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Insulation and vapor/air barrier retrofit for an old house

Insulation and vapor/air barrier retrofit for an old house


Old 04-30-10, 08:14 AM
Thread Starter
Join Date: Jan 2009
Location: NJ
Posts: 26
Insulation and vapor/air barrier retrofit for an old house

I will be gutting my living room soon and would like to add insulation and possibly a vapor barrier to the one exterior wall. The house is about 100 years old (as far as I can tell the house was built in 1907). The house is in Bergen county New Jersey which is considered climate zone 5. I have 2 x 6 framing (as in old, 2 inch by 6 inch rough lumber) sheathed with wood planks. The old wood shingles have been covered with vinyl siding. As far as I can tell there is no exterior vapor barrier.

From my reading it sounds like I want to use a vapor ďretarderĒ on the interior of the wall, as opposed to a true barrier.

The two options Iíve come up with are,

1, Use fiberglass rolls with kraft paper on one side. In this case the kraft paper vapor retarder will be against the sheetrock on the warm side of the wall. On the plus side this option would be relatively cheap. Iím also tempted to use fiberglass insulation in the interior walls for sound proofing.

2, Use a sprayed foam solution such as those offered by Tiger Foam. The sprayed foam will act as a vapor retarder as well as insulation, right? Iíd probably also want to use fiberglass over to foam. On the down side the foam is expensive - is it worth the extra money? Also, the foam is very sticky and Iíd need to do prep work to cover windows and anything else I donít want covered in foam.

If I really felt that the foam was be clearly better Iíd be willing to spend the extra money but considering that Iíd only be using it on one part of the wall Iím afraid that the wallís inherent draftiness (the wall cavities are not blocked) will negate the foams vapor/air barrier properties. I suppose I should block these cavities as best I can as part of this job.

Any suggestions? What sort of insulation and vapor barrier would people recommend in this situation?

TIA, Mike
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Old 04-30-10, 08:49 AM
Join Date: Oct 2008
Location: New England
Posts: 9,994
Hi Mike,
Use wood blocks for the cavities, they are a better fire stop where balloon construction exists.

Consider mineral wool, much better at blocking air movement and with wood planks for sheathing, there is a lot of leakage. If you have a true 6", you would need to add a slice to the 5.5" batts.

Flash and batt makes a very good package. Spray a quick 1/2" to 1" layer of foam to air seal and add insulation. Then fill the rest with batts. Again, my choice would be the mineral wool.

As for a vapor barrier, inside only, and an air barrier is much more important. The air barrier and vb can be one in the same, but at least have to be in contact with each other. Sheetrock is a good air barrier.

If you go with just fiberglass, waste a case of caulking and seal every seam of that wood sheathing. But I don't recommend fiberglass other than it being cheap.

For sound reduction, the mineral wool is far superior to fiberglass.

Fiberglass is also available in high density with a bit higher rating.

Old 05-03-10, 07:45 AM
Join Date: Feb 2008
Location: USA
Posts: 9
My two cents is offering up rigid foam if you can use it. It is 1/2 the price of sprayed foam and easy to install.

If you can stop all air movement then fiberglass is ok. So my exterior wall construction is 3/4 inch foam (several layers), 6mil plastic, then studs/fiberglass. Siding goes over the foam.

I am in Texas so our vapor barrier goes on the outside, but if you did foam on the outside with enough thickness, it should be ok for you too.
Old 05-03-10, 09:53 AM
Join Date: Oct 2008
Location: New England
Posts: 9,994
Just a comment, Kindrox is in Texas and the VB can go on the outside, but not in NJ. VB on the inside.

Old 05-03-10, 11:36 AM
Join Date: Feb 2008
Location: USA
Posts: 9

What do northern's do when it comes to foam? Are some of the rigid foams you can buy at the store open cell or something?
Old 05-03-10, 01:10 PM
Join Date: Oct 2008
Location: New England
Posts: 9,994
Most just ignore the guidelines LOL. But when rigid foam is applied to the outside, there are guidelines as to how much should be used. In my area, a minimum of 2" pretty much assures you the dew point will not go past the foam. Thus, if any moist air from inside the home gets inside the walls, little or no moisture will be deposited.

The real problem IMO is when the foil faced foam is used. The foil is an absolute VB, where the pink or blue extruded foam board will have at least some permeability. But time after time, I see 1/2" or 1" foil faced rigid foam going up before the new siding.

Some of the newer science articles are shying away from VB's. Since air sealing blocks most of the air leakage, they conclude the lions share of the moisture problem is already taken care of, so let the rest breathe. Interesting to see they have come full circle.

Old 05-07-10, 05:34 AM
Join Date: Feb 2008
Location: Lake Wales, FL
Posts: 463
The purpose of a vapour barrier, is to prevent the water vapour created inside the home, getting into the wood framing and making the wood wet, followed by mould, followed by dry and wet rot.
First of all deal with the creation of water vapour.
At the moment, your home is full of holes and the heat you put into the home disappears along with the water vapour through these holes.
When you block these holes, you then have to deal with the water vapour that you create by washing, cooking, breathing and sweating.
The best way to deal with water vapour is to vent it to the outside, the second is to use a de humidifier.
The best way is to fit extractor fans in the kitchen and bathroom and to use them, when cooking and washing.
Extractor fans fitted with shutters to keep out the cold and humidistats and heat exchangers are best, as they save money and will only work when required.
Then you need to fit a plastic membrane that is water vapour proof under the sheet rock to keep the remaining water vapour from entering the wall.
Fit sheets of polystyrene/styrofoam between the framing, make them a tight fit, use cans of foam to fill any odd shapes. completely fill all cavities.
Then fit a water proof breathable membrane (not water vapour proof) on the outside of the framing to enable any rain that gets in to dry outwards to the sky.
While spray foam is a better insulation than all the other available insulations, its easy to apply, provides an air tight fit in the most awkward places, it is expensive.
Depending on what you are trying to achieve?
The same thickness of polystyrene insulation will provide twice the effective insulation in real life as the other available insulation.
For a first rate Passive House result 16 inches of polystyrene will give you a room that will use no heat for most of the year, in the coldest of places.

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