Monopitch Truss questions

[pago cruiser]

Need to span 30' with a monopitch joist.

Unfortunately, my Structural guy is referring me to Joist Fabricators, and the couple near me (Tucson and Phoenix) don't seem to want to answer phones the last couple days of last week.

I have found online vendors, and they have a min pitch of 2:12 for monopitch trusses. I do not understand why.

For my snow load (20 psf), I can do this with a 20" flat truss.

Using the 20" as a "low end of the truss" min (per my Structural - but I have questioned him on this without a reply yet), this would make the "high end" 20" + 60" = 80". This seems... nuts.

I have a max height of 13'-6" in order to match the existing house. I can meet this if I could find a 0.5/12 pitched monopitch. I have also found a standing seam roofing vendor who will certify at this slope.

Has anyone used/found a monopitch truss at less than 0.5/12? Or anything less than 2:12?

While I could just use flat trusses, I prefer to use the standing seam roofing, (cheap and prolific around here) which means I need this 0.5/12 pitch. This is still about 2X the minimum pitch of a "flat" (0.25"/ft) EPDM roof.

I've attached a dwg excerpt with dims with a 1:12 and 0.5/12 pitch. But with the 1:12, I am still a foot too tall. And I cannot go "down", as I am having to match an existing patio grade.

While I have seen trusses hung from the headers, I need that 12" in order to accommodate the low profile garage door track.

TIA for any ideas. Something seems ...off here, but I cannot figure out what it is.

 

[u2slow]

Call around... more. In most residential contexts, a truss has a pitch. A 20" deep straight-truss is a more specialty item.

Is 13'6" truly the max height? or 'mean' height? This was an major distinction for my build. Basically the top half of a sloped roof doesn't count, and I got a higher ceiling in the center.

 

[pago cruiser]

I used a handy-dandy Roof Truss Span Tables guide from "Alpine Engineered Products" as a basis. They show a 20" flat truss as the most economical - and out of 2x6's can span 33'.

The 13'-6" is a match to the adjacent house parapet top. So I am stuck with this dimension.

The thing that seems the...oddest... is that my Structural indicated I need this minimum 20" height at the low end. Since I first posted this I talked to a friend in Minny Soda, and he suggested the Menards (like a regional HD) truss designer. Pretty slick. Although my zip is not in their service area, by using a local (Rochester) zip, I designed a monopitch truss with my span and loading - and it spit out a design that is 1:12, with a min height (heel) of about 4". This appears to work, and I (now) get a parapet height of 13'-2" - which would allow my inside height to raise from 9'3" to 9'-7". I think.

It looks like my Structural guy is winging it when it comes to joist design.

It irks me to hell when I (seemingly) have to be smarter than the guy I hired to do the job. Yet he has the PE stamp I need on the dwgs to submit to the city.

 

[u2slow]

Do you need a 'structural guy'? My truss company engineered/approved their own trusses... based on the design drawings submitted for the permit.

 

[pago cruiser]

The garage structure has to be stamped/signed by a structural engineer in my area. While he has excluded the truss design per se - as is normal - the building elevations are all based upon the dims of the trusses. Even if he is not doing the numerical calcs for the trusses, they must be based on what is reasonable possible.

Assuming that the min height has to be 20" appears to just be bad info. I really would have expected a SE to have more knowledge than me of typical Truss Design parameters and what is possible and not possible.

Per his (lack of) basic Truss knowledge, my entire building would have been a foot taller, or I would have had to make the doors shorter, or "drop" the floor and deal with concrete transitions, or some other (apparently) totally un-necessary trade-off.
grrrrr.

I am hopeful to actually get in contact with one of our local Truss suppliers this week, and hear it straight from them what is possible - or not. And then I will provide that to the SE to finish the Plans.

 

[Voi]

Is a vaulted mono truss or even a parallel chord truss with a taller front eave a possibility?

Using your compromise pitch of 1/12 gives 30" more for your overhead doors on the tall eave. Or 15" for 0.5/12.

That's with parallel chord. Is a flat ceiling a requirement?

My apologies if I missed something obvious. On my phone & not wearing my glasses.

 

[firebirdparts]

Design of that is trivial as you know. It may well be that they have a lot of productivity tools that just don’t go that low. It’s not normal. It’s not difficult either, but when you can push a button to design trusses you gradually accept the lack of necessary depth of capability.

 

[readhead]

Use a couple of steel beams front to back to make three bays. Hang flush purlins in the three bays, sheet the roof and install SSR roof. Sometimes you can get stuck on one solution and not consider other options.

 

[TRWham]

Yes, consider steel bar joists.

 

[RTBS]

You could go with a commercial type open web joist if you want a mono slope. There are a few different manufacturers they make them to your specifications. One company is Red Built. Your engineer could still be the engineer of record and specify a pre-manufactured item. Or like was suggested steel bar joists. Same concept.

Sent from my SM-G998U using Tapatalk

 

[brainypencil]

You could go with a commercial type open web joist if you want a mono slope. There are a few different manufacturers they make them to your specifications. One company is Red Built. Your engineer could still be the engineer of record and specify a pre-manufactured item. Or like was suggested steel bar joists. Same concept.

Sent from my SM-G998U using Tapatalk

I second your thoughts. Steel bar joists is the option for it.

 

[Sumboodie]

I used a handy-dandy Roof Truss Span Tables guide from "Alpine Engineered Products" as a basis. They show a 20" flat truss as the most economical - and out of 2x6's can span 33'.

The 13'-6" is a match to the adjacent house parapet top. So I am stuck with this dimension.

The thing that seems the...oddest... is that my Structural indicated I need this minimum 20" height at the low end. Since I first posted this I talked to a friend in Minny Soda, and he suggested the Menards (like a regional HD) truss designer. Pretty slick. Although my zip is not in their service area, by using a local (Rochester) zip, I designed a monopitch truss with my span and loading - and it spit out a design that is 1:12, with a min height (heel) of about 4". This appears to work, and I (now) get a parapet height of 13'-2" - which would allow my inside height to raise from 9'3" to 9'-7". I think.

It looks like my Structural guy is winging it when it comes to joist design.

It irks me to hell when I (seemingly) have to be smarter than the guy I hired to do the job. Yet he has the PE stamp I need on the dwgs to submit to the city.

That online?

I've been thinking of redesigning an outbuilding with attic trusses. Would be handle if I could play with truss designs.
I built my own using plans from the local truss plant but they don't do that anymore.

 

[pago cruiser]

Thanks gents.

Voi - Not sure what the difference is between a vaulted and a monopitch truss? The pics I cn find on the "vaulted" appear identical to the monopitch. The "flat-ish" ceiling is requirement because I need to sheet the water off the back only; and the southwest style of the house requires parapets on other sides.

Firebirdparts - Ha! I have seen that in several industries as well. "Yep, we used to do that; too much work, so we don't anymore".

Readhead - Our firm deals with some bigger commercial Structural firms sometimes; from talking to them, they have recently (this month) been getting delivery dates on commercial steel that are over a year out. A YEAR! He suggested staying away from steel if at all possible. The gent I talked with had recommended the Structural guy I am using - and he also cautioned about the difficulty of mixing (connections) steel and wood. So I went all wood.

TRWham - I may end up at least looking at these, if the local Truss guys keep not answering their phone.

RTBS/brainypencil - Looked at that site; a great reference. Will call them today - with the first question being deliverable dates.

SumBoodie - yep. Here is the link.

https://midwest.menards.com/TrussOnlineFob/index.do#/landing

But make sure you use a ZIP in their service area. I used 55902. Scroll down to (near) the bottom and click the "Launch Designer" button. You will then need to pick a store, select "Built to Order", then "Residential", and hit the pic of which type truss you want to look at. Note that you will need your loads defined - top chord live + dead, bottom chord live + dead. You can use their default values, but they are specific to the zip - in particular snow loads - which may over-ride your live loads.

At our house, we have seen no more than 2" of snow in any year for the last 12 years. But because we are at 4100' elevation - and the county requires snow load from 4000' to 5000' to be be calculated at 20 psf - we are stuck with using this value.

 

[Voi]

Voi - Not sure what the difference is between a vaulted and a monopitch truss? The pics I cn find on the "vaulted" appear identical to the monopitch. The "flat-ish" ceiling is requirement because I need to sheet the water off the back only; and the southwest style of the house requires parapets on other sides.

I understand why you need some slope on the roof, I'm wondering if you'd be okay with a ceiling inside that slopes a bit?

Then just use a parallel chord truss.

I actually like Red Head's solution the best if you can put in three overhead doors. Probably would work whether the purlins were on top or flush to the beams, depending on how much insulation you need.

I had planned to build my mono-pitch cabin this way but then ran into a draftsman who said it wouldn't work with our snow loads. Turned out to not be the case. So I'm familiar with the run around you're getting.

A vaulted mono pitch truss to my understanding gives a ceiling slope that is slightly less than roof pitch. Sort of a half of scissor truss. Believe I've seen them called a tapered mono pitch truss as well.

Honestly I wouldn't even consider them with the minimal pitch of your building.

 

[pago cruiser]

I thought of a sloping inside ceiling when my Structural guy said I need a 20" heel - "Well, hell then, I'll just use a 20" TJI." But that sloped inside ceiling concept just seems...odd. Surface mount lights would have different clearances, floor to ceiling storage racks might have different heights; and when I put in a scissors lift, I may really screw things up whether I bring in the truck nose in or back in, and lift it to the (same) height as previously...without remembering the sloped ceiling height.

I really like the (2) doors. The smaller for opening when working in the shop, and the larger for either moto storage or cars. I have about a dozen motos, which includes (4) sidecars...

I was able to get ahold of a local truss guy today - other than going with 2x6 on the top chord, he did not see any problem - which makes the heel now 6" instead of 4". He also suggested I add in at least a 6" overhang on the downside - a good idea I think.

At least this all now sounds doable. No quote yet, but he did say they are looking at 4-6 weeks delivery right now.

 

[imjustdave]

have you spoken to permit office on options or other ways to raise the roof up any. seems punitive you have to match height and look 100% of the home. Do ADU also fall into this requirement? do they distinguish between livable and non livable in the code. might be worth looking for a work around.

I have a height issue as well but owning more land eliminated this issue for me... now materials and labor have priced me out.

Sent from my SM-N986U using Tapatalk

 

[imjustdave]

what if you did a low slope gable roof? this would cut the run in half yes I agree an internal gutter would **** but nicer then flat roof.

could you build up the other building front face a foot or 2? it needs new siding to make it look better... wink wink tada taller building.

how much clearance do you need on the garage doors? for your auto?

Sent from my SM-N986U using Tapatalk