Fill to the top, if you are worried lob in some bits of eps packaging in the bottom

You could consider spraying the beads in layers as they go in with weal pva say 10 to 1 every 100mm approx

The beads won’t settle much so long as no voids, stir with garden fork to help them settle

Send pics, report back after 6 months - price sounds fine did you calculate quantity needed. Shame about the lockdown or I would be there to help

👍

I thought that price seemed expensive. My floor which was approximately 4m x 4m and average 750mm depth would have cost almost a grand!

I got all my beads free from a cavity wall installation company who had removed all their beads from older properties when upgrading them. Worth a look?

I would worry about draughts getting in above the beads and making the floor cold if you don’t fill right up.

Posted By: Kenny_MIts difficult to find supplier of the beads

Maybe try a local cavity wall insulation company?

Very interesting non existent risk

Providing the house is warmer than the ground under it, true for all buildings in the uk apart from cold stores. And no flooding or plumbing leaks. Then an interesting bit of science comes into play - the partial vapour pressure of the moisture in the air in the house will be higher than the partial vapour pressure of the moisture in the air in the ground. So a downhill like process acts and moisture moves from in the house to the ground, if there is a vapour impermeable layer on the floor the joists will be drier than they have been for the last hundred years, even the wall plates will tend to dry out

Posted By: gyrogearI would postulate that designer (1983) did not understand why he was doing it !

Attached below is an extract of the current Part C of the Building Regs. I would imagine that they were the same or very similar back in 1983 so your designer and Local Authority BCO (no private inspectors back then!) were merely complying with the regs.

Posted By: gyrogearHowever, the regulations do not explain WHY such ventilation is needed!

With good reason, the Building Regs Approved Docs tend to take a very cautious and risk averse approach. Most buildings in the UK are built in muddy fields by often semi-skilled labour. Part C of the regs also covers the risks from contaminated ground and volatile gases. Mitigation of ground contamination is not always what it should be and I imagine that's part of the reason for requiring ventilation of sub-floor voids - even when they are concrete and there's nothing that can rot.

Thanks all for the comments.

Posted By: Victorianeco
I got all my beads free from a cavity wall installation company who had removed all their beads from older properties when upgrading them. Worth a look?

Good call, although not sure if any are open at the moment with the lockdown.

Posted By: goodevansregular construction grade slab EPS costs in the region of £50 to £60 per cubic meter (+ vat) - and I'm sure that''ll be denser than loose beads.

I was thinking about looking into the price of EPS slab as a comparison so thanks for that. I suppose I could chuck some offcuts of EPS slab in the bottom to bulk it out a bit. In fact i'd imagine at the bottom layer small offcuts of any kind of insulation wouldn't do any harm, except for stuff that would compress or take up water of course.

Posted By: tonyI would worry about draughts getting in above the beads and making the floor cold if you don’t fill right up.

Thanks. I don't think draughts would be a problem in this case. One side is on to a solid hallway and the only external side doesn't have a vent and is a solid wall. The ventilation comes through from under the next room which is at a lower level so joist level is above floor level with respect to that room. The 4th side is on to a 1980's extension, the floor of which is not ventilated. The soil pipe goes under there but again at a lower level than the joists and this can be foamed shut. I'll try get it as high as possible but I wont be able to get access to every joist run to be sure that its fully filled everywhere.

Posted By: djhYou could try blowing them into place with a leaf blower or a 'shop' vacuum on blow.

Good call, but I don't have either! May need to improvise.


Regarding the discussions on ventilation. To clarify, its a standard period house arrangement, the joists are timber into solid stone walls, with ~1inch think floor boards. I am planning on fitting engineered wood floor on top of that now that I have removed the tiles (I'm aware that eng wood not recommended for bathroom but my wife wants it and as the bath in that room is never used its not likely to be an issue).

I'm aware that the normal arrangement is for the uf to be ventilated to ensure the timber remains dry, and have read the counter argument in other threads that as long as the joists are kept warm by the insulation below they should remain dry.

In terms of evaluating risk, what's the worst thing that could happen? I am presuming the answer to that is that water or water vapour builds up somewhere within the void. If it builds up below or in the middle of the insulation it should drain away through the soil. It could make the base of the walls a little damp, but I don't know of any reason why that would be a problem.

If it caused the joists to rot then I could end up having to lift the floor and replace the joists which is expensive and disruptive and would outweigh the benefit, but the question is, how likely is that? I suspect it is not very likely, but the biggest problem is that I won't be able to access under the floor to check this.

I have thought before about fitting sensors. If I could get inexpensive component type humidity sensors that I could screw to a few joists and run the wires to an access plate then that would be a quick job. However, I am not sure where to begin with that or whether such sensors could be read with an ohmmeter or would need a power supply or an interface etc.

Edit: re humidity sensors, I just thought that I could just hammer a few nails into the underside of the joists and solder wires on to them, then run the wires to an access point in the wall. Measure immediately after filling and check periodically for any reduction in resistance over time.

It is possible to push beads around with a broom

Its easy to see how the bottom of a joist with 300mm of EPS underneath it is about the least likely place in the room to attract condensation, but what about where the joists enter the wall?

While the middle 80% of the joist will be warm, the ends will be in a very cold outside wall, probably even colder than normal due to the insulation keeping the heat in the room.

If condensation will migrate towards the coldest part, is there a risk that it will collect there?

Thanks Tom.

Unfortunately, EWI is not possible for more than one reason, and removing and repositioning joists would be too disruptive and costly to be worthwhile. As it stands I was only supposed to be replacing the tiles with eng wood, and I just thought of the EPS fill as a relatively quick win while the boards were accessible.

Unless I am misinterpreting, it sounds like you are saying that joist ends could be the weak link here. While they might not be colder, they could be as cold, and they would be part of a thermal bridge between the wooden floor and the external wall.

I suppose the joists being cold are only an issue if moisture can reach them. I am planning on fitting a few mm of XPS underlay, so that should minimise any vapour that can reach it from inside the house. Not sure of the risk of moisture heading up through the walls to the joists as there will not be a DPC

Just trying to make sure I have thought through and understand all the implications and risks here.

The joist ends will be in a warmer bit of the wall than the courses below so moisture moves away from the joist ends too

Posted By: Kenny_MBeing doing a bit of research on this tonight. Thought others might be interested.

Interesting link. Thanks Kenny.
I see that one of the conclusions from the report is: 'Most insulated floors in this sample meet or exceed the critical thresholds for mould growth for significant periods' which confirms my earlier comment about the risk of mould growth.

FWIW, while I haven taken an interest in the developing research in this area, so far I've always chosen to replace timber ground floors with well insulated concrete slabs.

A big influence in my caution was seeing a room filled - covering every surface, floor to ceiling - with rampant dry rot. It was actually a ground floor room in an old bank that had been sealed up without ventilation for several years, rather than a floor void, but a graphic illustration of some of the potential risks.

I have seen it, I will never forget the smell.

It has nothing to with filling floor voids with insulation.