[Greenbuilding] Roofs

[Lawrence Lile]

>Couldn't you do it right over the 
shingles (in case it rained during the construction and to save time)?

You can only put so much weight over the roof.  With asphalt shingles, I
think the rule is 3 roofs is all you get.  When I reroofed my house
there were four layers so some people cheat on this, but your building
inspector won't be pleased with this tactic. 


>    What would the cost be to get someone to do this--compared to 
removing and replacing the shingles. 

Removing the old shingles takes a lot of elbow grease but is
surprisingly cheap. It's a day's work for a crew of five on most average
houses. The right way to do it is to remove the old shingles, you could
get away with leaving them on if there is only a layer. I wouldn't add
foam and purlins and so forth over an old roof, this is just shoddy
practice.  Yeah, if it looks like rain you need tarps, no way around it.



>Unfortunately, it's not a simple 
roof. I imagine the price of the material has gone up a lot. Hasn't 
steel gone up, like 700% in the last ten years?

When I did my roof last summer, "barn metal" style roof with the screws
was a little more expensive than asphalt, architectural standing seam
(no screws penetrating the face, lasts a lifetime) was two or two and a
half times as expensive as asphalt.  A pro can put the metal onto any
shape roof.  I went with the standing seam, so I won't be up there when
I'm past 70 trying to patch up a 20 year old leaking roof.  


>   Also, i'm in minnesota, not arizona, so another option could be to 
insulate (foam sheeting) on top of the existing roof and put the 
purlins and steel on top of that. My attic is finished, so I can't 
insulate it any better without demo-ing the ceiling.


Minnesota, eh?  Yes adding foam sheathing on top of your roof, after you
tear off the shingles, and after you replace any rotten plywood that is
under there, is an option, but it is unconventional and you'll be told
by a contractor "It can't be done".  Keep looking until you find someone
creative.  Unless you add purlins you won't be able to do more than 1.5"
of foam in this way, the screws get too long to be practical.  I'd think
the purlins would be stronger and more wind resistant. 

Make sure you include snow guards like these

http://www.alpinesnowguards.com/standing-seam-snowguards.html

it is really scary when a big chunk of ice comes skiing off the roof.
You'll need snow guards wherever people can walk, to protect mechanical
equipment, overhead wires and landscaping.  Don't use the glue-on type
that can pop off, use the kind that clamps a tube like a little fence.  


--Lawrence Lile