MOB without vapor barrier

Heating, insulation, ventilation, VMC, cooling ... short thermal comfort. Insulation, wood energy, heat pumps but also electricity, gas or oil, VMC ... Help in choosing and implementation, problem solving, optimization, tips and tricks ...
airsp
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MOB without vapor barrier




by airsp » 22/11/11, 01:04

Hello everybody

I study MOB carefully and I would like it to be well insulated (especially from the hot).

At the same time, I would like breathable walls and that is why I would like to do without a vapor barrier or vapor barrier.

I had thought of making a lime hemp concrete.
No vapor barrier and application of an earth or lime coating on it.

The problem: it's not too insulating, not too intimate, quite expensive and time-consuming to implement.

Do you have any ideas ?
15cm insulation in the middle embedded in hemp concrete for example?

Thank you
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minguinhirigue
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by minguinhirigue » 22/11/11, 13:49

Hello,

You plan to build an MOB with slightly thin walls, the only solution for what you are describing is the insulating panel to be coated. Depending on your budget and your interest or not for ecology, you will find this type of panel in polymers, various mineral wool, but also in hemp wool and wood wool.

If you are looking for both good protection against heat, a wall coated with lime and breathable in MOB, we can offer something like this:
1) interior clay panels, more coated.
2) flexible insulation in the thickness of the amounts of your choice (Métis insulation for example for the ecological and the social).
3) exterior panel to be coated type STEICO protect 40mm ou Isonat Cover or even Homatherm energy +

The insulation in the center can vary in density according to your phase shift needs (roofing or not, qualities of the inner layer?).

Personally I find it a shame to make a building all in wood to end up dressing it with lime, but each one has these tastes.

Good luck.
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tdahlent
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by tdahlent » 23/11/11, 15:11

You're mistaken about vapor barriers.
Breathable walls are a misconception in construction. It's very attractive, but it doesn't work, especially with the French construction method (interior insulation).
You risk creating a dew point that will eventually moisten your insulation, and there hello the renovation!
In addition, it is believed that breathing releases stale air, while this breathing is insufficient for this (this is the role of manual ventilation and VMC).

Believe me, the vapor barrier remains the best ally.
See the DELTA documentation:
http://www.doerken.de/bvf-fr/pdf/prospe ... etique.pdf

On the other hand, to protect you from the heat under a roof terrace, there are products not bad at SOPREMA (reflective waterproofing). To see on their site.
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by dedeleco » 23/11/11, 15:17

The basic physics of the dew point is a vicious cowardice easy not to understand !!!

Especially in the USA with almost 38 ° C and 100% humidity in summer for a month and -30 ° C sometimes in winter!

Their wooden houses, air conditioned, completely rot!
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by tdahlent » 23/11/11, 15:20

It's clear. I only focus on our temperate regions. The calculation for the Antilles or for the USA is completely different.

But to put it simply, you must have an Sd value on the inside (vapor barrier) 5 to 6 times greater than that on the outside (bracing or other). Hence the recommendations at Sd> 18 meters.
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by dedeleco » 23/11/11, 21:03

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chatelot16
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by chatelot16 » 23/11/11, 23:11

when it's cold outside it absolutely has to be more airtight inside than outside: why be against the vapor barrier on the inside of the insulation?

if the sealing on the inside side is average, the outside side must be strongly ventilated: it risks spoiling the insulation by too much draft

of course in hot weather with air conditioning it would be necessary to put the vapor barrier outside the insulation so to be good at all seasons in countries where the air conditioning is essential it would be necessary to put the insulation between 2 vapor barrier and mechanical ventilation insulation check
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by minguinhirigue » 30/11/11, 08:45

I don't ask myself the question for the USA or the Antilles, I confine myself to the European climate ...

The vapor barrier can be useful, I'm not against it.
But when it comes to a timber frame house, I agree that letting the water vapor migrate naturally allows a little sanitation of the indoor air (this is not enough, against many d other pollutants, adequate ventilation is required, natural or mechanical).

Indeed, we all prefer a good leather or gore-tex jacket to an old k-way or waxed ... The walls of the houses are the same!
Why install a vapor barrier, very demanding since any point of infiltration (a nail for example) suddenly leads to local condensation, when we can by correctly choosing the layers of the wall let the water vapor spread gently everywhere, thereby limiting local condensation around weak spots (window frames, ducts, wall fixings, electrical outlets, air ducts and so on ...).

So the vapor barrier, when we can do without it, let's do it.
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