A weird question, I know. But I'm putting tyres on a concrete roof and filling them with stones to make a living roof.
However, I don't want to add too much unnecessary weight to the roof. The amount needed is approx 10m3 - so vermiculite isn't an option as I can't buy it in bulk and bags would work out far too expensive.
Any ideas?
Many thanks, Howard.
If you are buying flint, its all the same weight.
Maybe you can get pumice.
Have you tried a chimney/flue installer - they have vermiculite in large bags as it's sometimes used to fill in around stainless flues.
+1.
Chippings is going to weigh a lot, and there won't be very much variation with size or material. Limestone is a bit lighter than granite.
Suppliers will all tell you the weight per cubic metre, around 2.5 tons iirc.
If its too light, such as pearlite would it not blow away? Brian
10m3 is about 20+ tons of gravel/stone, are you sure the roof will support it?
Yes, I'm quite happy about the roof supporting the weight as the gravel I've already used was on the roof anyway (It's an old concrete reservoir).
However, I have knocked a few doors and access points through the walls and so, in those sections, I want to add less weight than before. It's probably not necessary, but I just don't want to take the chance!
Thanks for the pumice suggestion. I've found
Most of the bulk gravels are going to be much the same in terms of weight. Specialist lightweight gravel is not going to be easy to find at sensible costs. Dredged stone may be lighter from the point of view this is 'round' shaped, and therefore more airspace when in bulk.
You want a lightweight aggregate such as Leca:
How about something with a high proportion of sphagnum moss (or perhaps peat, but I gather that is out of fashion). You should get down to a density of around 1, or perhaps significantly less with plenty of vermiculite, without having something which is likely to blow away.
I wonder if you could lighten a "compost" by mixing in expanded polystyrene peanuts?
Weight is *definitely* the thing which would worry me unless it is something like an old military building like a pill-box or gun emplacement.
Also, even with vermiculite, when it's wet, it's going to get heavy.
Possible I guess, although IMO those polystyrene peanuts are bloody awful anywhere the garden, but I do put the starch ones on the compost heap. I'm sceptical about living roofs (as I am about most things, actually!). A swanky modern house recently built near us had one. They just had grass on it. It got too wet and soggy in winter, and dried out completely in summer and how they intended to keep it cut, I don't know. Eventually the grass just gave up and died and they dug it all out and got rid of it.
The OP does need to give serious consideration to drainage, watering, what he's going to plant there and maintenance. Too many eco-friendly people rush into these things without doing their research or giving it proper thought. Plants on a living roof have to be tough and able to cope with some quite extreme conditions. Plenty here
Rubber crumb is less dense than stone. Broken up scrap polystyrene packaging is light & cheap, maybe usable for the lower layers. Packaging peanuts are starch, not EPS.
NT
Don't they make the polystyrene ones any more? If that's the case, I shan't be sorry.
There's also slag (Ex steelworks). Very similar to pumice but much cheaper. Eg:-
you can still buy EPS
Vermiculite is the classical stuff for the purpose.
It is usually moderately alkaline with a pH of around 10. That's fairly high for most plants, and if higher than that I wouldn't want to try to grow anything in it.
Most common stones have a similar density range 2.5-3 T/M^3.
And the ones that don't will get a bit heavier when saturated with water. About the best bet for this sort of thing on a small scale is the round pumice horticultural medium sold as perlag or hydroleca and mixed with some peat based compost. These days it is very expensive:
You may be able to find it cheaper elsewhere in bulk.
Coke is probably the most reasonably priced low density porous material easily available in bulk. OK if the plants are not boron sensitive.
And a structural engineer to check out the roof for load bearing.
Wickes had similar far cheaper last time I looked.
NT
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