Leaking shed flue plate

I moved into this shed about three years ago, it has a little wood burner in it with a flue that runs through the roof. The problem seems to be that on top of the roof, the flue passes through a 18" square ali plate that is nailed down on top of the felt, While I have resealed underneath the plate every year with silicone, when the fire is used , the plate gets hot and expands , then buckles , letting water in underneath it.

Any one else sorted this problem? As far as i can see there are three ways to go, one is to build up a ridge of felt underneath the plate, layers of felt and black stuff, so water running over the roof , runs around the hole in it.

The second would be to bend the plate so its still square and flat round the edges, but the centre is raised , say by 1 ",the intention would be if the plate expands it will raise the centre more and not wrinkle the edges. But I have not got a clue how to bend it, other then the edges need clamping to keep them flat!.

The third way would be to open up the fixing holes and use oversize washers on top, so the plate can move about. I wonder if one can maintain a decent water seal though?

The fire is not a great success as it needs constantly feeding and gets through a small sack of soft wood offcuts a day, I am really tempted to abandon it!

Frank

Does the stove have a grate ? I f so bin it, wood is best burnt on a bed of wood ash, it will burn slower. I s the roof flat ? I have 2 stoves in similar positions except the plates are steel so don't distort. The best way is to fit a kind of mini roof over the existing one and big enough to let water clear the area. Mine are welded steel to a steel pipe, but can be done by clamping round the pipe. Have not explained this very well but you get the idea. Mine have been in use for 20+ years and are still ok. Ask if you need more info'.

Is this a flat roof or a pitched one?

Is it a single wall or twin wall flue?

If pitched then it is normal to have the top edge under the felt not over it.

If flat then you may need to raise the flashing while making a raised section, dam, around the flue then seal to the roof with Butyl rubber sealant tape.

Butyl rubber sealant tape may be a better option over silicone as it does not set as such and remains flexible (more so than silicone) and sticky, when I did the roof on my property there are 4 pipes passing through the membrane all sealed with this tape and no leaks to date, mind you water has to get pass the roof tiles first, that said we did have heavy rain before the tiles went on and no leaks.

Bob

Hi There,

A Decktite flashing would be the best option as it is rated for high temperature use, and can be fastened to both the flue and the roof - it uses a flexible silicone rubber boot which takes up expansion and could be screwed tight down onto the roof.

**LINK**

Might be worth a try..

Neil

Hello Frank,

The usual arrangement for flue penetrations of this sort is to have an upstand around the flue on the lower plate and then a stepped collar lowered down and clamped to the flue to form a labyrinth seal over the upstand.

In your case an upstand can be a welded on ring and the collars are available from flue suppliers, both angled and flat to suit pitched or flat roof structures.

If your flue is single wall as I supect it is from your description, then stove efficiency will be very poor and have a high appetite just to try and keep it hot. A twin wall flue will make all the difference to working and solve the expansion trouble you are experiencing at the same time.

Regards Brian

Edited By Brian Wood on 02/03/2015 10:59:49

Frank,

I forgot to add that properly seasoned and dried hardwood is the best fuel, softwood burns much too quickly and can tar up the flue to boot.

Brian

Hi

I use the same as Neil proposed on my 4" flue (other sizes are available) and find it works a treat. I also fitted a damper plate in the flue just above the combustion chamber of my woodburner to control the draft and keep the temp down so that I can use wood kindling under smokeless fuel brickettes to maintain a longer burn.

Russ

I'll second the Decktite as Neil suggests. We used these on a lot of jobs. We always backed things up with a storm collar above the Decktite; to keep the worst of the weather away from the joint where the Decktite meets the flue.

Steve

JS told me the story of how his flue plate buckled, so he made a thicker one, that broke the wall instead!

He did say how he solved it in the end, I suspect it was a bit like Steve's solution...

Neil

Thank you all for you replies, that Decktite system looks as though it might just work. But the hole in the shed roof is a lot larger then the flue, so I will have to wait for the good weather and take it all apart to measure it. If its a 3" flue in a 6" hole then its too marginal, the hole could be even larger. I have "repaired" it with plastic bags and bricks, looks very rustic!

Its a cheapo single wall flue, and a felted timber sloped about 18" in 6', Um, 1 in 4?

I have only used the fire about 10 times this winter, I prefer electric because I don't have the hour + warm up time. The thought of storing more wood does not appeal to me as I already have a pile of wood that a friend gave me some 4 years ago for the house wood burner. We ceremoniously light the wood burner every Christmas day. I prefer the convenience of the gas central heating.

One upgrade I have done is to surround the flue with a very wide open duct with a very powerful fan at the top, trying to blow the heat away from the stove corner down the length of the shed. I was finding that the stove was melting plastic 9" away from it , yet I was still freezing at the other end of the shed.

Frank

Just be careful of fire risk. Tar build up in the chimney can burn and a very impresive blowlamp effect can soon get the pipe red-hot. Been there.