Insulating timber floor - advice please

[lylbf]

Good morning all,

Would appreciate advice on the following that I'm thinking of doing.

I have a 1930s semi with stripped pine floors throughout the ground floor. Very pretty and all, but really draughty at the moment. Could I fit insulation boards between the joists to keep the heat in better? I have a cellar that runs under the whole of the house so access is not a problem, but am wondering about the practicalities:

- how deep insulation to use? Should it be flush with the underside of the floorboards or sit below them to allow air to circulate? (I can provide measurements for the joist depth and separation if that would help).

- What's the best method of holding the boards in place? I've seen netting suggested, or staple guns, or tape, or just sitting it on some nails hammered into the joists.

- There are several airbricks in the cellar that I assume I wouldn't want to cover up: from memory they sit just below the board level, so how close would I take the insulation to them?

- What about lagging pipes and moving cables?

- Anything else I should be aware of?

Many thanks for your help. Will answer any questions as best I can (bearing in mind I'm a bit of a DIY novice).

 

[DAZB]

Using 2" Celotex foil faced rigid insulation cut tight and friction fit between the joists is my preference. Leave the face of the boards flush with the face of the joists and that way you benefit from the remaining 4 or 5" of air flow/cushion and also do not lose any headroom in the cellar. Go as tight up to the walls as you can also and cut around airbricks if you have to so they are unrestricted. As an extra means of keeping it in place you could also apply 4" foil tape along the joists which will also overlap onto each board by an inch and tape any joints between boards. Lagging any pipes is also a good idea.

 

[lylbf]

Thanks, that's very helpful. Can I just confirm - should the insulation boards be right up against the underneath of the floorboards?

 

[freddiemercurystwin]

Tight up against the boards and any gaps sealed with expanding foam, either use nails or battens to support, don't rely on just friction fitting.