redsky49
Well-known member
Several posters have inquired as to the amount of insulation they should install. Many of the responses to this issue have been typically been 'If some is good, more must be better'. Well, not necessarily so.
As a starting point, the code mandated minimums have been established following research by professional organizations to achieve a balance between performance and cost. You will be well served to at least meet these minimum code requirements. But does it make sense to exceed these minimums, and by how much? Well, lets take a look at an example of heating requirements.
Assume a 10' x 10' wall section, in this case sheathed with1/2" x 8" lapped siding (this is similar to a garage recently posted on this site). Environmental conditions for this exercise are 70 degrees inside, 30 degrees outside. Okay, here we go.
Existing wall, no insulation, R = 0.81: 4920 btuh
Now lets add R-13 Fiberglass insulation to the existing wall.
Existing Wall + R-13 insul. (total R-13.8): 280 btuh
Wow, what a decrease in heat loss! Almost a 95% reduction. So more must be even better, right? Let's see.
To go to more fiberglass matt we will have to go to a deeper wall cavity. Now we are framing with 2x6 instead of 2x4. But let's put that additional cost aside for the moment.
Existing Wall + R-19 insul. (total R-19.8): 200 btuh
We have another winner! Down to only 200 btuh. However, this is only a 4% further decrease in heat loss, with almost a doubling of the insulating material (3.5" vs. 5.5-6.5"), and about a 60% (prices vary widely) increase in insulation costs. Plus we still have to figure in the increased framing costs for the larger wall framing. In some cases you can increase the stud spacing, but even then, framing for any opening will be more costly and of course the floor and top plates will have to be the larger 2x6 size.
Hmmm... Not so much benefit for the substantially higher cost. But is there a payback for the 80 btuh saved at this higher cost? 80 btuh is the equivalent to the heat output of a 23W incandescent bulb. So you can afford to run a couple Christmas tree bulbs! Not such a good deal.
So. Some insulation is way better than none, and too much insulation doesn't make much sense economically.
But we still want to save money and conserve energy. What to do? A good place to start would be the windows.
Assume that we would like to look out our imaginary wall. Let's install a 3'x4' window. How does that affect our heat load? We will start with a single pane of glass (for the moment we will disregard the window frame).
Our single pane, 12 sq. ft. of glass at the above design conditions: 499 btuh
Not so good, but we know that better glass is available, such as double glazed glass.
Dbl. pane, 1/4" air space: 264 btuh
Well, almost cut in half, but it's still almost as much heat loss as the entire
R-18.8 wall. But there are still better windows available.
Dbl. pane, Argon filled, high E glass 154 btuh
Still a high heat loss and we haven't even considered the frame yet, or the infiltration of outside air at all the seams and gaps.
There are other considerations as well in constructing an energy efficient facility, but the above should lend some light on insulation. I also would reference you to an earlier post concerning some outrageous claims regarding insulation:
http://www.garagejournal.com/forum/showthread.php?t=39298
The point is that some thought should be given to all aspects of the structure, not just the insulation. There are ways to conserve but look before you leap.
Disclaimer: The above data is simplified for discussions sake, but does not skew the comparative results. Performance data will vary at differing temperature conditions and between different manufacturers. YMMV.
As always, offered only as opinion
As a starting point, the code mandated minimums have been established following research by professional organizations to achieve a balance between performance and cost. You will be well served to at least meet these minimum code requirements. But does it make sense to exceed these minimums, and by how much? Well, lets take a look at an example of heating requirements.
Assume a 10' x 10' wall section, in this case sheathed with1/2" x 8" lapped siding (this is similar to a garage recently posted on this site). Environmental conditions for this exercise are 70 degrees inside, 30 degrees outside. Okay, here we go.
Existing wall, no insulation, R = 0.81: 4920 btuh
Now lets add R-13 Fiberglass insulation to the existing wall.
Existing Wall + R-13 insul. (total R-13.8): 280 btuh
Wow, what a decrease in heat loss! Almost a 95% reduction. So more must be even better, right? Let's see.
To go to more fiberglass matt we will have to go to a deeper wall cavity. Now we are framing with 2x6 instead of 2x4. But let's put that additional cost aside for the moment.
Existing Wall + R-19 insul. (total R-19.8): 200 btuh
We have another winner! Down to only 200 btuh. However, this is only a 4% further decrease in heat loss, with almost a doubling of the insulating material (3.5" vs. 5.5-6.5"), and about a 60% (prices vary widely) increase in insulation costs. Plus we still have to figure in the increased framing costs for the larger wall framing. In some cases you can increase the stud spacing, but even then, framing for any opening will be more costly and of course the floor and top plates will have to be the larger 2x6 size.
Hmmm... Not so much benefit for the substantially higher cost. But is there a payback for the 80 btuh saved at this higher cost? 80 btuh is the equivalent to the heat output of a 23W incandescent bulb. So you can afford to run a couple Christmas tree bulbs! Not such a good deal.
So. Some insulation is way better than none, and too much insulation doesn't make much sense economically.
But we still want to save money and conserve energy. What to do? A good place to start would be the windows.
Assume that we would like to look out our imaginary wall. Let's install a 3'x4' window. How does that affect our heat load? We will start with a single pane of glass (for the moment we will disregard the window frame).
Our single pane, 12 sq. ft. of glass at the above design conditions: 499 btuh
Not so good, but we know that better glass is available, such as double glazed glass.
Dbl. pane, 1/4" air space: 264 btuh
Well, almost cut in half, but it's still almost as much heat loss as the entire
R-18.8 wall. But there are still better windows available.
Dbl. pane, Argon filled, high E glass 154 btuh
Still a high heat loss and we haven't even considered the frame yet, or the infiltration of outside air at all the seams and gaps.
There are other considerations as well in constructing an energy efficient facility, but the above should lend some light on insulation. I also would reference you to an earlier post concerning some outrageous claims regarding insulation:
http://www.garagejournal.com/forum/showthread.php?t=39298
The point is that some thought should be given to all aspects of the structure, not just the insulation. There are ways to conserve but look before you leap.
Disclaimer: The above data is simplified for discussions sake, but does not skew the comparative results. Performance data will vary at differing temperature conditions and between different manufacturers. YMMV.
As always, offered only as opinion
Last edited:
