Semi-rigid radial ducting - routing around obstacles, RSJs, gradients and flow rates

[oranjeboom]

Weekend spent in the loft getting things prepped for plumbing and building studwalls (for creating an atrium hallway downstairs) and I have been trying to plan routes for my MHVR ducting. Most of the ducting will serve a bungalow with ducting to go via loft, but will also have to route it into a 2 storey extension that has been built onto the other side of a gable wall, i.e:

 

 

 

Most likely will end up going for the semi-rigid type stuff. My only real concern is that there are likely to be a few obstacles in the way that will have to be navigated around which means the ducting will have to go up by 500mm and then come down again by the same amount, a bit like so:

 

 Sorry about my drawing skills!

 

This up and over is not really avoidable and obviously that's the whole point in this type of ducting to make installs easier and navigate walls, machinery and limited space. My main concern is with condensation getting stuck and collecting at any of the bends. I assume if it is sufficient lagged with insulation, I should not have any issues with condensation?

 

I will try and create less of a gradient to improve the flow rate:

drawings skills still not getting any better!

 

 

 

There are many factors that will affect flow rates and the more bends that get introduced the worse things get, so in terms of positioning the ducting, should I just try and make each bend/gradient as smooth as possible?

 

There's only really one tight area where I will have to either navigate around an RSJ by either going under (blue route) or punching holes through a cavity and  SIP wall (red option - least favoured):

 

 

Some of the quotes I have received include a preliminary routing plan but Of course they are not aware of actual obstacles in the loft - do they fine tune the plans later on once they've received my ££££ or is it a case of me just deciding a 'best fit' once I get to install it?

 

I've had enough of cowboys so this is something I want to do properly myself! Hoping I can get as neat as some of these install pics!

 

 

 

Lastly, are there any issues if I run some of the ducting along the purlins of the roof? Obviously will need to find a way to insulate the ducting sufficiently, but would like to keep the ducting off the floor of the attic if possible to keep future cowboys from walking/leaning/sitting on them!

 

Thanks in advance! I'll have some other newbie questions after I've ready and deciphered some of the quotes received so far! 

 

OB