Surface/rainwater drainage design for extension

[Alex3012]

Existing Drainage.docxProposed Elevations.pdfProposed Drainage.docx

Hi All,

 

I was hoping that you might be able to point me in the right direction please!

 

Mid planning for a 5m rear extension to my bungalow. I have designed the extension myself and submitted planning and now looking at getting started and planning for building regs. I'm concerned about the rainwater/surface drainage and have prepared a couple of ideas in the existing/proposed drainage plans and elevations attached and was hoping for some advice before submitted to my BCO. The extension is 5m to the rear making the total roof size 14.55m long x 8.15m wide. The garage is 8.25m x 2.75m. I have calculated the total area to be drained at approx. 197m2 making for a 3m3 soakaway if it was just one (but I think this is far too big for 1 soakway?)

 

A couple of questions if I can please:

• Is it normal to drain one side of the roof to the rear and the other to the front? I couldnt see anything online. 
• Are my roof size/volume calcs correct?
• Can I drain all to the rear? Wouldn't this cause a large influx of water to the rear of the house over the 14.55m span of guttering?
• If all done to the rear from reading online a 3m3 soakaway is just too big for one soakaway so would need 2 one at front and one at rear?
• Does anyone have any other ideas please, I'd really like to not have to dig up the front garden aswell if possible!

 

Many thanks in advance

Alex