Why strengthening is required ?

Allen,
Mate, got to watch out for the site works. There are a couple of options:
1. Speak to your consultant, they should be able to let you know what to expect as far as costs go.
2. If the consultant has no clue, ask a neighbour in the area that you are building what the soil type was and how much they paid for site costs. They may be reluctant to tell you how much but you should get an approximate. If it's a new sub division, ask one of the builders that are currently building there.
Worst thing you can do is go in thinking that it will be 5 and it turns out to be 15.
Regarding the strengthening item. Make a phone call to any structural/civil engineer and they should be able to provide you with some information. Your slab type (waffle/raft slab) will have an affect on what you can place where.
Hope this helps.

Our first project home was with Allcastle and I believe this phrase is referring to the strengthing of the upper level floor, not the slab.
It's a standard clause to cover their behinds in case you decide to put extremely heavy objects on the upper level.

As a side note we were very VERY happy with the home that Allcastle built for us and their level of customer service was excellent throughout the entire building process.

It's a shame Allcastle don't build split level homes. If they did we would be building with them again.

We built our Allcastle home in 1999. 2 storey, 4 bedroom, triple garage.

Site supervisor was easy to get in contact with. He always returned our calls the same day we called. And we called a lot. Nothing seemed too much trouble.

During the build we noticed some small errors. First they delivered the wrong coloured gutters to what we specified. But we let them know before it was installed so that was a small crisis averted.

During the build we asked for a couple of variations such as installing a cavity sliding door to the loungeroom and a few extra downlight. That was all taken care of without any trouble.

They missed installing a couple of sensors on a couple of the windows for the alarm.. but as soon as we let them know they fixed it up.

Build quality was great as far as we could tell. My wife and I aren't experts but we found no serious problem during the final inspection walkthrough. A touch up on a few painted areas was all that we asked for and it was attended to without a problem.

We lived in the house for 7 years. No cracked plaster. No cornices coming away from the walls. No cracked tiles. No leaks in the wet areas. No cracks bricks. Everything was fine. Passed the building inspection no problem when we sold it.

I'd have no hesitation in recommending Allcastle. Of course with all builds you need to keep an eye on the progress to make sure things are done to your satisfaction. You will always find problems. But any we did find Allcastle attended to without any hassles.

That reference will normally be in regards to a timber subfloor construction where bearer & joist spans are calculaled to carry 'normal' floor live,dead & point loads.
Extra loads such as for a water bed or 10 ton pianos require extra strengthening of the subfloor as in extra joists or a stump directly under the load point etc. It is not unusual.