 

[hsad]

Thanks for input guys!

I forgot to point out that this residence is in a area with fairly high 1/50yr snowload (5.1kPa)

bring everything back into alignment and add nails to the plates to correct the separation (assuming no plate deformation has occurred)

The plates are slightly deformed. I'm concerned that they will want to walk back out.

The TPI requires that the gap between the truss and plate does not exceed the thickness of a business card as a guide. Allowable value due to gap varies: 1/32 - 100%, 1/16 - 60%, 3/32 - 40%, >3/32 - 0%. I will check to see if they can be refastened. You may not get enough nails in to provide equivalent attachment. There is little additional capacity and the plate size is minimised.Having said all that, it is probably best that you use new plywood gusset plates with nails and LePage Premium PL Premium adhesive.

I'm in Canada but the TPIC here gives same guidelines.

They probably worked their way loose from decades of thermal and moisture cycles. I would go back with 1/2 plywood on both faces without plates as dik suggested. The loads on gussets at the peak are not usually huge.

This is exactly what I have heard and it seems like what happens with these plates that have thick teeth and shallow embedment.

I've made several trusses with plywood gussets. I used ring shank nails and let them go on to the other side, just for better grip. I'd go to the WEB site for the US Forest Products Lab in Madison, WI. for some info. When I built mine they had many guides for how to do this with plywood gussets.. Doing like Ron says with re-using the plates may work, but who furnishes short ring shank nails and then all that hand work? No way. Assuming you will use a nail gun, I'd rip off the metal first and use plywood, otherwise plenty of problems with the plates in the way there. I'd also be prepared to replace a bunch of joints if one is bad, many may also be ready to go.

I like the idea of having them use a nailgun.

Was there any sort of warranty on this? How old? if new, has the truss supplier been given an opportunity to come up with a repair?

Not sure who the truss supplier is (likely are not even around). The home is in a forestry driven community, it seems they slapped all these homes up very quick when the pulp and paper mills came in.

As for repair:
Determine the loads in the web members and connect for full load to gusset.
Determine the resultant force for the web members in the direction of the chord member.
Connect the gusset to the chord member for this force.
Get yourself a beer... you worked hard for it...

Perfect was exactly what I have done so far.

 

[oldestguy]

Should the workers decide not to use plywood, but re-use the metal plates and nail thru the existing holes, (can be done if you know how), BUT most nails from the gun are only half "capped" and may just slip into the big hole with no grip. It might be roofing nails will work. I'd do some testing because a bunch of closely spaced "fat" nails in bone-dry wood, may splinter the heck out of the pieces of 2x's. That's where plywood with spacing the nails is better.

 

[dik]

My understanding of TPIC is that you cannot repair or re-use truss plates.

Dik

 

[dik]

I forgot to point out that this residence is in a area with fairly high 1/50yr snowload (5.1kPa)

What area? Mountains? I'm in Winnipeg.

Dik

 

[medeek]

I like the idea of plywood gussets with glue and nails on new construction but would it be easier to use screws on a retro or repair job especially when you have a gypsum ceiling involved and you don't want to shake everything apart?

If one did use screws what Simpson fastener product (or other comparable brand) would you recommend?

A confused student is a good student.
Nathaniel P. Wilkerson, PE

http://www.medeek.com

 

[EngineeringEric]

Nails are not being driven by hand, they are shot. So tight spaces isn't as much of an issue and may even be easier than screws. So not too big of an issue and the nails are typically far more ductile and when they are crimped they can be used as double shear with plywood side members.

Screws... i think you are looking at single shear and you may run into issues with ductility depending on the screw type. I am sure simpson makes a small screw from plywood to 2x material

 

[oldestguy]

I'd bet using screws in this dry wood that splitting would be far more a problem than using nails driven with a gun and likely the job with nails will go much faster.

 

[hsad]

What area? Mountains? I'm in Winnipeg.

Mountainous interior of BC.