Decking project advice

[sphannaby]

Hello again everyone, I'm starting to get back on the forum again now. Been a hectic time finishing the house off, I was forced to change job locations just as we were moving back into the house which caused all sorts of problems and we ended up living in disarray for a while!

House is pretty much done now with the exception of a bit commissioning left to do and some flooring contractors to have a date in court with.

 

With the onset of our 3 day summer rapidly approaching my better half has turned her attention to our garden.

 

Just to give you some background I have attached some basic sketches of what I currently have and what I plan to achieve.
In the 1st picture I have tried to represent the current state of our garden. The slopes are not exact but they give a fairly good idea of how it is.

The 2nd picture shows our plan of how we want it when finished. The decking area is 6.5m wide and 7.5 long.

I had planned on outsourcing all of the work but funds have dried up a little so I am looking to take it on myself now.

The right hand side of the garden as you look at it is definitely going to be levelled off for turf to go on. Plan was to have a retaining wall at the top end and to right hand side as required, this will be built by my father in law who is a brickie.
One of the issues causing me a headache is the land which the decking will go on. When we had people round to quote they said they would simple take out of the top section of the decking base area and put in in the bottom to level it out and this would mean there would be no waste from that section. I was happy enough with that but my father in law informed me that this would then create a different height step between the levelled turf area and this new decking base area. He stated this would also need to be retained somehow. When I asked the lads who quoted the job they stated pieces of 3' x 2' would be used to retain this. My father in law reckons that wouldn't be good enough and a proper retaining wall would be needed.
So my next thought was to take the decking base area down level to the same level as the turfed area and build the decking up from there. This would require another retain wall but that would be around the perimeter of the area rather than hidden underneath the decking. I feel this would look neater and also allow for greater flexibility in later years should we ever decide to get rid of the decking.

My main question is if I level the decking base area down the same as the rest of the garden this will give me a height difference of 500mm from base to my desired finished deck height. Is this a suitable sort of height to be able to build up to using a bearer and joist decking frame?

Once I know that I can get my head round things a little better. 

I have done a bit research but had a few other questions hoping others can help with:

1 = Am I correct in thinking I should have bearers down first and these should be attached to steel supports which are concreted into the sub base? If so does anyone have any recommendations for supports to use?
2 = How would I go about calculating what size bearers and joists to use?
3 = I read that decking should have a 40:1 incline ratio to prevent water pooling. Am I correct in thinking this should be achieved by putting the incline direct at the bearers rather than packing the deck boards?
4 = Because the length is 7.5m I guess I will struggle to get single length of deck boards. Would I be better cutting boards to 3.75 so I have a uniform joint line down the middle or is it better to stagger the joints for more stability (for example as you would with laminate flooring)?
5 = With regards to the full length steps the Mrs has stated she would like wide steps, say 2 or 3 full boards (I have done my sketch based on 2 boards). From what I have been able to find on the internet I can't seem to find any pre-made stringers that would accommodate this. Am i just looking in the wrong places or are these generally no available for wider steps (total make up height of steps will be 500mm)?

 

Any pointers would be greatly appreciated.

 

Cheers

 

 

 

Edited April 23, 2017 by sphannaby

[Tennentslager]

1. Why not use plastic, last forever.

http://www.recycledplasticbuildingmaterials.co.uk/plastic-fencing/recycled-mixed-plastic-square-post-with-point-90mm-x-90mm.html

If the ground if firm bash them in with a sledgehammer

If not. Use postcrete.

2. 90x90 posts staggered on each joist 1200 apart. 5*2 treated joists @ 600 centres.

3. Yes, no need for packers if you trim the underbuild to suit?

4. Up to you but I'd go for the latter.

5. If your decking is 145/150 wide, that's a 450 step. Time to make your own stringers I suspect.

Hope this helps.