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I have fitted a bike rack onto the underside of my roof truss mounting a plank of wood 22mm x 150mm x 2.4m which spans over 4 bottom chords of the truss roof structure. The bike rack will hold around 90kg of bikes.

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I’ve since been worrying if this is OK since learning that trusses are not great at downward weight. My bottom chords are quite small – 35mm x 70mm

My garage is ~6m x 3m with the bottom chords running the 6m length.

Do I need to be concerned and if so, how should I remedy. I am thinking to either:

  1. Sister joist an additional beam onto each bottom chord down the 6m span. Which would be 2 x 3m lengths glued and nailed into the existing chords.
  2. Install a beam down the 3m span (width ways) close to each gusset plate as possible.

I’ve removed the bikes until I can be comfortable with this. Cheers!

Michael Karas
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Sausage
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    I'm not an engineer, so you can take this for what it's worth. These trusses (the entire assemblly) are designed exactly for downward forces. Your additional weight is near the tail of the truss, not the middle, which is good. Have you noticed any downward deflection? If not you should be fine. – RetiredATC Jan 01 '23 at 03:28
  • It is quite standard to do this, here in NZ. Many people make attic spaces by either putting runs of decking timber OR sheets of particle board, on top of the chord. It would be best to spread the load over more than one truss and, preferably run the timber all the way from one wall to another. – Rohit Gupta Jan 01 '23 at 11:27
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    Another idea if you are concerned about the additional weight. If you are interested in adding another beam at the green line, don't do it there. Add it where you want to hang you bikes at and use that as the support instead of the trusses, Adding a beam to resupport the trusses in theory will not work. Under load the bottom chord moves up and down as a load is applied. The bottom chord is not supposed to be attached securely to anything unless using a special clip to allow up and down movement, – Jack Jan 02 '23 at 18:29

2 Answers2

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Attach "Z" bars to the block wall on the left and the block pillar on the right. Then span a 2x8 or 2x6 beam across. Hang the bike rack from the beam and the weight is supported by the block walls. No issues with the trusses.

RMDman
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I am in the States, so I needed to covert kilos to pounds. 200 pounds of bikes hanging from 5-2X4" truss chord bottoms, approx. 10 ft (3 meters) to the truss plate, breaks down to 40 lbs to each 2X. A 2X4 in my experience will handle that load readily. The best thing you did was to tie all of them together, so all of them work together.

If I am thinking correctly, the 2X4s in that section, or perhaps all the length are in tension, working together with the downward force from the roof above. The roof trying to push the walls out, the cords keeping that from happening and the zig zag webbing, breaking up the spans of the 2X4s so each shorter span can handle the overall weight better.

There is more to it than that, but this is the simplified version. At least what I understand of it.

You should be good to go, in my opinion.

Jack
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