Rafters 4 feet on center

[mark handler]

Guessing purlins are 16" on center?

Give the owner/builder the option of building it as planned and load up a bay with tube sand or other weight to design snow loading. Or 25 or 50% over. You can measure deflection with a straight edge and a tape measure.

Guessing??

 

[mark handler]

OK, but 2021 R802.4.1 says " For other grades and species and for other loading conditions, refer to the AWC STJR." https://awc.org/codes-and-standards/span-tables/

That document provides rafter span tables for loading up to 20 psf dead and 50 psf live, with a choice of L/180 or L240 deflection criterion.. And Appendix A.3 of that document tells you that the allowable span is based on, among other things, the load per unit length on the rafter, which it says is based on the psf loading and the member spacing. Which makes it clear that if you double the member spacing and halve the load, you'll get the same load per unit length and the same allowable span.

Use of span tables from the WFCM is allowed per R301.1.1, although I haven't checked if it has an prescriptive tables that would be helpful for 48" o.c. rafter spacing. https://awc.org/publications/2018-wfcm/


I agree that the flat-wise 2x4 purlins are outside the scope of the prescriptive design allowances I'm aware of and would likely need to be eliminated to prescriptively design the roof in the OP, in favor of one of the prescriptive options per Table R803.1 or Table R503.2.1.1(1).

As to the rest of your questions, those are all things you need to know to apply the span tables found in the prescriptive allowances.

Cheers, Wayne

AWC span charts for rafters DO NOT have 48" centers.
There is no 48" spacings RR in their tables

PDF Viewer

 

[wwhitney]

AWC span charts for rafters START at 2x6.
There is no 2x4 RR in their tables

There are no 2x4 rafters in the proposed assembly. There are 2x10 rafters 48" o.c. and 2x4 flatwise purlins at an unspecified spacing.

Cheers, Wayne

 

[ICE]

The weak point will be the attachment to the building. I have never been a fan of joist hangers used to resist a roof from pulling away and cutting the number in half.... well that is not helping. But hey now, it's just a patio cover.

 

[bill1952]

Guessing??

Yes, a simple and hopefully non-offensize way - something you seem not capable of - to say that information has not been provided in this thread.

 

[bill1952]

The owner agreed to allow me to do some load testing as mentioned, just to find out what the results are

I hope you mean you will direct the owner/builder to do testing you require.

 

[ICE]

Guessing purlins are 16" on center?

Give the owner/builder the option of building it as planned and load up a bay with tube sand or other weight to design snow loading. Or 25 or 50% over. You can measure deflection with a straight edge and a tape measure.

Speculating? You're kidding right?

 

[Paul Sweet]

Table R803.1 allows 1 1/2" T&G. The T&G implies solid sheathing, not spaced sheathing.

Load tests should be for at least double the required snow load. (IBC 1709.3.1 since load tests aren't addressed in the iRC) Deflection only has to be checked at the required snow load.

 

[Plumb-bob]

Table R803.1 allows 1 1/2" T&G. The T&G implies solid sheathing, not spaced sheathing.

Load tests should be for at least double the required snow load. (IBC 1709.3.1 since load tests aren't addressed in the iRC) Deflection only has to be checked at the required snow load.

Load testing should be done by an engineer. What would the judge say? He would say the building official is not trained or qualified to perform load testing.

 

[bill1952]

In NY, lable it an ag building and it's exempt from building codes and all is fine. If the lean to is primarily storage, the basis of NYs ag building exemption, I'd give them some slack.

Speculating? You're kidding right?

I was presuming and suggesting inspector 102 should be sure it was within the span limits of the ply sheathing (which I believe would have to run up and down slope, perpendicular to the purlins.)

2x4 flat spanning 4' is common in post frame buildings - and that's to 60 psf snow load. And o.c. spacing is greater based on the metal roofing.

Seems like it was the BOCA periodical that published an article on load testing as a means to demonstrate compliance to a prescriptive code. Was for guard infill iirc. A 1' sq of ply, eye, rope, pulley, post, and 50 pound weight. So put weight double the snow load on it for a week. It won't fail.

And for fun I just put an old weatherd notched 2x4 flat on blocks more than 4' apart and jumped on it quite a bit. 200 lbs + a little. deflected about 1/2 to 3/4". No sign at all if failure in bending.

Too bad lawyers and litigation have turned so many into wussies.

 

[my250r11]

Table R803.1 allows 1 1/2" T&G. The T&G implies solid sheathing, not spaced sheathing.

This is the way I understand it. Also have done it this way. It was also an engineered design. 1 1/2" sheathing is heavy and not much fun to carry on a roof with a slight breeze.