Is this a terrible idea?

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Hi folks, looking for some help.

I have a victorian house with old floorboards. On the plus side, they are an attractive feature. On the downside, they are drafty and provide no noise insulation at all which with three children running around and shouting is not a happy place to be!

What I am planning to do is the following:

- Take up all the boards and go back to joists.
- Fill the void with sound proofing insulation
- Lay 18mm ply accross all of the floor area
- Put the original floor boards back down (replacing any that are broken with salvaged wood of a similar age)
- Sand down and refinish the boards

Is this a good idea or not? It seems a really simple solution but I cannot find any examples on the internet of anyone having done it so I'm suspecting that I may be missing something? Would anyone be willing to offer advice?

Very best, Nathan
 
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You may.struggle to get the boards up without breaking lots of them - it"s a bit of a lottery. You will also need to shorten the door(s) and fit a threshold to accommodate the difference in finished floor level (which may add a trip risk)

Best soundproofing material for voids is probably mineral wool batting, cut bang to size. You ideally need some form of noise decoupling between the joists and the sheet material flooring - something like old fashioned flooring felt will do although the are modern closed cell foam rubber strips as well. A cement fibreboard such as Versapanel at 16mm (33db sound reduction , when joints are properly sealed with an acoustic sealant) will perform better acoustically than 18mm plywood, chipboard or OSB as a subfloor (watch out, though, because 16mm Versapanel is quite heavy at 60kg per 1200 x 2400 sheet), but you must lay your floorboards and Versapanel at right angles to the joists. I'd consider glue bonding the floor boards to the cement fibre board as opposed to nailing it. Leave a 10mm gap all round your sub floor and the original walls/skirting and also between the reinstated floor and skirting (the idea is that noise from the edges of the floor cannot be physically transmitted to the walls). Fill that gap with a compressed edging tape such as Compraband (this is a highly compressed closed cell rubber foam material and expands to fill the gap)

Note that Versapanel is just one product and that the reason I gave that as an example is that I am personally familiar with it, however other cement fibre boards do perform similarly - so look at the manufacturers spec sheets for full details

Also note that cement fibreboard is very dusty to cut and rapidly wears carbide tipped circular saw blades (we use PCD or polycrystaline diamond saw blades, carbide grout holes and TCT jigsaw blades to cut it, but then we are doing very large areas so we can justify the cost). Forget about using a score and snap technique as recommended by some people, at this thickness you need to use a rip saw or a powered cement board shear to cut the stuff
 
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Thanks JobandKnock! Extremely helpful advice - thank you for taking the time to respond in such detail...
 
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that's good. A lime-plaster L&P ceiling is thick, dense and heavy. This will be a problem when it falls down, but until then it will block sound well.

use a builder's vac to clean the rubble and broken nibs off the top of the ceiling while it is exposed. It is possible to reinforce it with metal lathing and temporary bracing from underneath to prevent it falling down.

I agree with putting the dense sound-reducing mineral wool batts between the joists to reduce airbourne noise a bit.

not so keen on raising the whole floor by 18mm though. A carpet and felt underlay would be better for impact noise.

The mineral wool will cut draughts. pack it well, especially round the edges of the room and where air currents enter. Look at joist ends and gaps in the mortar, fill them with mortar or with fire resisting pink expanding foam. ordinary loft insulation will insulate and block draughts but is too light to make much difference to noise (it muffles it a bit) and is cheap enough to full fill the void. Do not use yellow fibreglass which sheds irritant dust and fibres. Look for the brown mineral wool treated with ecose.

as you have an old ceiling do not use nails or hammers. It may fall down at the slightest provocation.
 
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If you are going to use foam, go for an acoustic rated foam (e.g Soudal Soudafoam) or a fire rated acoustic foam (e.g Soudal Fire and Avoudtic Expanding Foam).

I'm fully with John on the use of screws as opposed to nails when working above old lath and plaster ceilings
 
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Rather than ply under all the floorboards, can you fit a lip on one edge from underneath (take board up and turn over to do) that will prevent the draughts?
 
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The mineral wool will block draughts. It needs to be tightly packed round the edges of the room, where they enter, then laid over the whole void to prevent air movement. Loft insulation is cheaper, but being less dense is not much good for sound reduction.

There may be other holes in the ceiling over partition walls, pipes and light fittings.

You can use fire foam to seal cracks. I have not used the soundproofing foam but I can see the advantage.

I have used the lathing and pour method to repair old L&P ceilings as an amateur, and was very pleased with the results, but it is slow and labour-intensive so would be expensive if you had to pay someone to do it. I have also had L&P ceilings reinstated by a limework specialist, and that was expensive (and unbelievably filthy)
 
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Just thinking aloud---- lathe and plaster ceilings commit suicide after 150(?) years. Given that the OP has the floorboards up, is there anyway to extend the life of the ceiling (other than paster boarding under it and using really long screws- which then creates a extra lip where it meets the "run in situ" cornice)?
 
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One problem is that over time the snots (the bits of plaster which get pushed through the lath and curl over them, supporting the visible plasterwork, tend to fracture. It's a combinstion of vibrations (traffic, footfall, etc) building settlement and even the laths themselves shrinking (the were often installed damp or even wetter). One technique i have seen used is to csrefully vacuum out a small area, spread a glass fibre mesh over it then spplying epoxy resin
This is repeated until the whole roof is done. Not cheap, though.

We did try a ceiling repair on one project where an extra layer of reinforced plasterboard eas applied over the existing lath and plaster ceiling with shadow gap bead all round. It worked after a fashion, allowing us to retain some of the (listed) run in situ cornice mouldings, but the technique couldn't be applied where the ceilings had cracked and sagged too badly.
 
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One problem is that over time the snots (the bits of plaster which get pushed through the lath and curl over them, supporting the visible plasterwork, tend to fracture. It's a combinstion of vibrations (traffic, footfall, etc) building settlement and even the laths themselves shrinking (the were often installed damp or even wetter). One technique i have seen used is to csrefully vacuum out a small area, spread a glass fibre mesh over it then spplying epoxy resin
This is repeated until the whole roof is done. Not cheap, though.

yes

another method, the one I used, is to clean off the broken snots, and support the ceiling from below with a large board pressed against it to take up any sag (if there are any broken snots or rubble remaining, they may lie on top of the ceiling and cause damage if pressed against joists or laths); then hoover it; then fix expanded metal lathing to the sides of the joists; then pour a runny hard plaster mix over the lathing so it binds to the (now clean) old plaster ceiling. If the laths are in near perfect condition the lathing can be omitted.

when fully hard and dry, cautiously remove the deadmen and lower the supporting board. If there are cracks or small holes the poured plaster will tend to fill them, so you must use a supporting board it will not stick to (I used laminated chipboard as I had it to hand)

This was a method from 1970's building technology so might have been surpassed now. I believe parts of Hampton Court were done this way.

The old nails are very likely to be rusted away, especially above or below a steamy and splashy room, or if the roof has leaked, and the laths may be rotten or perished.

A lot of old ceilings will have been shaken loose or cracked during WW2 bombing. Teenage daughters who like to slam doors may deliver the finishing touch.

If you have coving, cornice, roses etc, in Victorian or later work they were probably pre-cast in a workshop and nailed up, so you can drill and screw them to the joists. If parts are missing you can take off an existing part to cast a new mould.

In some cases this decorative work is run on site using a profiled trowel, which is more skilled.

This kind of restoration is rather slow and painstaking. It gets quicker the more you do and is easier from a loft where there is no floor to take up. You must take great care not to put a foot through the ceiling.

A thick, heavy lime plaster ceiling is remarkably soundproofing. You may only realise when it is taken down.
 
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Yes, should have pointed out the need to support the ceiling from beneath and the need to clean thoroughly and completely. :oops:

I did do a couple of ceilings where we simply supported the centre section of the flat ceiling with boards and props, cut round the edges with a multitool then very carefully removed all of it a bit at a time (leaving the cornices and ceiling roses in place) before relathing (with cleaved chestnut lath and iron tacks) and having the lime plasterer replaster the flat parts of the ceiling.

Run in situ cornices in this part of the world are found in buildings as late as the 1890s. They are a right sod to deal with as they often (in my experience) can contain cement render or even bricks. I was taught many years ago how to set the tracks to run these (normally just dead straight laths) and how to make up the moulders (basically just a plywood backer to which the plasterer affixed a zinc sheet profile - all this is done on site)
 
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I would have thought that acoustic insulation packed in would be enough to reduce sound and drafts?
If the ceilings below are in such a bad state that they might crack and fall down, I'd overboard and skim (which I've done in my 1930s bungalow)
 
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