When installing 2x4 purlins to the trusses or rafters for meal roofing, which is the preferred method; screws or nails ? Seems screws would have more bite and uplift hold, but nails more shear strength . I main concern is with uplift from the wind. -Thanks

Contractors use nails for that application. They are faster esp with a nail gun. I generally use screws on everything around the farm. I feel they hold better and don't back out. I had not thought about shear strength guess since I have yet to hav a problem.
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I removed a sub-floor once (3/4 T&G plywood) that had been fastened with screws, the floor had only been down for a year. At least 3/4 of the screws were broken, that was a revealing surprise. I don't know if it was bad screws,or if the constant expansion and contraction of the building caused the failure.

I have never lived in tornado country, so maybe screws on a roof are a good idea?? In earthquake country it's best that a building is somewhat flexible.

Do you reckon expansion/contraction or the constant flexing from traffic walking over it?

Mike

instead of purlins on top of trusses, cut blocks and nail between where the purlins would be.
if you are going to put them on top and use screws, do not use "grabber" screws, get "deck" screws. deck screws are thicker.
If you go with nailing on purlins, use 31/4 ring shank nails in an exterior finish.

trapr, beat me to but I was going to suggest ring shanks. If uplift is a concern consider strapping it.

Code will say nails. Some kind of screw will work but the standard deck screw is too brittle and will break over time.

Ring shank nails or coated sinkers if uplift is a concern. I like coated sinkers.

Mike, you can use my nail gun and my hose and compressor. The nails have some kind of glue/ cement on them and the speed that they are driven heats up the glue and they are tough to pull.

That sounds like a case of the screws being over driven at installation. With the cordless tools these days there can be a lot more torque than you need. Screws will easily break if over driven and the installer may never know if quantity is stressed over quality work

One question not yet answered is how are you putting your purlins? If you are putting your purlins on end (like a pole barn) you wont find a nail gun that will shoot a 5" nail. Therfore you will be using pole barn hand spikes that are ring shank. If you are laying them flat a 10d-16d ring shank sinker would work nice as you can get them in a framing gun which would be way faster.

Constant flexion or movement however small will break screws. Generally floors are screwed and glued down here which is acceptable because the glue prevents movement.

If you build a floating dock with screws a year later you can usually disassemble it by hand. Also, when putting down deck boards over 2x6 we nail because the larger width boards expand and contract too much. Put down 2x12 cedar decking and in two years the boards will be loose.

Try it yourself. Drive a screw into a board and bend it to 90 degrees. It will snap off. Try it with a nail and you can bend it back and forth till your arm gets sore.

That's why Ontario building code prohibits screws for structural framing. Screws are great for assembling things and getting stuff right, but we always nail it off after.

If I have a nail gun I can get things just as tight though in most cases and way faster also.

Nails for your application without question.

Nails

when putting in nails from a gun or by hammer putting them in at different angles besides the coating or ring shank will also help pull up.


so that the nails are like a cross staked trap. I do the same with screws.

Google versico commercial roofing screws, they're 1/4 in. thick, and come in many length

Google versico commercial roofing screws, they're 1/4 in. thick, and come in many length

The floor had almost zero foot trafic on it in the year or so it was down.

Nails- specific kind of nails. I don't know the brand off - hand.

"Hurricane Ties" (galvanized plates bent for specific applications) and ring shank nails will hold better than screws or nails will by themselves.

Always used screws.

When we first started using Paslode nail guns I thought the nails were kind of pathetic because they were smaller diameter. That is until I realized that the color on the shank of the nails does two things. First, it acts as a lubricant because the friction of the nail being driven liquifies the colored stuff on the nail shanks, and then when the nail stops it hardens instantly and acts like a glue to bond the nail firmly in place. Not always, and not with every type of nail but sometimes you'll tear the head of the nail before you get the nail out with a puller. depends on the wood.