Over roofing question
I have an ice damming issue to resolve – and a roof that needs to be re-done. I reside an hour or two Northwest of Toronto, ON Canada. Zone 6 I believe.
My original plan was to convert my story and a half attic to a hot roof system with a ventilated standing seam steel roof on top (the venting is necessary due to our snow loads – the steel would have an airspace below but the roof still a hot roof I believe). It is currently a vented unconditioned attic so my plan was to strip the roof (or not) – backfill the current ventilation space with dense pack cellulose via the drill and fill method – then over roof with 5″ of polyisio (approx r-30), tape/foam seams – strap, sheath, membrane then steel. Then on the inside batt the roofline and gable ends leaving more than 50% of the insulation on the exterior for the sake of the dew point. I would also remove the current attic floor insulation.
The above method – to me is the gold standard. It does however require a bank account lined with gold – which I do not have. I can appreciate the absolute BEST way to do something – but at the end of the day – it’s a roof, and I’d rather not go into a significant amount of debt for it if I can avoid it.
I have had a couple reputable steel roof contractors recommend simply leaving my attic the way it is then adding 2″ of polyiso (R-10-12.5) on top of the current roof – then strap and roof after taping or foaming the seams of the iso. The polyiso in this method’s only job would be to eliminate the current leakage which is causing the ice dam problem.
I’m a bit skeptical of this method – but these guys have been doing this for 25 and 36 years and say it quite simply solves the ice dam issue – and does so at a MUCH more reasonable cost. I understand the latter method does absolutely nothing for the R value of my attic as it’s outside of the current vent space. It’s also not a ‘green’ solution per se, but if it solves my ice damming issue and is within budget – why should I not do it?
I have this sneaking suspicion I am missing something – that’s where you come in.
Thanks so much for your help.
The points of air leakage seem to be coming from spots in the sloped portion of my story and a half. A soffit vented bathroom fan – two stink pipes – and a chimney – all appear to have not been air sealed properly. I can’t access them from the attic. I suppose I could pull the sheathing in those areas and air seal from the outside and be on my way – but I still have another source to worry about…
Edited to add information
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