Floor insulation - worth it ?

[ricky101]

Hi,

Have got a suspended timer floor (chipboard) in our small 1980s bungalow, the underside is easily accessible due to the large void at one end.

Wondered how worth while insulating under it would be?

Our gas heating bill is around £500 a year, so would the cost of the insulation realistically be recovered this century ?

Assume Kingspan or polystyrene etc are the materials of choice, but should it be pushed up against the chipboard floor or an air gap left.
Also does a vapour barrier need to be fitted and if so on which side of the insulation ?

thanks

 

[tony1851]

Floor insulation is probably the least cost-effective when compared with upgrading walls and roof.
But you will notice some improvement.

The normal Building Regs standard depends on the area and perimeter of the floor, but is usually 3-4" of Kingspan, so would go with that thickness. It's expensive but you can get seconds cheaper.

Cut it to 'friction fit' and push it up directly under the floor boarding. Some nails driven underneath at an angle will prevent the pieces falling down.

Don't bother with a vapour barrier.

 

[geraldthehamster]

Floor insulation is probably the least cost-effective when compared with upgrading walls and roof.
But you will notice some improvement.

The normal Building Regs standard depends on the area and perimeter of the floor, but is usually 3-4" of Kingspan, so would go with that thickness. It's expensive but you can get seconds cheaper.

Cut it to 'friction fit' and push it up directly under the floor boarding. Some nails driven underneath at an angle will prevent the pieces falling down.

Don't bother with a vapour barrier.

For draught prevention I cut the Kingspan/Celotex slightly undersize when I lifted my floor, and filled the gap between it and the joists with expanding foam. Also provides additional fixing for the insulation.

Make sure your air bricks still ventilate the space under the insulation.

Cheers
Richard