MOVING AIR COMPROMISES R-VALUE?
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(Posted to cheap-shelters 5/04.)
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Doug posted: "I wouldn't think it would be compromised any more than, the R value of insulation in a conventional attic space that has ventilating air circulation, would be."
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Lots of attics -- even roof decks -- are vented but it's rather passive as there is a place for the hot air to get out but not much of one for cooler air to get in. I've heard attic temps should be no more than 10 or 15 degrees warmer than outside air on a reasonably warm day -- if that gives you any idea of how many structures are NOT properly vented. Once that attic gets
hot, the whole ceiling becomes a heater radiating that heat down into the living space -- a problem made worse by "decorators" who choose black or dark-colored shingles which turns the whole attic into a pizza oven from hell.
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It's my understanding that Fiberglas insulation is designed to function in a "dead air" space and that air moving constantly across the exposed surface of it will compromise R value, I just don't know by how much. This particular pallet gothic arch shape is anticipated to have unrestricted air entering at the bottom of
the roof/wall arch and exiting into the mini-attic and back outside from there. So it's a concern that the minimal R value -- at least initially -- not be compromised too much by the moving air.
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sail4free
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Wednesday, May 19, 2004
GOTHIC ARCH LINKS:
==========
If any of these links are dead, puhleeze let me know so I can update -- or delete -- them.
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Gothic Arch “eyecatchers” in Ireland:
http://www.lawrencetown.com/folly.htm
==========
Good overview of greenhouse shapes and coverings:
http://www.hightunnels.org/planningmaterials.htm
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Some great interior shots of glued laminated arches with exposed T&G ceilings -- links to residential and other types of buildings:
http://www.utsdesign.com/p_religious.html
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With a span of 46.2 m, this simple store building is the longest clear span glue laminated arch building in Australia.
http://oak.arch.utas.edu.au/projects/view_projectinfo.asp?projID=132
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sail4free (If link displays on more than one line, the link may not work -- safer to copy & paste into address window anyway.)
==========
==========
If any of these links are dead, puhleeze let me know so I can update -- or delete -- them.
==========
Gothic Arch “eyecatchers” in Ireland:
http://www.lawrencetown.com/folly.htm
==========
Good overview of greenhouse shapes and coverings:
http://www.hightunnels.org/planningmaterials.htm
==========
Some great interior shots of glued laminated arches with exposed T&G ceilings -- links to residential and other types of buildings:
http://www.utsdesign.com/p_religious.html
==========
With a span of 46.2 m, this simple store building is the longest clear span glue laminated arch building in Australia.
http://oak.arch.utas.edu.au/projects/view_projectinfo.asp?projID=132
==========
sail4free (If link displays on more than one line, the link may not work -- safer to copy & paste into address window anyway.)
==========
GOTHIC ARCH LINKS:
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The outgrowth of the gambrel, the gothic roof further expanded the loft space with a series of built-up rafters cut to a precise curve creating a smooth continuous arch. The gothic roof was promoted around 1915 by commercial, mail order firms such as Sears, Roebuck & Co. The gothic arch was praised for its attractiveness and its ability to withstand the most extreme prairie winds. Though their popularity was short lived elsewhere, gothic barns were widely embraced in North Dakota and continued to be built into the 1950s with few apparent design changes.
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http://www.lib.ndsu.nodak.edu/collections/exhibits/barns.php
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Photos of gothic arches built by HS students using blocks of wood -- no glue -- an example of the built-in strength of the shape as it almost perfectly follows the unseen load lines:
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http://www.royalhigh.edin.sch.uk/departments/departments/CDT/s2_structures_02_03_class_2c.html
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sail4free
==========
==========
The outgrowth of the gambrel, the gothic roof further expanded the loft space with a series of built-up rafters cut to a precise curve creating a smooth continuous arch. The gothic roof was promoted around 1915 by commercial, mail order firms such as Sears, Roebuck & Co. The gothic arch was praised for its attractiveness and its ability to withstand the most extreme prairie winds. Though their popularity was short lived elsewhere, gothic barns were widely embraced in North Dakota and continued to be built into the 1950s with few apparent design changes.
==========
http://www.lib.ndsu.nodak.edu/collections/exhibits/barns.php
==========
Photos of gothic arches built by HS students using blocks of wood -- no glue -- an example of the built-in strength of the shape as it almost perfectly follows the unseen load lines:
==========
http://www.royalhigh.edin.sch.uk/departments/departments/CDT/s2_structures_02_03_class_2c.html
==========
sail4free
==========
Saturday, May 08, 2004
GOTHIC ARCH LINKS:
==========
The structural advantages of the Gothic Arch Shape -- in stonework:
http://www.mtholyoke.edu/courses/mtdavis/222/barrelvault.html
==========
Success of Gothic Arches as greenhouses -- requiring no heat OR mechanical ventilation:
http://www.newfarm.org/features/0802/greenhouses/page2.shtml
==========
Lots of FREE building plans:
http://www.public.iastate.edu/~mwps_dis/mwps_web/d_plans.html
including the glued & nailed 1X2 gothic arches @
http://www.public.iastate.edu/~mwps_dis/mwps_web/ut_plans.html#Anchor72015
==========
Small illustration of gothic arch -- “classic” shape would be the middle one:
http://perso.club-internet.fr/vinz666/En/Glossaire/Texte/Arc-brise.htm
==========
Read about the Aurora Ice Hotel -- made from ice in a gothic arch shape:
http://www.adn.com/front/story/4385998p-4396365c.html
==========
==========
The structural advantages of the Gothic Arch Shape -- in stonework:
http://www.mtholyoke.edu/courses/mtdavis/222/barrelvault.html
==========
Success of Gothic Arches as greenhouses -- requiring no heat OR mechanical ventilation:
http://www.newfarm.org/features/0802/greenhouses/page2.shtml
==========
Lots of FREE building plans:
http://www.public.iastate.edu/~mwps_dis/mwps_web/d_plans.html
including the glued & nailed 1X2 gothic arches @
http://www.public.iastate.edu/~mwps_dis/mwps_web/ut_plans.html#Anchor72015
==========
Small illustration of gothic arch -- “classic” shape would be the middle one:
http://perso.club-internet.fr/vinz666/En/Glossaire/Texte/Arc-brise.htm
==========
Read about the Aurora Ice Hotel -- made from ice in a gothic arch shape:
http://www.adn.com/front/story/4385998p-4396365c.html
==========
Tuesday, May 04, 2004
PALLET GOTHIC ARCHES 101:
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(Originally posted to cheap-shelters 5/04/04.)
==========
In playing around with pallet quonsets: considering dome shapes, adding "snow caps" to increase the slope of the upper two ridge facets, etc., I drew up what I call a "2/3 width" gothic arch shape to see what would happen to that shape using 3' long chunks of 2X4.
==========
It seems that just about any shape with curving sides and a pointed ridge is called gothic arch. This is how I would draw what I call a "2/3 width" gothic arch shape where the height is 2/3 of the width which gives a good combination of floor space without excessive height. If you'd like to draw a similar shape, follow these directions: Draw a line (for the floor) which is 12" long. Mark the left end of the line point (A) and the right end of the line point (D). The 4" mark is point (B) and the 8" mark is point (C). Draw a vertical line from the 6" mark straight up about 8". Set the pivot of your compass at point (C) and the pencil end at point (A). Draw an arc from point (A) to the vertical line extending up from the 6" mark. Re-set the pivot of your compass at point (B) and the pencil end at point (D). Now draw an arc from point (D) to the vertical line. This illustrates what I call the classic gothic arch shape. It's easy to see how the further away the pivot point is on this line from the pencil point creates a shape increasingly taller without increasing the width.
==========
What I found was the two curved lines (for this smaller shelter which is approximately 16' wide) meet each other at the ridge at a 45 degree angle. This places each ridge facet at 22.5 degrees below horizontal which is 5 in 12 (considerably more than the 3 in 12 required for shingle warranty but not quite as steep as the 8 in 12 of the "snow cap" option for the similar-sized pallet quonset which is a deviation from the original criteria). The gothic arch shape can be achieved within the original criteria (3' long 2X4s salvaged from used and FREE pallets) and doesn't require the 6-1/2' boards needed to frame the "snow cap" for the quonset shape.
==========
I found that four more 3' wide facets (for a total of five facets on each side) meeting each other at 15 degrees would take me to the ground and provide a structure about 16.5 feet wide and 11.5 feet tall. (I would shorten the two ridge facets as needed to achieve a 16' width = a more conventional dimension which lends itself to sheet flooring without waste and facilitates other building "norms.")
==========
Snow considerations aside, I like the looks of the gothic arch much better than the half-circle quonset and it still lends itself even more deftly to the option of a dome shape for those intent on "living in the round." The gothic arch shape also "goes vertical" slightly quicker than the half-circle quonset shape which gives more useable floor space inside. For the basic application, though, increasing the height is a double-edged sword. It provides more conventional vertical wall space on the two "ends" for doors and windows but then there is all this towering overhead space which cries out for attention and seems to detract from this small, simple, low-cost design.
==========
By keeping it simple -- THWOCK! (That's the sound the KISS hammer makes when it smacks against my forehead), everything ends up safer and closer to the ground. There is still room for optional crossties and a full 4' wide flat ceiling on the inside for ceiling lights, exhaust fans, ceiling fans, porch lights and all their related wiring inside a vented mini-attic. If a 2 story is desired, the whole thing could be easily built on top of a post and beam first floor which allows the economical pole-barn approach for the 1st story walls.
==========
Because the lowest wall facet doesn't lean in very much -- only about 3-1/2" up 36" from the floor, we can still use conventional base cabinets in the bath and kitchen and be able to put conventional furniture near the curving walls.
==========
With the pole-barn approach for the bottom floor walls, we can use regular girts and metal siding for the low-cost pole barn wall transition to the ground and have more conventional contrast between the wall and the roof. Metal siding also provides better protection for the wall from ground splash of water dripping from the roof. To vent the roof, one option is to "cheat" the rigid arches out 1-1/2" beyond their bottom plates to create an air gap for incoming air. This gap can be covered with 1/8" mesh galvanized hardware cloth (much stronger and and more durable than window screen) to keep the bugs out.
==========
To avoid having to install two layers of roof decking, I'm still playing with the idea of covering the ribs with housewrap, installing 1 x 2 or 2 x 2 furring strips to the top edges of the ribs and then attaching the roof deck to the top face of the furring strips. This would create a gap for ventilation to preclude moisture buildup in the structure and would also help to cool the roof deck. Being able to vent excess heat from the roof deck helps a shelter stay cooler longer and also maximizes the serviceable life of the shingles. In snow country, a "cold" vented roof deck keeps the snow from melting, flowing to the edges and freezing which creates ice dams. Ice dams do a lot of damage in some climates. If metal roofing is used, a vented roof deck keeps the metal cold and the snow is much more likely to just slide off and not build up on the roof. Otherwise, the snow DOES tend to build up and hold heat as insulation. The snow melts next to the roof, flows to the edges and freezes with resultant ice dams and the damage they cause. Roof deck vents could vent into a mini-attic and then out large screened openings in both ends of the shelter.
==========
Our latest "evolution" has been to install a layer of 2x2s in line with the arch ribs and attached to the bottom edge of them. This moves the inside face of the ribs in beyond the plywood gussets so we don't have to work around them for interior finish. If R11 Fiberglas insulation is stapled to the 2x2s, this leaves a 1-1/2" gap shy of the bottom of the roof deck for ventilation. One or more layers of solid foam insulation slabs can be installed on the interior with combined potential R value of R23 or R35 IF polyurethane foil-faced sheets are used (Thermax or similar). These sheets can be tacked in place, covered over with 6 mil clear plastic (vapor barrier) and then held in place with longer screws through 1/2" sheetrock. The 16" spacing allows 1/2" sheetrock ceilings where the heavier 5/8" sheetrock must be used with the wider 24" spacing typical of most modern truss roofs.
==========
If a solid deck of plywood, OSB or individual boards is secured to the outer edges of the arch ribs, how important would a layer of roofing felt be for this application? (Felt could still be installed, just more problematic.) Perhaps we can nail shingles to the deck directly without felt or anything underneath? This would sure simplify roofing on a 2 story as one could deck the lowest facet and lean out over the top edge to shingle most of it. Then deck the next facet up and lean out over it to nail on some more shingles. Only the two uppermost portions of the ridge facets would have to be done outside sitting on the roof. One could install the ridge cap as they go and work themselves off to one end and down an extension ladder. This would eliminate any need for scaffolds and would sure minimize ladder work which gets real hard on the feet after a few hours.
==========
sail4free
==========
==========
(Originally posted to cheap-shelters 5/04/04.)
==========
In playing around with pallet quonsets: considering dome shapes, adding "snow caps" to increase the slope of the upper two ridge facets, etc., I drew up what I call a "2/3 width" gothic arch shape to see what would happen to that shape using 3' long chunks of 2X4.
==========
It seems that just about any shape with curving sides and a pointed ridge is called gothic arch. This is how I would draw what I call a "2/3 width" gothic arch shape where the height is 2/3 of the width which gives a good combination of floor space without excessive height. If you'd like to draw a similar shape, follow these directions: Draw a line (for the floor) which is 12" long. Mark the left end of the line point (A) and the right end of the line point (D). The 4" mark is point (B) and the 8" mark is point (C). Draw a vertical line from the 6" mark straight up about 8". Set the pivot of your compass at point (C) and the pencil end at point (A). Draw an arc from point (A) to the vertical line extending up from the 6" mark. Re-set the pivot of your compass at point (B) and the pencil end at point (D). Now draw an arc from point (D) to the vertical line. This illustrates what I call the classic gothic arch shape. It's easy to see how the further away the pivot point is on this line from the pencil point creates a shape increasingly taller without increasing the width.
==========
What I found was the two curved lines (for this smaller shelter which is approximately 16' wide) meet each other at the ridge at a 45 degree angle. This places each ridge facet at 22.5 degrees below horizontal which is 5 in 12 (considerably more than the 3 in 12 required for shingle warranty but not quite as steep as the 8 in 12 of the "snow cap" option for the similar-sized pallet quonset which is a deviation from the original criteria). The gothic arch shape can be achieved within the original criteria (3' long 2X4s salvaged from used and FREE pallets) and doesn't require the 6-1/2' boards needed to frame the "snow cap" for the quonset shape.
==========
I found that four more 3' wide facets (for a total of five facets on each side) meeting each other at 15 degrees would take me to the ground and provide a structure about 16.5 feet wide and 11.5 feet tall. (I would shorten the two ridge facets as needed to achieve a 16' width = a more conventional dimension which lends itself to sheet flooring without waste and facilitates other building "norms.")
==========
Snow considerations aside, I like the looks of the gothic arch much better than the half-circle quonset and it still lends itself even more deftly to the option of a dome shape for those intent on "living in the round." The gothic arch shape also "goes vertical" slightly quicker than the half-circle quonset shape which gives more useable floor space inside. For the basic application, though, increasing the height is a double-edged sword. It provides more conventional vertical wall space on the two "ends" for doors and windows but then there is all this towering overhead space which cries out for attention and seems to detract from this small, simple, low-cost design.
==========
By keeping it simple -- THWOCK! (That's the sound the KISS hammer makes when it smacks against my forehead), everything ends up safer and closer to the ground. There is still room for optional crossties and a full 4' wide flat ceiling on the inside for ceiling lights, exhaust fans, ceiling fans, porch lights and all their related wiring inside a vented mini-attic. If a 2 story is desired, the whole thing could be easily built on top of a post and beam first floor which allows the economical pole-barn approach for the 1st story walls.
==========
Because the lowest wall facet doesn't lean in very much -- only about 3-1/2" up 36" from the floor, we can still use conventional base cabinets in the bath and kitchen and be able to put conventional furniture near the curving walls.
==========
With the pole-barn approach for the bottom floor walls, we can use regular girts and metal siding for the low-cost pole barn wall transition to the ground and have more conventional contrast between the wall and the roof. Metal siding also provides better protection for the wall from ground splash of water dripping from the roof. To vent the roof, one option is to "cheat" the rigid arches out 1-1/2" beyond their bottom plates to create an air gap for incoming air. This gap can be covered with 1/8" mesh galvanized hardware cloth (much stronger and and more durable than window screen) to keep the bugs out.
==========
To avoid having to install two layers of roof decking, I'm still playing with the idea of covering the ribs with housewrap, installing 1 x 2 or 2 x 2 furring strips to the top edges of the ribs and then attaching the roof deck to the top face of the furring strips. This would create a gap for ventilation to preclude moisture buildup in the structure and would also help to cool the roof deck. Being able to vent excess heat from the roof deck helps a shelter stay cooler longer and also maximizes the serviceable life of the shingles. In snow country, a "cold" vented roof deck keeps the snow from melting, flowing to the edges and freezing which creates ice dams. Ice dams do a lot of damage in some climates. If metal roofing is used, a vented roof deck keeps the metal cold and the snow is much more likely to just slide off and not build up on the roof. Otherwise, the snow DOES tend to build up and hold heat as insulation. The snow melts next to the roof, flows to the edges and freezes with resultant ice dams and the damage they cause. Roof deck vents could vent into a mini-attic and then out large screened openings in both ends of the shelter.
==========
Our latest "evolution" has been to install a layer of 2x2s in line with the arch ribs and attached to the bottom edge of them. This moves the inside face of the ribs in beyond the plywood gussets so we don't have to work around them for interior finish. If R11 Fiberglas insulation is stapled to the 2x2s, this leaves a 1-1/2" gap shy of the bottom of the roof deck for ventilation. One or more layers of solid foam insulation slabs can be installed on the interior with combined potential R value of R23 or R35 IF polyurethane foil-faced sheets are used (Thermax or similar). These sheets can be tacked in place, covered over with 6 mil clear plastic (vapor barrier) and then held in place with longer screws through 1/2" sheetrock. The 16" spacing allows 1/2" sheetrock ceilings where the heavier 5/8" sheetrock must be used with the wider 24" spacing typical of most modern truss roofs.
==========
If a solid deck of plywood, OSB or individual boards is secured to the outer edges of the arch ribs, how important would a layer of roofing felt be for this application? (Felt could still be installed, just more problematic.) Perhaps we can nail shingles to the deck directly without felt or anything underneath? This would sure simplify roofing on a 2 story as one could deck the lowest facet and lean out over the top edge to shingle most of it. Then deck the next facet up and lean out over it to nail on some more shingles. Only the two uppermost portions of the ridge facets would have to be done outside sitting on the roof. One could install the ridge cap as they go and work themselves off to one end and down an extension ladder. This would eliminate any need for scaffolds and would sure minimize ladder work which gets real hard on the feet after a few hours.
==========
sail4free
==========
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