Antique insulation's R value?

Brad White_194

the house had a good blower door test, you are ahead of the curve, not just in lower infiltration, but in <i>knowing</i>. All good.

Glad I could be of help..

I am eager to hear if anyone knows what the stuff really carries as a rating. Mine was just a S.W.A.G.

Brad

joe_94

Antique insulation's R value?

Does anyone know the R value of this ?
The 1940 house is insulated with very nicely installed stuff that is stapled to the studs before the plaster board lath was applied .
It is much like a flat bag of one inch of coarse sawdust, faced on each side with paper, that has a tar layer in it.
In a 3.5 inch stud bay this leaves dead air on each side of the bag.
Rest is 3/4" plaster walls.
3/4" wood sheathing [1' x 12"'s].
Aluminum dutch lap siding underlaid by aluminum foil: 35 year old Alcoa and looking good.

It sure is hard to do a heat loss calculation on sawdust in a tar paper bag.

An odd note: I lit some of the sawdust scraps on fire. It did not flame. But it resolutely smoldered and slowly burned WITHOUT STOPPING.!

Thanks to Wallies for R thoughts. joe

Brad White_200

Dang...

Not sure exactly what that is, but a conservative guesstimate might have an R value per inch of not more than 2.0, especially given that the stuff (whatever it is) might have settled in the bag. If it is an inch as you say, call it R 2.0 at best, R-1.5 given settlement and that the edges may be thinner than the center. Just a guess. That would include the value of the asphaltum paper, which is usually negligible at about 0.06 R per layer.

The other part is the air space held "captive" on either side of that. Realistically, I would think that the air would be free to flow around the bag, even if constricted at the edges. Again, my conservative side would take just one of those air spaces at an R value of 0.97 at the very most.

The sum of building materials (plaster/rock lath, sheathing boards and indoor/outdoor air films, (but exclusive of any air spaces or insulation), typically is between 2.5 and 3.0 "just for showing up".

So the way I would figure the wall R-value between the studs would be: (2.5 + 0.97 + 1.5)= 4.97. Call it R-5 on a good day, but at least if there is good air sealing, you will get a default benefit of any still air not accounted for.

Now, that is all BETWEEN the studs. You have to figure x percentage of that portion, say 80%, and 20% of the portions AT the studs. If 3.5" of softwood at 1.25 per inch, the stud portions would be about 6.8 all told.

So, (0.20 x 6.8) + (0.80 x 5.0) = 5.36 aggregate R value.

For calculation purposes, I would not use more than an assumed R value of 5.36 and a u-factor of 0.187. That is about twice the heat loss of a batt insulated wall with some gaps.

If the opportunity exists to blow in some dense pack cellulose or some low-pressure expanding foam, I would do so, for air sealed integrity if nothing else.

My $0.02

Brad

joe_94

Thank you, Brad. Once again your light shines.
In fact the product overlaps the studs, and its fellow bats at the edges, very tightly...clamped as it is by the plaster board lath.The place rates well on a door/leakage test.
joe

PS_3

I may have the same stuff in my 1940 Cape in Central MA, similar tar impregnated 1" thick "paper bag" batts but the light brown filler is kind of fluffy and fibrous, not quite sawdust consistency. I thought a mineral wool derivative?

joe_94

Yep, that's it. It is brownish and a little fluffy,as Massachusetts Man states. It may be a treated sawdust.
I once heard a trade name for it.

Don't smoke it.

nicholas bonham-carter

early insulation

was it called excelsior?
also often used in early packing as a shock absorber [as well as popcorn!]--nbc