Flat Roof Drainage...

[Mulberry View]

Our scheme has a single Car Port with a 10° monopitch roof which is linked to the house by a walkway with a flat-roof over.

 

This is the roof plan...

 

 

The Car Port is to have a gutter along the low edge, which will drop water onto the Link Walkway roof, which is essentially a flat roof. The water will fall towards the bottom corner as denoted on the plan.

 

From this drawing, I have assumed a kerb is installed at both edges, with the water dropping through a "Plug'ole" before being directed into the adjacent RWP.

 

Does anyone have any words of advice as to how this fall arrangement is organised with firrings? Or can you suggest a better way?

 

I did debate arranging the fall to simply run from right to left and into an integral gutter along the right-hand edge, so in essence the water from the roof above will drop directly into the integral gutter below and the water falling on the flat roof will fall also into the integral gutter.

 

Any thoughts/advice would be appreciated, as always.

[Spinny]

What is the roofing material and how will the underside be finished ?

[Mulberry View]

8 hours ago, Spinny said:

What is the roofing material and how will the underside be finished ?

 

Likely to be a single-ply membrane. I can see the fascias being Aluminium flashings of some sort. The underside needs to be a flat ceiling, though I'm not sure if it can be plastered as it is essentially outdoors...

[Spinny]

is there any case for extending the underground drain over to the carport ? 

Might you be washing the car under the carport ? Would you have use for a ground level drain gully to take ground water running away on any adjacent hardscaping ?

(just wondering about taking the water away from the main building rather than towards it)

 

PS Just looked at your 3d image - seems you do have a hard surface between carport and main building - this would normally run off away from the house - potentially to a ground drain ? Do you plan to have a tap (and electric light & power) to the car port ? Lighting under the walkway ? You could bury the services or take them across inside the walkway structure ? Garden/external lighting planned ?

Edited 8 hours ago by Spinny

[saveasteading]

14 hours ago, Mulberry View said:

Any thoughts/advice would be appreciated

Mine is that we should all do our bit to minimise water use and flooding. So have you plans for water butts?

Also, if your ground can take it, to have your paving drain naturally to ground.

The rain landed there for millions of years and we should try not to rush it away downstream.

[Mulberry View]

2 hours ago, Spinny said:

is there any case for extending the underground drain over to the carport ? 

Might you be washing the car under the carport ? Would you have use for a ground level drain gully to take ground water running away on any adjacent hardscaping ?

(just wondering about taking the water away from the main building rather than towards it)

 

PS Just looked at your 3d image - seems you do have a hard surface between carport and main building - this would normally run off away from the house - potentially to a ground drain ? Do you plan to have a tap (and electric light & power) to the car port ? Lighting under the walkway ? You could bury the services or take them across inside the walkway structure ? Garden/external lighting planned ?

 

The area between the Main House and Car Port will be permeable stone. There'll be the same stone leading up to the Car Port. The Car Port itself will be screeded to fall towards the entrance. The run up to the Car Port is uphill. I'm not planning to wash the car anywhere near the Car Port to be honest.

 

The area under the Link Roof will also likely be a permeable solution, probably a Thermowood decked walkway leading from the front door to the Car Port.

 

The Car Port and Link Roof are Posi joisted. There will be lighting and electric to the Car Port and Link, probably ceiling downlighters. Solar PV on the Car Port. I expect this will all be taken care of in the Posi structure.

[Mulberry View]

1 hour ago, saveasteading said:

Mine is that we should all do our bit to minimise water use and flooding. So have you plans for water butts?

Also, if your ground can take it, to have your paving drain naturally to ground.

The rain landed there for millions of years and we should try not to rush it away downstream.

 

We're planning to have a borehole.

 

Most of the ground around the place is permeable. We have a 60m driveway leading to the house, this is all 150mm Geocell, with Type 1x infill. This will eventually be topped with something like Cotswold Stone. The Cotswold Stone will carry on up to the building, to the Car Port and in the area between the Car Port and Main House.

 

We have an ENORMOUS soakaway. 92 crates. This will deal with the rainwater.

What more can we do?!

 

Now, back onto the flat roof?! 🤣

[Spinny]

Our builder had to get someone with the right cutting equipment to cut timber lengths into the right taper for the furrings. Best to cut two lengths from each rectalinear timber. 

What is needed depends on your structural 'joist' layout and desired slopes. If all furrings/slopes are orthogonal to the joists then different furring thicknesses only are needed without the tapers.

 

It is possible to get PIR slabs cut into multiway tapers to provide slopes, so you lay them on a flat surface and they create whatever contour you want on top. Of course you have no use for their insulation value outside.

 

Will you have a roofer doing the single ply ? You could consult with them. Some single ply manufacturers have specific makeups/specs to be followed to provide a guarantee.

Edited 5 hours ago by Spinny