[Greenbuilding] Desert roofs

[Dan Johnson]

We're still designing this new house in Phoenix, trying to price
workable systems. Our three options for roofing are:

1. Pale-colored metal roof. I'd use regular galvanized, but I'm
concerned that the low emissivity of unpainted metal will inhibit
cooling after dark--any thoughts on this?  The paint increases the
reflectivity somewhat too.  The metal roof would go on 2x4 sleepers
over a membrane and structural deck, creating a vented 3.5" airspace.

2. Living roof (5" of dirt and native plants) high thermal mass, no
problems with UV degradation of the membrane. Insulated cavity below.
This will take a specialist.

3. Pale-colored fibercement shingles/tiles, over vented airspace,
over membrane and insulated cavity. These absorb a lot of UV, but
reflect most visible and near-infrared, and have good emissivity. A
regular  tile roof contractor can do installation.

In the critical summer months, most radiation hits the roof and
little hits the walls, excepts blasts on the east and west in the
morning and evening.  Regardless of direct sun, there is also a 35-40
degree air temp difference between inside and outside.

--Dan


--- Lawrence Lile <LLile at projsolco.com> wrote:

> I'm interested in this conversation, since my family has some
> property
> in Phoenix.  Eventually we'll have to replace the windows. Let me
> know
> what you end up using.  
> 
> Right now we are replacing air conditioning.  I'm trying to
> convince my
> brother-in-law to put on a metal roof, and insulate the attic, to
> cut
> down on the size of the unit.  HVAC guys are recommending 4 ton
> units in
> a house that would use 1.5 tons in Missouri. Yow!  "But it's a dry
> heat"
> they say there.  Seems like you could save a lot with a little more
> insulation and a reflective roof.  
> 
> Do you see a lot of metal roofs going in?  We are having trouble
> finding
> a metal roof contractor to even quote us.  
> 
>  
>  
> Lawrence Lile, P.E., LEED AP
> 
> -----Original Message-----
> From: greenbuilding-bounces at listserv.repp.org
> [mailto:greenbuilding-bounces at listserv.repp.org] On Behalf Of Dan
> Johnson
> Sent: Thursday, May 17, 2007 12:02 PM
> To: greenbuilding at listserv.repp.org
> Subject: [BULK] [Greenbuilding] Desert windows - fiberglass?
> Importance: Low
> 
> Looking for windows to put in a new house in Phoenix, with a very
> low
> U-value (0.3 or less) to fight against 115 deg F heat.  I'm
> concerned
> about the durability of fiberglass frames in that intense UV
> environment.  In my experience, anything synthetic left in the sun
> turns to powder in a few years.  Are fiberglass actually OK?  
> 
> Desert window options:
> 1. Fiberglass frames - UV degradation?
> 2. Aluminum frames - hard to find thermally broken Alu frames for
> residential windows, otherwise splendid
> 3. Wood - forget wood in the desert. It will last a year
> 4. Vinyl - avoid vinyl (see dialogue elsewhere); same UV
> degradation
> as fiberglass?
> 
> FYI: also have a good shading scheme, exterior blinds, etc.
> 
> 
>        
>
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Dan Johnson
danjoh99 at gmail.com


       
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