Floor joists in contact with ground

[thias]

Pulling up the parquet flooring in the house we've recently purchased and I noticed the ends of a couple of the floorboards below were white and a chisel went straight through them.

Lifted the boards up to find the joists resting on some loosely placed bricks and then direct to soil, with some of the soil building up around the joists. The property has zero air bricks.

The floor itself is solid, I had no incline of a problem until I exposed the boards and we think the parquet's been down for at least 50 years so the timber doesn't appear to be in a particularly bad condition, all things considered.

What's the best course of action? Lift the joists, treat them, excavate some of the soil and re-lay the joists on proper sleeper walls? Taking the opportunity to fit some PIR between them too?

IMG_4584

• thias
• 16 Apr 2021

IMG_4583

• thias
• 16 Apr 2021

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• thias
• 16 Apr 2021

IMG_4581

• thias
• 16 Apr 2021

 

[mikeey84]

If there is no ventilation the joists will just continue to rot.

You need to either get some airbricks installed, or if that is not possible, consider a solid floor.

If it were me, I would be replacing rather than treating, and wrapping the ends of the new joists in dpm

 

[thias]

Our current plan is to install air bricks and replace the joists/boards in that area.

We had considered a solid floor, and UFH, but given the property doesn't have a DPC, that I can see, we'd have no where to tie in the DPM and I'd rather not just leave it lapped behind the skirts.

 

[mikeey84]

Sounds like a good plan. And definitely install insulation whilst you are doing it.

I understand rockwool or similar is the best option

 

[JP_]

Would solid board insulation be better? Better u-values for the depth you have.
I'd clear it all out and replace any joists that are badly rotten, and spray the whole lot with a wood treatment (eg everbuild triple action) and insulate.
But you need airflow under the joists to prevent it rotting again.

 

[mikeey84]

Solid boards are better insulation, but given how little heat is lost through conducting and convection in floors, rockwool is less work, cheaper and very good at blocking draughts which is where you will see the bigger difference

 

[thias]

The existing joists are notched and resting on the external walls, is this ok?

Id like the replace with deeper joists so we have room for more insulation but that would mean making a bigger notch in the new joists or raising the floor height?