# Superinsulation retrofit with rigid foam-anyone done it?



## cbcansurvive (Jan 29, 2009)

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

Residential Exterior Wall Superinsulation Retrofit Details and Analysis

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.


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## Alice In TX/MO (May 10, 2002)

I haven't read the article yet, but I will!

You may also want to look into radiant barrier paint for the underside of the roof decking. We did this in my mother's (1957 construction date) home, and it has helped tremendously to reduce heat gain in the attic.

You will be pleased with Hardi siding. We've used it on two remodeling projects so far. Outstanding product.


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## Ky-Jeeper (Sep 5, 2010)

I second the super insulating along with the radiant barrier. You may look into some shade trees.


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## Darren (May 10, 2002)

I think you will end up saving a lot of money on heating and cooling costs. The only caution I would suggest is to look at the flame spread specs on the insulation. Some foam insulations will melt from very high heat. The resulting liquid is akin to gasoline. ASTM establishes the standards for foam. The foam will have the ASTM standard reference printed on it. Make sure it's the right spec for your needs.

I was on a project where the contractor bought a trailer load of non-compliant spec sheet foam. The architect restricted the use. It was Ok to use for underground foundation perimeter insulation and other areas where it was separated from the interior by concrete block. It was forbidden for use in other areas.


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## tom j (Apr 3, 2009)

with foam ,, the one thing you better check is water vapor ,, it causes condensation and you can end up with more then you want ,,, mold , health problematic because of mold , rotting wood ,, it can and does lead to a big repair


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## MushCreek (Jan 7, 2008)

One big energy loss is if the A/C ducts are in the attic. Here in FL, probably 90% of the houses have A/C ducts in the attic, ABOVE the insulation! Duh! They are starting to insulate the roof itself now, so the ductwork is at least in semi-conditioned space. Our attic here in FL is about 130 degrees on a summer day- not a good place for ductwork! We also have single pane windows, and no insulation in the walls. If we were staying, I'd be looking at every way I could to remedy this, but we are building in SC, so I'll focus my money and effort on the new house.

External foam, even an inch, is very effective, because it stops the heat from conducting through the studs. Add a good taping job to reduce air infiltration, and it is very effective indeed. They are finding that air infiltration is more of a problem than the lack of insulation.


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## SolarGary (Sep 8, 2005)

Hi,
Just to add to your collection of material on the exterior insulation:
-There is an article in one of the last two Journal of Light Construction that covers retrofitting exterior insulation to a house in a lot of detail with a lot of good how-to info. I think they have also had some articles in the past on the same, so it might be worth buying the CD that has all the past issue.

- There are a couple references to exterior insulation articles on this page of my site: http://www.builditsolar.com/Projects/SolarHomes/constructionps.htm

I think what you have in mind is a good idea -- especially given that you plan to replace the siding anyway. It would be a shame to put new siding on without getting some insulation in there.

The attic insulation project is sure to pay off well. Be sure to seal all the penetrations from living space to the attic with Great Stuff or the like before you put in the new insulation. Also, if you have ducts going through the attic, seal all the joints with duct mastic, and insulate the ducts if not already done -- this in itself can be a 30% gain on some homes.

The book "Insulate and Weatherize" by Harley is very good for all the insulating jobs -- very hands on.

Some other things to think about:
- Window heat gain can be a big factor. The best solutions for window heat gain go on the outside and stop the sun before it gets through the glass. Some ideas here: http://www.builditsolar.com/Projects/Cooling/passive_cooling.htm 
particularly in the shading section.
For a south wall, overhangs or awnings also work well.

- If you have east and west facing windows that get sun, these can also be a big heat gain, and some form of external shade can be a big help.

- You could think about some other forms of exterior shading for the south wall -- trees, exterior shading structures that sit away from the wall a bit and shade it.


Being a solar guy, I have to mention the possibility of revamping the south wall to include a large area of solar air heating collector. This can be integrated with your siding change and addition of insulation, and would add very little (maybe nothing) to the wall cost. While it might seem that this would make your summer heat gain worse, if you have good insulation behind the collector and a way of venting it in the summer, it will add very little heat gain. I live in a cold climate, which makes the payback faster, but my full south wall thermosyphon solar collector on my shop paid back its cost of materials in less than one heating season. There may come a day when you don't want to do the wood heat anymore, so, some solar gain may look pretty good 


Edit: the exterior insulation article is in the June, 2011 issue of the JLC

Gary


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## oldasrocks (Oct 27, 2006)

We bought this house 11 yr ago. It was a nightmare to heat or cool. I then found they had put nothing under the vinyl siding. The curtains would almost blow off the windows inside.

I stripped off the vinyl siding and caulked around the windows. (not done before!) I wrapped the house with the fabric used under siding and installed Hardy Board, wood grain colored. I went under the house and sprayed foam on the footer concrete. Before I did this the pipes would almost freeze up as the temp would be close to freezing under the house. Now it stays close to 50 degrees.

A lot of heat is lost through floors no one thinks about.

We do need some more insulation in the attic but over all we are good. Our propane usage has halved by the above improvements. We've used 350 gallons total since a yr ago in March. We cook and heat water with propane also plus our genny kicks on occasionally propane fired.


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## Bat Farm (Apr 21, 2010)

We didnât retrofit but installed the foam as part of our original build so I donât know how helpful this will be but hope it has some value.

We added 1â rigid foam board to the middle of our building envelope based our research (often at JLC and Building Sciences). The walls of our crawlspace were insulated for the same reason. We have been in our house for 4 years now and are very glad we did.

The foam not only helps with thermal bridging as has been mentioned, but helps the house to have a more solid âfeelâ. There are no drafts and rooms are the same temperature regardless of their position in the house. The foam also muffles sound so if you have neighbors that can be a good thing. 

Since we live in both an earthquake and hurricane zone we have Â¾ â sheathing as the base of our envelope. The 1â layer of foam is next - well taped and with a small gap for drainage of any water that makes itâs way past the foam. You can use products made for this - I think Grace has one called rainslicker, canât remember for sure - or furring strips, either way remember water always wins! Our final layer is Â¾â T1-11. This sandwich makes our walls stronger and more projectile resistant which is good in our area. When researching our impact resistant windows we discovered that the average modern wall has less resistance than the windows we were buying. That is a little weird to me, but Iâve seen the average construction and I believe it. 

Do you have sheathing in place already? If you do and it has house-wrap you may want to remove the wrap before adding the foam. It will depend on your climate, I can only speak for our hot, humid climate. We do not have wrap since we dry to the inside which means our insulation doesnât have facing and the inside of our house is less humid than the outside for the majority of the year. So any moisture that does find itâs way into the wall system (past the sheathing which should not happen but just in case) will be dried by our dry indoor air. 

Are you going to have to remove your windows for the siding re-do? I am wondering because our windows are flanged over the foam like they would be with house-wrap (we had to improvise with the tops). If not you can probably put the foam over your flanges but you will need to be very careful with your flashing. 

For cutting we used razor knives which went about Â½ way through then we snapped the break the rest of the way. It took very little practice to get pretty good at that. I liked a sharpie for guide lines they make good easy to follow marks. For fine tuning and notching we used cheap serrated steak knives. I read somewhere that electric knives work well too. 

We started each wall at the windows and worked our way across the bottom of the wall then up towards the roof. Once we got above the 1st floor we went with a JLG lift (so fun!) I would take measurements and call them down to DH. By the time I got down low enough to reach he would have the piece cut and ready for me. We bought two matching roofing squares for the angles under the eaves, that way my number and his matched (well most of the timeâ¦ ) 

Here are some pictures of our installation in progress. I'm afraid they are not in any sort of order.


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## HeelSpur (May 7, 2011)

I believe some have their houses to tite, a house needs to breathe.


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## gobug (Dec 10, 2003)

I follow HeelSpur's comment and add. New super insulated structures create indoor air which is very polluted. ASHRAE has new rules which apply to single family dwellings that have been adopted into International Building Code (IBC). These are specific to air quality issues inside super-insulated homes. They have guidelines now on how many parts/million of contaminants. There are many variables, like kitchen and bathrooms have different standards than the other rooms, and a HRVU (heat recovery ventillation unit). may be required. An HRVU is basically a big air-to-air heat exchanger. I do not have any experience in this area, and look forward to other's thoughts. This is hard to accomplish on a retrofit because ductwork would be as complex for the fresh air as the heated air.

Good luck and thanks for starting this thread.
Gary


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## SolarGary (Sep 8, 2005)

gobug said:


> I follow HeelSpur's comment and add. New super insulated structures create indoor air which is very polluted. ASHRAE has new rules which apply to single family dwellings that have been adopted into International Building Code (IBC). These are specific to air quality issues inside super-insulated homes. They have guidelines now on how many parts/million of contaminants. There are many variables, like kitchen and bathrooms have different standards than the other rooms, and a HRVU (heat recovery ventillation unit). may be required. An HRVU is basically a big air-to-air heat exchanger. I do not have any experience in this area, and look forward to other's thoughts. This is hard to accomplish on a retrofit because ductwork would be as complex for the fresh air as the heated air.
> 
> Good luck and thanks for starting this thread.
> Gary


Hi,
I don't claim any experience in this area either, but from what I have read its quite hard on a retrofit to get the air sealing good enough so that an HRV or ERV is needed. 
A blower door test can be done after the retrofit to see how tight the house is -- seems like in most cases people are trying to figure out why it still leaks so much after all the sealing effort 
Having a house that is too tight is a problem I'd love to have.

Gary


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## gobug (Dec 10, 2003)

I have a book;The Masonry Stove, by Ken Kern, in which he tells the history of using wood to heat a structure (as well as cook). What relates to this thread is that he wrote that older houses leaked air from everywhere and all the inside air went up the flue. He further wrote that that leakage made those old houses healthier than modern homes heated with wood.

Another thought is how much cleaner the outdoor air was that long ago.
Gary


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## fishhead (Jul 19, 2006)

I pulled the siding off 3 walls and put up 1" blue foam and new windows before replacing the siding. I also pulled the sheetrock in my bedroom and put insulation in the cavities. There really wasn't any to speak of before doing that.

I ended up with a comfortable house. My heating bill is the same but I don't have to wear a sweatshirt and hat when it's -30 F outside.

I tried to keep the the foam tight to the next sheet but I'm sure there is plenty of gaps to release the moisture.

Next is to pull the sheetrock from one room wall, insulate, resheetrock and then put down 1" of blue foam on the floor covered with 1/2" plywood and paperbag flooring.


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## Warwalk (May 25, 2011)

The foam board should make a tremendous difference. However, with regard to the attic, I would shy away from cellulose personally. For years I had an insulation company here in Atlanta, and for many of those years I used both cellulose as well as fiberglass. Cellulose manufacturers are keen to point out that their product doesn't burn... and for the most part it doesn't. But, what it will do is smolder... and smolder... and smolder. To wit, one day I got an anxious call from my guys to hustle in to the shop. Normally they'd arrive a little early and load the "blow truck" with product, and so it was odd that they wished me to hurry in. When I got there, they showed me the inside of the blowing maching (the hopper). It was ash. It was also about the temperature of a grill when holding your hand over it, just before putting on some burgers. To this day, I can't say what happened. I don't know if someone threw a cigarette in there, or whether a machine part overheated (although the machine worked fine afterwards), or what. Long story short, that cellulose smoldered overnight, until it was nothing but hot ash the following morning. So, with that in mind, while the cellulose itself might not burn, the rest of the attic ~could~, as I'm assuming it's 100% wood that's dry as a bone. My suggestion: Look into foam. It will seal the entirety of the attic better than any blown product, and since heat rises / cold sinks, should be your first priority. If having a foam company out is too expensive, look into 2 part canister packages (such as sold by Fomo or other).


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