Ask Me Help Desk - Increasing chimney / flue height

Increasing chimney / flue height

My house has a gable roof. The chimney is not centered at the roof apex, but comes through the roof slightly downslope (maybe 12 - 18 inches or so) from the highest part of the roof. The chimney cap extends through the roof and is basically equal in height to the highest point of the roof, and the flue tile extends beyond the chimney cap about 6 inches, meaing the very top of the chimney is only about 6 inches above the roof which is too close. Also, there is no chimney cap. All of this was pointed out to me by a fireplace inspector

I am thinking of just adding a 2 foot clay flue tile equal in size to the current flue tile (attaching it with mortar) to increase the chimney height to a safe level, and also adding a cap onto the new flue tile. I do not plan to wrap the flue extension in stone like the rest of the chimney.

Will this work? Anything I need to be aware of such as special tye of mortatr, etc.

It's not going to attach at all. Your going to have to wrap the extension in stone or brick.

Quote:

Originally Posted by KeepItSimpleStupid

It's not going to attach at all. Your going to have to wrap the extension in stone or brick.

Do you think it would work to place a larger diameter flue tile over the existing flue tile (sort of like a sleeve) which would give a 6 inch overlap and let the new flue tile rest on the chimney cap?

I have no idea. I do know it will look ugly.

Get a flue liner that exactly fits the existing one.

A picture would better help for us to describe our own personal ways to address this repair.

Why is it you want to raise the chimney height?

Back to you,

KBC

Quote:

Originally Posted by KBC

Get a flue liner that exactly fits the existing one.

A picture would better help for us to describe our own personal ways to address this repair.

Why is it you want to raise the chimney height?

Back to you,

KBC

The chimney is not quite centered at the highest point or apex of the gable roof. It is 1 to 2 feet downslope from the roof's highpont. Therefore, the top of the chimney is below the roof highpoint. Need to raise the chimney fro safety reason (sparks landing on roof, etc.) and also to make it draw bettre by being at least equal to or above the roof highpoint.

Sorry I don't know how to do pictures. I have another possible idea for attaching same size flue liner. Instead of mortar which gives zero lateral support to the butted flue liner, what about some type of construction adhesive, maybe something especially made for tile or masonry? The joint would be abouut 15 to 18 feet above the firebox so heat shouldn't be too much of a problem. In addition, the joint would be outside of the chimney and expsosed to the cold air wichh would help keep temperatures down. In addition, I could use metal dowels with one drilled into each of the four lengths of the rectangular flue liner to help provide lateral support. Potential issue with that is I'm concerned about drilling into the old flue liner coming out of the chimney crown as it's old and it may be brittle, even with a very small masonry bit. The new flue liner extension being added wouldn't be an issue as far as drilling I wouldn't think.

WHat are your thoughts about this idea?

I wouldn't mess with the old liner.

To raise the liner for draw is understandable,but is it really necessary?

If you Haven't had problems with this chimney,don't do anything with it,the inspector is just covering his butt telling you things like this.addressing a possible,not a reality.

What is the existing chimney made of? Stone you said?

It will be hard to match the stonework and mortar color,but if this is totally a necessity,you'll have to accept this as a given.

I would add a new flue liner,exact size as the original,then face the liner with the stone façade,to approx. 1-2 inches from the top,then install a chimney hood with screening.

KBC

Quote:

Originally Posted by KBC

I wouldn't mess with the old liner.

To raise the liner for draw is understandable,but is it really necessary?

If you Haven't had problems with this chimney,don't do anything with it,the inspector is just covering his butt telling you things like this.addressing a possible,not a reality.

What is the existing chimney made of?,Stone you said?

It will be hard to match the stonework and mortar color,but if this is totally a necessity,you'll have to accept this as a given.

I would add a new flue liner,exact size as the original,then face the liner with the stone facade,to approx. 1-2 inches from the top,then install a chimney hood with screening.

KBC

Thanks so much for the responses. One last question related to attaching the 2 foot new liner extension piece. WhHat do you think about using construction adhesive (mortar / tile adhesive) rather than just runnig a bead of mortar at the joint where the two liner pieces connect? It seems like that would provide much more lateral support at the joint and keep wind from possibly blowing the liner extension off the chimney. I agree about not playng around with the old flue liner (50 years old) sticking up through the chimney crown.

Are you not going to put a façade to the new liner? Only add the new clay pipe?

You need to find a better way to keep the liner adhered to the existing chimney,mortar or construction adhesives won't do much.

I can't tell you what adhesives will do inside a functional chimney,or that they will or won't fail,I don't think they make an adhesive that won't be not only flame proof,much less to expand and contract with the changes that area will go through.

The height of the flue pipe must be 2 feet higher than the peak of the house 10 feet away// and 2 foot higher than any window that is also less than 10 feet away// no short cuts on this one// the masonry surrounding the added 2 feet of flue must also be built up to house the new one should cost about 650 dollars for labor and materials hope this helps chip