Replies

1. 
   csnow | Dec 16, 2003 07:35pm | #1

   You should be able to get away with rocking everything except a couple of access ports.  Plenty of room to hose cells up there with trusses.

   Better yet, sheath the entire thing with rigid foam for a continuous thermal break.  Screws with fender washers (or those plastic things used for roofing underlayment) through the foam would hold the load of the cells.  If you need lateral bracing, you could run strapping under the foam.

   A number of folks here have posted pictures of a spun fabric material used to hold cells in place, but seems unneeded for a ceiling.

1. 
   Mongo | Dec 17, 2003 09:32am | #6

   I like that technique of rigid foam.

   I only use a few nails w buttons to hold the sheet in place, and gap the sheets by about 1/4" when installing. I then use canned foam to foam the gaps and seal the ceiling tigher than tight. Easy installation since the sheets don't need to break over the framing.

   Then furr 16"oc, going through the rigid foam to attach the furring to the framing. Drywall is screwed to the furring.

   It's a great system.

2. 
   MojoMan | Dec 17, 2003 02:01am | #2

   With luck, Mike Smith will offer suggestions about reinforced poly. Around here (MA) it is standard practice to nail 1x3 strapping to ceiling joists 16" o.c. The drywall is screwed to these. You could staple up poly, and then nail up strapping. The strapping will hold up the poly and insulation and give you plenty of area to screw and glue your drywall. (Is gluing drywall common practice? I've never seen it done here.)

   Just curious about building practices in your climate: How will this roof be ventilated? Do you use any kind of radiation barrier?

   Al Mollitor, Sharon MA

1. 
   JohnWiles | Dec 17, 2003 02:34am | #3

   AL

   No, drywall is not normally glued in this area. I am evaluating it as an owner- builder to provide a higher quality (more durable) installation. I will let it float near the walls. I plan on 5/8' fire rated drywall throughout the house (ceiling and interior walls) to reduce fire insurance permiums. Exterior walls alreday have 4-hour fire rating.

   There have been some words in FHB about not venting the truss area or attics. With a blown in (almost blind) insulation, it will be difficult to keep the insulation from filling the entire space. I hope to have a good vapor barrier (probably painted) upward so that not too much moisture will be in that area.

   The walls will be made of Perform Wall ICF which should allow drying to the outside in our very dry SW climate. No room for vents in the parapet walls with this ICF, but I probably could cut some if the inspector demads it.

   With a white roof (probably metal) and R-60 ceiling insulation, I will probably forego the radiant barrier. I might consider one if I could identify something rigid that I could install between the truss members that would also serve to keep an air space between the overfilled insulation and the roof sheathing. I will probably glue and nail the sheathing for an extra rigid roof membrane.

   John Wiles

1. 
   MojoMan | Dec 17, 2003 05:10am | #4

   Thanks for the info. I spent a week in Scottsdale last April and found the homebuilding interestingly different than the way things are done around here. It was beautiful in the spring, but I couldn't help but imagine how the summer sun must be the primary consideration in the design of a home.

   Al Mollitor, Sharon MA

3. 
   Mongo | Dec 17, 2003 09:25am | #5

   John,

   There is also a fabric that cen be glued/stapled to the bottoms of the trusses. The netting contains the cellulose, and will still allow you to glue the drywall.

   Bravo on the 5/8ths everywhere.

   The cells will act as a bit of a radiant barrier in your truss space. Not a barrier per se, but the upper few inches of the cellulose will absorb the radiant energy. The bulk of the cells will prevent transmittal of the heat into the living space.

   With the 5/8ths rock and paint, you really don't need a vapor barrier either.

   That said, I'm a New England guy and our climates are obviously different. Therefore, the "grain of salt" rule applies to this post.<g>

   Used to live in Tucson, my daughter was born there. Enjoyed the area.

4. 
   Ruby | Dec 17, 2003 05:15pm | #7

   After living with a flat roof for 30+ years and so do many of the people I know, I feel sorry for anyone today still building them and expecting them not to leak rather sooner than later.

   Can't you folks that want that look build a little higher parapet around the SW style house, to hide a gable roof in there and so have some decent slope?

   It may not rain much here, but enough for those roofs to be an eternal nuisance.

   Many, after living with flat roofs for years, decide to forgo the look and rebuild those roofs to a pitch that will have a chance to shed water at a reasonable rate.

   Go by Raton, NM, and you will see most roofs so altered.

   On 1/2" per foot, you may eventually, if not right off, have some spots where water stands.

   I wish you good luck!

1. 
   JohnWiles | Dec 17, 2003 06:20pm | #8

   Hi Ruby:

   Thanks for the comments. The locals use only 1/4" per foot if that. Leaking depends on quality of construction and materials. Most commercial buildings have "flat" roofs.

   My 16 year-old house had a leak. One of the skylights had an improperly welded seam and a 25 year storm got the water level up to the crack.

   I plan on using 3/4" sheathing and trusses at 16" on center with a metal roof open at the south end. I will be at 5500 feet and a little snow can be expected every year or two. I expect that the 1/2" slope and the various tolerances will keep pondiing to a minimum. We are down to 6" of rain a year in the southern part of New Mexico (way south of Raton) which usually comes in a few localized thunder storms. With no real rain in the area and not much cold weather, building techniques/quality are a little lax.

   As an owner/builder with a budget, I am working to balance energy efficiency (for my off-grid PV system) in a cooling region with budget constraints while keeping the structure relatively simple for a first-time home builder.

   John