"Faulty Towers".....Funny, Faulty Decks.........Dangerous !
Faulty Towers was a hilarious British comedy. it was a sit-com staring one of the founding members of 'Monty Pythons Flying Circus'.
Faulty decks though that's a different kind of story, and if you are unlucky it's appearing on a balcony or deck near you.
Take a look at the example below and remember just because it's been there for a while doesn't mean that it always will be (there).
At 'A" you can see the short remnant of the original cantilevered beam built into the original floor framing of this building. The joists of the current construction are sistered onto either side. This is nailed with 4" common nails, not galvanized.
"B" Is the top end of the diagonal brace, a 4 by 4 bracketed by the sistered joists mentioned above. The same type of nails are used, but smaller ones.
"C" the base of the same diagonal brace is set into a shallow pocket in the cement bonded stone foundation wall. There is a horizontal steel pin, basically a spike nail pining it from moving.
So whats wrong with that you say?
Well: Nails are just pins that lock things in place . The weight transfer has to be wood resting on wood.
Nailing wood the side of another wood member without notching it in to support it from underneath means the weight transfer is being done on the nails. Nails can not resist the stress over time.
They seem to work when everything is new and tight. Then things get a bit loose and flexible. For a while there is a little 'wow' deflection felt. It can last for years. You'll even forget about it. "Oh, it's OK, it's aways been like that".
The nails loosen from wood shrinkage, wood degrades from water exposure and nails rust, loose diameter and loose their hold strength.
Then one day it's not OK. gravity wins, you loose.
At 'C' water collects here, keeping the wood wet, slowly rotting and the spike nail rusting.
To be safe:
A and B have to be bolted though with non rusting blots that pass through all the wood members and clamp them together. The number an spacing have to be staggered to prevent check splitting down the length of the grain.
C needs a rust proof bracket that holds the wood brace end off the stone to allow it to dry after rains and holds it securely on the stone foundation with through bolts. Lag bolting and cinch anchor bolts cannot be guaranteed to work on all kinds of stone.
Now look around the corner to this part of the structure:
Here we see some of the more common problems with decks.
The ledger board (against the wall), has no flashing and only has two (E) lag bolts set in mortar.
Now look at where the joists join onto the ledger (D). You can't see the nails because they are very small. There's only 5 of them and they are not galvanized.
To be safe; The ledger board has to be solidly attached. That means at least 5 bolts in this much space.
Ideally the bolts should be through bolts but if the stone is too friable then shorter lag or cinch anchor bolts can be used provided they are doweled into the stonework with epoxy. Of course they have to be galvanized or made of non-rusting alloys.
I've seen some amateur use of tapcons here (cement or masonry anchoring screws). They should never be used - they have even less shear strength than nails. They fail by just breaking off. The metal is not strong enough.
The ledger has to be flashed to keep it dry or wood rot decay will be a problem. Don't count on pressure treated wood to be sufficient. Remember you are not building for the weekend or just the next ten years, you're building for forever.
Lastly; Joist hangers - the proper type will not rust and each joist will be secured with 14 nails not not just 5 'toed' nails.
DO NOT use screws at any structural joints including joist hangers or any other bracket that transfers weight.
Fire code requires that all structural weight bearing or transferring joist brackets (and other similar hardware attachments) be only attached with nails (not screws or ring shank nails). This is for the safety of firemen so that when floors burn through, the joist and other horizontal timbers be allowed to release and fall without pulling down the walls on top of the firemen. Screws disrupt that release.
So if you're looking at property anywhere in the Montreal area and you need a full inspection............