Whilst I've got this floor up...... insulate?

[If in doubt...]

Decided to re-board the floor in this walk through / hall way which was previously a bedroom - as it was badly laid - I'm laying new laminate flooring through this room in to the room shown beyond. Everything from the arch threshold and beyond is a brand new extension with highly insulated floor so I'm just replacing this side of the arch. This old floor is ventilated beneath the new extension floor via telescopic vents.

Would it be worth putting some PIR insulation under the boards I'm about to replace? Theres a 100mm gap directly under the chipboard as shown which I'm thinking shouldn't be fully blocked, but there are also the smaller low level gaps in the red brickwork as shown so could it be part insulated, say 50mm PIR, or is that likely to be detrimental? The walkway is only 2.5m x 2.5m so not a major part of the house but it now has a high vaulted ceiling which is well insulated up above so whilst I'm doing the floor I thought it worth considering.

Thanks

 

[JohnD]

Heat losses from floors are mostly due to draughts.

There is no convection, and little radiation or conduction.

Mineral wool is better for blocking draughts because you can stuff it tightly between joists with no precision cutting required.

Start round the edges of the room because draughts are worst under the skirting where there is a gap.

Clean out dirt and rubble, especially organic material. Lag pipes. Cables can be above or under the insulation, but must not be surrounded.

Do not block ventilation gaps, especially airbricks.

When reassembling the floor, add struts (noggins) to support all cut edges and joints.