steel bearers ?

ok am putting the deck/verandah on and am thinking of steel bearers from the back of house to existing stumps / verandah posts just under 3 mtres wide gap to span putting them 450m apart using 100mm c purlins as the bearers would i need a extra set of stumps in this gap ie about the 1500 mark or is the steel stronge enough to use by its self also what about weight

also is the only way to fasten the decking to the steel bearers drill and screww and would this hold as good as nails in wood

cant post pic or plans as cant work out how to do so
hope u can get the idea
thks david

I can give you the info on Duragal because I've just finished the frame for a deck with it. What's the joist span?

3 metres is pushing the upper limits of lightweight structural stuff. You have to go up to 3 or 4mm to get that kind of span and you'll need a joist span of around 1.8 metres.

Duragal is a box section. I don't think C purlin would handle that kind of span at all.

As for fixing the deck, most people will tell you to screw it down. I nailed mine with a dacronised twist nail as recommended by OneSteel. They say "the use of screws to attach timber decking to joists on external decks and verandahs is not recommended".

thks have decided that i will have to use wood anyway as the steel wouldnt fit at one end the way i wanted
had decided to put in second row of stumps as thought 3mtres was a bit much

cheap deck is starting to cost a fortune for lol

I assume that you wants joists (spaced 450 mm apart), to go out the 3 metres. and the decking to running parallel with the back of the house. Bearers (spaced 1-3 metres apart) go on the stumps, joists on top of bearers and decking on top of joists.

100x50 bolted to the wall (called a ledger) will be sufficient as a bearer. One across the verandah posts. (size depends on distance between posts/stumps) and one midway (again size depends on distance between posts/stumps)

You could have joists 3 m long, but would require 170x45 or 190x35 F7 (treated pine rating)

If you only have to span 1500 with a middle bearer then only need 90x45 if it spans the whole 3 metres. the cost of the extra bearer and stumps is offset by the savings on the joists, as there are a lot more joists.

There should be a few threads that have the sizes for bearers. Otherwise post the size of your deck, length, width, height which way you want to run the decking boards.

and the timber you want to use (I'd recomend rough headed treated pine, not rough sawn. It has a rippled finish. More consistant sizing and generally straighter.)

I'd suggest getting the book "Decks and Pergolas Constrcution manul" by Allan Staines. I got mine at Bunninngs for about $20-30 and it has all the tables you need and other useful info.

many thks for reply so i can use treated pine joists and not have to have hardwood is a covered deck more a verandah than anything so will be out of most of the weather???

Hardwood has a higher "F" rating, so is stronger, which means smaller sizes required. But it is more expensive and doesn't like exposure to weather. I would use treated. Just need to make sure you get "F" rated timbers, which for treated is usually F7.

Both houses I have owned had hardwood joists/bearers and were 15 -20 years old. hardwood all but rotted through. very scaring as these were both on the second floor. When demolition time came around, it took very little effort.

Make sure you use joist tape.