Best way to attach bracket to timber? - Woodworking Talk - Woodworkers Forum
 
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post #1 of 6 Old 11-22-2017, 10:38 AM Thread Starter
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Best way to attach bracket to timber?

This is for a structure that will support solar panels. I know the Building and Safety inspector will want to know that the attachment method is such that it will protect the joist from moisture incursion through the mount point.

What I'm thinking at this point is to drill a pilot hole, squirt silicone caulking in there with a gun and apply some on the bottom of the L bracket. A good amount will ooze out and I should get a good seal. An alternative for the brackets would be to make rubber gaskets out of some thin (about 0.030 in) rubber sheets I have. I could also dip the lag bolts in something like Tung oil or something else before installing them.

Normally these brackets and rails go on a roof. Not sure they do anything special to the holes but they probably do install a rubber sheet along with some flashing to divert rain water.

Any thoughts? Easier is better. I just need to make the inspector happy and protect the structure from early moisture damage.
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post #2 of 6 Old 11-22-2017, 12:11 PM
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If you could make your bracket where it screws to the side of the timber it would help. On the top no matter what sealant you use water will get in there. On the side, water is more likely to drain away. For what you are doing exterior decking screws would be sufficient. You could still use the silicone however be sure not very much oozes out. It will seal the wood preventing the it from accepting stain. A better sealant would be a metal building product called tacky tape. It's more like chewing gum.
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post #3 of 6 Old 11-22-2017, 01:15 PM
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You need to use wood (or whatever mounting structure) that is treated/made so that moisture is not a problem.

If you are not doing this and are using standard untreated wood it does not matter how you treat each individual hole.

Most inspectors will be looking for sound engineering principles for a safe structure and how it meets building codes.. They probably will not be inspecting each hole to see if it is waterproofed. That is your responsibility.

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post #4 of 6 Old 11-23-2017, 01:55 AM Thread Starter
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Quote:
Originally Posted by Steve Neul View Post
If you could make your bracket where it screws to the side of the timber it would help.
Agreed. I've been told that with solar installations inspectors like to see standard hardware. Since pretty much everything out there is designed for roof mounting you end-up with stuff that is far less than ideal for what I am building.

If I had the freedom to do it my way I would machine a bunch of flat 1/4 inch (overkill) rectangular plates with two holes for the joist and to holes for the rail and do exactly as you suggested, screw the plates onto the joists from the side.

I need to figure out if I can get the real story from a local inspector. I have a feeling some of these solar hardware companies are selling based on a script and have no flexibility whatsoever.
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post #5 of 6 Old 11-23-2017, 02:14 AM Thread Starter
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You need to use wood (or whatever mounting structure) that is treated/made so that moisture is not a problem.
The plan is to use Douglas Fir, cut and drill all holes and then paint it before assembly. From everything I've read so far opaque paint --as opposed to any clear coating-- does far better over time. I have exactly zero interest in having to re-coat this structure every year. So I'll give it a few coats (whatever might be necessary) of good outdoor paint and move on.

Still, as you screw the thing together there's the potential to create an opportunity for moisture to do harm over time. That's what I am trying to think through right now. To some extent I am over-engineering this. I know.

One thought I had was to dip the screws in something like Tung oil before installing them. I'm using Simpson load-rated screws designed for this application. They don't need holes drilled so maybe dipping them in some kind of oil will protect the fibers the screw goes through.
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post #6 of 6 Old 11-23-2017, 07:33 AM
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Quote:
Originally Posted by marthincho View Post
Agreed. I've been told that with solar installations inspectors like to see standard hardware. Since pretty much everything out there is designed for roof mounting you end-up with stuff that is far less than ideal for what I am building.

If I had the freedom to do it my way I would machine a bunch of flat 1/4 inch (overkill) rectangular plates with two holes for the joist and to holes for the rail and do exactly as you suggested, screw the plates onto the joists from the side.

I need to figure out if I can get the real story from a local inspector. I have a feeling some of these solar hardware companies are selling based on a script and have no flexibility whatsoever.
It won't shorten the life of the pergola that much. It's just been my experience with wood structures any time a fastener is installed in the top where it's exposed to direct heat from the sun and water the screw hole opens up wider and the wood cracks where it deteriorates more. Places a short distance where a screw was put in a vertical surface did much better. Either way the structure was ready to come down anyway. Most people they will build a structure like that and use a deck sealant once and decades later wonder why it's rotting away. A structure like that needs a deck finish at least annually. It doesn't have to be a pigmented sealant which alter the color it can just be clear.
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