Green roofs

[skdadl]

I see that Tommy Shanks is around (or was), and others will know some things about this, so I ask:

Could just about any building/house have a green roof? as in some turf and some ground covers at least growing up there? Or does a building have to be designed/reconstructed to allow a little gardening up top?

I suppose most houses don't have access from inside, which is a problem.

[alisea]

Halifax's Ecology Action Centre bought a new home in the summer of 2005; we moved in after months of renovation in the spring of 2006.

One of the things that almost everyone wanted, right of the top of their heads, was a green roof.

Sigh.

It turned out that the structural load of a green roof is much heavier than that of a regular flat roof, and the building needs either to be designed to carry it in the first place, or massively re-engineered with new supports.

If you're building from scratch, green roofs are great, but you can't just dump a load of earth over your house and hope :-(

Caveat re the above links to the new home pages: the photos are large, and take a long time to load. The website's being redesigned.

[deBeauxOs]

Pitched roofs may be tricky, I believe that flat roofs work best.  Here's a link to a green roof retrofit.  

With only small adjustments to the already sturdy structural system, the one-story roof over a former train shed was covered with an extensive green roof.

In this context, "extensive" refers to a low-maintenance groundcover in shallow soil, which collectively weighs little more than a conventional roofing system. (This contrasts with "intensive" roofs with deeper soil and diverse plantings, which require higher maintenance and more substantial structural support.)

A waterproofing, root-resistant, single-ply roofing system was applied, then covered with 4-inches (10-centimeters) of soil. This soil is 75 percent inert — mixed with expanded slate — to keep the depth of the soil from decreasing over time.

Plants selected for the roof are indigenous to alpine environments. Even though the building is near sea level, these plants were chosen because they are hardy even under extremes of temperature, wind, and drought. They grow rapidly to form a dense vegetation mat with shallow roots, thriving even in harsh soil conditions.
...
The alpine plants also have fibrous roots to protect roofing membranes, and they impose no special irrigation or nutritional requirements. Snodgrass notes the importance of architects collaborating with local horticulturists to determine an optimal plant list for each project.

Green roofs can reduce the surface temperature of a roofing membrane significantly — by up to 40 degrees Fahrenheit (22 degrees Centigrade) on hot sunny days. This buffering can double the life expectancy of the membrane, while reducing the "urban heat island" effect.

The results when googling those terms.

[alisea]

Cool! I suspect that some commercial buildings may be more easily retrofitted -- our small office building was built originally as a house. We had to reinforce the structure just to get an office occupancy permit for the second floor, which had been a rooming house (an electrical contractor had been on the ground floor). Apparently offices are heavier than residences :-)

[skdadl]

I was afraid that much planting at all might be too much for an ordinary house, although I was thinking that a very thin layer of soil could take some ground covers.

After all, people do get up there and walk about and work, yes?

At least ten, maybe fifteen years ago, John Bentley Mays, who is an art/architecture critic for the G&M, wrote about his home in, admittedly, a restored flat-top warehouse not all that far away from me -- I think it's two storeys inside but I could be wrong. Anyway, he put a deck up top, with planting boxes all 'round the sides (and maybe even some containerized shrubs and such). I remember his discussion of how heavy all that was, but of course I don't remember how he solved the problems.

Actually, when I think of it, there are a couple of houses across the lane from me that have decks on their roofs. How did they do that? Those must be heavy.

[alisea]

I suppose it depends on how you define 'green roof'. I tend to think of a full-fledged sod roof, like Tommy Shanks was talking about wrt the War Museum on LeBreton Flats. A deck with some planters would not be nearly as heavy. A lot of the weight from a full green roof comes from the earth when it's saturated after a rain -- and you'd have a lot more run-off if it's simply a wooden deck.

I think the main lesson is: a structural engineer can be Your Very Good Friend when retro-fitting  :lol:

[skdadl]

Humph. They probably expect to get paid, though. Just like women and artists and editors.   :wink:

[alisea]

Humph. They probably expect to get paid, though. Just like women and artists and editors.   :wink:

Yeah, all these bloody people with training, skills, and experience, who don't understand They Should Just Give It Away!

(yeah, I'm grouchy. Got asked to do a strategic planning weekend workshop today For Free, as a) I work for an NGO, so you'll understand about limited budgets and b) you know what we're doing is Really Important! Arrrrrrrr...)

[Herr Magoo]

Ryerson's new Engineering building, on Church between Gould and Dundas, has a green roof.  It's pretty cool.

[skdadl]

Is there a viewing platform anywhere, Herr M?

[Herr Magoo]

Not specifically.  Just anywhere higher.  :)

[Tommy Shanks]

Could just about any building/house have a green roof?

Sure, Skdadl, just about.

Of course depending on the type and size of the roof area you may have to have some reinforcing of its structural system and deck. There are  some types of green roofs that consist of modular, low-rise pans that contain grasses and such, or pre-cultivated blankets that do the same. These are much lighter then a purpose-built green roofs and tend to be limited (because of their thin layer of soil) in what can be grown. You should always check with someone and determine if your roof can withstand the potential dead-load of saturated soil layer, as opposed to the live-load of people being up on a roof deck occasionally.

The more common type of green roof built now is this (I'll use images because, hey, I like pictures):



I've seen roofs of this type that have a growing-media bed of up to 8 or 10 inches, which allows you to plant a much wider variety of plants then just grasses and such. However, these can get up to 200 lbs per square foot of load, much heavier then what is normally expected for a roof. As well, using a roof of this type requires (usually) a concrete deck, an electronic leak monitoring system, heavy duty water and moisture barriers, etc. It is by no means a common application.

But if you do want to put one on your house (or even a portion of the roof you can.

Even sloped roofs, like this one in Iceland which (I think) uses a type of cultivated blanket that has been used there historically.

[arborman]

Our apartment building just replaced our roof, and we looked into installing a  green roof in the process.  Sadly, it would involve far too much cost to retrofit the structure - and we just could not afford it.

However, we are currently negotiating with a solar power startup company to be a 'model' condo for solar electricity and heating.  Yay!

[skdadl]

This is quite neat - about green roofs in NYC, starting out in Brooklyn.

[Holly Stick]

It sounds good.