Acoustic insulation of 2nd floor flat floor (under boards)

[vapd]

I'm a freeholder of a 2nd floor split level flat and I need to get acoustic insulation from the flat below sorted, for my benefit. The building was built over 100 years ago as a hotel and converted to flats in the mid 70's. There is no acoustic insulation, there wasn't even thermal insulation in the lofts when I bought the place a while ago.

I have been researching what to do and my current question is: The advice is to use 100mm depth of 60kg/m3 acoustic mineral wool between the floor joists. I have floor joists of about 250mm depth over lath and plast. As I understand it, being way above ground, I don't have to worry about ventilation? (That's question one). Question two is: is 100mm of 60kg/m3 more effective than 200mm of 40kg/m3? Two thirds the density but twice the volume=more mass but all the advice says 100mm of 60 is better. But I don't understand why. Also some advice says to fill that void completely and some says there is no point in more than 100mm.

This is the only part of the acoustic insulation I am interested in at present. separating the boards from the joists and putting mass loaded vinyl down will happen later. I am renovating the property from the top down but I need to get some insulation in for airborne noise as soon as possible as the guy who lives below me drives me nuts with his constant coughing (heavy smoker), silly laugh and monotone whiny voice.

 

[JohnD]

As the ceiling below is L&P you can expect it to fall down sooner or later, so do not lay your insulation on it.

You can fix light battens to the sides of the joists as supports, or use netting fixed to the tops of the joists. Roofers batten is very cheap. If you use battens you can lie a layer of plasterboard, cut to fit, on them. This will give extra soundproofing and is also a fire barrier. If you see any gaps or holes in the ceiling, block them as noise passes through holes. They are common round pipes and cables. Usually I'd say use expanding pink fire foam, but it might bulge into the flat below, so flop some dampened kitchen roll or cardboard over the gaps before applying the foam, the water will make it harden quickly, and the tissue will prevent it leaking through the gap. Hoover off the dirt first (it will be very dirty)

Notionally, you own the top half of the joists, and the downstairs flat owns the lower half.

Do not use nails or a hammer as the vibration may trigger the L&P to crack and fall. This really is very common, and creates terrible mess and cost. Avoid any chance of being blamed for it. Screw your floor and any battens into place. Fire foam can also be used to seal round the battens and plasterboard and it will stick them in place once set.



How thick is your existing carpet and felt underlay?

 

[vapd]

Thanks for the information.

The current carpet is over some sort of semi rigid wooden material. I'm not sure what it is. It's cheap stuff no doubt, I've only had it up in the kitchen, where it is under lino, to tackle a slow draining sink (pipe was up and down like a yo-yo). The building is in a deprived area and neglected both externally and by the individual freeholders (I'm the only owner occupier) so it is safe to assume that anything that has been done to the place was done close to as cheaply as possible. My carpet and underlay will be the last things to be done, my wooden sash windows need a lot of work, the plasterboard is blown in some areas (water ingress from chimney stacks, blown render and flashing that should be fixed this year). So I have no intention of new carpet or underlay for quite a while, assuming you were going to recommend I do something with that.

So, with 250mm to play with, would you use 100mm of 60kg/m3 stuff? Or would you go more? I am assuming that as the width between the joists in the two lofts was not consistent (in the same stretch it would vary by 20 or more mm along the length) it won't be consistent with the floor joists which makes batton awkward I believe? I had thought it would be the only option but now you say about the netting I think that will be the best solution. Thanks for the info on the expanding fire foam and how to use it without messing the ceiling below!

 

[vapd]

Actually, I only have 200mm to play with between the bottom of my boards and the top of the ceiling. Also, here is a pic of the material under the lino in the kitchen. Same stuff is under the carpet in the hall outside the kitchen and the front room so proably also on the stairs and the back room and the bathroom.

 

[JohnD]

That's hardboard (badly) laid under the vinyl (not lino)

It is intended to cover the joints in the floorboards so they don't show though, but yours is so badly laid that the joints in the hardboard show through as well.

If you ever want to lay any, start it the centre of the room, and put factory edges together ( they will fit perfectly) and smaller pieces round the edges, with any cuts facing the skirting. It is usually stapled down.

It looks to me like it will be fairly easy to get your floorboards up.

Start in a small room for practice.

The acoustic mineral wool is surprisingly heavy and 100mm should help a lot. You might use plasterboard as well in your bedroom where noise will be more irritating. In parts of Scotland, coal ash was sometimes used, and very messy when it fell through.

Loft insulation is very lightweight and mostly air, though it deadens reverberation,

 

[Tigercubrider]

Use a bread knife to cut acoustic rockwool. It should be slightly larger than the gap and squeezes in, but don’t ram it in.

If using plasterboard, mix up some plaster and “grout” the joints or where it touches the battens. The more airtight you can get the better.

Fill the gaps in the floorboards.

 

[vapd]

Thank you!

So, am I right in thinking that if the width between joists varies along the length of each void that fitting batten and plasterboard (acoustic or otherwise) will involve a lot of work? Or do I just attach batten close to the bottom of the joists and then roughly cut the plasterboard and then fill the edges with expanding pink fire foam? Because, at the moment, using net suspended from above the joists sounds a lot eaisier.

 

[vapd]

Quick question, where I have had floor boards up in the kitchen to check over pipes, I'm looking at that (two water pipes and a gas pipe running through the void between the joists as well as some electrical cables) thinking the only acoustic insulation possible will be loose fill. So I have some Thermofloc loose fill which, when chucked in by hand, is supposed to be 35kg/m3. And I'm just wondering if 200mm depth of that would have a similar effect as 100mm of 60kg/m3 insulation. It does not matter that much, I'm just wondering. Also, would it be okay putting loose fill into a void like this next to a wall or is that going to increase any issues with the ceiling below by an unacceptable amount?

 

[JohnD]

Plasterboard is very easy and quick to cut.

Actually, you don't usually cut it. You mark it with a pencil, or hold a straight edge against it, and score the paper coating with a craft knife. Then you support one side of it with a batten or something, press down, and it will snap along the score.

You don't need to be very accurate when it will overlap the battens and you can foam the joint. Foam will easily fill a one- inch gap, and will do more if you want. Use an application gun, not a bare can.

I see plenty of work for your canister vac to do.

The black "pipe " is I think black electrical conduit. The original single wires have been pulled out and more modern pvc t&e threaded through the save the effort of making a new chase. The end of the conduit can chafe or cut the cable so it ought to have a protective ferrule. There may be a way of bodging protection onto it, someone may know a good way.

The mineral wool is fairly easy to cut and squash into place in irregular gaps and round pipes and cables, I don't think you need loose fill.

 

[JohnD]

I like to paint gas pipes yellow as a warning to be very careful. It's not a requirement but one day you might be glad you did. No need to be neat, just slap it on.

 

[vapd]

I use a Henry for vaccuming everything and it will have to do! I think it will!

How would you acoustic insulate that section?

 

[JohnD]

Clean it out and cut a piece of mineral wool to roughly fit