Looking to improve acoustic and thermal performance before relaying wooden floor

Question

We are about to lay new wood floor in the entire upstairs of an old Victorian house. This seems like the perfect opportunity to acoustically (and thermally) insulate the floor to separate it from downstairs.

I was initially thinking about putting 25mm acoustic roll in-between the joists (1st floor) but I can't find any information about if 25mm will be sufficient e.g http://www.roofingsuperstore.co.uk/product/25mm-knauf-earthwool-acoustic-roll-4-x-600mm-x-200m-2400m2-pack.html

Then I thought about the idea of using 100mm loft insulation roll as its cheap but can't find out its accoustic properties. e.g http://www.wickes.co.uk/invt/109449

Should I use acoustic roll or loft roll?

What thickness should I use?

What is the cheapest option for me?

Thanks for your time!

Answer 1

If you want to reduce the sound of footsteps, you should use a soundproofing underlayment (which is essentially a sheet of rubber).

If you want to reduce other noises in the rooms, such as voices, TV, etc., then the insulation is a good choice. You should use enough to fill the cavity; if the cavity is 100mm thick or more, then the 100mm loft insulation should provide significantly more sound insulation. The actual difference in performance between regular building materials and their "soundproof" counterparts at equivalent thicknesses are typically quite small, making the added cost difficult to justify. Specialized construction techniques are much more important than specific materials for achieving overall good soundproofing (in other words, the difference between no insulation and insulation is much bigger than the difference between normal insulation and special insulation).

As far as a thermal barrier, if you're heating/cooling both levels, then you're not likely to benefit much from it (and it could even reduce comfort by allowing some rooms to get too hot/cold).

Answer 2

If you use standard loft insulation (to save money) you will need to increase its density for it to be effective. Roll sections of it like a tight sausage and wedge it between the beams so that you have a snug fit. It will lessen acoustic (air) transmission of noise (mid to high frequencies) but not impact noise.