I have a corridor added to the side of my house which is raised just over a meter off the ground, the house sits on a basement.

The floor of this corridor and the bathroom it connects to is a concrete beam construction ….if you can picture it it it is like an “L”shaped extension, corridor and bathroom raised off the ground by one meter.

It is sucking the heat from the house and always very cold and in winter and causes condensation.

So I want to insulate under this floor if i use panels its A, expensive and B,Will be fixed and i need access to pipe and cables that are below this floor, So how about packing this space with straw bales quite cheap 1 euro per bale easily removed for maintenance …

Is this a stupid idea ? the space is dry and enclosed so I dont see fire being a hazard but maybe I am wrong.

can you not jam polyurethane batts between the beams below the block infills from underneath? easy to remove for access. Stable, effective. Not recylable though.

Straw bales would be an open invitation to your local vermin.

Foam would just wedge into the spaces between the beams and would either hold themselves in or be simply held in – either way it would be easier to move than straw bales and would last a lot longer.

That said I’m not sure the floor is your only problem if the extension is that cold. Is the whole thing properly insulated and heated?

It has insulated walls and roof but nothing under the floor. the under floor is basically open.the only available polystyrene sheets are backed with plaster board and expensive in comparison.there is electric radiator in the bathroom but nothing in the corridor.

Over the years they’ve had a couple of straight straw built houses on grand designs, basically straw bales staked together then rendered. I don’t recall anything more except I think wiring was stiff copper sheathed stuff, fire protection or rodent protection.

Mice will make a cosy home in any dry spot whether the spot has man made or natural material so I don’t think that is a big concern for straw. It’s cheap, try it, see how it goes.

Use 100mm+ wood battens drilled into concrete, fill with glassfibre/similar, then use roof breather membrane to hold it up/close off from vermin, roofing battens to hold up. Mark where all your services are.