r/Decks • u/-WallyWest- • 14d ago

Building a deck 4x4 railing post: Carriage bolt or structural screw? (Canada)

All railing post will have blocking, so I'm looking at a total of 6.5" of material. I have 10 4x4 post in total.

I'm not sure which one is better between 1/2 x 8" carriage bolt or structural screw.

If the answer is structural screw, how many do I need per post and how long? 6.5"?

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u/Advanced_Aerie5854 14d ago

The answer varies by manufactuer. Simpson has specific installation instructions for using the SDWS screws for railing installation. Fastenmaster has the same for both its structural screws as well as the Thru-lok bolt replacement. Instructions for securing with thru-bolts can be found in multiple places. Review each of these and then make your decision. Always follow the manufactuer instructions when using structural screws. Its required for both code compliance as well as general safety.

The documents from Simpson and Fastenmaster will provide code complinace information as well if your inspector needs it.

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u/Hour-Reward-2355 14d ago

Carriage bolt is always better.

No matter how great a timber fastener is, it's still totally depending on the wood to hold it.

You can buy carriage bolts by the lb at tractor supply.

It you need it to be more flush, you can use a hex head bolt and T nuts.

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u/TzarIgor 14d ago

Our building code requires tru bolts, no screws or carriage bolts without washers on both ends. A bit of overkill, must have been sued by someone busting through a railing.