Can I reframe one bay of roof trusses to create a more comfortable opening between posts?

Submitted by pearapplecherry t3_124nsfl in DIY

At my parents' house and they have a loft with a sleeping space. It's a fan truss with an open space in the middle (pardon the junk in the way; little bit of hoarding here), so the picture shows one side from the center space. I'd like to open up one of the 24 o.c. bays so that it's a little easier to get in and out of the bed without smacking your head on the joist or shimmying through the framing in the middle of the night.

I know the trusses are braced above the ceiling, so I'd likely need to brace at the connection, but with enough overengineering, is this safe? Is it likely to reduce the lifespan of the structure?

I have no issue with losing a little space between bays if it means I frame the heck out of it, but I don't want to compromise the truss's load path without an abundance of caution. Generally I don't fuck with trusses once they're in and sheathed, but I've seen way sketchier things done in other projects. Any advice for a cautious DIY'er with a bit of framing experience?

https://preview.redd.it/c6zym8ti8hqa1.jpg?width=3000&format=pjpg&auto=webp&v=enabled&s=e32caf599e8459d00f0c0b319c663fa8449b557b

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ziggy3610 t1_jdzz72a wrote

The only responsible answer is no. Anytime you compromise a truss you need an engineer to sign off on it.

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brock_lee t1_jdzza0v wrote

Anything you do there once removing the triangle of the truss, you compromise the integrity of the structure.

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clemclem3 t1_je0agff wrote

Glad we've got the responsible answers out of the way, now we can go to the practical answers

In order to remove that support you have to figure out what work it does and how you can transfer any loads it's carrying to some other structure. This is done all the time in balloon framing whenever you have an exterior penetration (Windows and doors) or mechanical or HVAC

Each truss is rated for the load it's carrying so in order to remove one the first thing would be to double up or somehow increase the strength of the trusses on either side and then bridge those two with blocking or a header. It's not rocket science but it is engineering. Because to do it correctly you have to have a good understanding of the work of each of these framing members and ideally the mathematical tools to be able to calculate loads. Trusses do more than hold up the roof. They also keep the walls from bowing out and keep the ceiling from sagging. Any solution has to solve all of these problems.

And finally there is a practical consideration. Whatever you do that deviates from standard framing practice can impact the resale value of your home.

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Enchelion t1_je0jo5u wrote

Can you? Yes, but hire an engineer to take a look and run the numbers for you to spec out the proper approach. It'll be a few hundred dollars at least.

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so-very-very-tired t1_je110j3 wrote

No. Trusses are engineered for the exact specifications of their use. There is no modifying them (short of hiring another engineer to completely re-engineer it all for you).

Also...is that a bed? Is someone living up there? Most roof floor/truss systems aren't designed for actual live loads of people living in the space.

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Jovial88 t1_je146pb wrote

Make sure you're allowed any weight in the trusses at all. Are they attic trusses with a real floor system below?

It's possible you could find the drawings with your local building department if you can't find a copy.

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so-very-very-tired t1_je18n3h wrote

Replying to Navlgazer (#2,422,101)

It's not about the weight of an individual...it's what the truss system is rated for in terms of live loads.

They're usually not rated for live loads above/beyond storing your xmas decorations and maybe some boxes of old clothes and the like.

A residential floor it typically rated for 40lb live load. I believe (but don't quote me) roof truss floors are only required to be rated for 20lb live load if only used as attic storage space. And builders tend to use roof trusses for being cheaper to build/install and rarely over-build.

Granted, you can certainly get trusses that are rated much higher, and perhaps that was done here.

For example, there are things called 'attic trusses' which are designed to usually handle 30lb live loads on the floor. The other main advantage is that they are designe to leave a larger open space in the middle (vs your standard roof trusses which use all of the diagonal members as in the OPs photo). These are great when used but they're rarely used by default simple due to them costing a lot more.

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John_B_Clarke t1_je25rig wrote

Spend the 20 bucks or so for a copy of "Aircraft Structures" by David J. Peery. Start working through it. You don't have to go all the way through to get yourself to a point where you can calculate stresses on a roof truss.

Get a copy of your local building code so you know how much load it needs to carry.

Once you're there, do the calculations and see if you're comfortable with the result, make up a test article in the back yard or garage and put loads on it (load it to whatever code requires and see how much it deflects, then load it until it breaks to know how much margin you have) to be sure, and then modify away.

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dengh t1_je25s4q wrote

All of the other 'no' answers, plus that space is not permittable as a living space. Completely separately from the mechanical issues bedrooms have egress requirements that there is no way that space meets.

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pearapplecherry OP t1_je3dk5c wrote

Replying to so-very-very-tired (#2,423,149)

Great point - I don't remember the exact load calcs, but we've had movers and all sorts of awkward heavy heirlooms up there in the past with no real issue, it really is just holiday junk at this point. I respect the abundance of caution though.

And to clarify no it's not an active living space; my dad set it up as a covid quarantine (which fortunately was never necessary) and decided to stick it in the corner and save space for more the aforementioned junk.

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