Flues through pitched slate roof

[Tetrarch]

I'm building a small lean-to to accommodate an external fireplace for a woodburner and a pellet boiler. I therefore have two flues that I need to punch through the pitched slate roof.

Currently, these flues exit their respective appliances fairly flush to the house wall. They therefore need to angle out in order to clear the guttering.

Is it best practice to bend the pipe within the fabric of the lean-to and then to go straight up through the 30-deg roof or is there an argument for punching through the slate perpendicularly and then inserting the bend afterwards?

Regards

Tet

 

[noseall]

I'm building a small lean-to to accommodate an external fireplace for a woodburner and a pellet boiler. I therefore have two flues that I need to punch through the pitched slate roof.

Currently, these flues exit their respective appliances fairly flush to the house wall. They therefore need to angle out in order to clear the guttering.

Is it best practice to bend the pipe within the fabric of the lean-to and then to go straight up through the 30-deg roof or is there an argument for punching through the slate perpendicularly and then inserting the bend afterwards?

Regards

Tet

Bend early on where the flue gasses are at their hottest...?