Insulate a loft

[spiidey]

Good afternoon

We’re considering insulating our upstairs rooms properly, by insulating the loft space directly above these rooms.

This is for a combination of both heat loss and sound.

We live in a relatively new build property (2006) which has soffits around the whole expanse of the loft to allow the loft to breathe. The loft itself has not been converted and has the usual timber trusses supporting the roof.

We're looking to use Rockwool rw5 in between the joists on the floor of the loft:-

http://www.rockwool.co.uk/products/...(formerly known as RWA45, RW3, RW4, RW5, RW6)

Is this product ok to use in a loft without any insulation/plasterboard on top of it (for issues like condensation risk etc)?

Also, what depth can we use - can we only use this up to the height of the floor joists, or can we go higher?

 

[freddiemercurystwin]

So there is no insulation above the ceiling? And it was built in 2006?

3 layers of 100mm is the norm. Some of the sheds may still be doing deals on insulation.

 

[spiidey]

So there is no insulation above the ceiling? And it was built in 2006?

3 layers of 100mm is the norm. Some of the sheds may still be doing deals on insulation.

There is insulation but its thermal insulation only - we're looking for something a bit meatier/denser that will also help with sound insulation.

So 3 layers of 100mm = 300mm depth/height (30cm)?

 

[freddiemercurystwin]

So 3 layers of 100mm = 300mm depth/height (30cm)?

Still a bit confusing but yes, 3 layers @ 100 ea is 300 overall.

 

[kbdiy]

Current regs specify a minimum depth of 270mm but there should be something approaching this depth already, dependent upon when the build was actually completed. I can't really see how insulating the loft with anything thicker/denser will help with noise suppression as there are so many other factors which will have far greater influence on noise transmission.

 

[spiidey]

Current regs specify a minimum depth of 270mm but there should be something approaching this depth already, dependent upon when the build was actually completed. I can't really see how insulating the loft with anything thicker/denser will help with noise suppression as there are so many other factors which will have far greater influence on noise transmission.

Struggling to understand how bog standard thermal insulation in a roll can achieve anywhere near the sound reduction levels of a heavy, 100kg/m3 rockwool slab!

This is also why I asked whether we should be incorporating a sheet of plasterboard (soundblock?) over the top of the wool insulation to act as a further barrier for sound.

Equally, what other factors will have a far greater influence on noise transmission?

 

[kbdiy]

Equally, what other factors will have a far greater influence on noise transmission?

Walls, doors, windows, floors - any of these will permit transmission of sound/noise so I can't see how stuffing the loft with any kind of dense material will have any impact at all.

I was not suggesting that thermal insulation would have any effect either. Why are you so convinced that sound insulation in the loft is going to make any difference at all if you don't treat any of the other areas?

 

[spiidey]

Equally, what other factors will have a far greater influence on noise transmission?

Walls, doors, windows, floors - any of these will permit transmission of sound/noise so I can't see how stuffing the loft with any kind of dense material will have any impact at all.

I was not suggesting that thermal insulation would have any effect either. Why are you so convinced that sound insulation in the loft is going to make any difference at all if you don't treat any of the other areas?

Maybe I wasn't clear in my original post - I completely agree that all other aspects need to be considered, particularly windows.

However, our ears can clearly determine that the main source of noise is through the ceilings in the upstairs bedrooms - therefore minimising the noise coming from there will go some way to reducing the overall noise impact.

 

[tony1851]

What noise is coming through the ceiling??

 

[spiidey]

After a lot of fiffing and faffing last year we're now about to progress with this.

n our loft, we have the plasterboard from the ceiling below attached to the underside of the loft joists, with thermal wool insulation 300mm high above this. We are intending packing in the RW5 above the plasterboard and between the joists, to a depth of 150mm, and then laying the existing thermal wool insulation back over this.

I know others have questioned why we are doing this but as I say one of the areas we get a lot of noise from is the loft, addressing this will then allow us to understand what residual noise we are left with and therefore where, if anywhere, we need to target subsequently.

Two issues:-

1. Is there any issue with what we are proposing in terms of condesation / allowing the loft to breathe? The loft has soffits attached to all sides of the house.

2. We have downlighters / spot lights in our bedrooms / bathrooms directly below the loft space. When we moved into the house, the exposed part of these lights (i.e. the parts of the lights that protrude into the loft space) were houses in a 300mm cubic plasterboard box (presumably to allow the heat to dissipate but would welcome confirmation on this). Given our proposal above, do we need to alter this at all to a larger space - if so why?, if not, why is the 300mm cube box sufficient?