ICE AND SNOW

[Chuck White]

As a general rule, if you use screws they go in the flats, if you use nails they go in the ribs!  ;)

[PineNut]

I have some metal roofs and the screws are in the flat part of the metal. There are two different types of screws used to hold it down. The older type has a dished shaped washer head with a neoprene washer under it. The other type has a cup shaped washer head. The neoprene washer is inside the cup. When pulled completely down, the neoprene washer is compressed the correct amount and not too much. Also the edges of the neoprene washer are protected from the elements. I have both types and I prefer the cups.

[Chuck White]

Next question, should the point of the screw go all the way through the purlins or OSB?

I've heard yes because you don't want frost forming on the end of the screw as it will tend to push the screw up!

[47sawdust]

With a sheathed ,4x8, you don't have much choice but to penetrate the sheet.When using purlins I prefer a rough cut 2x4.It allows a bigger rafter spacing,a larger overhang and prevents screw from working loose.Mind you I only use this method on out buildings.A house or heated building should be sheathed and have ice/water shield and /or a membrane such as 30# felt,tri-flex etc. to prevent condensation.Use good trade practices relevant to the area you live in,and yes metal roof is screwed through the flats,but nailed through the ridge according to ABC roofing supplier installation guide.

[luap]

Got to thinking (it can be dangerous and costly) the other day since I have a metal roof on the house and the metal has ridges every 9" apart why not run PEX in the ridges and pump hot water threw them to get the snow to melt. Normally it will slide off by itself, but this year we have not had a above freezing day for 52 days and the next week supposed to have below zero temps all week. Snow and ice build up is about 30" now. The water could be heated with a heat exchanger plumbed into our heating system and closed off when not needed. Of course you'd need to have anti freeze in that system. What do you all think?

I think any heat is going to melt the snow only in proximity to your pex, the water will run down the roof and when it contacts the cold eave it will freeze and build an ice dam making the problem worse. The best solution in the snow country is a double insulated, vented roof.
luap