Insulation – In stud cavities Part 1
There are two different categories of insulation — open cell and closed cell.
For example, fiberglass insulation is open cell.
Roll out a batt of fiberglass insulation, place a 1 1/2″ x12″ pipe vertical on top of the insulation and pour 1 cup of water into it.
That’s right — it runs right through.
This means it is a porous (permeable) type insulation.
Using porous type insulation in stud cavities, then covering the insulation with 6 Mill poly and sheet rock, you have made a perfect wall.
Until you add people –
First, they are going to want electrical in the wall. This means holes through the sheet rock and poly allowing moisture to pass into the cavity.
Next, they’ll add pictures and wall decorations. Now we make several holes leading into the stud cavities.
Each 1/4″ diameter hole lets 30 liters of water (as vapor) into the stud cavity.
Having open cell insulation allows the water to freeze on exterior wall sheathing.
In the spring the frost thaws and the water migrates down the base plate and starts the rotting.
If we install an open cell insulation in the stud cavity instead, moisture has a very hard time migrating into the cavity.
Fiberglass insulation — made from sand
Mineral wool insulation — made from slag steel
Cellulose insulation — made from paper
Urethane insulation — made from Urethane (oil base)
Polyurethane insulation — made from Urethane (oil base)
Icynene Insulation — made from water (water base)
If you have allergies Icynene Insulation is the easiest on your sinuses.
Some insulators are spraying 1″ of urethane into the cavity and filling the rest of the cavity with fiberglass, which does no good.
The urethane is in the wrong location in the cavity — it must be installed on the warm side of the wall. The same is true with foam insulation board installed behind vinyl and aluminum siding.
Installing poly or urethane film on the cold side of the wall only ads in the ability of collection of moisture pasting through the wall cavity allowing it to condensate on the film and migrate to the bottom of each stud cavity.
Only way for the water to escape is to work it’s way through the bottom plate and the floorboards.
This turns the boards to soggy wood and in 2-3 years the wood first starts to rot until the water has a way through, the next years the wood dry rots, which is no better.
For more information on open cell insulation http://www.home-elegance.com/articles/74/insulation-in-stud-cavities-part-2/