How often should rails be fastened to the roof?

[Davehal9000]

Am about to mount 4 each 200 panels to a shingle roof. What is the requirement for how often you anchor the rails to the roof? Is this based on length of the rails?

 

[Ampster]

Am about to mount 4 each 200 panels to a shingle roof. What is the requirement for how often you anchor the rails to the roof? Is this based on length of the rails?

It is based on wind loads in your area and in some cases the thickness of the rails. Both Iron Ridge and Unirac have calculators that also describe how deep fasteners must go into rafters. A minimum of two per rail is obvious but each install is unique so best consult those tables which are going to be free compared to an engineer, and more useful than the free advice that you will get from the Internet.

 

[Davehal9000]

These are Tamarack rails, if that helps any. Wind and snow was low if I remember from the charts.

 

[Ampster]

These are Tamarack rails, if that helps any

It doesn't help give you the engineering calcs unless Tamarack offers the same service that IronRidge or UniRac offer. If you are not needing a building inspection try connections every 48 inched on each rail imbedding 5/16 lags 2 inches into the rafters. I picked 48 inches assuming rafters on 16 inch centers. You could probably get by with a 12 inch overhang of the rail before the first and last lag bolt.

 

[Mike 134]

It doesn't help give you the engineering calcs unless Tamarack offers the same service that IronRidge or UniRac offer. if you are not needing a building inspection try connections every 48 inched on each rail imbedding 5/16 lags 2 inches into the rafters. I picked 48 inches assuming rafters on 16 inch centers. You could probably get by with a 12 inch overhang of the rail before the first lag bolt.

Just an addition to the good advise above stagger the mounts to have each truss/rafter carry about the same load. Will require a couple of extra roof mounts but it's a better install that way.

 

[Ampster]

Just an addition to the good advise above stagger the mounts to have each truss/rafter carry about the same load. Will require a couple of extra roof mounts but it's a better install that way.

Yes and depending on the total length of the rail that staggering can be as easy as starting from opposite ends of the rails or depending on the direction of prevailing winds put the extra lags in with windward rail.