Insulating under a floor.

25 Sep 2011
Reaction score
United Kingdom
I'm new to this site and looking for some advice about replacing a wooden floor. I bought a Victorian bungalow last year. It has a big footprint and solid walls and is really cold in the winter. The floors are pine T and G over wooden joists, but with alterations to plumbing and electrics over the years the boards are a bit of a mess, wobbly in places with lots of cuts. I want to install wooden flooring but don't like the idea of a floor that I can't raise if something goes wrong underneath. I've found a cheap source of 1inch oak boards and thought I'd work through the house a room at a time removing the pine and installing a solid oak floor.

I'd like to insulate under the floor as I go but don't want to cause condensation or problems of any other sort. Any advice would be much appreciated.

Many thanks
Sponsored Links
First advise I would offer is:
Are you aware when insulation is present, where electrical cables are routed it can effect the current capacity that the cable can safely carry.
Also if wish to help prevent having to lift floors in future. I would reduce the risk of possible problems.
So electrical cables should not have any junction boxes or jointed together in the floor/ceiling void, continuous cable with no joints will prevent terminals becoming loose.
Cables should be installed to prevent mechanical damage from screws, nails etc...
So at least run cable 50mm either side of top and bottom of joists.

Much the same with the plumbing reduce joints, no compression joints, speed fit etc....
Thanks for the info. I was thinking of laying a layer of foil bubble under the oak boards to stop drafts coming up between them and add to the thermal properties of the floor. Either that or putting a layer of foam board type insulation between the floor joists. Would either of these methods cause problems to the electrical cables. I'm afraid I'm a bit of a novice and don't want to do more harm than good. I've found a source of oak floor boards which works out at about £20 per metre and so it would be a new floor for less than the price of a floor covering.

Any thoughts?
Any thermal insulation if totally surrounding the cable, will have an effect.
Don't at any cost use polystyrene, it could have an additional effect on the cables if in contact with them. It could cause in time the PVC insulation of the cable to fail.
The best method is to avoid contact.
How deep a void have you, where the insulation is to be installed? I would keep it as tight to the floorboards as possible, leave the ventilation below the insulation.
Sponsored Links
There's a good 40-50cm below the floor I would think. I should be able to use kingspan or similar, right under the oak if that doesn't cause condensation problems and I would imagine that this would be clear of all cables. I guess I could unclip and move any in the way?
If you do unclip the cables, make sure they are either rest or fixed back at a secure location to prevent stress to the cable.
But you have plenty enough space for a nice thickness of insulation.
Do an internet search to see if the glass wool type product can be bought at subsidised prices.
Energy companies sometimes offer this, as well as B&Q on ocassion.
£3.00 (ish)for a 1200mm wide roll is not unheard of.
Yes there are about a gizillion threads covering this in the Floors section, seek and ye shall find, as mentioned chicken wire and Rockwool or similar is the cheapest/easiest solution.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

Sponsored Links