Five months seems along time to get a permit for our rather modest undertaking, all things considered. It's not as if we are building a whole house or building a swimming pool
Part of the dilemma is that the City staff who work on residential scale projects have very little experience evaluating green roofs, and tend to "throw the book " of regulations at it. At various times I spoke with four different layers in the system, and while they are all very positive and helpful, only the manager seemed to truly understand what was going on.
They might have green roofs for condominiums well under control, but they do need more staff training on residential scale undertakings, if only to save time in the permitting process.
Part of the dilemma was that I did not understand the minute details needed on one key element, until very late in the process.
Key points going forward....
- Make sure your roof is designed for the load 2 - 3 kPa (40 - 60 psf) - depending on your planting aspirations - right from the get go. 254mm - 305mm joists at 406mm or 300mm centres. The smaller sized 150mm or 200mm timber is just not strong enough, especially at the wider spacing.
- Be realistic about your horticultural aspirations, as the the depth of your growing medium is the limiting weight component when wetted.
Sedums vs wild flowers and grasses vs a vegetable garden vs shrubs vs trees?
1,200 kg/m3 is a good place to start for a light weight growing medium at "field capacity".
- Green roofs is "dead load" and you also need to include the self load of the roof, along with the snow load.
- Wind uplift is a key concern at City Hall - they don't want your installation blowing away and nor do you. This was a very time consuming matter!
I could not find a strictly Canadian solution for the complete calculations.
You will need to use NBC 2010 (or better) for the raw wind pressure information - q(1/50) and composite pressure - gust coefficients, etc
It appears that the German uplift calculations, as documented in the engineering report prepared by Strodthoff & Behrens GmbH; “Assessment of positional security against wind uplift for a roof planting system that is permeable to wind”, report No. 1/21010/10.99 dated Nov. 25, 2009", are acceptable when an independent (engineering) consultant provides site specific results for your installation.
Examples of these calculations can be found in a number of web sites, including the XeroFlor sites : www.xeroflor.com and www.xeroflorcanada.ca
I am willing to pass on my Toronto contacts via off-line communication.
- Professional engineers who stamp the drawings for their own home are not immune from additional independent 3rd party analysis and reporting requirements. My drawings had three different stamps on parts of them, not counting the structural engineer from the original house. Professional engineers stamps cost money and take time!
Part of our dilemma is that a building permit issued on 01 October is not useful in the current 2014 growing season. The lead times for some of the required input "product" would put the installation into late November or even December.
So we have flagged it for May in 2015 and will be stepping forward vigourously at that time.
Words to the wise - If you want a (Toronto) Building Permit ready to go in May then get started in October the year before.
On ward and upward!
