Joists to sit on a wall plate

[iwanttodiy]

hi guys

I’ve found a lot of info about fitting joists which are conventional, however I don’t think I have come across an answer to my particular situation.

I’ve just removed an old concrete floor. It was too high with 0 insulation and no space to insulate above without messing up floor levels, and also wanted to facilitate better under void ventilation for the rest of the house as it is primarily a timber suspended floor.

So, I’ve dug out, laid hardcore, sand blinding and concreted, I’ve left just over 150mm below the joists for ventilation.

Now, on one side of the floor, I have an option to put in masonry hangers or wall plate with jiffy hangers. The problem is the other side of this wall, is a concrete floor with insulation. I can’t use a wall plate, as that would mean it would need to be bolted into the insulation or hangers as that would have the same problem.

Now my ideas are
1) like the rest of the existing floor, build a 3 brick course wall on top of the concrete oversite (50mm) and sit DPC and a wall plate on top, then sit the joists on top of the wall plate.

2) bolt the wall plate lower in the bricks / concrete under the insulation and sit wall plate on top.

3) get masonry hangers that are shorter than joists and fit them on top of bricks and under insulation, drop in joists.

I’m inclined to go with option 3 as the cheapest and most efficient solution, but not sure if shorter hangers affect the loading of the hangers, or if hangers would work if there is no loading above it.

Would appreciate any feedback as aiming to fit the joists in this weekend.

 

[tomfe]

I am having difficulty understanding what you are doing. I think you've done this:
So you've dug out a concrete floor and are going to replace it with a timber suspended floor?
I can't really understand why you're done this but ok. You're going to butt up this new floor with a existing concrete slab.

You'd probably be better off with option 1.

But it would be far easier and cheaper to put some duct work in for ventilation then insulation and screed.

 

[Notch7]

hi guys

I’ve found a lot of info about fitting joists which are conventional, however I don’t think I have come across an answer to my particular situation.

I’ve just removed an old concrete floor. It was too high with 0 insulation and no space to insulate above without messing up floor levels, and also wanted to facilitate better under void ventilation for the rest of the house as it is primarily a timber suspended floor.

So, I’ve dug out, laid hardcore, sand blinding and concreted, I’ve left just over 150mm below the joists for ventilation.

Now, on one side of the floor, I have an option to put in masonry hangers or wall plate with jiffy hangers. The problem is the other side of this wall, is a concrete floor with insulation. I can’t use a wall plate, as that would mean it would need to be bolted into the insulation or hangers as that would have the same problem.

Now my ideas are
1) like the rest of the existing floor, build a 3 brick course wall on top of the concrete oversite (50mm) and sit DPC and a wall plate on top, then sit the joists on top of the wall plate.

2) bolt the wall plate lower in the bricks / concrete under the insulation and sit wall plate on top.

3) get masonry hangers that are shorter than joists and fit them on top of bricks and under insulation, drop in joists.

I’m inclined to go with option 3 as the cheapest and most efficient solution, but not sure if shorter hangers affect the loading of the hangers, or if hangers would work if there is no loading above it.

Would appreciate any feedback as aiming to fit the joists in this weekend.

Is there a reason why you cant just sit a wall plate on packers and work off that? You could use a concrete block laid flat then a sleeper timber laid flat then a wall plate. I presume the joists are finishing where the concrete oversite starts, so you cant just run the joists further and just let them sit on the sleeper.

 

[iwanttodiy]

I can't really understand why you're done this but ok

Building inspector wanted cross ventilation and suggested taking out the old concrete floor for venting.

It also benefits me as I can better insulate, and use the same subfloor material as the original house.

I’ve attached a quick sketch showing the location of the timber.

I could do option 1, but the concrete oversite is only 50mm thick. A sleeper wall would require proper strip foundations, which I guess would need to be at 1m depth and 250mm thick.

 

[Notch7]

Put in a timber beam from side to side and hang your joist hangers from that.

Say 2no 9x2's bolted together......

I assume you cant run your joists the other way?

 

[iwanttodiy]

Say 2no 9x2's bolted together......

That could work, I will need to use 6x2 from one wall to the other and jiffy them.

I could also rebuild the wall under the insulation with dense concrete blocks on their sides. Leave a hole for the vents, and bolt the 6x2 across.

Alternatively, I could cut part of the concrete, insulation and screed out, maybe by 100mm and then sit the joists directly on the wall. Not sure if a wall plate is a must for a timber floor