post frame structure breaking the rules

[billconner]

Thought this was interesting. Shelter on St Lawrence River so lots of snow and wind. 2x8 rafters, 2x6 ties mid span (?), 2x10 headers sandwiching 2x6 posts with a 2x10 flat on top, and some diagonals. Just interesting I thought. At least 3 years old from my experience, probably some longer.

 

[nadogail]

The fact that the Shelter has survived does not invalidate "The Rules"

 

[Stuart in MN]

What rules are being broken?

 

[billconner]

2x10 rafters on 24" centers with 17' span and 60 psf snow load seem very undersized, coupled with rafter ties half way up the span. Interesting no ridge board - just rafters butted and one-by purlins at ridge. I'll assume it's an engineered design but just so far from prescriptive code requirements. Interesting is all.

 

[theoldwizard1]

The purlins (2x4) appear to be set on edge.

 

[rjacobs]

Looks better than half the **** I see professionals put together....

 

[billconner]

Pretty sure the purlins are 1x4 flat, 2' on center on rafters 2' on center. Seems like good craftsmanship, just design different design choices. The 2x4 diagonals from posts to rafters are definitely different. But among the various post frame "kit" manufactures, there are a lot of fundamental differences. I look at Hansen Buildings with posts and pairs of trusses 12' on center and purlins on edge on joist hangers between top chords, and see no one else doing that. Compared to some plan book post frames which seem like the get the bigger hammer approach to structural design. Just interesting to me.

 

[Old Man Roger]

Never seen anything like that before. I would love to hear the reasoning for the design.

 

[joe_padavano]

Span tables are based on stiffness, not strength. A shelter isn't a residential structure. And as they say in the financial disclosure statements, "past performance is no indication of future gains". The fact that it has held up for a whole three years doesn't mean anything. My hand-hewn log house doesn't comply with any building codes, but it's been standing for 300 years.

 

[Voi]

2x10 rafters on 24" centers with 17' span and 60 psf snow load seem very undersized, coupled with rafter ties half way up the span. Interesting no ridge board - just rafters butted and one-by purlins at ridge. I'll assume it's an engineered design but just so far from prescriptive code requirements. Interesting is all.

On my phone & not seeing details in the picture. Will look at is more closely later.

Is the span really 17' or is it 8.5'?

 

[billconner]

It's 34' eave to eave, I'd say that's 17' rafter span. 50' long do gable posts don't do much for middle section. I do like rafters instead of trusses.

 

[nadogail]

If it has a good history of doing what it was intended to do, why question history?

If the structure fails, an examination into the cause of failure and analysis of design might be warranted.

If it ain’t broke; don’t fix it.

 

[Old Man Roger]

If it has a good history of doing what it was intended to do, why question history?

If the structure fails, an examination into the cause of failure and analysis of design might be warranted.

If it ain’t broke; don’t fix it.

The idea of codes is to keep the structure from blowing away or falling on peoples heads. Just because it hasn’t happened yet doesn’t mean it won’t. What if the building just hasn’t been exposed to a snow load or a big gust of wind yet?

 

[racecougar]

I look at Hansen Buildings with posts and pairs of trusses 12' on center and purlins on edge on joist hangers between top chords, and see no one else doing that.

That is how I had my building constructed, though my trusses are 8' OC.




I framed the ceiling with 2x6's with joist hangers between the bottom chords (the trusses were designed with this in mind).

 

[Old Man Roger]

That is how I had my building constructed, though my trusses are 8' OC.




I framed the ceiling with 2x6's with joist hangers between the bottom chords (the trusses were designed with this in mind).

The structure in your first picture looks like a matchstick house compared to the structure in the original post lol I assume you have a lighter snow load?

 

[racecougar]

The structure in your first picture looks like a matchstick house compared to the structure in the original post lol I assume you have a lighter snow load?

Thanks?

Yes. This is in MO, not NY. Both photos are of the same building at different stages of construction.

 

[Old Man Roger]

Thanks?

Yes. This is in MO, not NY. Both photos are of the same building at different stages of construction.

Ahh ok, the first picture wasn’t finished.

 

[JohnKal]

That is how I had my building constructed, though my trusses are 8' OC.




I framed the ceiling with 2x6's with joist hangers between the bottom chords (the trusses were designed with this in mind).

Mine is built this way also, only double trusses 10’ OC. Location, central NY.

 

[Voi]

It's 34' eave to eave, I'd say that's 17' rafter span. 50' long do gable posts don't do much for middle section. I do like rafters instead of trusses.

On my laptop for the moment and can see more detail. Are the rafters birdsmouthed?

Also, here is a previous thread about a pavilion that collapsed.

Collapsed Pole Style Shelter - Negligible Lateral Support

Picnic Shelter That Collapsed

www.garagejournal.com

 

[billconner]

The use of trusses automatically means engineer. The rafters and ties are more typical of non-engineered buildings. And who knows they might have claimed it was agricultural, so no codes would apply in NY. Or it might have an engineers calcs behind it.

I'd guess it's 10-12 years old, based on owner telling story of how a one season just out of college gig turned into 14 years. I think it was his retired general contractor dad's retirement gig.

 

[billconner]

I think the rafters are not bird mouthed but use a bracket, but then the dbl header is not loaded equally. Next year I'll do more photos.

 

[Wolley]

Looks like about an 8 pitch so the snow probably slides of the steel before it piles up too much. Wind probably blows right through with out much lift. When the nails rust out in 50 years he might have some problems

 

[My Old Tools]

There would be tremendous lift in a cross wind. That roof is effectively a wing.

 

[firebirdparts]

I see a lot of "pavilions" and picnic shelters built, even on government land, that are fundamentally wrong, forces are backward, that sort of thing. A lot of them are old. Sometimes you'll see evidence of later bracing as the building started to obviously relieve itself.

That does not look terribly overkilled, but I was surprised to read 2 x 10 rafters are "very undersized", although maybe Bill meant to type 2 x 8. To me, a 2 x 6 in that building would be undersized. At that point, you might be in real danger in upstate new york.

I'm not competent (or more accurately too lazy) to really appreciate the forces you get into with the rafter ties above zero.

 

[billconner]

yes - 2x8 rafters - sorry. My build has 13'-6" rafter spans on 16" centers (I wanted to use 2x12 on 24" centers but not quite) so even 2x10s on 24" centers at 17' would seem light to me. 60 psf snow loads really get up there and IRC doesnt seem to give credit for pitch and steel - that seems to need an engineered building.

 

[mcbane]

Thought this was interesting. Shelter on St Lawrence River so lots of snow and wind. 2x8 rafters, 2x6 ties mid span (?), 2x10 headers sandwiching 2x6 posts with a 2x10 flat on top, and some diagonals. Just interesting I thought. At least 3 years old from my experience, probably some longer.

When it comes down it will be interesting to see the failure mode. I saw a similar “design” fail due to essentially zero roof diaphragm strength. Trusses likely designed for 240 psf but over a period a three days while the roof held no more than maybe 100 psf snow, the ridge line translated and the trusses all slowly tipped over. As you might expect, a total loss.

 

[PassnThru]

The use of trusses automatically means engineer. The rafters and ties are more typical of non-engineered buildings. And who knows they might have claimed it was agricultural, so no codes would apply in NY. Or it might have an engineers calcs behind it.

I'd guess it's 10-12 years old, based on owner telling story of how a one season just out of college gig turned into 14 years. I think it was his retired general contractor dad's retirement gig.

I had thought until now that you were talking about a structure built on city property like a park so it didn't surprise me - their 'codes' are different from 'your' codes.

 

[Sumboodie]

The use of trusses automatically means engineer. The rafters and ties are more typical of non-engineered buildings. And who knows they might have claimed it was agricultural, so no codes would apply in NY. Or it might have an engineers calcs behind it.

I'd guess it's 10-12 years old, based on owner telling story of how a one season just out of college gig turned into 14 years. I think it was his retired general contractor dad's retirement gig.

How so? I have built trusses as well as my Dad and there was no engineer.

 

[PoorUB]

Thought this was interesting. Shelter on St Lawrence River so lots of snow and wind. 2x8 rafters, 2x6 ties mid span (?), 2x10 headers sandwiching 2x6 posts with a 2x10 flat on top, and some diagonals. Just interesting I thought. At least 3 years old from my experience, probably some longer.

Snow load? It looks like about a 6/12 pitch, metal roof, I bet it sheds the snow right off.

 

[billconner]

It's a resort - cabins for rent during summer.

The building code require trusses to be engineered, but agricultural buildings are exempt in some jurisdictions.

It may shed snow, but prescriptive building codes - not designed by a registered design professional - don't take that into account IMHO.