Being a residential designer, I feel this might be right up my alley.
All blocks, sloping, flat, large, small, have good and bad points.
How do sloping blocks affect the cost of building?
Sloping blocks affect the cost of building in several ways, depending on the style of home you are building, how sloping, what the ground condition is, etc,. For example, a severe slope calls for a pole home. This means little ground work has to be done, apart from scraping, possibly levelling at a point (say if you are to walk from front/ rear door directly to the ground) and all the footings for the poles.
For a 'slight' sloping block (it is all relative), say 2 metre crossfall, if you decided to go for slab on ground you will be up for say $60k+ worth of ground work, before retaining walls, and before beginning building the house.
Typically sloping blocks call for homes built off the ground, with timber subfloors, due to the reduction in groundwork required.
Also consider, how do you want the yard to work once the house is built? If you cut & fill the building pad, you will have banking areas reducing the useable yard. Not a problem if you are on several acres, but say half an acre this can be painful. You may consider retaining or even terracing the yard, at great additional expence.
Is it worth paying a considerable amount more to get a level block?
MMM depending on your circumstances, how much more level, and ultimately what you want out of it. It may cost you more to build a pole home several metres off the ground, but an equivalent flat block may cost even more. Really depends on prices in the area you are considering.
I like sloping blocks, because it gives so much scope for what you can do. I have seen houses on sloping blocks that have had rooms and decks built off them over years, that almost look like an adults playground when done- a bridge to the pool deck, which steps up to the billiard deck, which leads to the theatre deck......
How does the quality of the land affect the type of house that can be built?
Ground quality can affect the type of house that can be built, but in most cases there are solutions to most situations. For example, heavlily clayed areas (brisbane are more consistantly seeing 'E' sites- ie. extremely reactive) means additional rio and concrete in a slab on ground, and possibly even a different type of slab. Granite under the surface may push the cost of building up considerably, as it has to be broken to create footings. Again, a slab re-design or even going to a pole home may help this.
Is it going to be more hassle/cost than it is worth to build in these conditions?
Ultimately depends on prices in your area, and what you want. The best thing to do is put an offer on a block subject to all your usual conditions, and soil test/ site inspection (organised by yourself). This will allow you to approach a builder, engineer or designer who can advise of likely problems on site. That way you get a reasonably accurate, ballpark figure which you can start working with. Then you know, if the builder says it will cost an extra $50k to break granite a hundred ml under the surface, that flat block you looked at yesterday for an extra $40k may be worth the extra expence.
"My one peice of advice when building on a slope, don't put your foundations down on top of a cut & fill job... Cut a wedge out of the slope, but always build supports into the existing ground rather than use fill to bring it up level.."
This comment is not exactly true. Would be nice if you could always just cut and not fill, but it is simply not practical, or cost effective. Building on fill is ok, providing the engineer has designed accurately for it. The fill must be machine compacted in 200mm layers. Then piering must be drilled down to natural ground. This, inturn with a stiff slab, will ensure minimal or no movement.
What I will say is, if you can afford it, and by all means it is not imperative, but if you can afford to, have your footings designed one grade higher than required. That was always my plan, if I ever built.
Any more questions, or email site details/ soil test/ contours etc, and I will try to help out more, if I can.
Cheers
