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I have very low trusses on my shed. Do I need them? Is there a way to give me more headroom without replacing the whole roof? The shed is approximately 6m x 2m has six trusses going across and they are about 5ft 6in high at the bottom chord.

Could the bottom chords be raised or could some of them be removed?

low rafters inside

the outside

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    To be honest, I'm not sure if you just want to cut out ceiling joists/rafter ties or if you want to completely remove the roof, extend the walls upward then reinstall/rebuild the roof higher. Too many possibilities for us to read your mind.
    – FreeMan
    Feb 21 at 15:08
  • You have a kingpost truss, evidently. Whether you can replace that with some other structure without the roof failing is hard to know. The bit of wood going across the bottom is a truss lower chord (not really a joist) but in any case not a rafter. Rafters are the bits directly holding the roof up, though in this case they are also truss upper chords.
    – Ecnerwal
    Feb 21 at 15:44
  • How much height are you hoping to gain? In theory you could raise the bottom members somewhat, retaining the posts they support, but I'm not sure that's worth the effort. Is there some specific gain you hope to achieve?
    – isherwood
    Feb 21 at 15:57
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    A full-size photo of the entire truss would be more useful than this cropped thumbnail.
    – isherwood
    Feb 21 at 15:57
  • I’d like to gain a foot, or even just take some of the trusses out so it’s more usable. I may be out of my league here. Thank you all for your help.
    – Mark
    Feb 21 at 16:07

6 Answers 6

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Now that we have a pic of the roof system, I'd say that the answer to this question is "No".

Well, that's a qualified "No". If you were to completely tear the roof off and rebuild it with a different kind of roof structure, I'm sure you could build in a taller ceiling. For example, a steeper roof pitch with a ridge board/beam and actual rafters, with collar ties raised by 0.5 meters or so would buy you more headroom. The question is, would it be enough? [1]

The other option would be to engage a Structural Engineer to design the changes to the existing roof to ensure that it won't collapse on your head. Don't know what hiring an SE would cost, but I'm 99.9999% certain that it would be less expensive than the hospital bills for whoever gets injured in the collapse of a self-designed structure, plus loss of income, possible lawsuits, etc., etc., etc.

[1] I did something similar in an addition I just built - it's 16' across, which is pretty close to your 3m in width. The roof is roughly 4:12 pitch, and I've got collar ties at 24" (~61cm) above the wall top plate, giving me 4' (~121cm) of sloped ceiling (from 8' (~243cm) to 10' (~305cm) tall) on each side and 8' width of 10' tall ceiling in the middle.

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I suspect your best bet (short of completely rebuilding the roof structure) would be to raise the whole thing (as a unit) and extend the walls upward to meet it.

That sort of project is usually best handled by someone with experience in jacking up parts of buildings or entire buildings without having the whole thing come crashing down due to a mistake. Such a person would also typically have the large quantities of temporary support material required to do that safely, which can be inconvenient and expensive to source if trying to do it yourself, one time.

If such a person or company is not available to you, then it's possible that completely rebuilding the roof structure would be more cost-effective.

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First, you need to get your terms straight. The rafters are those diagonal pieces to which the roof is attached. You can't remove those, obviously.

What you seem to want to remove/raise are the the bottom chords of those home-built trusses, which are acting as collar ties. In principle, yes, as long as the rafters are properly tied to the top plate AND you add either appropriate collar ties OR plywood/OSB gussets below the ridge, you should be able to raise the usable head space. But from the look of the shed, this strategy does not seem to be worth it. The roof sheathing already seems mended, the shingles have a lot of moss growing on them, and the roof looks to be in an overall poor condition. I know it's easy for me to spend your money, but it seems that the best plan for you would be to remove that roof, raise the walls (perhaps 1m up), then build a new proper roof on top using the common method of joists and rafters.

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An LVL ridge beam is another option. The peak where the rafters meet is basically a hinge, so the horizontal pieces act as tension rods to prevent the walls from moving outward. The ridge beam would restrain the hinge and therefore avoid the need for the rafter ties.

The 6 m span could be accomplished with modern LVLs, and you would need a big post at both ends of the ridge to carry the weight down to a foundation. I see a window at one end, where that would need a large header installed above it.

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The bottom chords of your roof is what is holding the rafters (the long beans under your roof decking) from flattening. Also, there isn't a lot of "other structure" to keep the roof stable, so cutting them would effectively be destroying the roof structure, and only time would be needed for a proper roof failure.

Some people have suggested removing the roof and raising the walls. If you are considering this route, I would suggest replacing the walls with taller ones. The strapping and bracing to ensure that the wall doesn't buckle at the "extension" point is non-trivial, and will likely require removing the sheathing and metal bracing. By the time you do that, you might as well have rebuilt the wall.

Remember that the roof doesn't just apply pressure down the wall, wind shear also means it applies some load laterally on the walls. Walls with pre-built "bend" points are problems that need reinforcement, or the wall will collapse under the roof in high winds.

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Could you remove the bottom chords? Probably yes.

Would it be easier than rebuilding the whole roof? No.

The rafters translate downward pressure on the roof into outward pressure on the walls. The chords then resist that outward pressure so you don't just push the walls over.

The two alternatives to that would be:

  1. Replace the chords with a ridge pole and uprights so that downward pressure on the peak of the roof turns directly into downward pressure on the ground (note that this would then result in weight on edges of the roof translating into an inward pressure on the walls and you'll have to make sure the walls are capable of withstanding it.)
  2. Replace the chords with flying buttresses or similar on the outside of the building to reinforce the walls.

Neither of these approaches are likely to be significantly cheaper than just replacing the roof. And they certainly won't be quicker.

Could you raise the chords? That depends on the weight of the roof and the expected snow load. Raising the chords will increase the strain on both the chord and the rafters. You would need some very careful measurements and a bunch of trigonometry. Since you're asking the question here, you almost certainly want to find someone with practical experience at such projects who can visit in-person. There are lots of little details in such work that are best not overlooked.

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