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Old 07-25-11, 02:22 PM   #1
IHDiesel73L
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Default Superinsulation retrofit with rigid foam-anyone done it?

In doing research on energy efficient retrofits for existing homes I came across this case study from Building Science:

RR-1012: Residential Exterior Wall Superinsulation Retrofit Details and Analysis — Building Science Information

Our home is a two bedroom, one bath ranch with a gable roof sitting on a full basement built in the late 1960s in northwestern New Jersey. It's also worth noting that the rear face of our roof faces directly south with only one large maple tree shading less than half of it. The rear of the house is in full sun basically all day. The windows are vinyl double pane-I'm not sure of their energy rating. The home was built as part of a development and the amount of insulation used was standard for the time I suppose-fiberglass batts in the 2x4 exterior walls and 6" fiberglass batts in the ceiling. Our first winter we spent nearly $2000 on heating oil (it was also hovering around $4.50 a gallon at the time) and our first summer the central air ran constantly to keep the house around 77 degrees. Basically, the attic has inadequate insulation and many air leaks (recessed lighting, fixture boxes, wiring penetrations, etc..) which need to be sealed. I've done a fair amount of research on air sealing and insulating and will be tackling the job this fall. With a free blower rental from Lowes I should be able to do the whole job for around $1200 and achieve an R-60 rating with cellulose. Obviously this will do a lot to keep heat from escaping through the attic in winter as well as keep heat from infiltrating the home during the summer, but I feel as though this is really only half of the problem.

This is what led me to looking at superinsulating the walls. Our home is not overly large or complicated (25' x 65' rectangle) and the vinyl siding is faded and even cracked in some areas-I've never been crazy about the color either. In short, it would be desirable to replace it, thus opening the door to the superinsulation project. I would plan on following the Building Science details 100%, utilizing polyiso foam and Hardi-plank as the exterior cladding. I'm hoping to gain a little insight here about what I can expect in terms of performance. Though conserving heat in winter is definitely a concern, for the past two years we've heated almost exclusively with wood that I source for free. Free wood is better than $4.00 a gallon oil, but it would be nice to burn maybe three cords a winter instead of the five I burned last year. My main concern is the summer. Our central air unit (I believe that it's undersized for our home when you factor in the amount of direct sun we get per day) simply cannot keep up with the heat gain from the sun. This is easily observed by seeing how the unit performs at night vs. during the day. During the day the unit will run continuously and struggle to keep the house at 77-78 degrees when the temperatures run into the nineties. At night however, when its still 85 degrees outside, the house cools much easier because there is no solar radiant load on the house. The question is, would the combination of an R-60 attic, R-40 walls, and perhaps energy saver blinds (there are four windows on the south face of the house) make a dramatic difference in the summer? Right now we are paying $200-300 a month depending on the weather in July and August to cool our home (and it never really gets that cool), so saving on energy bills is obviously a motivation, but even the study I've cited concedes that payback periods tend to be long. The real benefit, as far as I'm concerned would (hopefully) be simply feeling more comfortable in our home. Just curious if anyone else has undertaken this and what their results were.


Last edited by Daox; 07-25-11 at 02:55 PM..
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Old 07-25-11, 02:53 PM   #2
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I would highly recommend having an energy audit done before doing work. While you may be right on about needing the insulation (and it certainly wouldn't hurt), air sealing is a MUCH bigger deal normally. A good auditor will tell you where the leaks are and how you can go about fixing them.

That being said, I recently went to a speaker who talked about doing deep energy retrofits on existing homes. Their target was ~70% reduction in energy usage and they were achieving it mainly by putting 4 inches of polystyrene on the outside of the house and then residing it. They of course did air sealing along with that via tyvek and other means.
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Last edited by Daox; 07-25-11 at 03:04 PM..
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Old 07-25-11, 05:01 PM   #3
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What is your attic like? can you get to all the corners up there? pulling up the fiber glass and getting rid of it is going to help alot when you add new insulation as the fiber glass is going to allow air leaks from cracks and gaps and holes from wiring to keep causing problems.
What is best is to pull up the fiber glass and air seal with expanding foam, you can get cheap cans that are hard to use or you can get gun foam that uses larger cans with a application gun, or you can get a big can, it's easy to wince at the price of expanding foam, but there really isn't anything that does better in air sealing an old house, so to air seal with foam like this you find each and every wire that goes in to the attic and seal around it, same with vent pipes and duct work, light figures and chimneys need to be build up around with fire proof rock board or whatever meets code in your area, some recessed light fixtures are safe for contact with insulation, others are not, so make sure you know what you have so you don't start your house on fire! you can also get fire stop expanding foam that should be safe for around brick chimneys and some insulated double wall chimney pipe, but again, check to make sure that what you are using is safe for the application.
After you have everything sealed up make sure that your attic has enough venting from the sofets and that there is some sort of ducting to keep those vents from becoming blocked when you add insulation, a poorly vented attic will hold heat in the summer and hold condensation in the winter, it will also shorten the life of your roof costing you more money in the long run.
After your attic is sealed and vented then you are ready to blow in your R60 insulation and be done in the attic.
If your house was part of a mass development, then pull some trim off a window and check around it, see if there is insulation between the window and the framing of the house, fiberglass does not count as insulation, if you want to know why I say this then pull out a chunk of fiberglass and check out how much dirt it has been filtering from the air that is been passing around the window or door, foam is again the best choice of around windows and doors as it insulates and seals from drafts.

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Originally Posted by Daox View Post
That being said, I recently went to a speaker who talked about doing deep energy retrofits on existing homes. Their target was ~70% reduction in energy usage and they were achieving it mainly by putting 4 inches of polystyrene on the outside of the house and then residing it. They of course did air sealing along with that via tyvek and other means.
I checked out that first house they did the 4" of foam on while they were working on it and it was pretty impressive! it's about two miles from where I work.
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Old 07-25-11, 05:09 PM   #4
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10 maybe 15 years ago my parents took a late 60's house and wrapped it with 1.5" or 2" rigid foam before putting on vinyl. they replaced the old aluminum single pane with storm windows at the same time. It made a big difference on comfort of the house but I wasn't living there to pay attention to the bills.
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Old 07-25-11, 08:41 PM   #5
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One point that I forgot about is, apparently if you wrap your house in foam in a humid enough climate then you either need to make sure it's super tight and go with the 4" or more, or make sure it can breath and drain, because if you just wrap it in plastic, or a small amount of foam you can create a water tight condensation point on the inside, get 4" of foam or even more and the inside of that foam stays warm enough in the winter that water will never condense on it.
It helps to fill out the user profile a bit so we have an idea of where you live and what issues you are dealing with.
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Old 07-26-11, 10:14 AM   #6
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Oh! I have a lot to say on this topic! Later this summer or maybe next spring I will be doing this to my house and I will certainly document it. I don't foresee me getting a job like this this year. I'll respond more this afternoon.
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Old 07-26-11, 11:55 AM   #7
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Quote:
Originally Posted by Ryland View Post
One point that I forgot about is, apparently if you wrap your house in foam in a humid enough climate then you either need to make sure it's super tight and go with the 4" or more, or make sure it can breath and drain, because if you just wrap it in plastic, or a small amount of foam you can create a water tight condensation point on the inside, get 4" of foam or even more and the inside of that foam stays warm enough in the winter that water will never condense on it.
It helps to fill out the user profile a bit so we have an idea of where you live and what issues you are dealing with.
I will fill it out, but just for the purposes of this thread, I am in NJ, so humidity is a factor, but I think the Building Science plan does account for that in terms of drainage plains, etc...
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Old 07-26-11, 12:55 PM   #8
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I live in Western Oregon where the Heating Degree Days are about 4500.

I started my energy retrofit years ago. I used to think that putting fiberglass in the wall was enough, but I have since learned that just putting fiberglass in the wall is just a little better than nothing.

Since then, my approach has been to remove the inside finish layer, fir out the wall thickness to 6 inches, and fill the walls with rigid foam, caulking an foaming at all edges and seams, and staggering layers, and caulking an foaming, etc. It's a tremendous amount of work, but the results are encouraging. I'm considering external insulation too. I did not know about thermal bridging until relatively recently. Exterior insulation should remedy this.

I have a friend in this area, who has wrapped his house with 3 inches of EPS foam and he is reporting very good results. However, he is also reporting post-retrofit need to control drafts, so the advice given above concerning air leaks before retrofits is very important.

Also, as randen has said, considerations affecting dew-point are very important, and are affected by local humidity & temperature & insulation thickness. You do not want the dew-point to occur inside your wall or at a wood layer.

I see that BuildingScience.com has free information concerning all of these issues.

And lastly, when you have achieved the level of air-tightness and insulation that you seek, you'll need a mechanical HRV or ERV to assure a healthy indoor environment, so it's good to consider where it will go before you start your work.

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Old 07-26-11, 10:17 PM   #9
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I just came across a good report on three insulation retrofits:

http://www.buildingscience.com/docum...rgy-efficiency

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Old 07-27-11, 12:29 AM   #10
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i don't really have anything to add to your original question, but thanks for posting that link.

in the meantime, there are some temporary fixes that may provide relief from some of the radiant heat on your south wall. i, too, have an undersized air conditioner and have had to get creative to make it work. (the first year the ac was serviced no less than 5 times--we were attempting to keep it at 89 degrees inside)

anyway, some of the easiest modifications i have done provided substantial relief. many of these could easily be moved when you do the rigid foam thing.
1) deep awnings! i can't say enough about how helpful these are. we only have them on the west side because it is the only side the hoa doesn't monitor.
2) on my overhang outside the backdoor i hung a round curtain rod from ikea. a dowel or pvc pipe would work too. i then sewed a (relatively) straight seam down a beige king size flat sheet i picked up at a thrift store. for most of the day i pull the sheet out of the way by twisting it and pulling it to one side but from about noon to 7 pm i keep the sheet pulled across to provide shade. the temperature between this five dollar set up and the house is much lower than the outside. the surface temperature of the exterior wall is much lower as well.
3) landscape poles with shade cloth attached. also facing west.
4) consider tinting the windows, although this may not be good for you in the winter.
5) consider building exterior solar screens for your windows. they aren't difficult to make and can be taken off for winter..
6) if next year still presents the same challenges consider planting a rapidly growing vine up a trellis about a foot from the house.winter squash works well. for mine on the problem side of the house i actually removed the flowers to prevent fruiting.

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