When we bought our home, we we told that insulation was blown in the walls.  Since moving into the home, we are having aircoming through the walls
 
We would like to do some more insualting.  Should we blow in more insulation.  Or can we foam--that is can the 2 be mixed.  We foamed the  roof deck and the attic is comfortable.

The plaster is in excellent condtion

Any help would be appreciated

To foam it and get a perfect air seal you'd have to vacuum out the blown insulation, and unless you're willing to open up the siding enough to reliably shoot half-pound foam intp the cavities with a gun, you'd have to use slow-rise foam and cross your fingers that you don't get any blowouts or cracks in the plaster. It typically takes removing at least 12-15" of siding & sheathing to be able to gun-spray a cavity, and if there are any internal obstructions at all it shouldn't be done that way, since large voids would be inevitable. 2lb foam would require removing all the siding to spray it, or use slow-rise with even higher risk & expense than low-density slow-rise.

Do you know what type of blown insulation you have in there? Rock wool, fiberglass, cellulose, or...???

Rock wool and fiberglass pass considerably more air than cellulose, and cellulose dense-packed to 3lbs/ft^3 density passes a small fraction of what "2-hole method" ~2-2.5lb density cellulose. If it was lower-density cellulose that may have settled, it's usually possible to do a dense-packing re-blow and get much lower air infiltration. I'm not sure how well that would work with other fibers. But if there's been a lot of settling due to "fluffing" during the original installation, dense-packing it on the top-off will reduce the infiltration, just not as much as if it were all-cellulose.

It's possible/likely that the previous installer didn't fully probe the cavities and missed some obstructions resulting in less than full coverage. Infra-red imaging would be able to detect any voids like that, and it could only need spot-remediation. (Again, dense packed cellulose blown from the exterior has lower risk of messing up your plaster than slow-rise foam, and gets you 99% of the way toward the perfect air seal you're looking for with foam.) Large voids would be easily detectable using an infra-red thermometer, but subtler stuff would need a camera.

Remove some siding from the outside of the house and check the cavities. It's not hard to do this.

WE are looking at adding the insulation when the vinyl siding comes down hopefully by the summer.  Hubby thinks we have cellulose insulation. WE have done  of foam insualtion and have been pleased with the roof decking.  Was hoping that we could foam the falls but I quess not  Removing the old insulation sounds rather time concuming

If you are taking the siding off, then you might add a layer of rigid foam.

Where would we put the rigid foam board.  WE have 100 yr old wood under the vinyl

 

Posted By trister on 21 Feb 2010 12:36 PM

Where would we put the rigid foam board.  WE have 100 yr old wood under the vinyl

 

It's common these days to retrofit R4-R6 of rigid foam sheathing to the outside of that 100 year old planking before putting up the the siding.  This adds about an inch of wall thickness, but dramatically improves whole-wall performance since it more than doubles the R-value at the studs (which are otherwise a thermal short-circuit.) See this Oak Ridge Nat'l Labs calculator.


If you're willing to add a lot of thickness it's not unreasonable to add 3-4" of rigid isoboard to the outside of the structural sheathing, but the modifications around windows & doors etc becomes much more extensive than just adding an inch.

Typically what I see suggested is to apply whatever thickness of foam you wish, then put furring strips over the foam, screwed into the original studs, then hang the new siding from the strips. This gives you the straightest installed siding, and prevents you from having to use a lot of long nails to attach the siding.

Posted By aardvarcus on 22 Feb 2010 08:26 PM
Typically what I see suggested is to apply whatever thickness of foam you wish, then put furring strips over the foam, screwed into the original studs, then hang the new siding from the strips. This gives you the straightest installed siding, and prevents you from having to use a lot of long nails to attach the siding.

That's right!

And more: By having a back-ventilated siding liquid water from wind-driven rain penetrations will always be able to escape the assembly, enhancing the drying capacity of the wall structure.

Thanks for the suggestions.

However, I will not be putting up vinyl or other siding.  The home will finished with its wood siding exposed.

Does anyone have any additional suggestions. 

Posted By trister on 24 Feb 2010 10:30 AM
Thanks for the suggestions.

However, I will not be putting up vinyl or other siding.  The home will finished with its wood siding exposed.

Does anyone have any additional suggestions. 

So you're saying your stackup is:

Great outdoors|wood planking/siding|insulated stud cavity|plaster & lath   ????

This would be a disaster- you need SOME sort of drain-plane or weatherizing between the outer wood and the stud cavity or it'll take on wind-driven moisture like a sponge.

Most homes even 100 years ago would have

Great outdoors|wood siding|tarpaper (felt)|shiplap or t&g planking|stud cavity|plaster & lath 

In this stackup the tarpaper forms an air barrier & drain-plane protecting the structural siding (the ship-lap or t&g planking) from bulk water incursion and to a lesser extent, air incursion into the wall.  Inserting foam between the weatherization layer (felt or houswrap) and the structural siding (planking) is the preferred location:

Great outdoors|wood siding|tarpaper (felt)|rigid foam insulation| shiplap or t&g planking|stud cavity|plaster & lath

If you are intent on keeping the wood siding on the outside you have basically two choices.

One-As was mentioned before, call in a professional to vacuum out all the cellulose or other wall insulation, and then pour slow rise closed cell foam into the cavities. With the current water situation, I wouldn't feel comfortable with anything in the cavities that might absorb water. I don't know how well this could work, but it would be better than what you have now.

Two- (This probably isn't the best method, but this is how I would do it.) Rip out all the plaster, create a "weep area" at the top and bottom of the cavity next to the wood siding. This could easily be accomplished by spacing out the last wood siding piece with a shim to open up a 1/4" gap. Cover the outer inch of the bottom plate and the area leading to the weep gap with some good quality tape, like sip system or pella window tape to prevent water damage. Next, put in a 1/2" rigid foam board spaced away from the wall about a half inch basically creating a ghetto drainage plane inside the stud cavity. Caulk where the bottom meets the tape to make sure all the water ends up outside. Fill the rest of the cavity with some fiberglass insulation. Cover the walls with a layer of plywood or osb for additional structural strength. You can now cover the entire wall surface with 1" foam board, then apply 1/2" drywall to the wall with 2" or 2 1/2" drywall screws. Try to keep from creating vapor barriers, so use things that can breath a little bit.

Hope you like crown moulding. Punch holes through the plaster near the ceiling and have an insulating contractor top of your walls. Hide the patches with crown moulding. Take off exterior base trim and window/door trim and foam perimeters, use a high quality polyurethane sealant along the bottom plate. Remove the window sill and drill through the frame to insulate cavities below windows. If the window frames are original and there is replacement windows you should check to see if the weight pockets are insulated (assuming double hungs) most often they are not, most replacement window contractors do not insulate those pockets.
What I prefer to do on the old homes is punch through all the exterior plaster wherever I want to insulate and run new electrical ect and then skin over the remaining plaster with new drywall, it's faster more effective and you get to upgrade the electrical at the same time.
Air is not going to come through good plaster, you need to find the true source, often around windows and doors and from the basement from leaks under the mudsill and leaks in the bandjoist.

Thanks again for the suggestions,

I forgot ti mention that we are in process for historic registry for the home.  The plaster must remain.  We have moulding for hanging  pictures.  We cannot add crown moulding. 

windows have to stay--do have storms that don't do much--thinking of interior storms--any suggestions

Is our own option addition more blown in insulation. 

The joys and pleasure of a old home

thanks for hanging in

If you can access the top plate from the attic, you can actually drill the holes for vacuuming out and filling with slow rise from there. Vacuuming this out will take professional equipment, so you might contact someone who would be capable of doing it and get their opinion.