Comment by jaclaz | Hacker News Reader

Comment by jaclaz | Hacker News Reader

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Not at all to try giving any lesson on the matter, but using membrane is a modern (and cheap) way to solve an issue that the Romans some 2000 years ago had solved in a much "cleaner" way.

In Italian it is called "scannafosso", this is the "modern" (and cheap and "wrong") way:

https://www.coffeenews.it/wp-content/uploads/2010/02/scannaf...

and this is how it was done traditionally (as said since Romans times) and "right":

https://www.coffeenews.it/wp-content/uploads/2010/02/scannaf...

The idea is that the walls must be permeable and areated, the membrane keeps the outside rain/water/humidity outside BUT it also keeps the internal humidity/vapour inside which is a good start for moulds and similar, and in any case it is definitely not healthy.

BTW the effect is not entirely dissimilar to what happens (hopely happened as nowadays it is more rare that new houses are built without appropriate ventilation) in modern houses built along "energy efficient" rules, any house in an energy class better than D (C, B, A and A+) without a mechanical air ventilation system is simply and plainly unhealthy for its occupants.

>> Not at all to try giving any lesson on the matter, but using membrane is a modern (and cheap) way to solve an issue that the Romans some 2000 years ago had solved in a much "cleaner" way.

...Proceeds to give lesson :P

If I'm understanding it correctly its basically a space dug down and left empty to keep the walls ~60cm away from the foundation? In most places, but especially SF, there isnt space for an extra meter on each side of the houses

>If I'm understanding it correctly its basically a space dug down and left empty to keep the walls ~60cm away from the foundation?

Exactly.

There is no actual need of 60 cm, which is only a "sane" width to allow inspection, the external wall and "air chamber" can be much smaller, see as an example:

http://docplayer.it/docs-images/41/9277133/images/page_8.jpg

and if there is not enough space for the above (25-30 cm) a wall of porous/hollow bricks (thickness 10-15 cm) will still do better than waterproof membrane alone.

>In most places, but especially SF, there isnt space for an extra meter on each side of the houses

I know, and I am not at all saying that it is a universal solution, and - besides - it costs a lot more than plainly applying to the house foundation and earthed walls this or that kind of non permeable membrane (there are bitumen based, PVC based, synthetical/chemical liquid compounds, bentonite, etc.).

Still if you are building a house and have the needed space, it is money well spent, I have seen tens or hundreds of recently built houses using membranes notwithstanding the availability of space (because it is easier and cheaper) with humidity/mould problems that cannot simply be resolved without mechanical ventilation (besides when needed repairing the waterproof layee(s)).

That was interesting, thanks.

But you might be pleased that the most modern system at least in Finland actually has little of the same features than the romans had. If you look at the same membrane I posted earlier, it has little knobs that hold it little bit away from the wall:

https://monosilla.files.wordpress.com/2014/11/screenshot-201...

I don't know the English word for it. It's not perfect, but lot better than couple decades ago. They used to paint the concrete with tar. This "patolevy" is cheaper, easier to install and allows little bit of ventilation.

Yes, I know those, though - technically - they are not a waterproofing membrane, they are intended (at least here) to be only a mechanical protection and a separation layer, and the height of the knobs is anyway too small to have an actual ventialtion.

Besides - usually the "top" of the layer is not properly sealed/protected so - over time - the space (at the bottom)is filled with fine sand/dust brought by wind/rain, of course preventing any ventilation where it is more needed.

"Bigger brothers" do exist, like:

https://www.youtube.com/watch?v=dnxj9mTN9NE

still they are usually placed over the waterproofing layer, this should guarantee:

1) that the actual waterproofing is not punched by a stone or whatever when filling the excavation

2) that the waterproof membrane is not "immersed" in humidity

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