We bought a rather large home that was built in 1978. Nearest we can tell it has typical fiberglass batt insulation inthe 2x4 walls with no vapor barrier. The outside of the home has really nice newer steel siding and we would rather not strip it to add rigid insulation then have to reside the whole home. However we plan to update the complete interior, most of which has nasty wallpaper that needs stripped, so we are debating on stripping all the sheetrock off of the inside of the exterior walls and getting it spray foamed. Question is would we gain much by doing this over just leaving the fiberglass batts in place? We also have already planned to replace all the windows and we plan to do all the work ourselves other than contract out the spray foam installation.. Thanks for your input.

Potential solutions that don't involve a complete gutting of the walls from the inside are somewhat climate dependent. Where is this house located?

Posted By Dana1 on 09 Jul 2012 02:36 PM
Potential solutions that don't involve a complete gutting of the walls from the inside are somewhat climate dependent. Where is this house located?

Home is located in Western Kansas

I'm not sure how you're going to replace the windows without messing with that nice steel siding unless you have wide trim bands around the windows currently, but another option you have that is a good one, at least in my cold climate, is to drill and fill dense pack cellulose into the walls.

Typically your fiberglass batt will be very heavy and compressed down to 1 1/2" or so giving enough room for a dense pack tube to get in. With you not concerned about the drywall you could do it from the inside, typically we remove 1 row of siding on the outside and fill from the outside. We have done this successfully with measured leakage reduction and complete coverage. If you are taking off the gypsum, I would air seal with either picture framed foam application or a flash fill then dense pack cellulose or BIBS.

I dont think its ever worth it to completely spray foam a cavity except in a very few circumstances.

Western KS is the warm edge of US climate zone 5/cool edge of climate zone 4. Dense-packing cellulose or new-school high-density fiberglass and leaving the batts in place (as greentree suggests) will work, and is the "right" way to go from a bang per buck and total performance. Dense-packing will perform comparably-to or better than open cell foam. Going with cellulose rather than fiberglass yields a very slightly lower whole-wall R, but adds more thermal mass to the wall and acts as a seasonal hygric buffer to better prevent moisture from building up in the sheathing in winter.

Going with closed-cell foam even at R7/inch (or about 2x that of cellulose) would only add ~R2 to the whole-wall R value, due to the severity of the thermal bridging at the framing, and would be only modestly more air-retardent than a dense-packed fiber solution. (This is why putting the foam on the outside of the sheathing is so much better than foaming the stud bays- you get the full-R of the foam when it isn't being short-circuited by the framing.)

In this climate if there is at least 1/4" of ventilation gap between the steel siding and the structural sheathing there is no need to install an interior side vapor retarder, and the risk of wintertime moisture hitting high levels in the sheathing is low, independent of the insulation type. Avoid highly vapor retardent interior finishes such as vinyl or foil wallpapers, since that only impedes drying toward the interior. Standard latex paints are class-III vapor retarders, which are just about perfect for moisture control in your climate & stackup.

Posted By greentree on 09 Jul 2012 09:13 PM
I'm not sure how you're going to replace the windows without messing with that nice steel siding unless you have wide trim bands around the windows currently, 

I plan to cut back the siding with a circular saw to just past the nailing flange then trim it out with a wider trim.

Posted By greentree on 09 Jul 2012 09:13 PM
I'm not sure how you're going to replace the windows without messing with that nice steel siding unless you have wide trim bands around the windows currently, but another option you have that is a good one, at least in my cold climate, is to drill and fill dense pack cellulose into the walls.

Typically your fiberglass batt will be very heavy and compressed down to 1 1/2" or so giving enough room for a dense pack tube to get in. With you not concerned about the drywall you could do it from the inside, typically we remove 1 row of siding on the outside and fill from the outside. We have done this successfully with measured leakage reduction and complete coverage. If you are taking off the gypsum, I would air seal with either picture framed foam application or a flash fill then dense pack cellulose or BIBS.

I dont think its ever worth it to completely spray foam a cavity except in a very few circumstances.

I thought about the cellulose but was concerned with it not getting to all the cavities to properly fill the void because of the batt thats already in there. This is the product i am thinking about going with at the moment....... http://injectionfoam.com/home-insulation.aspx if you watch the video it shows how its used with batts currently in place and how well it does in sealing the whole cavity. I would appreciate everyones input on it. Thanks

When dense-packing cellulose they snake the blowing hose to the end of the cavity with air-only blowing to ease it by the batt, then back it up a 8-12" and start blowing the fiber, not all that different conceptually from the non-expanding injection foam applications. This is very different from the low-density 2- hole methods where a nozzle is inserted into the lower hole first, blow till it's spittin' out the top hole, move the nozzle to the top hole to finish. Dense-packing is very reliable, and has no settling/sag issues (quite a different case from low-density 2-hole methods.)

Non-expanding injection foam such as Tripolymer can get you there, but it doesn't air-seal as well as spray polyurethane, and is comparable to dense-packed fiber for air-sealing tightness. (It doesn't bond to the studs and isn't very flexible, so seasonal micro-gaps appear.) Injection foams tend to run ~ R5/inch to dense pack cellulose @ R3.7/inch, but in a wall with a 20-25% framing fraction it ends up being less than an R1 difference in whole-wall R, less than a 10% reduction in comparative heat loss for usually far greater than a 10% increase in upfront cost, but go ahead and have it quoted both ways.

The applications where non expanding injection foams really shines is in retrofitting some masonry walls (where you usually can't use fiber, and never cellulose), in climates where filling the cavity is safe, but even in those climates not every cavity wall is a good candidate.

The cavity in a cavity wall is essentially a "rainscreen", a gap between the siding & structural wall that allows the outer wythe/siding to dry in both directions, and allows the inner wythes/wall to dry into the cavity as well. When you fill it up the convective purges of the cavity cease, raising the moisture content of the masonry. While the foam won't wick moisture from the outer wythe inward, the inner wythes are now relying on the high vapor permeability of the foam to dry toward the exterior, but if the outer wythe is often rain-wetted, that's simply not happening, and where structural timbers meet the brick there is an increased risk of rot. ( Big overhangs to keep the rain off the wall and good exposure to sun help.) In colder climates the higher moisture content of the exterior wythe of a an injection foamed cavity wall can result in freeze/thaw spalling of the brick face &/or a more rapid deterioration of the mortar. So it's usually only applicable to temperate climates- it's a very popular retrofit in the UK (which is roughly a warm-edge of US maritime zone 4 type of climate.)

I found a company who covers my area that does both the foam injection and the dense pack cellulose in wall cavities that have batts already installed. They quoted me $1.40sq ft for the cellulose and $1.60sq ft for the foam so not much difference. They said they had more experience with the cellulose. So i guess i need to determine which is actually better in the end, foam or cellulose? I have to defer to you guys on this. Thanks

Cellulose is lower risk- unlike foam, it's removable without tearing your house apart (should that ever be necessary), and if thermal imaging finds a spot that was missed it's easier to spot-remedy. It's also more protective of the structural wood due to it's capacity to wick liquid moisture and buffer wintertime accumulations. Once non-expanding injection foam sets up it's pretty rigid- not as tough as polyurethane to hack into, but it's no picnic.

In practical terms the performance differences between them are "in the statistical noise"- either will be a real improvement on '70s vintage low density batts installed at "typical" detailing levels.

If cellulose, insist on "borate only, sulfate free" product, even if it means dry-blowing a "stabilized" product normally used in wet-spray applications. It shouldn't make an appreciable cost difference, and many/most installers avoid goods with sulfate fire retardents in the first place, but put it on the table. The borate fire retardents also kill wood-boring insects (termites, carpenter ants, carpenter bees, wood boring wasps, etc.) by killing off the gut-flora that enables them to digest wood. It doesn't render the place termite proof, but it helps.

Posted By DENALI on 10 Jul 2012 12:30 PM

Posted By greentree on 09 Jul 2012 09:13 PM
I'm not sure how you're going to replace the windows without messing with that nice steel siding unless you have wide trim bands around the windows currently, 

I plan to cut back the siding with a circular saw to just past the nailing flange then trim it out with a wider trim.

You make it sound so easy.

Posted By greentree on 10 Jul 2012 10:30 PM

Posted By DENALI on 10 Jul 2012 12:30 PM

Posted By greentree on 09 Jul 2012 09:13 PM
I'm not sure how you're going to replace the windows without messing with that nice steel siding unless you have wide trim bands around the windows currently, 

I plan to cut back the siding with a circular saw to just past the nailing flange then trim it out with a wider trim.

You make it sound so easy.

Nothing easy about it but its what needs to be done.

How "water tight" or moisture proof is the home? One thing to remember is that if you keep the drywall intact and simply blow in the insulation, you really never know what's going on BEHIND the drywall. If you have a leaky wall, when cellulose gets wet it loses R-value, not to mention when wet the borates in cellulose can leak from the cellulose and can damage your drywall, carpeting, electrical and even corrode anything metallic.

My buddy bought an older home and was going to just cut a hole and blow in the cellulose. I told him that he should rip down the drywall to see what is going on in the wall cavity, especially on a wall with a lot of windows. He finally agreed to do it and he was shocked to see the amount of water intrusion and wood framing rot the walls had. There were literally 2x4 studs that were so rotted they fell apart when you hit them with a hammer. In the end he had to rip down the entire sheetrock, go and waterproof the exterior sheathing, re-frame the wall, and then fill it with cellulose. It cost him A LOT of $$$$$ but his home was built in the 1970's and they did not do a good job of keeping the water from entering into the wall cavity.

Cellulose works great but it MUST be kept dry and placed in a sound and properly built wall cavity. The home is over 40 years old and you can run into issues if you don't know how tight that wall cavity really is:

Read this article:

 Too much cellulose in the wrong place

Insulating Old House Walls

Read this article:

 Too much cellulose in the wrong place

Insulating Old House Walls

I dont believe this house to have any moisture issues but regardless those article make me want to steer clear of cellulose for my application and lean more towards foam.

Wet borates are not corrosive- wet sulfates are, which is why it's worth specifying "borate only, sulfate free".

As a rule, steel siding has an air gap between the steel and structural sheathing, which limits any bulk water penetrations at the seams from getting into the structural wall. The biggest bulk-water penetration issues are around how the windows & doors are flashed, and they're replacing the windows. A leakage history might be read there, but it's always critical to do new flashing right.

Most competent cellulose installers have seen the horror movies, (even starred in 'em), and will let you know if yours has issues that need to be straightened out before insulating. Dense-packers probe the cavity pretty well in the process, and can tell pretty quickly if there's more material going in than should be (indicating a large hole in the sheathing, etc.) With 2-hole method it can take a bit longer to figure some of the issues out.

In this location, with back-vented steel siding on the exterior, it doesn't need an interior side vapor barrier.

Posted By DENALI on 11 Jul 2012 12:16 PM

Read this article:

 Too much cellulose in the wrong place

Insulating Old House Walls

I dont believe this house to have any moisture issues but regardless those article make me want to steer clear of cellulose for my application and lean more towards foam.

The second article actually says blown-in AND foam are bad, he advocates no wall insulation and fiberglass batts with outward facing kraft paper in the rim; if you want to believe that more power to you. The first article, which I've read before, has cellulose coming out of slate roofing and soffit vents which indicates someone tried dense packing the soffits from the ATTIC to try and solve ice dam issues. Both of those articles have nothing to do with what you are looking at doing. Thanks to Lbear to again post irrelevant and inaccurate content. If you are more comfortable with the foam do it, but I promise you would be disappointed if you had the foam injected and then were able to remove the wallboard and see the quality of fill, it will not be complete or air tight like they lead you to believe.

Posted By DENALI on 11 Jul 2012 12:16 PM


I dont believe this house to have any moisture issues but regardless those article make me want to steer clear of cellulose for my application and lean more towards foam.

In the end it will be a judgement call and it might work with no issues or you might encounter issues. I would ask the company if they will stand behind their work IF their is a moisture related issue. If so, get it in writing. 'Greentree' made a generous offer of offering to pay you for any and all damages you should experience because he is guaranteeing you that his advice is 100% sound. I would have a lawyer type up a contract and have Greentree sign it.

The reality of this conversation is that you will get "internet forum" advice and it may differ from one person to another. Those articles I posted discusses insulating older homes walls by pumping cellulose and/or foam and the problems they experienced due to lack of vapor barrier, moisture intrusion and the lack of seeing what is going on behind the drywall. Take it or leave it, it's your call but beware of people who claim their advice is 100% infallible because in the end when YOU experience problems which will cost you thousands of dollars, they will not pay your bill.

 

Denali- just rip down your house and build full ICF, including roof, floors, windows and doors. 100% problem free forever.

Posted By DENALI on 11 Jul 2012 12:16 PM

Read this article:

 Too much cellulose in the wrong place

Insulating Old House Walls

I dont believe this house to have any moisture issues but regardless those article make me want to steer clear of cellulose for my application and lean more towards foam.

If you think cellulose mis-installed due to inadequate integrity/structure of the cavity being filled is a problem, you should see what it's like to fix a foam-job gone bad!  Cellulose that manages to find it's way to inappropriate areas can be cleared out, often with a vacuum cleaner.  Foam, not so much- you have to tear the assembly apart and start hacking away at it.

Balloon-framing without top plates pretty much ended in the 1940s- a house built in 1978 would always top plates to the studs (usually doubled to accomodate random rafter spacing) and would have used plywood sheathing (but this you can verify). You're unlikely to encounter even a big-knot-hole sized defect for the insulation to escape through, but a competent insulator would figure much of this out even before submitting a bid.  This is totally standard stuff in insulation retrofits- if you use an established and experienced contractor you won't be starring in one of the horror-shows.

That second article has lots of colorful disinformation on the particulars and is more appropriately about truly antique homes in climates colder than yours that do not have back-ventilated siding like yours and was never previously insulated like yours  

In older frame homes clapboards were often nailed directly to studs or to air-leaky t & g or other plank sheathing and the stud cavity itself was the back-ventilated part that purged any moisture getting by the clapboards or migrating through from the interior via air leaks or vapor diffusion.  To make it even worse, paints were of very low vapor permeance lead-bearing alkyds, which forces the siding to dry toward it's back side, since it can't escape out the front.  When you add insulation to a wall like that it impedes the drying-air flow behind the  clapboards/sheathing, and with the insulation blocking the heat from the interior the clapboards/sheathing run cooler, making them (not the insulation, as the article would have it) the condensing surface for the air in the stud cavity, moisture builds up in the siding.  When the moisture content stays consistently high in the siding, the paint will fail.  In extreme cases liquid water condenses and runs down the interior side of the siding/sheathing to rot the bottom plate.

This is so NOT your type of construction.  Yours has back ventilated  metal siding- the moisture-susceptible sheathing can still dry toward the exterior faster than interior moisture drives can supply more moisture, and since it's already an insulated wall, that thesis has been somewhat tested.  Using a more air-retardent insulation would  slow down any drying resulting from air leaks to the exterior, but it would also dramatically slow down moisture that was entering the cavity from air leaks to the interior.

There are houses more than 100 years old in the Canadian midwest insulated with cellulose during construction that are still standing, despite the lack of interior side vapor retarders and despite 100 cooler-longer winters of moisture accumulation in the wall cavities, moisture that wicks into the cellulose under condensing conditions rather than into the structural wood. Cellulose can buffer quite a bit of moisture before it begins to lose R value, and as long as it isn't installed in such a way that it ends up wicking in bulk moisture/rain, is protective of rather than a hazard to the structural wood.  (It's a safer bet than rock wool or fiberglass as a retrofit into an antique, but it's still worth investigating the stackup and construction before proceeding.)

Posted By lzerarc on 11 Jul 2012 05:22 PM
Denali- just rip down your house and build full ICF, including roof, floors, windows and doors. 100% problem free forever.

En su suenos- dream on!     

Nobody EVER has bulk water migration problem from mis-installed window bucks in my ICF dreams too.