Kitchen Extractor Vent. Cold draught

[roadster]

My extractor hood exhausts directly out onto the kitchen extension roof. It didn't work for years then finding myself on the roof clearing moss I pulled the "mushroom" off the pipe and realised that it was restricting the air flow. Inside the mushroom was plastic mesh, I assume to stop anything crawling into the pipe. I cut some of it out and hey presto! it works......

Now I get a cold draught through the cooker hood.

Is there something to terminate on the roof that 1. stops the backflow of air, 2. opens to let the exhaust air out, 3.stops rain getting in, 4.stops anything crawling in.

There seems to be loads of things that are fitted vertically but I couldn't see anything for a pitched roof?

 

[stem]

Any chance of a photo? I can't envisage what you are describing. Doesn't the pipe exit vertically via the pitched roof?

The mushroom is there to stop wind and rain entering the pipe, but should be open at the sides to let the air out. You are right about the mesh and the insects, but mesh doesn't stop airflow either. Was the mesh/mushroom blocked by something? What symptoms make you say that the extractor hood hasn't worked for years? Has it ever worked prior to your modification?

 

[roadster]

Any chance of a photo? I can't envisage what you are describing. Doesn't the pipe exit vertically via the pitched roof?

The mushroom is there to stop wind and rain entering the pipe, but should be open at the sides to let the air out. You are right about the mesh and the insects, but mesh doesn't stop airflow either. Was the mesh/mushroom blocked by something? What symptoms make you say that the extractor hood hasn't worked for years? Has it ever worked prior to your modification?

The pipe exits so the underside of the mushroom is parallel to the roof tile and, crucially, is only about 1/8 inch clear. The extractor has never had a decent airflow until now, e.g. if the frypan was overheated it couldn't clear the fug. It can now. If I ease the mushroom vent thingy, say, 1/2 inch clear of the roof the force of air blows it off completely. The mesh wasn't blocked, just too fine mesh.
I think it is the wrong thing to use. There are others on the roof just to ventilate the roofspace I guess.
All the vent kits I have seen (B+Q etc.) are for wall mounting, not roof mounting and have a gravity louve action.

 

[stem]

Sounds like the vent was too close to the roof tiles to let the air escape. How about a "chinese hat" type? click here for an example. It has a coarse mesh, positioned so that a side wind blows straight through and out the other side, and the "chinese hat" stops direct wind and rain entering.

 

[roadster]

Sounds like the vent was too close to the roof tiles to let the air escape. How about a "chinese hat" type? click here for an example. It has a coarse mesh, positioned so that a side wind blows straight through and out the other side, and the "chinese hat" stops direct wind and rain entering.

Yes, that looks good. Sometimes its just a case of knowing the right terminology to put into google...............