Roll Top Chimney Pot

The installer is reminded that The Building Regulations: Approved Document J will apply to the fitting of a flue terminal facility in respect of height and position.

A chimney pot should always be used to obtain a satisfactory chimney performance. The chimney should not be terminated with just a mortar flaunching.

Inspect the chimney pot, confirm it is undamaged and ensure it is suitable for use with the flue system and the type of fire installed.

Inspect the chimney stack for cracks and repair any defective mortar pointing. Check that the flue lining is sound and totally clear of debris. Any mortar ingress into the flue liner should be wiped clean to ensure smooth passage for the flue gases and for sweeping.

A damp proof course should be installed below the top layer of brickwork. The space between the outside of the flue liner and the chimney stack should be filled with insulating material such as weak lime mortar or lightweight vermiculite type insulating cement. Ensure the top of the chimney stack is flat.

When lifting large chimney pots onto a roof, the chimney pot should be fitted with suitable slings – correctly positioned. The chimney pot should be carefully hoisted avoiding damage to the building and ensuring the safety of the installer. The chimney pot should be embedded into the top of the chimney stack by 125mm or one quarter of the height of the chimney pot, whichever is the greater.

Mix the mortar using a sand/cement ratio of 3:1. Apply a layer of mortar in the gap between the chimney stack and the flue liner and embed the chimney pot over the flue liner and press down onto the mortar. Ensure the chimney pot is vertical and securely placed.

Complete any outstanding brickwork (such as corbelling) around the base and then apply the mortar flaunching. The mortar should fill the void between the chimney pot and the chimney stack. The mortar flaunching should be smooth and tapered out at an angle between
25˚(minimum) and 45˚ to the edge of the brickwork to allow rain to run away.

In warm dry weather the surface of the mortar flaunching should be dampened regularly to prevent it drying out too quickly and cracking.

Ensure all gaps are filled in the mortar flaunching and brickwork to prevent the ingress of water and to avoid losing mortar bonding.

Use a smoke test to check for leakage and to ensure that the chimney pot is working correctly. Close the fitted appliance and warm the chimney flue with a blowlamp or similar heating device for approximately ten minutes. Put smoke pellets in the appliance firebox (or bottom of the chimney or the appliance recess) and light. Close the appliance when smoke has formed and allow the smoke to make its way up the chimney. Check for leakage throughout the length of the chimney.

After the installation, the flue and chimney should be warmed through gradually to prevent cracking and the drying out of mortar between the flue and the chimney pot. This must be done before initial use (on first firing) or after long periods without use.