# Superinsulation retrofit with rigid foam-anyone done it?



## Badfish740 (Jul 25, 2011)

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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## SolarAndWood (Jul 26, 2011)

I'm in the middle of the project but don't have the results yet.  2x6 and 2x8 foam walls, 3/4" ply, heavy felt, 1" foam board, tyvek, protecto on the windows and wood siding.  My walls/siding had to be redone anyway, so I have done it a section at a time from the foundation to the roof.  I should end up with 35+ walls and 60+ in the attic.  I heat exclusively with free wood too but as I'm sure you know it isn't free and doesn't get any cheaper as you get older.


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## begreen (Jul 26, 2011)

How are you handling doors and windows? Are you redoing trim to handle the extra thickness?


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## SolarAndWood (Jul 26, 2011)

I am replacing all the doors and windows as I go.  Literally, picked the house up, rebuilt the load bearing walls and dropped the house back down on it.  Then, trusses with big overhangs over the old flat roof to shade summer sun while letting in winter sun that also will allow a pile of cellulose in the attic.


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## Huskyforlife (Jul 27, 2011)

If you are having trouble cooling your house then invest in some blinds or curtains and keep them closed during the day.  That will help tremendously.  Also, do the attic insulation and air sealing.  R-60 is a good number to shoot for.  Weatherstrip the hatch (or if you are like me and hardly ever need access, then tape it shut).  Also, I assume you have center A/C with ducting - seal the ducts with mastic and tape and insulate them.  

Once you do these things you will see a definite improvement, and probably be at a manageable level for heating and cooling.

Additional foam board insulation on the exterior walls is a lot more work.  You have a ranch, so it's simpler in the fact that you will not have to deal with staging, but it is still a time-consuming process.  I plan on doing it myself someday (I'm in the same boat you are, I have a house built in the early 70's with 2x4 R-7 insulation in the walls).  My scenario had me going with 1" iso, furring strips for foam adhesion/rainscreen, and then Hardiplank.  I plan on re-flashing all my windows during the process and trimming with Aztec as well.  Keep in mind if you go with Hardi you need to follow the installation instruction, flash and seal the end and you have to buy the shears since you cannot cut it with a regular saw like vinyl.  I think my material costs came to around $3.25/SF last time I estimated it. Good luck.


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## Badfish740 (Jul 27, 2011)

Huskyforlife said:
			
		

> Additional foam board insulation on the exterior walls is a lot more work.  You have a ranch, so it's simpler in the fact that you will not have to deal with staging, but it is still a time-consuming process.  I plan on doing it myself someday (I'm in the same boat you are, I have a house built in the early 70's with 2x4 R-7 insulation in the walls).  My scenario had me going with 1" iso, furring strips for foam adhesion/rainscreen, and then Hardiplank.  I plan on re-flashing all my windows during the process and trimming with Aztec as well.  Keep in mind if you go with Hardi you need to follow the installation instruction, flash and seal the end and you have to buy the shears since you cannot cut it with a regular saw like vinyl.  I think my material costs came to around $3.25/SF last time I estimated it. Good luck.



It will definitely be a lot of work, but worth in the end I think for a few reasons.  First, with the downturn in the housing market, we'll be here long enough to realize the energy savings, plus, I really feel that as time goes, on modifications like these will be extremely attractive to homebuyers as the proof will be in the utility bills.  There are a couple of good videos by DIY'ers on the net that walk you through Hardi installation so I've been looking at those.  It seems once you get the quirks of dealing with cementitious products down you're set.


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## jimbom (Jul 27, 2011)

Reading your post it is clear you have an excellent grasp of HVAC load.  In my opinion, you cannot overestimate the loss due to infiltration.  Every hole in every top stud, bottom stud, dry wall, and door/window framing should be sealed.  It will make a tremendous difference.  Check it out for a season and then consider the next best investment opportunity to save energy.


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## Huskyforlife (Jul 27, 2011)

Badfish740 said:
			
		

> It seems once you get the quirks of dealing with cementitious products down you're set.



The fiber cement board is definitely my choice for siding.  It retains the look of wood while being thermally stable and non-combustible.  Only downsides over vinyl is that it is more expensive and you have to paint it (though nowhere near as often as wood).


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## DaveH9 (Jul 27, 2011)

[/quote] 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.[/quote]


I recommend exhausting your attic with an thermostatically controlled attic fan. I did that on our  home (similar to yours) and it made a big difference. The hot attic air radiates through the ceiling insulation. I'm in the process of replacing the soffits now to get even better ventilation. Used the window AC once last year and twice so far this year. I too am planning a foam board and hardy board siding retrofit.  I'm going to keep the windows and add storm windows. 

You might consider PV for your south facing roof, that will pay you back quickly in NJ and absorb some of the heat gain into your attic.


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## woodgeek (Jul 28, 2011)

In the summer the stack effect is reversed and you draw heated attic air into the house--airsealing will help a lot.


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## jebatty (Jul 28, 2011)

Your project is very worthy. Be sure to consider adequate ventilation with air/air heat exchanger(s) or otherwise when you're done. Not only a need for fresh air, but also need to control humidity/mold potential. I'm sure our 1500 sq ft 1956 house has plenty of air leaks, but we heat 24/7 with a wood stove in the living room so we need air from somewhere to maintain a good draft, and I figure those air leaks do the necessary job. Plus the stove heats the house comfortably without any supplement to handle all the cold northern MN has to offer. It's actually exciting to weather the -30 to -40F winter cold snaps.


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## benjamin (Jul 31, 2011)

woodgeek said:
			
		

> In the summer the stack effect is reversed and you draw heated attic air into the house--airsealing will help a lot.



This, plus the typical inadequate ridge and especially soffit vents both contribute to heat gain.


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