cellar is dry but damp, has nothing in it but wine! suspended floor is 1800’s solid oak, with very small uneven gaps between the supporting joists…
So that would make fitting rigid panels and absolute PIA. Damp makes it not suitable for regular glass fibre as that absorbs moisture and collapses in structure. Rockwool is great for fire stopping and impervious to damp.
Sounds like a very hefty construction that has obviously been in situ a very long time.
I would be very cautious about fitting any totally damp proof layer to the underside of the joists, as separating them from the damp atmosphere below to which they are accustomed, could well, over a period of time, cause splitting, warping, or twisting as they dry out. The room above the cellar is now probably kept warmer than was ever the case when the floor was constructed, so there may have already been some drying of the timbers.
These old cellars were often deliberately constructed to be damp in order to stop the wine corks from shrinking in storage.
I think you need a sort of halfway house between the need for insulation and the need for keeping the floor structure in good order.
As @Corona has suggested I should think that rockwool between the joists is probably a good solution for reducing the cold coming up through the floor, and the least arduous to fit. You could cut strips of rockwool slightly wider than each inter-joist gap, squish them into place initially. and then fit thin battens across the underside of the joists to hold the insulation in place.
You will have to screw the battens to the joists as trying to nail into oak of that age will only result in bent nails. You will also need to pre-drill the screw holes with a steel drill bit as a wood drill bit will just ‘light up’ red hot with ancient oak. This resolution will leave the underside of the joists exposed to the humidity in the cellar that they have been used to ever since they were installed.
Old houses have great character but are a pain to work on. There is never really a quick fix and one has to be careful to respect the needs of the materials from which they were constructed.
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Thankyou for this… we are at the moment doing nothing to the suspended floor, other than timber treating all the exposed timber work… however we have 4 small opening windows the glass seems to be original and drips with condensation so considering relacing glass with double glazing. The work load to insulate and fit battens is probably going to be frustratingly lengthy , and the gain maybe miniscule. So maybe we wait makesure the floor is properly sealed and the gap between skirting and floor does not leak cold air… then wait and see if we have a cold snap!!
Because I don’t like the fibres from rockwool, I would use a geotextile fabric on the underside of the joists from below, very breathable and easy and clean to fit.
That’s a good idea for those who are fibre averse. No doubt it could be stapled to the battens that would hold the rockwool in place. However, there is of course an additional cost which could be significant if it is a large cellar.
An alternative would be a Panama hat hanging on a nail just inside the cellar door, especially if visits into the cellar are infrequent.
@JWM Replacing the windows with double glazing will reduce the condensation but not the cause. The existing windows were made to be openable for a reason, and simply opening them from time to time will increase ventilation and reduce excessive humidity, thus reducing if not eliminating the condensation. Obviously you will want the windows closed in the coldest of weather, but why not leave them open for the rest of the year and see how things go. Could well be a much easier and cheaper option than double glazing.
Don’t forget that in the first instance someone went to the additional expense of having opening windows instead of just fixed panes to allow in a bit of light. The intent was to be able to open them for a reason, so I recommend that you follow their lead. The builders of yesteryear didn’t have modern academic qualifications, but they did know what they were doing, and the building method used would have been adapted to make it suitable for the particular location in which you are situated.
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Exactly ..as I read this and condensation on glass windows means it needs ventilation . And you want this cellar space to be cool and unheated .. what you want to do is stop drafts coming up … So you don’t actually need insulation as much as draft suppression .. What you don’t need is something hermetically sealing below …
windows are open most of the year … so we will go for draft proofing of floor above
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If the floor above feels cold on the feet and you don’t want to continuously loose the valuable heat in the room through the floor, insulation is exactly what is needed, basic principles insulation slows down the movement of hot to cold, cellar cold, room warm.
Heat rises ..cold sinks . Drafts are a much more significant heat loss mechanism than conduction . Wool in any of its forms hung under floor joists would allow vapour flow and supress air flow . Now your suggestion on Rock wool is not a bad alternative and could be kept in place by garden chicken mesh stapled to the joists ..
We had something similar ..except the cellar was not subterranean .. .It was a root store with a clay floor. and a bedroom above .. The son sleeping above complained about smells … . The cellar was used presumably for wines and ciders and had rotten crude timber shelving . Ripped out the shelving and I put a damp proof membrane on the clay , then dumped a tonne of gravel on the 10 sq metre ..So the smell was gone …I would have sealed off the floor above , but the T&G oak flooring was gapless ..
Yes they are, there will be a temperature difference between the ceiling of the room above and it’s floor but no insulation will mean a bigger differential. So in one breath you say vent the basement (good) but in doing so you will reduce the temperature of the floor above, hence by adding a thermally reducing rockwool or other insulation the warmth of the room will not be lost into the floor and cellar. Whilst chicken wire will support the rockwool it doesn’t stop loose fibres blowing/floating around and I would not want to be breathing that in in a cellar, hence using low cost geotextile fabric to prevent it.
From practical experience I can say that this is unlikely to work in a satisfactory manner. We are told that the joists are oak, and that they have been in situ for at least 130 years and probably a lot longer. Additionally, we don’t even know if the joists were new oak when they were installed. They will be hard as iron by now and I doubt that staples will penetrate deeply enough to hold for any length of time.
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absolutley correct re hardness of wood
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Nail guns do staples .. but a cordless power drill making pilot holes and then a electric screwdriver l can hold a mesh in place .in even the strongest oak ..and you are more likely to have these . I am much more a believer in screws than nails for fixing timber.
Then even in old oak there are tannins that eat iron/steel so non ferrous is favoured
Trouble is the non ferrous screws are too soft and shear off.
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Ahh yes, on a posh build I worked on we had to put a hardened wood screw in first after pilot drilling, then brass fitted to finish with the slotted screw heads lined up with a ruler 
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That lining up screw heads business really gets up my nose…it’s from cabinet work, not carpentry/joinery. Thankfully now most screws are pozi, even some brass ones!
You get it on doorhanging too. I never line them up, in fact if they happen to look that way, I change them 
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I’m not a fan of battery tools. I find them to be too heavy, especially when working overhead. Call me old fashioned if you wish, but I prefer the ‘feel’ of a manual screwdriver so that one can tell if the screw is gripping or whether it may shear off before being driven home.
I agree with you about preferring screws to nails, and a bit of some of the modern adhesives adds the belt to the braces.
I sort of know what you mean, but if youve got fifty 150 mm screws to put through Douglas into old oak beams to level a floor its impossible to do by hand. A good, powerful cordless impact driver with Torx head screws is an absolute necessity (and once you’ve started using an impact driver you’ll wonder how you ever managed without one).
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