Insulating old farm house from the inside

15 years ago

Greetings, I'd appreciate any input on what I plan on doing with our 1850's farmhouse to upgrade the insulation envelope. We just tore out our first room, removed plaster, lathe and brick nogging from the walls and are ready to start rebuilding.

Here's the plan:

Insulate the irregular old stud cavities with foam board that has been cut and fit a quarter inch shy and then "mortared in" around the edge with expanding foam to wedge it tightly in to the cavity.

Frame what I understand to be called "floating" walls (2x4, 24" OC) against the exterior walls, putting unfaced batts between the new studs, going as thick as needed to make up for the space the fitted foam doesn't fill.

Finally, put up a vapor barrier and then 5/8 drywall.

The final cross-section will be (from outside to inside):

clapboard siding

sheathing

old studs/fitted foam in between

new studs/batts in between

vapor barrier

5/8 drywall

The assumption:

I think that I should use OPEN cell foam board and expanding foam (for the mortar) for the fitted foam I'm doing. This is because I don't want to create 2 vapor barriers, which I believe would happen if I used closed cell foam along with the barrier that goes right behind the drywall. It's my understanding that everything behind your vapor barrier (from the inside) should have some degree of breathability, and the open cell foam seems like it would allow this. Is this assumption correct?

The outright questions:

How does this sound as far as an insulation strategy?

How do I secure the unfaced batts between the new studs, do they just wedge in there?

What should I use for the vapor barrier that goes behind the drywall, just plastic? What mil?

Thanks!

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Comments (4)

MongoCT
15 years ago
nathan,

Can I offer an alternative that is easier, less expensive, less labor, and will give you better thermal, air infiltration, and sound deadening performance? And DIY-friendly?

Look at the "spray insulation in ceiling" thread, scroll down a ways and look at the photos of the horizontal furring strips on the stud walls with the blown in cellulose insulation.

It makes for a great wall, and the horizontal strips allow you to get "standardized" 16" spacing on the walls.

The blown in cellulose is also great for filling all the nooks and crannies inherent in old non-standard framing.

As to your other questions:

"How do I secure the unfaced batts between the new studs, do they just wedge in there?"

If your new wall has "standard spacing", 16" on center, or 24" on center, then get unfaced fiberglass batts. They will friction fit between your stud. No fasteners required.

"What should I use for the vapor barrier that goes behind the drywall, just plastic? What mil?"

6-mil poly. You can buy it in 10' by 100' rolls at the box stores.

Mongo
nynathan
Original Author
15 years ago
Thanks Mongo, the loose fill cellulose does sound like a good way of filling the irregular cavities, and I like that cellulose is greener than fiberglass, BUT my main concern is that I've heard cellulose fill will settle over time and since my house is 150 years old, I want a lasting, effective solution.

This is a machine rental where you feed it bales of material and spray it with a hose, correct? Build the walls, put up the vapor barrier and spray it in through the top - the vapor barrier holds it in as it fills the cavity?
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Adding another layer, or two, over the plaster will have the same detail-deadening effect on the inside as extra layers of stucco will on the outside. You'd have to move all your trim, fir out all your opening jambs (window and door) etc., to fix this but then you also must extend or re-wire your outlets and wall switches .... well, it's a big job! Re insulating to the max in the attic. I was not suggesting insulating the undersides of the roof, unless you have heated/conditioned space just under the roof. In that case it should probably be done, but you can't just tack up insulation under the roof sheathing. You must arrange to have some channeled air -baffled barriers between the top-side of the insulating material and the underside of the roof. Look for info about insulating a cathedral ceiling to see what I mean. As for the walls, if they aren't plastered up there, then I would rip out sheet rock or paneling and insulate and, more importantly for rooms at the top of the building, install a vapor barrier before reclosing the wall. I wouldn't insulate between the floor joists on the enclosed space, but of course I would between the floor joists of any unenclosed, unheated space. And I would consider using an insulating product with the highest R-value per inch of depth. When insulating (assuming you're are not doing the whole house) put your money and effort into the upper areas/surfaces first, and then cut the infiltration pathways by caulking and sealing like a demon. I'm not familiar with a stucco-coated house, but in a frame house with wood siding, you could see evidence of moisture being trapped in the walls when paint peels off the outside, or mold grows on the inside walls or your walls get stinky and moldy internally. Not a pleasant thought! Good planned ventilation (kitchen and bath fans, primarily) goes along way to fixing this issue. But you can also but vapor retardant paint on all your walls and ceilings, which reportedly helps a lot. Now for the op-ed on this subject: Plaster by itself, especially old plaster on wooden lath, can be a huge moisture mediator, all by itself. And hollow walls allow a good deal of vapor and air to move harmlessly to the outside. (At least in wood-clad house, I'm not familiar with stucco.) All the steps we take in closing up a house in the name of energy efficiency may, paradoxically, be somewhat interfering with the time-tested engineering of these old building systems. And certainly, I believe the standards that are used for new houses which require intense efforts at moisture/vapor management are successful and necessary in builings built of more complex man-made components. But I'm not so sure that one should blindly transfer the standards of one building system backwards to buildings of another construction system. The good news is that older buildings can be quite tolerant, and apparently unharmed, by tightening up and some insulating (especially of attics) without vapor barriers. Just be aware that you can, even in the laudable effort to improve energy costs and loss, create another problem. For myself, beyond the above steps, I try to achieve overall building energy efficiency in different ways, on other systems (heating, laundry, appliances, lighting) and "forgive" the energy inefficency I can't cure unless I tear down more of the still-intact wall covering materials. And naturally, whenever I have an occasion to open a wall for any reason, then that portion in insulated and vapor barriered before closing. I find one of the most satisfying things about living in and owning an old building is that it keeps me aware that there are many different solutions for things, and the latest and greatest modern notion may have nothing on what was common a hundred years ago. Have you looked into the useful series of Preservation Briefs from the National Park Service? I'll attach a link; many topics are available for free on-line and I've always found the info very helpful. They cover a wide range of topics including energy efficiency for old buildings, and most importantly in your case, care and repair of stucco (along with window repair, roof, plumbing, building assesment, etc.) HTH Molly Here is a link that might be useful: Series of Preservation Briefs, List of topics
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MongoCT
15 years ago
nathan,

Settling was indeed a problem with blown in insulation, but that's in years' past.

These days we use "dense packing" when blowing into confined framing bays, like wall stud bays, or ceiling rafter bays.

If you blew a thickness of cellulose, say 24", it'd be fairly low density, all fluffed up with air. Come back 6 months later and it will have settles in height until it reached it's natural settling density of 2.7 lbs per cubic foot. Come back five years later it'll still be at that settled depth and at that settled density.

so we "dense pack" the cells, running a fairly lean mix out fo the blower, and look for about 3.5 pound per cubic foot. The only way to know what you;re getting is by experience.

The easiest way for a DIY to gain that experience is to screw together a mock stud bay; a couple of 2x6 studs, a cap and sole plate, and a sheet of ply on each side.

Drill a hole in one sheet of ply, insert your hose, and blow in the cells, working the hose out of the cavity as you blow. You can caluculate the volume of the bay, then working with the 3.5 lb/cf density, find out how many pounds of cellulose you need to be stuffing into that bay. Each bag of cellulose weighs a certain amount, to it's fairly easy to figure.

Then unscrew the ply off one side of the mocked up bay and see how well your coverage is. Then repeat.

Once you get the knack, then you can have at it. It's a sight/sound/feel thing when dense packing, but easy to accomplish.

Since your walls are open to the studs, you can use mesh netting on the faces of the studs, then dense pack, then drywall. The mesh netting makes it easy to see that the bays are being properly filled.

There are some photos posted in the "spray insulation in attic" thread. SLightly different method as those walls also have furring strips on them.

If you were to just hang the poly vapor barrier then blow in the cells, the cells would blow the poly off the wall.

Dense packing can even bow out 1/2" drywall on 24" studs. 16" framing is usually okay, upping to 5/8ths inch sheetrock is near bulletproof.

You can also wet spray cellulose into open stud bays. The wet cells stick in place due to the water content. But there is a certain amount of operator skill required there so that the minimum amount of water is used, as drying times before being able to hang the sheetrock can be lengthy.
Personally I don't wet spray.

Mongo
orchidca
15 years ago
We have gutted our 1915 kitchen. We're located in an area of heavy rains in the winter. Should we put tar paper against the interior of the siding in the house before putting insulation in? There was mold on the interior of the siding(north facing),which we treated.

Is there a better material to use than tar paper, that is a moisture barrier yet breathable, before putting the insulation in (rigid in some places, bats in others)

Next question: Do we need to put plastic up after we put the insulation in, before doing sheet rock?

thanks so much, orchidca

Insulating old farm house from the inside

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MongoCT

nynathan
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Insulating old farm house from the inside

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MongoCT

nynathanOriginal Author

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nynathan
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