So when I said the slope of the demand curve will change, what I...

So when I said the slope of the demand curve will change, what I meant is that it will be steeper, ceteris paribus.

Actually, on reflection, the curve might not be steeper, as such, but what it will do I expect is undertake an upward structural shift. i.e., higher underlying demand per dwelling unit over time.

Actually, on yet further reflection, any structurally higher underlying demand won't manifest itself immediately, but will occur in a phased manner over time, so the curve will not undergo a one-off structural shift without changing slope, but will, in fact steepen.

Or maybe not? I think I'm confusing myself now; I wish I had stayed awake during that particular economics lecture...

At any rate, whatever the demand curve ends up doing, I think it will be a positive thing for an industry-leading company like Dulux.

From my vague memory of microeconomics (I was awake, but not present), an underlying rise in demand necessitates a shift of the demand curve to the right. Perhaps what you may be indicating is that any such potential shift of the demand curve (due to a fundamental change in the use of building materials) may occur over a drawn out period of time??
One other thing to keep in mind with an eye to the future, are raw material prices - particularly oil. Who knows where the crude oil price will go (it appears low!), I believe it is an important input cost in the paints and coatings business.