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locating rafters on shingle roof

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x98myers7

Solar Enthusiast
Joined
Jul 12, 2022
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anyone have tips/tricks for finding roof trusses without drilling holes? a "normal" stud finder does not work through the shingles and 3/4" ply.

i'm thinking of using some magnets. climb up into the attic and place a magnet on each side of a rafter, then go up on the roof and use a magnet to "find" the edges. then, measure out 16" on center from there.

others have also suggested to get an 8" long 1/8" drill bit, and drill a pilot hole from in the attic to the outside directly through the center of the truss, then measure on center from there. seems reasonable, just doesn't allow me to precisely measure from on the roof
 
I've used a magnespot successfully in the past. Depends on how thick the roof is though, if it's got thick tongue and groove, etc..

Locating rafters/studs with 100% accuracy is the bane of many a professionals existence.. so don't feel bad. Mark a few locations on the roof with marker or something before drilling, see if they have the spacing you expect. Use a small drill bit under a shingle first as a pilot hole.. if you miss it, fill it with roof tar, put the shingle back down and go again.
 
Trade trick is use a common claw hammer, lightly tap on the shingles with a hammer, the thud sound will go lower, with sponge/flex feel away from rafter and when you hit the rafter, it becomes no flex and almost no thud sound, more like a tap sound. Takes some practice. If you miss when you pre-drill for the lag-bolt ( required not to split the rafters ), if you miss, move an inch and just use roofing cement to fill as it will be under the flashfoot ( using IronRidge racking ) so no harm.

Also, you can't rely on 24" centers, on my roof there was at some places a 2" variations. By the end I got pretty good at it :oops:

Another trick for mounting the railing is to pull a line with nylon string ( horizontal from each end of the roof ) and use quick clamps to hold tight and measure from the bottom edge of the roof to keep the rows straight for the starter railing, you can't rely on the shingle rows to be straight!
 
Great info here, thanks.
Not intending to thread jack... What if one has a metal roof over shingles (with 2x4s between the shingles and metal)?
Would it be safe / secure to lag the solar mounting hardware, likely unistrut, into the 2xs? Would it be better to try to hit the rafters as well?
 
Solar Guppy said:
Trade trick is use a common claw hammer, lightly tap on the shingles with a hammer, the thud sound will go lower, with sponge/flex feel away from rafter and when you hit the rafter, it becomes no flex and almost no thud sound, more like a tap sound. Takes some practice. If you miss when you pre-drill for the lag-bolt ( required not to split the rafters ), if you miss, move an inch and just use roofing cement to fill as it will be under the flashfoot ( using IronRidge racking ) so no harm.

Also, you can't rely on 24" centers, on my roof there was at some places a 2" variations. By the end I got pretty good at it :oops:

Another trick for mounting the railing is to pull a line with nylon string ( horizontal from each end of the roof ) and use quick clamps to hold tight and measure from the bottom edge of the roof to keep the rows straight for the starter railing, you can't rely on the shingle rows to be straight!
Click to expand...
X2!!
Did my first install and tapping with the hammer worked the best. I did drill test holes every 6th truss and measured from underneath to be sure they were on 24" centers. (Not all were)
 
Ohms42pA said:
Great info here, thanks.
Not intending to thread jack... What if one has a metal roof over shingles (with 2x4s between the shingles and metal)?
Would it be safe / secure to lag the solar mounting hardware, likely unistrut, into the 2xs? Would it be better to try to hit the rafters as well?
Click to expand...
Unistrut isn't a listed product for solar panel mounting rails, and code requires lag bolt into the rafters. Using strapping ( 2x4 in your case ) over shingles is a hit and run method, one should strip the roof, not go over existing shingles.

If your pulling a permit, you will need listed hardware and a PE wet stamp plan with letter stating the building ( trusses and wall to truss strapping ) has been inspected by the PE and will meets the local required codes.

I can't recommend highly enough, go with IronRidge, it makes the process much simpler and high quality. You can mount/remove a panel in a minute once the railing system is installed and the flashfoot will NEVER leak. They have an online design tool so you can make a plan to code and create a materials list to maker ordering simple.
 
I used this racking and my AHJ accepted Tamarack’s load spec data you can find here :

www.solar-electric.com

Tamarack Solar 89167 84" 8 Module Kit 1.6 Inch Rail Flush Mount Black Finish

Note: This unit is being phased out, Please look at the Tamarack 90743 Rail Flush Mount.
www.solar-electric.com www.solar-electric.com

No wet stamp was required but they were able to inspect the joists from below to be sure everything was properly anchored.

I used the Quick Bolt 2 mounts without the L brackets since Tamarack provides them.

Your AHJ will have the final say if you are pulling a permit.
 
Solar Guppy said:
Trade trick is use a common claw hammer, lightly tap on the shingles with a hammer, the thud sound will go lower, with sponge/flex feel away from rafter and when you hit the rafter, it becomes no flex and almost no thud sound, more like a tap sound.
Click to expand...

For me a rubber mallet works better than a claw hammer. Give it a try next time.
 
Solar Guppy said:
I can't recommend highly enough, go with IronRidge, it makes the process much simpler and high quality. You can mount/remove a panel in a minute once the railing system is installed and the flashfoot will NEVER leak.
Click to expand...
Installing 17 kW on a metal shop building with IronRidge right now. Pretty good system. The design tool is great.

JoeHam said:
I used the Quick Bolt 2 mounts without the L brackets since Tamarack provides them.
Click to expand...
What did you think of those QuickBolts? Looks like a promising alternative to FlashFoot for shingled roofs.
 
OzSolar said:
What did you think of those QuickBolts? Looks like a promising alternative to FlashFoot for shingled roofs.
Click to expand...

I’ve been happy.

Easy to use and holding up fine.

I did add some sealant under them although it’s not required.
 
Solar Guppy said:
Unistrut isn't a listed product for solar panel mounting rails, and code requires lag bolt into the rafters. Using strapping ( 2x4 in your case ) over shingles is a hit and run method, one should strip the roof, not go over existing shingles.

If your pulling a permit, you will need listed hardware and a PE wet stamp plan with letter stating the building ( trusses and wall to truss strapping ) has been inspected by the PE and will meets the local required codes.

I can't recommend highly enough, go with IronRidge, it makes the process much simpler and high quality. You can mount/remove a panel in a minute once the railing system is installed and the flashfoot will NEVER leak. They have an online design tool so you can make a plan to code and create a materials list to maker ordering simple.
Click to expand...
Thanks for the reply and advice.
No permits needed in my rural area and no grid interaction. Suppose that's what I get for using the local Amish to install a new metal roof on the house when they built the garage.... It's held up great for years so far.
 
Ohms42pA said:
Thanks for the reply and advice.
No permits needed in my rural area and no grid interaction. Suppose that's what I get for using the local Amish to install a new metal roof on the house when they built the garage.... It's held up great for years so far.
Click to expand...
It's not unusual to install a metal roof over an existing roof using 1x2's underneath to attach it to.. it's just not the *best* practice. It's certainly a cost / labor effective method if your roof can tolerate the additional weight. I suppose it would depend on the overall condition of the original roof, budget, etc..
 
cs1234 said:
It's not unusual to install a metal roof over an existing roof using 1x2's underneath to attach it to.. it's just not the *best* practice. It's certainly a cost / labor effective method if your roof can tolerate the additional weight. I suppose it would depend on the overall condition of the original roof, budget, etc..
Click to expand...
Depends a lot by state. California seems to allow two layers max. Hawaii doesn't have limits; I was going to do standing seam and the contractor was going to put it over the mod-bit.
 
Solar Guppy said:
Unistrut isn't a listed product for solar panel mounting rails, and code requires lag bolt into the rafters. Using strapping ( 2x4 in your case ) over shingles is a hit and run method, one should strip the roof, not go over existing shingles.

If your pulling a permit, you will need listed hardware and a PE wet stamp plan with letter stating the building ( trusses and wall to truss strapping ) has been inspected by the PE and will meets the local required codes.

I can't recommend highly enough, go with IronRidge, it makes the process much simpler and high quality. You can mount/remove a panel in a minute once the railing system is installed and the flashfoot will NEVER leak. They have an online design tool so you can make a plan to code and create a materials list to maker ordering simple.
Click to expand...


YES to Solar Guppy although he should have added electrical licenses and if grid tied, see what his utility demands. I was going to do my own install but my electrical my construction supervisor licenses expired several years ago. My town would have OK'ed my permit with proper documentation including the PE stamp BUT my utility (Eversource) demands a currently licensed electrician for them to deal with.

After looking at the documentation hurdles AND 400W panel sizes and weights I considered the ladder roof risks especially if there is wind. I hired Great Sky Solar to do my installation which is scheduled for the 2nd week in September.
 
thanks for everyone's input.... but i'd like to keep it on-topic.

I ordered a 12" long set of drill bits. I think I'm going to start by approximating with a mallet where the trusses are. I will measure from the roof peak down and drill a pilot hole from the attic out.
 
x98myers7 said:
thanks for everyone's input.... but i'd like to keep it on-topic.

I ordered a 12" long set of drill bits. I think I'm going to start by approximating with a mallet where the trusses are. I will measure from the roof peak down and drill a pilot hole from the attic out.
Click to expand...
Just as an FYI whose racking system are you using?
 
Solar Guppy said:
Don't do that, as it will likely NOT be under the flashing for the rail mount.
Click to expand...

sure it will. i'll measure from the outside first. the space i'm mounting to is next to a gable end, so I can cheat and easily reference from that.
 
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