Thread: digging post/stirrup holes for deck

I have only gone 450mm deep on most holes except for the the two I have hit water. I kept digging because the ground got too soft so I tried to get harder ground, which ended up being water.
If i put a sole plate in will it be ok to fill with concrete without the worry of the post sinking?

Dan, I could be wrong though but why don't you refill some dirt or small stones back to those two BIG holes, then use sole plates in them?

Ray

I think thats what I will do, I might put a little dry concrete in below the sole platel aswell.

Probably best to put in some crushed rock. then about 100 -200mm of concrete, let it set, us ethis as your sole plate and put stump in and more concrete. wont go anywhere then.

I’ll go for 145x45 bearer and joist as mako recommended, this is my only option because I have a small concrete slab (1780x1000) just outside the backyard sliding door, so I can’t dig down to gain clearance The 1500mm clearance on the house end is the measurement from the surface of this concrete slab to the surface of the floor in the house. So I have two issues:
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1 The deck surface will be 145+19-150=14mm above the floor in the house, my concern is when it rains, the water will flood into the house from under the sliding door. How do I stop this from happening? Seal the bottom of the door from inside and outside?
2 I have to skip one stump in the concrete area due to its length of 1780mm > 1500. I’ll leave the first bearer straight onto the concrete, so I’ll have to use H4 timber for my first bearer. Is it ok to go this way? Remove that piece of concrete sounds too hard, don’t know how deep it goes into the ground. Any better idea?

ok. I think i understand what you are saying. To span over your slab you could use 120 x 45 which can span 2200mm You could actually use this size for all your joists but still use 140 x 45 bearers. 120 x 45 can be hard to find at some timber supliers (eg Bunnies) or you could cut some down to size from 140. How are you going to attach the 1st bearer near the house? Can you mount it to the house under the door sill? if not you will have to anchor it down th concrete with brackets but it will have to be about 126mm (x 45mm)...126mm bearer, 19mm decking and 5mm under door hight = 150mm. Once youve attached this bearer span the 120mm joists over the concrete and have the next bearer just past the slab which you can attach to stumps.

Mato, I’ve attached a rough drawing to help understanding my situation, if I can’t use 120x45 as bearer and I can’t bolt the 1<SUP>st</SUP> bearer to the wall because it will block those air holes. Then my plan is as in the drawing: I’ll plant 4 stumps in the 1<SUP>st</SUP> row for the 1<SUP>st</SUP> bearer (140x45), bearer will bolt to stumps and the green part of the bearer will sit directly to the slab. Red color is the small gap (<20mm) I’ll leave to air flow. Stump 1 will span 3000mm to Stump2 (green part of bearer in slab), Stump2 will span normal size (1500) to Stump3. In this plan, joists will be 140x45 or 120x45.

Ok, now i understand. Sounds ok to do it the way you say but am i right that you have only 150mm from slab to door level? if this is the case you will have to 'check' out 10mm from the bottom of the bearer where it goes over the slab so the total decl level is same a door.

Yes, I only have 150mm from slab to door level - that's the pain

If it's ok to 'check' the bearer off 10mm, it'll flush the door level! If I do this, the bearer will still sit on the slab, do I need staining the bottom of the bearer?

Ray

Yeah i would seal the timber where it will sit on the slab, even with some paint and if your fussy lay a strip of malamine under it. You can get this stuff from hardware stores and looks like tar. Just works as a moisture barrier. You might even look at putting an angle bracket in the middle of the slab to hold the bearer in place.Just some sort of galvanised strong bracket and dyna bolt to slab and screw to timber. Not essential but wont hurt.

Thanks, mato. I almost come to the last bit of this plan - when I bolt the bearers to stumps:

1. what sort of bolt would you recommend?
2. I guess two holes per stump (90x90 t pine stump, 120x45 bearer and joist) would be enough, but at what position should I drill these two holes? I attached a drawing for this, but not sure if there's any rule of how far the hole should be kept from the side and top of the stump? How far the holes should be kept apart?
3. Any other tips for bolting?

Thanks heaps,
Ray

Originally Posted by remonyan

Thanks, mato. I almost come to the last bit of this plan - when I bolt the bearers to stumps:

1. what sort of bolt would you recommend?
2. I guess two holes per stump (90x90 t pine stump, 120x45 bearer and joist) would be enough, but at what position should I drill these two holes? I attached a drawing for this, but not sure if there's any rule of how far the hole should be kept from the side and top of the stump? How far the holes should be kept apart?
3. Any other tips for bolting?

Thanks heaps,
Ray

Go the first option with M10 (10mm) galv cup head bolts and galv washers under the nuts.

Yeah fig. 1 is the go. You could also 'house' out the top of the stump where the beaeer will attach, so effectively the bearer has a lip to sit on. You dont have to house it out full 45mm, maybe 25mm.