With brick, the interior space of building was previously estimated at nearly 144 sq ft.
Now redo calculations with hardiepanel walls, which overlap slab (very different).
consider the width of one wall now (with 2x4 framing and 5/8 sheetrock)
3 9/16" + 19/32"
3 18/32 + 19/32"
3 + 37/32"
4 + 5/32
Two walls then add up to
8 + 10/32
8 + 5/16
So the interior dimensions are:
14'10" - 8 5/16" = 14' 1 11/16" = 14' 1.6875" = 169.6875"
12'6" - 8 5/16" = 11' 9.6875" = 141.6875"
Interior square footage is now:
24042.598 sq in
166.9624 sq ft
pretty close to 167 sq ft, so increase is about 23 sq ft., a 16% increase.
Now looking at adjusting the remaining variable, height, to hit an acoustic sweet spot, the best one seems to be:
9' 2"
Then, guess what, I hit the famous 1:1.28:1.54 ratio. That was actually the one I was originally aiming for when I went to brick and larger size (but before I realized how incredibly thick brick walls actually are). This set of dimensions also passes the 3 tests proposed by R Walker of BBC in 1996 (whereas the previous brick design couldn't, because height was too close to other dimensions).
Most other ratios in the range from 8 to 10 feet height aren't that bad, though there are a few clunkers:
9 feet exactly (! rather too close for comfort of the optimal at 9' 2")
8 feet 10 inches
8 feet 6 inches is in a fairly stable range of nice ratios, 4 inches removed from the ugly one at 8 feet 10 inches.
So either 9 foot walls with 2-3 inch height increase on sides, or 8 foot walls with 6 inch rise, would do nicely acoustically. Given 9 foot wall, I might rather up the max height to 9' 3" to avoid the clunker at 9 feet exactly, and still be close enough to the famous 1:1.28:1.54.
I'm less enamored of the 9 foot height now for a few reasons:
The roof gets to be rather high, difficult to work with solar panel attachments. Also tree/sky views may be blocked somewhat from bedroom window (and new slab position raises slab about 3 inches also compared with original site chosen). Solar panels and bottom edge of main house roof may be shaded.
On the other hand:
The taller height means less interference from trees generally (though not much difference). Solar panels shouldn't be put so low on main house roof anyway, the the "blockage" actually means in late afternoon the main house is being shaded from late afternoon sun...a big plus, especially if it blocks some late afternoon sun in the bedroom window (which I think it would). Of course the main advantage of greater height is more storage space, especially in loft, but also in perimeter shelving that I had originally planned Even if 2x4 shelf supports are at 6'6", meaning shelves at 6' 10", there is still oodles of space up to 9'. Could even have two rows of shelves if supports are allowed to go as low as 6'. And tall, as always, makes it seem awesome inside and possibly outside as well. Lower roof slope at 5:12, if desired, becomes costless to space inside (whereas 8 foot walls demand at least 6:12 pitch to increase space inside).
I will still go for 9 foot walls if slab construction goes as planned and hoped. If disaster happens, such as builder absconding with the funds (as I feared last week) and I need to start anew with someone else, I may roll back to 8 foot walls to save money. But there's not really as much at stake with this change in cost savings potential anyway.
**** Update
Builder didn't abscond with funds, but I'm letting him go with extra balance. Still, I think the 9'2" ceiling plan looks good, the extra height will be great for loft and perimeter shelving. Officially I'm asking for ceiling joists at 9'3 to 9'4 for ultimate ceiling height of 9'2 to 9'3. Actually there are no bad clunker spots well above 9'2, so safer to go slightly higher.
**** Update September 2011
I'm now thinking that an alternative to the 2" ceiling vaulting (which might pose problems to ceiling sealing, said to be extremely important) would be to 2x6 framing on the south and west sides, reducing possibly allowing better insulation on those critical walls as well.,
That actually works out fairly nicely. While the ratio is changed very slightly from the well known ratio, the charted performance looks essentially identical. As a first order approximation, I merely subtracted 2 inches from the length and width. That gives the ratio 1:1.29:1.55. I also tried adding back in 0.3 inch, and that didn't make a noticeable difference.
Now it's another matter whether good 2x6 framing can be done. 2x6 are not precut for framing, so that takes extra work.By the way, 2x6 framing on all sides, with the first order approximation of 4 inches lost, is a clunker, 1:1.27:1.64.
(Halloween 2011 update) I really goofed in the original 2x6 calculation on all 4 sides. Actually, that works the same or better than 2 sides. 1:1.27:1.53, still very close to the 1.28:1.54 Sepmeyer ratios, just on the other side. The low resonance area (dark green) actually starts a bit lower. Since 2x6 framing makes things nice and consistent, better thermal insulation, etc., at little extra cost (or even lower, since less trouble for the builder, one didn't even want to do mixed framing) that's what I am now specifying. Only (potential) issue is that Friedrich XStar air conditioner specifies max 8 1/2 inch wall thickness. That shouldn't be a problem, even with 5/8 sheetrock, 5/8 plywood, 5/16 thick siding, that makes wall under 7 1/4 inch thick, including felt.
Checking lumber sizes, I see that the difference is indeed supposed to be exactly 2" from 2x4 to 2x6. So the numbers above are good. 2x6's on just south and west sides (windowless too) works best. But framers might well not want to do it that way.
Now redo calculations with hardiepanel walls, which overlap slab (very different).
consider the width of one wall now (with 2x4 framing and 5/8 sheetrock)
3 9/16" + 19/32"
3 18/32 + 19/32"
3 + 37/32"
4 + 5/32
Two walls then add up to
8 + 10/32
8 + 5/16
So the interior dimensions are:
14'10" - 8 5/16" = 14' 1 11/16" = 14' 1.6875" = 169.6875"
12'6" - 8 5/16" = 11' 9.6875" = 141.6875"
Interior square footage is now:
24042.598 sq in
166.9624 sq ft
pretty close to 167 sq ft, so increase is about 23 sq ft., a 16% increase.
Now looking at adjusting the remaining variable, height, to hit an acoustic sweet spot, the best one seems to be:
9' 2"
Then, guess what, I hit the famous 1:1.28:1.54 ratio. That was actually the one I was originally aiming for when I went to brick and larger size (but before I realized how incredibly thick brick walls actually are). This set of dimensions also passes the 3 tests proposed by R Walker of BBC in 1996 (whereas the previous brick design couldn't, because height was too close to other dimensions).
Most other ratios in the range from 8 to 10 feet height aren't that bad, though there are a few clunkers:
9 feet exactly (! rather too close for comfort of the optimal at 9' 2")
8 feet 10 inches
8 feet 6 inches is in a fairly stable range of nice ratios, 4 inches removed from the ugly one at 8 feet 10 inches.
So either 9 foot walls with 2-3 inch height increase on sides, or 8 foot walls with 6 inch rise, would do nicely acoustically. Given 9 foot wall, I might rather up the max height to 9' 3" to avoid the clunker at 9 feet exactly, and still be close enough to the famous 1:1.28:1.54.
I'm less enamored of the 9 foot height now for a few reasons:
The roof gets to be rather high, difficult to work with solar panel attachments. Also tree/sky views may be blocked somewhat from bedroom window (and new slab position raises slab about 3 inches also compared with original site chosen). Solar panels and bottom edge of main house roof may be shaded.
On the other hand:
The taller height means less interference from trees generally (though not much difference). Solar panels shouldn't be put so low on main house roof anyway, the the "blockage" actually means in late afternoon the main house is being shaded from late afternoon sun...a big plus, especially if it blocks some late afternoon sun in the bedroom window (which I think it would). Of course the main advantage of greater height is more storage space, especially in loft, but also in perimeter shelving that I had originally planned Even if 2x4 shelf supports are at 6'6", meaning shelves at 6' 10", there is still oodles of space up to 9'. Could even have two rows of shelves if supports are allowed to go as low as 6'. And tall, as always, makes it seem awesome inside and possibly outside as well. Lower roof slope at 5:12, if desired, becomes costless to space inside (whereas 8 foot walls demand at least 6:12 pitch to increase space inside).
I will still go for 9 foot walls if slab construction goes as planned and hoped. If disaster happens, such as builder absconding with the funds (as I feared last week) and I need to start anew with someone else, I may roll back to 8 foot walls to save money. But there's not really as much at stake with this change in cost savings potential anyway.
**** Update
Builder didn't abscond with funds, but I'm letting him go with extra balance. Still, I think the 9'2" ceiling plan looks good, the extra height will be great for loft and perimeter shelving. Officially I'm asking for ceiling joists at 9'3 to 9'4 for ultimate ceiling height of 9'2 to 9'3. Actually there are no bad clunker spots well above 9'2, so safer to go slightly higher.
**** Update September 2011
I'm now thinking that an alternative to the 2" ceiling vaulting (which might pose problems to ceiling sealing, said to be extremely important) would be to 2x6 framing on the south and west sides, reducing possibly allowing better insulation on those critical walls as well.,
That actually works out fairly nicely. While the ratio is changed very slightly from the well known ratio, the charted performance looks essentially identical. As a first order approximation, I merely subtracted 2 inches from the length and width. That gives the ratio 1:1.29:1.55. I also tried adding back in 0.3 inch, and that didn't make a noticeable difference.
Now it's another matter whether good 2x6 framing can be done. 2x6 are not precut for framing, so that takes extra work.
(Halloween 2011 update) I really goofed in the original 2x6 calculation on all 4 sides. Actually, that works the same or better than 2 sides. 1:1.27:1.53, still very close to the 1.28:1.54 Sepmeyer ratios, just on the other side. The low resonance area (dark green) actually starts a bit lower. Since 2x6 framing makes things nice and consistent, better thermal insulation, etc., at little extra cost (or even lower, since less trouble for the builder, one didn't even want to do mixed framing) that's what I am now specifying. Only (potential) issue is that Friedrich XStar air conditioner specifies max 8 1/2 inch wall thickness. That shouldn't be a problem, even with 5/8 sheetrock, 5/8 plywood, 5/16 thick siding, that makes wall under 7 1/4 inch thick, including felt.
Checking lumber sizes, I see that the difference is indeed supposed to be exactly 2" from 2x4 to 2x6. So the numbers above are good. 2x6's on just south and west sides (windowless too) works best. But framers might well not want to do it that way.
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