new insulation in old house... which product?

15 years ago

Hello all,

I am new to construction/remodeling and would like to ask a few questions about insulating our home. My wife and I recently purchased a 1500sf 1850s era farmhouse in Northern VA. The interior of the home is in pretty good conditionÃ¢ÂÂ¦ the walls are lathe and plaster, and have been recently redone, so I would like to leave them alone if I can. The outside needs work. The siding is in pretty bad shape and there is no insulation in the walls. We are installing an open-loop geothermal heat pump to replace the old oil furnace, and we need to address the siding and insulation. There is also an uninsulated crawl space that needs to be addressed as well. My plan is to rip off the old siding and replace with hardi-plank (to preserve some semblance of the historic look). But I am really not sure what to do for insulation. Money is a factor, but we certainly donÃ¢ÂÂt want to create problems for ourselves in the future.

1) Which insulation system should we install?

2) Can a regular fiberglass batt installation be done well and suffice?

3) Should we spend the extra money on full-foam, and if so, which product should we go with? Will foam damage the lathe and plaster on the inside?

4) Can we split the difference and do some sort of a hybrid system (flash and batt)? If so, which products should we use and where does the vapor barrier go? Keep in mind that I will have the exterior of the house exposed to do the work, not the interior. I keep reading differing arguments about this approach and the moisture problems it can create, so I need some clear guidance here.

Most of what I have read already relates to new construction with products being applied to the inside of plywood sheathing, and working in towards the drywallÃ¢ÂÂ¦ however, our situation is reversed since we are taking all of the exterior siding off and re-insulating from there.

Thanks in advance for the help!

Tim

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Comments (5)

lucy
15 years ago
Pumped in cellulose is usually what's done now, though fibreglas is also used. It's not something you can do yourself though, definitely a job for the pros. I had it done earlier this year on an old place. A vapor barrier was not used. And the exterior was not 'exposed' at all, small holes were drilled under the siding (one board of which was removed at a time) and the stuff pumped in. A vapor barrier should either be already in place at the foundation level, and if not it's something you want to discuss with a good, reputable contractor, not necessarily the insulation people. I wouldn't think a hybrid approach would be very good (why do it?).
marys1000
15 years ago
I've always wondered about pumped in cellulose. Does it make wiring/rewiring hard in the future?
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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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Even better than formaldehyde-free Johns Manville Comfort-Therm encapsulated fiberglass batts is Owens-Corning Miraflex encapsulated long fiber spun fiberglass. The Miraflex looks and almost feels like dacron polyester insulation. The long fibers have a twist to them, and theis enables them to be used without binder. It also means that they don't shed fiberglass shards like tradtional products. They will shed a little, but it's far less. Consequently the itching and respiratory issues are much less. The downside is that Miraflex runs about twice the cost of competing products. But it's what I chose to insulate the floor of my attic and under the main home floor in the vented crawlspace. I like the fact that if I have to go in and do electrical or plumbing work, that the insulation will be much less nasty to move around and reposition. I am wondering why you want to put insulation directly under the roof, but perhaps that's an issue for a different thread.
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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
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Forget the paints. Insulate from outside the shell.
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fandlil
15 years ago
You should also give serious consideration to really high performance insulation in the floor of the attic because heat rises and is generally considered the most important source of heat loss. EnergyStar rated windows should also be put in the mix.

If/when you put in a new roof, make sure to get ridge vents, which will reduce the heat burden in the attic and lower your cooling costs in summer.

Insulation should also be installed under the floor of the first floor. There is some controversy over the need to insulate and ventilate the crawl space. Here in central North Carolina we keep the vents open year round except that we close the one closest to the boiler in winter. The walls of our crawl space are not insulated, but a heavy plastic sheet covers the crawl space unpaved dirt-- it's supposed to prevent moisture from rising from below.
lucy
15 years ago
You need to do wiring beforehand with cellulose, at least the big basic stuff with leads to clear spaces (or planned outlet boxes, etc.).
housekeeping
15 years ago
Are you sure there is no wall insulation? I can't imagine a recently redone lathe and plaster wall without insulation (and the necessary warm-side vapor barrier). Usually the dilemma is a house like mine with no wall insulation and original plaster and therefore no way to insulate without damage to the historic materials.

Don't get confused between the vapor barriers installed in the wall assemblies just underneath the interior wall finish, i.e. on the warm side of the insulation and the moisture and air infiltration barriers installed under the sheathing or other exterior cladding. The former is to block tramission of interior moisture into the insulation material where in cold climates it can condense and get trapped causing mold problems. The two later products are intended block exterior moisture, primarily rain, from being driven from the outside into the wall assembly.

The standard order of march in weatherizing an old house: insulate the attic cavities, first; then do a heroic job with the caulk gun to eliminate small air leaks, inside and out and install or replace weatherstripping around openings of doors and windows; then look at wall insulation. Note that under floor insulation is not high on this list even though it is an intuitive thing. Floor insulation projects are usually aimed at stopping air infiltration but most insulation materials aren't designed to combat infiltration, per se. However, tightening up other, higher, parts of the house will prevent them from drawing cold air up through the floor in the first place. This overall plan of attack is based on first doing the things with the most efficient payback in energy savings for the dollars invested. And sexy, or not, attic insulation and caulking are the top two.

For under your structure, you may need a vapor barrier laid on the dirt to stop moisture vapor from rising from the soil into your living space and the framing of the structure, and possibly ventilation of the crawl space (this is the controversial part and I think depends,greatly, on local conditions especially your outdoor drainage situation.)

BTW, I would carefully assess the choice between wood siding and Hardie-plank type products. They are not equivalent in how they look and I think the HP makes an old building look odd. Unless you siding is totally rotted, you can probably rehab most of it, then buy only a small amount to finish the job.

There is a series of National Park Service publications regarding the care of old buildings. One title is devoted to weatherizing old structures. I've attached a link below, scroll down the list of titles until you find the ones that interest you.

HTH,

Molly~

Here is a link that might be useful: National Park Service Preservation Brief Series - Wide range of old house topics

new insulation in old house... which product?

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lucy

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