A simple deck

[pelican]

Having looked at decking websites and searched for relevant posts here I've come up with a construction method that I hope is simple enough to suit my limited DIY talents.

It's a 3.0mx2.1m deck with the top surface about 200mm above approx ground level. The 3.0m side will be against the house wall and the deck will be built mostly over an area of existing uneven concrete. With 28mm decking and 50x150 frame and joists the underside of the frame and joists will be between about 20mm and 50mm above the uneven concrete slab.

I'm doubtful about accurately drilling a row of holes in the house wall to fix a 3.0m long ledger board. So will simplify by fixing 50x100 offcuts as "posts" at 600mm c/c along the wall; each post to be fixed with one rawlbolt. The 3.0m 50x150 ledger board to be screwed to each post with two 100mm screws. The outside frame of the deck to be 50x150 fixed at each right-angle joint by three 100mm screws into the end grain. In order to avoid joist hangers etc on the ledger board, 3.0m long 50x150 joists will run parallel to the house wall at about 400mm c/c; fixed to the outside frame by three 100mm screws into the end grain at each joint. Very short 50x100 posts will be fixed by two 100mm screws around the frame and along the joists at about 1.0m c/c to support the frame and joists about 50mm above the old concrete slab. The posts will just rest on the existing concrete slab. The decking boards will then be at right-angles to the house but I don't see that as much of a disadvantage when compared to simplifying the joist arrangement by eliminating joist hangers etc on the ledger board.

Points of concern; I think it's probably OK just to use very short 50x100 offcuts as "posts" fixed with two 100mm screws at about 1.0m c/c to keep the frame and joists about 50mm above the existing uneven concrete slab but I'm not entirely sure about just using three 100mm screws into the end grain to joint the frame and joists and not entirely sure whether a total of six rawlbolts (i.e. one rawlbolt at 600mm c/c) are sufficient to fix a 3.0mx2.1m deck back to the house wall? Anyone's comments about under or over-engineering would be welcome.

 

[foxhole]

I would not fix to house, a gap is required to avoid damp problems and would bury 100mm x 100mm posts to support near house so nothing rests on the uneven concrete.

 

[pelican]

foxhole,
I've read that, for example, ledger boards bolted to a house should have spacers between the board and brickwork in order to avoid damp problems but I've never really understood why damp problems would occur if the board is fixed below the DPC.

As with most other houses, my front door and back door steps were built directly attached to the house with the top step about 100mm below DPC. All of the new deck structure directly attached to the house would similarly be about 100mm below the DPC. The only difference I can think of is that the steps are brick/concrete and a deck structure is timber which may cause the house brick work to retain dampness longer.

 

[freddiemercurystwin]

foxhole,
I've read that, for example, ledger boards bolted to a house should have spacers between the board and brickwork in order to avoid damp problems but I've never really understood why damp problems would occur if the board is fixed below the DPC.

Just because the brickwork is beneath the level of the dpc it should (if possible) be kept open to the air, tis just good practice that's all. You may not get any problems at all however the Forum is littered with threads with people asking why they have damp inside yet no actual breach in level of the dpc externally.