- Oct 3, 2007
- 1,539
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.
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.
