The toronto market is high in demand but low in supply right now.

Current ROI is 8% ((12 x 9 x $600) - $21000)/$560,000Potential ROI is 14% ((12 x14 x $600) - $21000)/$560,000There are a few variables I haven't taken to account like what rate of interest you will be paying but where are you going to find such high returns.You can play with reducing the asking price to see if it would make much of a difference but I would suggest offering something like $530K and accept what ever she counters at if you really want it.The only thing I can say is that this may turn out labour intensive, so factor in an addition 10% on the rental ($60 per month per property) that you have to pay a property manager.

It's often possible to route supply lines through the house and by-pass any lines under the concrete.

So many variables with this one.

The problem is likely inadequate supply plumbing or some other restriction. 

Will it have an affect of over supply for sfr's? 

We personally stretch ourself thin to do deal but I have a financial background with high incomes and no incomes and other variable.

You can see much more general "trends" that might give you some guidance, but the reality is that there are huge variables that can shift a trend graph fairly quickly. 

I've heard other investors talk about 6%, either variable or only fixed for 5 year then adjustable.I'm willing to pay the 1/2 % higher to get the 80% LTV and fixed for either 15 or 30 years with no balloon.

If it is an older house, those were probably gas supply pipes for gas lights that would have been on the walls.