Trench fill foundation and slab to load bearing timber framed wall detail

[Josh Berry]

Hi, 

 

Bit of a noob here. I'm working on a barn conversion project at the moment (think 600mm thick stone external walls and mud floor). Floor is being dug out for trench fill foundations and floor slab, onto which will sit load bearing timber walls for an internal timber frame carcassing. I'm currently looking at sitting the timber wall directly onto the trench fill foundation, and building up the insulation and floor slab on either side, with the perimeter insulation and OSB board border acting like the side of a bucket. Does anyone have experience with this and does it work? The alternative I was thinking of was replacing the bottom bit of the timber wall with just one strip of block work, but this would be more complicated and would rather remove the extra step. 

 

Any help would be greatly appreciated!

 

Josh 

 

 

 

[Mr Punter]

The base of the timber is almost in contact with the cold foundation, so warm moist air may condense on this.  Could you use an insulated starter like Perinsul or Marmox Thermoblock at the base?  Also, you will need at least 100mm of floor insulation.

[Russell griffiths]

I would build your slab as a load bearing slab and sit the timber walls on top

what you are proposing is a very bad system that was proved to cause rot in a lot of timberframe houses a few years back. 

 

A full slab over the whole site is easier to detail with damp proof membranes and other stuff. 

[Josh Berry]

@Mr Punter I hadn't appreciated that...thank you. I will look into both those products ?

 

@Russell griffiths Oh interesting thanks. How would that work with the insulation in the floor - I'm guessing it wouldn't run under the load bearing wall unless it had a load bearing capability? Do you have a visual representation of what the build up might look like?  

[Russell griffiths]

All insulation is load bearing, you just need the load carrying capacity that your design needs

loads on here have an insulated slab with walls on top. 

You will need all the loads calculated then the slab design done. 

What are the walls holding up. 

 

You just continue the insulation over the entire floor and add reinforcement mesh and then concrete. 

[Josh Berry]

@Russell griffiths Thanks that is really helpful. The walls are holding up just one mezzanine floor with furniture and a bathroom. There are a lot of walls for in a small area too so the weight of the mezzanine should be well distributed. 

 

I'm guessing that under the insulation I would still thicken the foundation to bear the weight of the wall too? Might be overkill...

[Russell griffiths]

You only put the foundation under the slab in high load situations 

normally the ground is heavily compacted then stone added then heavily compacted then the load bearing insulation then concrete with reinforcement 

the concrete can be thickened in the area of the load

this is a general idea you will need to get a bit of professional input regarding loads and design. 

 

You will need more insulation than 100mm but less concrete,  

 

look up insulated rafts on here, loads have done them.