Decking ledger board - gap or not?

[Tarnation]

Hi, I'm replacing an old deck and I've found conflicting advice on securing the ledger board.

The ledger board will be load bearing (nothing unusual, general use decking) and my instinct would be to butt it up against the wall to spread the support, some people advise doing this and sealing the top of the join to the wall with caulk. The general advice in the UK seems to be to leave a gap between the wall and the board for drainage / to stop debris collecting.

The old ledger was directly against the wall, and practically rotted through, so I'd like to leave a gap of 5 - 10mm. My first thought is to use stainless steel washers around the wallbolts, then add spacers along the bottom edge of the board (more washers on clout nails) spaced at 8" intervals. Does this sound practical?

Any suggestions how to stop water getting into the holes for the wallbolts? or should the washers be tight enough to seal together?

I am intending to use Rawlplug Rawlbolts, but they don't appear to have any anti corrosion treatment - are zinc plated and passivated bolts required?

Any advice appreciated,

Tarn.

Deck details: 5m across, 3m projecting from wall. Deck is elevated 30cm at the wall, 50 cm at the far edge. The joists are supported by a ledger board along the house wall. The far edge has a beam supported by posts at 1.2m intervals. The sides are supported by another ledger board along one side and a post mid way on the other. Ledger boards to be attached with M10 75l wallbolts at 40cm intervals.

 

[Tarnation]

In case anyone is interested in what I did in the end...

I went with leaving a 10mm gap. Spacers on the bolts and spacers running along the bottom edge against the wall to set the gap. To provide support, I added posts to the outside of the ledger board. The ground next to the house was a patio at some point, so a bit of paving slab set down as a base and they were ready to go. All rock solid and the gap allows air to circulate and debris to fall through.

T