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Q

How to insulate under floorboards?

I live in a semi-detached 2-bed Victorian terraced house and I want to take off the carpet in the ground floor living room and sand the original floor. However, I understand I need to insulate underneath the floor and ensure that air is free to circulate from outside to prevent damp build up/ draughts. Can you tell me how to go about this, what materials I will need to buy and whether it is best to get the work done by an insulation tradesman or a flooring specialist.

My main concern is that without adding insulation underneath the floorboards, the room will become draughty and much colder caused by the void underneath/airblocks in external walls.

Ybobthebuilder_46 25th Feb, 2012 Insulation
1 Answer
A

Hi, If you lift the boards you will damage them, unless they are in very good
condition and you are extremely carefull. As far as I know there are no regulations that say you have to insulate below an existing floor, this is personal preference.
I have lifted several wooden floors before and nearly always come accross
other problems below, which would be the best time to right it, but can
obviously cause extra expense.
If you are concerned mainly of draught's, then you perhap's
should lift the boards and insulate, this would prevent
draught's aswell as insulate.
you will need to fix a batten the required thickness of
insulation down from the top of the battens, I would suggest 75mm kingspan, then cut sheets to required size
in between joists, and push in between joists onto the
battens, leaving the insulation level with top of the joists,
gun in any gap's with expanding foam, then fit the board's
back on top.
As for the air circulation, you will need airbricks on both
sides for a cross flow ventilation, this would normally be at
2m centres.
I wish you all the best of luck with it.
Kind regards

Paul Callaghan Builder 27th Feb, 2012
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