Trusses that are sagging

[justusandersson]

Not having been on site is always a problem when writing about something. A 5-minute visit would have gone a long way in this case. I now understand that the existing roof trusses are much worse than I imagined. Before you do anything, I think you should try to measure the deflection in the top chords as well. Also, try to get an idea of the ridge level by testing with the laser measurer at a few points.

As a bossespecial, I think you must support under the diagonal braces before reinforcing the top chords. Also, suspend the ceiling so that the movements of the bottom chords are not significant.

 

[M@ZE]

The reason for the deflection is the joint in the middle of the lower frame. What more or less supports the roof today is only the upper frame since the lower frame cannot bear any vertical load due to the joint. The roof trusses need to be reinforced as they are completely wrongly made. As I see it, there are two relatively easy measures. One, adding tension rods up to the ridge. Two, reinforcing both the lower and upper frames. Regardless, you need to prop up the truss before the reinforcement is done; these should be placed under the diagonals. You then suspend the under-roof from the new glulam beams so that it passes the truss with a distance, making the under-roof independent of how much the truss bends down from snow, etc. In the absence of anything else, I'll try to describe it with a picture

Thank you so much @bossespecial for the picture and description, I'm not quite on board with the last picture on the lower right side though

 

[M@ZE]

Not having been on site is always a problem when you need to write about something. A 5-minute visit would have gone a long way in this case. I now understand that the existing trusses are much worse than I imagined. Before you do anything, I think you should try to measure the deflection in the top chords as well. Also, try to get an idea of the ridge level by testing with the laser measure at a few points.

Like bossespecial, I think you need to prop up under the diagonal supports before reinforcing the top chords. Also, make sure to hang down the ceiling so that the movements of the bottom chords don't matter.

Oh my goodness, this is becoming more complicated (or more bothersome) than I initially thought. It almost feels like we could replace and make entirely new trusses, as everything seems to have been poorly done right from the start. I've tried to get those who did it to "find a time and stop by." One thing is for sure, it's incredibly good that I sensed something wasn't quite right just by looking with my eyes and that I posted the question here where I've received such invaluable feedback and help.

I understand it hasn't been easy to comment either since I didn't provide entirely accurate information from the start, but I've seen more the more I've investigated following your advice.

However, it has held for 10 years, but something must be done, I understand that.

 

[bossespecial]

And I who spent so much time on that figure, oh well, I'm not an artist anyway
It's supposed to represent a cross-section through the rafters and glulam beams where the subroof just passes by the rafter without being attached
The best thing would be if they fixed the rafters for you so you wouldn't have to deal with this.

 

[M@ZE]

And I spent so much time on that figure, well, I'm no artist anyway
It's supposed to represent a section through the trusses and glulam beams where the underlayment just passes by the truss without being attached
The best would be if they fixed the trusses for you so you wouldn't have to deal with this.

Hehe, you did it well @bossespecial nicely done too.

Yeah, I agree, that would of course be the best. But considering that he hasn't "found" a chance to come by, it can be interpreted as him not likely to come.

 

[M@ZE]

Just a thought, though I'm not sure if it's a good one.

But if you were to prop up the lower arm so that it's level or slightly above, place the laminated wood beam directly against the lower arm and screw it into the laminated wood beam. And also reinforce the upper arms with 45x195 as mentioned earlier in the thread.

Could that work?

 

[justusandersson]

Then the glued laminated beams will not be aligned with a vertical stud in the wall (if it's built as it should be). Instead, there will be an "angled" load on the wall plate that would need to be reinforced in some way. Not impossible, but it involves some extra work. The top plates must be reinforced as I have previously described. For the bottom plates, it might be enough to replace the nail plates over the joint with a proper joint (studs on either side bolted or screwed together). The purpose is to limit their deflection so that it fits within the space created by the glued laminated beams plus the hanging ceiling.

 

[crazytok]

M@ze, you should never have considered clearing space in the attic! Then you could have avoided all this.... so much extra work it became for you.

Justusandersson:
If he reinforces the top frame as you mentioned, wouldn't these still not be above the studs on the ground floor?

But it's open between the studs on the ground floor if I remember correctly. So he should be able to add an extra upright stud there as well, so he avoids the slant. He simply builds an extra truss side by side with the old one, and attaches this to the old truss. And reinforces the upright studs down towards the ground so that the new truss's load is on this?

 

[justusandersson]

If he reinforces the upper frame as you mentioned, don't these end up above the studs on the ground floor anyway?

Sure, there will be a small eccentricity, but the old upper frame rests on the old bottom frame and not directly on the wall plate. Ideally, one should make a symmetrical reinforcement on both sides of the old upper frame, but that might be overdoing it. If the walls are open on the inside so that the stud frame is visible, it is naturally easier, but I think it's better not to unnecessarily load the glued laminated timber beams.

 

[M@ZE]

Unfortunately, it is no longer open in the walls since I have insulated, plywooded, and plasterboarded. I also don't know if the roof trusses rest on the wall plate exactly where the vertical stud goes down now that everything is sealed off ...

 

[M@ZE]

M@ze, you should never have considered using the attic space! Then you would have avoided this.... so much extra work it has become for you.

Hehe, that was the whole idea from the start when the garage was built. But looking back, it of course feels heavy, but it still feels like something needs to be fixed with the roof trusses anyway to remove the sagging.

 

[M@ZE]

Then the glulam beams won't align with a standing stud in the wall (if it's built as it should be). Instead, there would be a "skewed" load on the wall plate that would need to be reinforced in some way. Not impossible, but it involves extra work. The top plates need to be reinforced as I described earlier. For the bottom plates, it might suffice to replace the nail plates over the joint with a proper joint (studs on either side bolted or screwed together). The aim is to limit their deflection so that it fits within the space created by the glulam beams plus any sagging.

Ok, so you think it's sufficient to replace the joint now with a "proper" joint after propping up the bottom arm level? Plus extra reinforcement on the top arms?

Hehe, you'll have to excuse me, but I'm rather confused now.

 

[justusandersson]

I understand that you are confused. Start with a truss and evaluate it.

 

[M@ZE]

I understand that you are confused. Start with a roof truss and evaluate it.

Ok

When you need to prop up the roof truss, do you use 3 (1 in the middle and 2 under where the braces go down)?

 

[justusandersson]

I would bet on two first, where the stagen goes down.