Roof truss installation

[bspace123]

Hello

I have just installed roof trusses which are designed to hold a metal roof. The installation manual from the truss manufacturer states to secure internal non load bearing walls using L Brackets, where the bracket is attached to the wall top plate and to the truss bottom chord. The manual states that the brackets are to be nailed right onto the top plate but only install nails half way in to the bottom chord. This is to allow the trusses to move.


The truss manual is located in the link below (refer to pg6):

https://www.mitek.com.au/wp-content/...stallation.pdf

The problem with this approach is, with long non load bearing walls, there’s no way of securing them to anything but the lower chord. If brackets are fixed loose to the bottom chord then the walls shake.

Is there any alternative approach that will allow better securing of the internal walls?

The truss manufacturer advise this is not their issue. Most other builders I know ignore the advise and fix the non load bearing walls directly to the trusses.

 

[RontheRedneck]

Your link doesn't work. I assume it points to something with slotted hardware. Something like this:

The idea is to allow the truss to move up and down a little with changes in moisture. If you fasten the trusses to the walls securely, the truss can actually pick the whole wall up and make one hell of a mess of the drywall.

You need to find a way to let the BC of the truss move one way or another. Maybe a clip on both sides of the truss will help.

It's a lot easier to do it right now than it is to fix a serious problem after the structure is in use.

 

[phamENG]

Regarding the 'truss shaking'....did you install bottom chord bracing? Even if that'll be taken by the ceiling, have you done any temporary erection bracing? Lot's of roofs have collapsed during construction due to ignoring this requirement.

 

[XR250]

I have never seen these installed on any job that I have witnessed (and that is a shit-ton).
Nail the MF truss down directly and be done with it.
I have observed maybe 5 walls in the last 25 years that have been picked up and gapped at the bottom by the truss lift.

 

[phamENG]

I have never seen these installed on any job

Me neither. I still spec them (or the little slip screws they came up with), but they get ignored. Oh well - if there is a serviceability failure or other problem with the truss as a result, I'm not paying for it.

But I wonder how much of that is our climate? We're still in a pretty temperate area (this weekend not withstanding...-2[sup]o[/sup]F wind chill? WTF?) so the big expansion/contraction movements that cause the truss uplift cracks are probably less prevalent than they are in New England or Montana or Manitoba.

 

[XR250]

@Pham,

Please stop spec'ing these dumb things. You are adjusting the Standard of Care so the rest of us can get sued!

 

[bspace123]

Apologies here is the link again

https://www.mitek.com.au/wp-content/uploads/2021/06/MiTek-Guide-for-Roof-Truss-Installation.pdf

The bracket shown in the previous post is the correct one.

I’m not concerned about the truss shaking, the trusses are braced with hoop iron, speed brace, roof battens and bottom chord timber ties. They are going no where, the bracing has been installed as per MF recommendations and is overkill imo. I struggle to see how the trusses will move with all this bracing in any case.


It’s the internal walls that shake because of these brackets which are attached loosely to the bottom chords to allow movement of the truss vertically. How can they move with all this bracing and what is the point of these brackets been fixed in this manner

 

[dik]

look up 'truss uplift'... It's caused by changes in humidity.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[Pmtottawa]

look up 'truss uplift'... It's caused by changes in humidity.

And temperature variations...

 

[RontheRedneck]

In my experience, truss uplift is 100% moisture related. Every time I've been out to see a house with issues the house has poor attic ventilation.

The most memorable case was a DIY guy who approached me at a home show. He said he has truss uplift in his new home, and wanted to know what to do about it. The first question I usually get is "Can I cut some of the truss webs so the trusses will settle down?" Obviously the answer is "NO".

I started asking the guy about the construction of his house. Were the bath fans exhausted outside or into the attic? He said they just ran up into the attic.

He said he has vented soffit and a ridge vent. I asked if he used proper vents at the heel of the trusses. He had never heard of them.

So I asked if he left ventilation space at the outside walls at the heels of the trusses. He said he crawled out there with the hose of the insulation and blew the soffit full of insulation.

No wonder he had truss uplift.


I don't recall ever being on a job that had truss uplift where the house had good attic ventilation.

 

[gte447f]

bspace123, I understand the issue. You are concerned about the non-load bearing walls not being braced, hence shaking, because the truss manual says to only drive the nails in the slots half way home. Obviously, that is going to be a problem, and is stupid advice in my opinion. You have to drive the nails home, otherwise the clip isn't actually doing anything. Just drive the nails flush. Hopefully, if there is any upward or downward force from the truss bottom chord it will be enough to overcome the friction between the head of the nail and the clip, allowing the nail to slide up or down in the slot as intended.

 

[XR250]

Another dumb Simpson piece of hardware that will never get installed properly. Same with the dumb scissor truss clips. Can we all agree to stop spec'ing these?

 

[bspace123]

I agree, they are useless. What’s even more annoying is the manufacturer species an alternative “engineered solution”, called a “fast fix” screw.

Link:

https://pryda.com.au/for-builders/pryda-fastfix/

Of course they sell this for triple the price of a batten (bugle) screw, which I find hard to believe that they are any different. Why do they even have these brackets when these are available? They do a much better job at bracing the walls than those L brackets do.

 

[Amit Bajpayee]

Roof truss installation is the process of installing the structural framework that supports the roof of a building. Roof trusses are typically made of wood or metal, and they are used to provide support for the roofing material, as well as any other loads that the roof may need to bear, such as snow or wind.

Roof truss installation typically involves the following steps:

Measure and mark the locations of the trusses on the building's foundation.

Cut and assemble the trusses according to the manufacturer's instructions.

Lift the trusses into place using a crane or other lifting equipment.

Secure the trusses to the foundation using bolts or other fasteners.

Install any additional support structures, such as purlins or braces, as needed.

Cover the trusses with roofing material, such as shingles, tiles, or metal.

Roof truss installation is a complex and technical process that requires skilled labor and specialized equipment. It is important to hire a qualified and experienced contractor to install roof trusses to ensure that the job is done safely and correctly.

https://agnisolar.com/

 

[XR250]

Seriously? Was this posted by a bot?

 

[phamENG]

That would be a very sophisticated bot. It seems more like attempts to get the URL in the signature line posted everywhere they can. Within their own "specialty" the responses are a bit banal, but they regurgitate tangentially related procedures that they clearly obtained from some general google searches for other subject areas.

You are adjusting the Standard of Care so the rest of us can get sued!

That's not my goal, but the inverse is. If I set the standard of care, I can't get sued (successfully)! But don't worry...apart from one firm that has offices in both of our localities, I think we're just far enough apart that our standards of care probably don't overlap.