Decking - ledger board position and fixing problem

23 May 2007
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United Kingdom
We're just completing a new build extension and planning to build a deck out from it, ie 2.5m out by 5.0m across approx. Deck boards 5.0m to run perpendicular to building so joists 2.5m going out from building.

There is a patio doors pvc sill below which there is a gap then the concrete sill - the sills are 3m wide. They protrude from the wall about 4 - 5cm (roughcast). Distance from top of pvc sill to underside of concrete sill is 10cm. Air bricks 20cm down from that.

I want to end up with top of decking sitting a little below the pvc sill but above the concrete sill.

Planning permission specifies 150mm x 50mm joists. The problem is that if I fix the ledger to the wall immediately below the concrete sill packed out by 10mm the top of the deck boards will come part way up the concrete sill.

I have two possible solutions but wondered what you think please and if there is another way ?

1 Ledger 150x50 just under the concrete sill, attach 150x50 joists with hangers then screw 50x50 to the top of all the joists to raise their level before attaching deck boards. The 50x50 would stop just before reaching the concrete sill.

2 Use 200x50 joists and ledger but cut away middle 3.0m of ledger down to 150mm. Use 200x50 joists but cut away last 4cm length by 50mm depth to allow for concrete sill. Using 200x50 seems excessive though.

I'll have a row of intermediate posts so was thinking that the joists on the other side would just be as normal, ie 150x50 set 50mm higher than those in option 1 or would start 50mm up from the bottom of the 200x50 in option 2.

Any ideas please ?
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