I’m planning on dropping the interior plaster (bad shape) in my 1892 colonial and insulating. I’ve heard bad things about just stuffing fiberglass in the wall with moisture etc. I gather that you need some sort of air space in the old walls. I was thinking of the following method:
walls are true 2×4
Install 1 1/2″ or 2″ polyisocyanurate boards inside in the stud bays, leaving a 1″ space between the board and exterior sheathing. Then use one of the DIY spray foams like Tigerfoam to seal the cracks, act as vapor barrier and provide the last 1″ of insulation.
What do you guys think?
Mike
Edited 1/13/2009 11:25 pm ET by Mikes8500
Replies
I can only tell you of my experience in this area. (Vancouver, Canada)
When I remove lath & plaster interior walls, naturally, I make sure all the bays are clean (sorry, without a profile nobody knows how much experience you have).
I like to use a foam gun to seal off the joist/floor/wall area - just a thin bead. Personally, given the choice, I prefer mineral wool but whatever, I fill the bay entirely with insulation. If I have the room, I like to put a 5/8" sheet of pink rigid insulation - if not (usually), a 6 mil vapor barrier, then the drywall.
Insulation is important, but just as important (IMHO) is a well placed, continuous and properly tapped vapor barrier, as well as sealing every hole where air can escape from conditioned to unconditioned space.
Quality repairs for your home.
AaronR Construction
Vancouver, Canada
spray foam the hole bay .you get max r/value and don't have to put up the plastic if you chose not to.i would use closed cell spray foam as it gives you more r/value
I suspect that the "sealing every hole where air can escape from conditioned to unconditioned space" does more than all the other insulation.Leaks are the main problem in older houses, though in extreme climates having a thermal break for the wall surfaces can have an impact on the feeling of comfort.
Either fill in your profile or tell us where you're doing this work and what kind of climate you have. That determines the optimum approach.
But what you suggest would offfer some insulation value, good air sealing, and some essential breathing space for the sheathing/siding to dry.
Do not fill the cavity completely with foam, as someone suggested. Since you don't likely have a weather-resistant barrier between your siding and your sheathing, the outer cladding will need a breathing space.
And do not use a poly vapor barrier, as someone else suggested, since it is air movement, not diffusion, which causes moisture problems generated from the inside during the heating season, and a sealed wall is as likely to trap moisture in as keept it out. A wall system should ideally be able to dry in both directions.
Solar & Super-Insulated Healthy Homes
Edited 1/14/2009 2:24 am ET by Riversong
Thanks guys, I'm located in Long Island, New York
Mike
Sorry, but I need to take issue with the poly VB. Although you are entitled to your opinion, I belive you are only seeing half the issue.
Insulation is only beneficial in minimally reducing air movement from heated to non-heated (or in air conditioned space, from cooled to hotter) environment. It's only use is to slow the dispersion of conditioned air to non-conditioned.
The 6 (or, as is more commonly specified, 12) mil poly is to stop air movement. The moisture issue is largely irrelevant.
I prefer rigid pink insulation over the studs to make a thermal break. It does, however, take away interior space since the foam is 5/8" thick.
On the exterior, being an older Colonial of the late 1800 vintage, the air will whistle through the surface, taking moisture in and out as the seasons change. We agree there.
On the interior, a proper range hood for cooking and a heat exchanger will more than take care of moisture problems.
Can we agree that air movement is the greatest issue facing lower heating/cooling costs?Quality repairs for your home.
AaronR ConstructionVancouver, Canada
Sorry, but I need to take issue with the poly VB. Although you are entitled to your opinion, I belive you are only seeing half the issue.
You can disagree, but what I shared is not my opinion but recognized building science. And what you've posted is full of misconceptions and misunderstandings.
Insulation is only beneficial in minimally reducing air movement from heated to non-heated (or in air conditioned space, from cooled to hotter) environment. It's only use is to slow the dispersion of conditioned air to non-conditioned.
Some insulations, like fiberglass and mineral wool, are ineffective at reducing convective losses, but that's not what they're designed for. Insulation is primarily intended to reduce conductive heat loss, which is why fiberglass traditionally had a paper or foil facing to stop air movement and why codes required a plastic "vapor barrier" to also minimize air movement in the 90% of homes that were insulated with fiberglass.
The 6 (or, as is more commonly specified, 12) mil poly is to stop air movement. The moisture issue is largely irrelevant.
Polyethylene sheeting comes in 4 or 6 mil, not 12, and it's code-required function is as a vapor barrier - to stop vapor diffusion into the thermal envelope. The only reason that a poly vapor barrier does any good is that it also serves, incidentally, as an air barrier.
Many building technology labs have demonstrated that 99% of the moisture load in a thermal envelope that is not caused by leakage is due to moist air transport. As little as 1% is typically due to vapor diffusion, hence vapor diffusion barriers are not necessary, but air barriers are.
Fortunately, well-sealed drywall serves as a near-perfect air barrier, and with latex vapor retarder paint it can meet the outdated code requirement for a vapor diffusion barrier.
The problems commonly encounted with poly vapor barriers is that they prevent drying to the interior of the thermal envelope, which often takes on environmental moisture from the outside or diffusive moisture in the cooling season. They have been found to create more problems than they solve.
I prefer rigid pink insulation over the studs to make a thermal break. It does, however, take away interior space since the foam is 5/8" thick.
A thermal break, however, is much more effective on the outside of the studs, and it does double duty as an outside air/moisture barrier.
On the exterior, being an older Colonial of the late 1800 vintage, the air will whistle through the surface, taking moisture in and out as the seasons change. We agree there.
Except, if air is whistleing through the cladding, then so is wind-drive rain. That's why it's so important to have a good weather-resistant barrier (WRB) under the cladding, such as rosin paper, asphalt felt, or polymeric housewrap.
On the interior, a proper range hood for cooking and a heat exchanger will more than take care of moisture problems.
I don't know if by "heat exchange" you mean a heat-recovery ventilator, but in addition to a range hood that actually gets used, a house requires bathroom exhaust fans that also get used during showering, an externally-vented dryer, and a minimum of 0.35 air changes per hour to maintain indoor air quality and to evacuate the 3-5 gallons of moisture that a typical family of four will put into the air every day.
Can we agree that air movement is the greatest issue facing lower heating/cooling costs?
Only in certain situations. If there is considerable convection occuring within fibrous insulation, then it's going to dramtically diminish its R-value. If there is considerable moist-air movement into the thermal envelope, then that's going to create condensation, mold, rot and insect problems in addition to robbing heat. In an otherwise well-insulated house, air exchange (controlled or accidental) can become one of the larger heat loss vectors. In a leaky house, excessive air exchange is going to lower the indoor RH to uncomfortable and unhealthy levels.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Ok. What approach do you recommend he *use*, then?
I would like to know this as well.
It seems the more info I get the more confusing everything gets.
What is so bad about removing plaster/lath dense packing cellulose and drywalling over that?
Air tight drywall? Vapor barrier paint?
Please tell me the cons of this as I have used this method before and thought I was doing the right thing.
It seems the more info I get the more confusing everything gets.
Because there is far more uninformed disinformation in the building trades than science-based reliable information. And the tighter and more efficient we make our buildings, the more sophisticated they have to be to avoid problems - mostly moisture-related.
Whereas our old houses were like our old carbureted, distributor/coil-sparked car engines that almost anyone could work on, our new houses are like our new computer-controlled car engines that require an engineering degree to understand.
What is so bad about removing plaster/lath dense packing cellulose and drywalling over that?
If there is no outside well-sealed weather-resistant barrier (WRB) and properly-installed flashings in the cladding system, with old leaky siding and old leaky windows, then all you're doing is creating a big sponge to hold water in the walls. If, in addition, you don't carefully seal all possible air leakage points on the inside skin (drywall, trim, partitions, mechanical penetrations), then you're creating paths for moisture-laden air to exfiltrate into the thermal cavity in winter or infiltrate in summer and you're guaranteeing moisture-related problems, including mold, rot and insect infestations.
And, if you haven't first taken care of draining and drying the basement or crawl space, venting the kitchen hood and bath fans and dryer to the outside, properly graded the ground around the house (min. 1/2"/ft for 10') and installed rain gutters which remove water to at least 10' from the foundation, then you're creating a moisture monster which will rot out in short order.
Additionally, once you've tightened up the house, you'll probably need controlled mechanical ventilation to guarantee indoor air quality and elimination of the 3-5 gallons of water per day that a typical family puts into the indoor air.
Air tight drywall? Vapor barrier paint?
For an interior air-barrier, you can't beat the air-tight drywall aproach. But that requires caulking or gasketing all framing assemblies to each other as well as sealing all penetrations, using air-tight electrical boxes or polypans and roof flashings on plumbing stack ceiling penetrations, as well as caulking or gasketing the drywall to bottom and top plates and door and window openings and where partitions meet outside walls. Then, if you'd like, you can use a vapor retarder primer on the drywall to meet building code requirements, though this is not necessary except in extreme northern climates (10,000 DD) if proper ventilation and moisture-management is employed.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 1/15/2009 1:00 pm ET by Riversong
So now that after 100 years the house is open from the inside and I see the felt they put on the walls before they nailed their lap siding directly to the balloon framed studs, and I see no signs of water infiltration or damage, then I can reasonably assume that the felt is a reasonably good WRB no?
Flashing is good, no water penetration anywhere.
Should I seal(w caulk or spray foam) around each stud and bottom or top plate in each cavity before the cellulose? Or is cellulose itself a good air barrier to protect the inside of the house?
Instead of gaskets and such for penetrations thru drywall to keep the airthightness of it, is spray foam ok? Sprayed on/in after the DW is hung?
Thanks for the fact based respones, for me at least, the picture is getting a little clearer.
So now that after 100 years the house is open from the inside and I see the felt they put on the walls before they nailed their lap siding directly to the balloon framed studs, and I see no signs of water infiltration or damage, then I can reasonably assume that the felt is a reasonably good WRB no?
Felt is a great WRB, sometimes more effective than plastic housewrap since it will diffuse liquid water through rather than trap it against the sheathing. But no evidence of water inside an uninsulated wall that had every opportunity to dry does not mean that there is no water intrusion. In fact, any siding will allow some water in sometime over the life of a structure. But once we insulate and air-tighten an old wall it has no ability to dry and may begin to accumulate moisture, mold and rot.
Should I seal(w caulk or spray foam) around each stud and bottom or top plate in each cavity before the cellulose? Or is cellulose itself a good air barrier to protect the inside of the house?
I would not seal the cavities as you'd just be further reducing their drying potential (unless there are cracks or holes that you can see daylight through). But I would seal any wiring or plumbing penetration within the walls, particularly those through the plates (vertical chimney effect). Cellulose, if installed to at least 3 pcf density, is an excellent air barrier. But you also need to protect the cellulose from indoor moist air by sealing the drywall well, particularly around outlet boxes (I recommend Lessco polypans and Tremco acoustical sealant).
Instead of gaskets and such for penetrations thru drywall to keep the airthightness of it, is spray foam ok? Sprayed on/in after the DW is hung?
Better than nothing, but only flexible EPDM gaskets or acoustical sealant maintain their seal over time. I highly recommend Tremco for this purpose.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
"Some insulations, like fiberglass and mineral wool, are ineffective at reducing convective losses, but that's not what they're designed for. Insulation is primarily intended to reduce conductive heat loss, which is why fiberglass traditionally had a paper or foil facing to stop air movement and why codes required a plastic "vapor barrier" to also minimize air movement in the 90% of homes that were insulated with fiberglass."<!----><!----><!---->
Please explain how insulation, ie fiberglass works.
Doesn't the addition of spun glass increase the conduction between the wall/sheathing?
I thought that the air was a good insulator except for the fact that there are convective currents in the cavity.
Is the insulation function different for cellulose?
thanks
Edited 1/15/2009 11:07 pm ET by CHRISWALL
Please explain how insulation, ie fiberglass works. Doesn't the addition of spun glass increase the conduction between the wall/sheathing?
Completely dead air has an R-value of about 5/in, so it is an excellent insulator. The function of all bulk insulating materials is to trap dead air and do so with materials that themselves are as non-conductive as possible.
I thought that the air was a good insulator except for the fact that there are convective currents in the cavity.
So, while bulk insulations will reduce or eliminate convective loops within the wall cavity, they're value (by which they're rated) is in preventing conductive losses (while also inhibiting convective and radiant transfer).
Since heat moves by four mechanisms - conduction, convection, radiation and evaporation (latent or enthalpic heat) - an ideal insulator will address all four. But they are rated, for better or worse, only on conductive resistance (R-value).
Is the insulation function different for cellulose?
While the function isn't different, the effect is quite different since dense-pack cellulose will virtually stop air movement and hence stop convective moisture movement (but not moisture diffusion). Fiberglass is notorious for not preventing internal convection (it's used for furnace filters to stop dust not air), and for doing little to reduce radiant transfer (as glass has high emissivity), which is why kraft paper or foil backings were standard, and will do nothing to stop moisture diffusion or air transport.
In fact, cellulose is so effective at stopping air movement that it is accepted as a firestop in lieu of solid wood blocking. Also, while fiberglass loses R-value when the temperature either drops below or rises above room temperature (which is, of course, when it's most needed), cellulose actually increases in R-value slightly as it gets colder.
And, because of its high safe moisture storage capacity (up to 30% of its weight) and high hygroscopicity, cellulose will protect wood framing form moisture saturation and buffer the indoor RH if it is not isolated by a vapor barrier.
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
Edited 1/16/2009 1:38 pm ET by Riversong
Ok. What approach do you recommend he *use*, then?
The OP's suggested approach would be perfect for that old house, since he maintains a breathing space behind the outer cladding/sheathing for drying, a good air barrier in the insulation system, a reasonably good R-value, and a vapor impermeable layer (foil-faced foam) that will always remain warm enough to avoid condensation (no double vapor barriers).
Riversong HouseWright
Design * * Build * * Renovate * * ConsultSolar & Super-Insulated Healthy Homes
>>Insulation is only beneficial in minimally reducing air movement from heated to non-heated (or in air conditioned space, from cooled to hotter) environment. It's only use is to slow the dispersion of conditioned air to non-conditioned.Huh?
"Ask not what the world needs. Ask what makes you come alive... then go do it. Because what the world needs is people who have come alive."
Howard Thurman
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Keep in mind the the idea that insulation doesn't cause moisture problems, moisture causes moisture problems. I would recommend making every effort to remediate interior sources of moisture as part of your project. Make sure you have a dry basement. Many old houses have leaky foundations and bulkheads, dirt crawlspaces, poor grading around the house coupled with poorly working gutters. Be sure to address these as well as installing proper venting of stoves, showers, etc. as others have mentioned.
Also keep in mind that if you have old siding and windows without a proper weather resistant barrier, any insulation you add may slow the drying process to the point where mold and decay can begin. It is common as well for insulation in old houses to cause problems with exterior paint adhesion (old siding is typically painted only on the visible surfaces). Basically, insulating walls of old houses without bringing the exterior cladding and barriers up to modern standards may run the risk of causing future damage to the home. Without insulating the walls, you can increase the energy efficiency of the house by insulating the basement and attic, detailing the drywall installation to reduce air leakage, installing a high efficiency boiler, or adding storm windows.
We went whole hawg on a house. Before we insulated, we caulked around the 2x's where they joined the sheathing. Even without insulation, you would have to open the door to know the wind was howling outside. What a difference stopping air movement made. Next, we laid down a layer of aluminum wrap, leaving a 1/2" gap to avoid heat conduction that would otherwise result from contact. We didn't use anything exotic. We just went to a restaurant supply place and bought large commercial roles for around fourteen dollars. A couple rolls took care of a lot of building. Once the insulation was back in and the rock on, summer hit. Cooling was vastly improved, even after we converted to open beam ceilings.
About 15 years ago I stripped the exterior walls down to the frame. Removed the tar paper faced rock wool R7 and replaced it with R12 fiberglass. I then covered the walls with 6 mil PVB. Then I used blue Styrofoam 1 inch R5 24" wide along with 2X2 horizontal strapping (screwed and glued). For electrical outlet attachment I used 2X4 24" long attached to studs. Drywall screwed to horizontal strapping, this has held up well for over 15 years. I used 1 inch SF so as not to cause crowding where I brought wiring into that space. Otherwise 1 1/2 inch would make more sense. I am in a cold, relatively dry in winter zone north of lake Ontario. Today i would probably use closed cell, foam in place methods.
When it's cold outside the back of the sheathing will be below the dew point and any moisture in the air, (FG insulation is 96% air so it has very little conduction) will condense on your felt. There it will sit until the outside of the wall heats up enough to evaporate it through the siding. Felt can absorb quite a bit of water and release it later when things are dryer.
If the felt reaches saturation the condensation will pool on the bottom plate and rot the outside of the studs. I've seen that here in sunny California.
I would use 1" XPS, fill the balance with FG or cellulose and the airtight drywall approach. Will that work on Lon Gisland?
OB
Edited 1/16/2009 1:02 am ET by klhoush