sound proofing - joist foam strips

[MarkyP]

I'm almost ready to lay a chipboard floor in my loft conversion. I've been thinking about the issue of sound transmission. I've tightly placed 150mm of rockwool RWA45 between the (220mm) joists which is already far more sound insulation than any other house I've ever owned but I'm having one last look at options before I put the chipboard down. (The option of adding resilient bars and double layer of PB below just would have been too disruptive, it's a large bungalow and would have been 5 rooms' worth of ceilings to take down and replace. 

 

however, I recently saw a system which uses a dense foam strip over the top of each joist, and then the chipboard laid atop this but floating rather than nail or screw fixed. I'm assuming this is helpful in reducing impact noise through the joist structure. Does anyone have any experience with this solution?  I have loose laid some of the chipboard floor to create a temporary storage deck and it sits nicely on the joists with no bounce or rocking so wondering if actually it might be easy enough to float the 22mm deck, gluing the T&G sheets but not screwing into the joists, leaving this 10mm dense foam pad to absorb some impact noise. The joists are at 600 centres so one concern is that heavy furniture in one area might cause some flex in the chipboard between joists, lifting it elsewhere due to the absence of screws.

Edited February 18, 2019 by MarkyP

[Mr Punter]

I have only ever done floating chipboard over a solid floor, as I would fear the joins weakening if not fixed to the joists.

 

We used a product called ScreedBoard in a flat conversion. It is an overlay board with a soft backing so you would fit this over your chipboard. The sound test results were excellent.

[Onoff]

Mark the joist centres in case it doesn't work and you have to screw later. Spax flooring screws all day long for me in 22mm T&G chipboard. Superb design. 

 

https://tradefixdirect.com/woodscrews/flooring-screws?

[Thedreamer]

A couple of joiners are attaching the last bit of our chipboard as I type. I purchased these Spax screws they seem to be working well.

 

Don't forget the expanding glue foam as well.

[Moonshine]

Yes, the resilient layer between the floor and the joist is for impact noise and doesn't do much for airborne noise transfer. 

 

Question, are upstairs rooms going to be carpeted? if so carpet and a thick underlay are pretty good at impact isolation.

 

46 minutes ago, Mr Punter said:

We used a product called ScreedBoard in a flat conversion. It is an overlay board with a soft backing so you would fit this over your chipboard. The sound test results were excellent.

 

yep, ScreedBoard is a solution and performs well (see robust details E-FT-5 and E-FT-6), also if you are laying on a sub floor construction, similar products exist with a resilient layer under a interlocking chipboard (e.g 19mm JCW Acoustic Soundboard).

 

Speaking to JCW in the past they don't recommend putting their Soundboard directly onto joists, as the point loading over loads the resilient material.

 

I have specified joist caps before in a project where space was a premium and no sub floor construction, but the joist caps were only 50mm, where the joists on site were 75mm so they went with the regupol option.

 

https://www.customaudiodesigns.co.uk/acoustic-joist-cap.htm

 

https://www.soundstop.co.uk/ZMJCAP50.php

 

https://flooringwarehousedirect.co.uk/product/regupol-studwork-isolating-strip-self-adhesive-15m-roll/

 

It is imperative whichever option is taken that no rigid connections (e.g. screwed) are made between the new flooring and the timber joists, this includes the room perimeter and flaking strips should be used to make sure that the floor is truly floating.

 

Also note that the sub floor construction may help stiffen the whole construction (e.g. joists fixed together by boarding) and help with bounce. It may help the airborne sound insulation as you have doubled the surface mass, due to two layers of floor. 

 

 

[MikeGrahamT21]

British Gypsum make a product called GypFloor Silent: https://www.british-gypsum.com/white-book-system-selector/systems-overview/floors-and-ceilings/gypfloor-silent

 

This goes underneath your chipboard and should do the trick. I would imagine its fairly expensive though. Are you sure you need sound proofing if its just a storage space?

[MarkyP]

4 hours ago, Moonshine said:

Yes, the resilient layer between the floor and the joist is for impact noise and doesn't do much for airborne noise transfer. 

 

Question, are upstairs rooms going to be carpeted? if so carpet and a thick underlay are pretty good at impact isolation.

 

 

 

 

I thought upstairs was going to be carpeted, but seems the Mrs thought wood, hence my worry about impact noise.

 

regupol looks interesting, seems you can bond that to the chipboard, and then bond an engineered floor over that.

[MarkyP]

3 hours ago, MikeGrahamT21 said:

British Gypsum make a product called GypFloor Silent: https://www.british-gypsum.com/white-book-system-selector/systems-overview/floors-and-ceilings/gypfloor-silent

 

This goes underneath your chipboard and should do the trick. I would imagine its fairly expensive though. Are you sure you need sound proofing if its just a storage space?

I had looked at this, I guess the joist strips with floating timber deck is a cheap version of the same. I was thinking of getting the impact noise benefit without the cost and hassle of the full system. It's temporary storage of building materials, will be an occupied upper floor when done.