Bending or cutting roof truss bottom chord?

Question

Bending or cutting roof truss bottom chord?

fchris82 (Computer)

(OP)

2 Feb 24 14:58

I hope somebody can help me. I have fan trusses:

Chords are made from 35x90 timber.

The bottom chord is about 10m (33.28 feet). We have to move a new MVHR unit to the attic but the shortest edge of the unit is 60cm (23.62"), meanwhile, the largest gap between trusses is 58cm (22.83").

Which one is the safest?
a) Stretch/strut the gap with two telescopic struts in the middle temporarily, which is 80cm long.

b) Add one sister to one chord, cut it, and after the moving add another sister to the other side. I would use screws and wood glue.

c) Other?

(We have attempted to disassemble it but it is impossible because of some glued parts)

jayrod12 (Structural) · Answer 1 · 2024-02-02 16:22:05

Dismantle the unit into smaller pieces? I don't like either of those options, however the sistering one is the only one I'd even consider. Pushing the trusses with a jack or two are ripe with issues that I'd want to avoid. The connections of those members are not meant for out-of-plane loading.

ChorasDen (Structural) · Answer 2 · 2024-02-14 23:12:39

This looks quite tricky and prone to lots of issues if detailed or performed inadequately. Best to contact a local structural engineer who is experienced with wood design to come and review your situation, including local loading and provide a detail or plan of action to adequately meet your local legal code provisions.

structSU10 (Structural) · Answer 3 · 2024-02-15 02:15:51

can you make a hole in the gable end wall to get the unit in without messing with the trusses?

KootK (Structural) · Answer 4 · 2024-02-22 00:13:01

Quote (OP)
a) Stretch/strut the gap with two telescopic struts in the middle temporarily, which is 80cm long.

I like that one. Opening up the spacing between trusses from 22.5" to 24.0" should be a non-issue as far as damaging the trusses goes (3/4" per truss movement). That said, I would:

1) Disconnect everything that is currently attached to the bottom chords so that they will be laterally unrestrained between the ends of the truss and;

2) Reattach all of the stuff from #1 in case it's there to brace the bottom chord.

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Bending or cutting roof truss bottom chord?