Hello,
I'm looking at different types of vapor barriers and comparing technical characteristics and prices.
The common theme is that manufacturers specify SD as a metric, and I wanted to double-check to make sure I'm thinking correctly
A lower SD value = higher permeability?
For example, Bison vapor barrier has an SD value of 2.5, while Icopal MonoVap has 5.
Can we conclude that MonoVap is twice as diffusion-tight as Bison? Or is it not that simple to calculate?
I found a table where gypsum had a value of 0.1 and OSB 2.4.
Then it almost feels like OSB is a vapor barrier equivalent to the fabric from Bison?
I'm looking at different types of vapor barriers and comparing technical characteristics and prices.
The common theme is that manufacturers specify SD as a metric, and I wanted to double-check to make sure I'm thinking correctly
A lower SD value = higher permeability?
For example, Bison vapor barrier has an SD value of 2.5, while Icopal MonoVap has 5.
Can we conclude that MonoVap is twice as diffusion-tight as Bison? Or is it not that simple to calculate?
I found a table where gypsum had a value of 0.1 and OSB 2.4.
Then it almost feels like OSB is a vapor barrier equivalent to the fabric from Bison?
Found the following at Fuktcentrum; LTH:
Vapor Permeability Resistance
The resistance is often described with an Sd-value. The Sd-value is measured in meters (m) and can be simply expressed as "the thickness of the layer of still air that has the same vapor permeability resistance as the material" (δair =25 10-6 m²/s at +20°C).
Found the following at MBS(MiljöByggSystem)/ISOCELL:
Today, there are established limits for what constitutes a vapor barrier and what is a wind barrier. According to a classic rule of thumb, the vapor barrier on the inside of the wall should be 5 times as vapor-tight as the wind barrier on the outside. In roof constructions, the corresponding ratio should be 10. The vapor barriers used today, usually 0.20 mm plastic sheeting, are in fact so vapor-tight that the ratio becomes 200 or more. In the MBS Miljöbyggsystem, the interior vapor barrier is often replaced with a more diffusion-open vapor retarder. If the wind barrier has a vapor permeability resistance of sd: 0.15m, the vapor retarder’s value should be at least sd: 0.75m for the ratio to be 5. The result is that moisture can migrate in both directions and the wall can dry.
So:
"A lower SD value = higher permeability?" - yes.
"For example, Bison vapor retarder has an SD value of 2.5 while Icopal MonoVap has 5 in SD. ... Can one conclude that MonoVap is twice as diffusion-tight as Bison?" - yes.
"Then it almost feels like OSB is a vapor retarder equivalent to Bison's fabric?" - yes.
Vapor Permeability Resistance
The resistance is often described with an Sd-value. The Sd-value is measured in meters (m) and can be simply expressed as "the thickness of the layer of still air that has the same vapor permeability resistance as the material" (δair =25 10-6 m²/s at +20°C).
Found the following at MBS(MiljöByggSystem)/ISOCELL:
Today, there are established limits for what constitutes a vapor barrier and what is a wind barrier. According to a classic rule of thumb, the vapor barrier on the inside of the wall should be 5 times as vapor-tight as the wind barrier on the outside. In roof constructions, the corresponding ratio should be 10. The vapor barriers used today, usually 0.20 mm plastic sheeting, are in fact so vapor-tight that the ratio becomes 200 or more. In the MBS Miljöbyggsystem, the interior vapor barrier is often replaced with a more diffusion-open vapor retarder. If the wind barrier has a vapor permeability resistance of sd: 0.15m, the vapor retarder’s value should be at least sd: 0.75m for the ratio to be 5. The result is that moisture can migrate in both directions and the wall can dry.
So:
"A lower SD value = higher permeability?" - yes.
"For example, Bison vapor retarder has an SD value of 2.5 while Icopal MonoVap has 5 in SD. ... Can one conclude that MonoVap is twice as diffusion-tight as Bison?" - yes.
"Then it almost feels like OSB is a vapor retarder equivalent to Bison's fabric?" - yes.
Interesting observation regarding OSB as a vapor brake. Maybe I'm thinking incorrectly now, but can you add SD values from different materials to get a total value?
Does, for example, Bison vapor brake + OSB + gypsum give a total SD = 5 (2.5+2.4+0.1)?
Alternatively, would double OSB give an SD of 4.8? It somehow feels reasonable.
Does, for example, Bison vapor brake + OSB + gypsum give a total SD = 5 (2.5+2.4+0.1)?
Alternatively, would double OSB give an SD of 4.8? It somehow feels reasonable.
The problem is that it's difficult to join OSB boards in a way that maintains the seal.
We are going to have OSB on the outside as a wind barrier, and I expect any moisture that doesn't pass through the boards to escape through the joints. Looking at various tables, the value for OSB varies between 0.2-3.5x10^-6. In America, it's common to use OSB or plywood as an external wind barrier. Of course, the plastic must be sealed
We are going to have OSB on the outside as a wind barrier, and I expect any moisture that doesn't pass through the boards to escape through the joints. Looking at various tables, the value for OSB varies between 0.2-3.5x10^-6. In America, it's common to use OSB or plywood as an external wind barrier. Of course, the plastic must be sealed
Vapor resistance 1m (Sd-value) 40x10^3 s/m [Moisture Handbook, Nevander & Elmarsson (1994).
Oil-hardened wood fiberboard 3.5mm has between 20-70 x10^3 s/m [Moisture Handbook, Nevander & Elmarsson (1994)
Roughly based on the above, an oil-hardened board has an Sd-value of 1m. Vapor barriers sold today have an Sd-value of 4-5m.
According to my interpretation, one can use oil board as an air gap, then insulate with cellulose insulation, and then use a vapor barrier with an Sd-value of 5. If you want to be on the safe side, you might go for a vapor barrier with a higher Sd-value.
Oil-hardened wood fiberboard 3.5mm has between 20-70 x10^3 s/m [Moisture Handbook, Nevander & Elmarsson (1994)
Roughly based on the above, an oil-hardened board has an Sd-value of 1m. Vapor barriers sold today have an Sd-value of 4-5m.
According to my interpretation, one can use oil board as an air gap, then insulate with cellulose insulation, and then use a vapor barrier with an Sd-value of 5. If you want to be on the safe side, you might go for a vapor barrier with a higher Sd-value.
Lifting my old thread... I installed T-emballage vapor barrier 6 years ago.
Now I need to complete surrounding rooms, but my hardware stores have changed suppliers.
I'm thinking I want to find a product with equivalent performance, but I'm not sure how to convert the value to SD in whole numbers.
Calculating with T-emballage, I get 190,000 S/M. But what does that become in SD? 1.9?
Now I need to complete surrounding rooms, but my hardware stores have changed suppliers.
I'm thinking I want to find a product with equivalent performance, but I'm not sure how to convert the value to SD in whole numbers.
Calculating with T-emballage, I get 190,000 S/M. But what does that become in SD? 1.9?
Looking at this https://www.fuktcentrum.lth.se/verktyg-och-hjaelpmedel/materialegenskaper/omraekning-av-enheter/
It looks like 1M is 40,000 s/m
This would mean that 190,000 -> 4.75 M
It looks like 1M is 40,000 s/m
This would mean that 190,000 -> 4.75 M
That sounds reasonable, then it is on par with other Ångbromsar that have SD5.