Re: [GBlist] low tech green roof?

[John Salmen <terrain@shaw.ca>]

I doubt you would have a problem with the existing roof.

You could have the roof evaluated for loading by an engineer. Depending on
the age of construction, etc. the joists may well be acceptable for
additional loading (if they are older growth, high grade, etc.).  It may be
that the current 'dead load' rating on the roof assembly will allow for a
planted roof. There is often a lot of redundancy built into a flat roof. You
could determine this yourself by looking at the roof assembly, determining
if there is any existent sag, measure the rafter sizes and do some
calculations.

Essentially what you are doing is transferring a roof live load capacity
(eg. snow load probably rated at around 40 lbs per sq. ft and turning that
into a dead or continuous load). This could be fine. If you could design the
'roof greening' to be a light and relatively dry roof (using lightweight and
quick drainage, minimal growing medium and xeriscaping, etc. there should be
no reason you could not add a few lbs to the current live loading on the
roof.

If you are looking at redoing the roof surface entirely it may be that
replacing the current top with a lighterweight system will provide the
weight difference - especially if your current roof is tar and gravel or
gravel ballast. If it is gravel over a membrane currently just replacing the
gravel with drainage mats and light soil would be probably be equivalent
weight.

Also if the rafters are accessible it is not a difficult or expensive job to
increase their stiffness, a small cost in comparison to the cost of a green
roof - this probably only has to be done in the centre portion of the rafter
and could be as simple as adding a flat metal strap to the bottom or side of
the rafter. A 1" wide simpson type strap nailed to the bottom of a rafter
will allow for significant additional loading.

Let me know more about what the current roof is like and I could point you
in the direction of an appropriate design

best
John Salmen



----- Original Message -----
From: "David Bergman" <bergman@cyberg.com>
To: <greenbuilding@crest.org>
Sent: Friday, November 23, 2001 10:50 AM
Subject: Re: [GBlist] low tech green roof?


> I've asked this question on this forum before, but are any of the green
> roof systems you mention suitable for residential, i.e. wood joisted, flat
> roof structures? I'm still searching for a feasible, affordable green roof
> for our 6-story condo tenement-style building.
>
> David Bergman
>
> John Salmen wrote:
> >Hi Alan
> >
> >Yes I have but with membrane which is readily availabe (Firestone EPDM or
> >some equiv.seems to be 'in stock' at most supply houses in my experience
and
> >quite inexpensive.), however it is difficult to get a roofer to use it
for a
> >small residential job. I've used Platon foundation drainage as a drainage
> >board, I've also used gravel which is pretty low-tech. I would avoid
using
> >mineral batts for drainage as they could be an additonal source of water
> >contamination.
> >
> >One of the problems with 'green roofs' is the general toxicity of
materials
> >needed to waterproof quickly takes the shine out of the green in my
> >experience and the complexities of waterproofing are anything but
low-tech.
> >Torch-on and the companion products are pretty offensive materials. Same
is
> >true to a marginally lesser degree for most EPDM materials and glues.  I
> >would prefer to use a polyurethane membrane like Hypalon or keep to that
> >family of materials.
> >
> >And since roofs leak it is useful to look at each component of the system
as
> >providing some degree of resistance.
> >
> >On the natural side I have always wanted to try a roof incorporating the
> >inverted sod method (traditional icelandic roof). 7 layers of sod
> >alternating roots up and down. My thought is that a natural membrane is
> >formed in the breakdown of the grass under anaerobic conditions - similar
to
> >how ponds form.
> >
> >good luck and keep dry (having just been involved in getting yet another
> >flat roof to stop leaking)
> >
> >John Salmen
> >TERRAIN E.D.S.
> >
> >----- Original Message -----
> >From: "Alan Abrams" <awabrams@starpower.net>
> >To: <greenbuilding@crest.org>
> >Sent: Thursday, November 22, 2001 7:35 AM
> >Subject: [GBlist] low tech green roof?
> >
> >
> > > this is a request for *practical* information on
> > > detailing a green roof.  Does anyone have first hand
> > > experience building green roofs with commonly
> > > available, more or less conventional building
> > > materials?  I've looked at a few websites on the
> > > subject; they seem to require sophisticated membranes
> > > and drainage matts--I think it would be beneficial to
> > > be able to build with, for example, torch applied
> > > modified bitumen and ordinary foundation wall drainage
> > > matts.  Low-tech is good, no?
> > >
> > >
> > > Alan Abrams, AIBD
> > > 808 Aspen St. NW
> > > Washington, DC 20012-2510
> > > USA
> > > voice and fax 202.726.5894
> > > <awabrams@starpower.net>
> > >
> > >
> > > ______________________________________________________________________
> > > This greenbuilding dialogue is sponsored by REPP/CREST, creator of
> > > Solstice http://www.crest.org, and BuildingGreen, Inc., publisher of
> > > Environmental Building News and GreenSpec http://www.BuildingGreen.com
> > > ______________________________________________________________________
> > >
> >
> >
> >______________________________________________________________________
> >This greenbuilding dialogue is sponsored by REPP/CREST, creator of
> >Solstice http://www.crest.org, and BuildingGreen, Inc., publisher of
> >Environmental Building News and GreenSpec http://www.BuildingGreen.com
> >______________________________________________________________________
>
>
> David Bergman
> David Bergman Architect/Fire & Water Lighting + Furniture
> bergman@cyberg.com    http://www.cyberg.com
> t 212 475 3106    f 212 677 7291
>
>
> ______________________________________________________________________
> This greenbuilding dialogue is sponsored by REPP/CREST, creator of
> Solstice http://www.crest.org, and BuildingGreen, Inc., publisher of
> Environmental Building News and GreenSpec http://www.BuildingGreen.com
> ______________________________________________________________________
>


______________________________________________________________________
This greenbuilding dialogue is sponsored by REPP/CREST, creator of
Solstice http://www.crest.org, and BuildingGreen, Inc., publisher of
Environmental Building News and GreenSpec http://www.BuildingGreen.com
______________________________________________________________________