View Full Version : Chimney extension

David Banks
05-15-2008, 01:36 PM
House appears to have originally been a ranch and then a second floor added.
This chimney extension is not flush with original brick. It is set in and then started sky wards. I can see some cement at the intersection of old and new. They either built it on the old crown or added the concrete to get water away from this shelf.
Anyone know if this is correct construction? Appears to be slight lean in upper chimney. Inspection is tomorrow and I can get a better look then.
Bob? Anyone. Thanks

Bob Harper
05-16-2008, 06:49 AM
You can extend a masonry chimney as long as you follow the codes. The base must be capable of supporting the total weight. The connection to the house proper must still maintain a 1 inch clearance to combustibles. The flue tiles must be properly sized, installed, with the proper mortar and carried up ahead of the brick. Due to the circumstances, I think a Level II is certainly in order here. For one, it looks a little short.

If you are going to do this one, you'll need to do the heater flue at the other end of the house. That had to be extended, too didn't it?

David Banks
05-16-2008, 01:08 PM
Thanks Bob. You are always so helpful. Here are some more pics. The one at the other end of the house was for a wood stove in finished basement.
That one also has a lean to it and the footing appears to be under sized.
Also poorly constructed and is out of plumb both ways.
The vinyl siding was installed over 1 inch foam insulation, and there is no 1 inch clearance as one area was exposed. (See Pic) They also mortared where chimney meets house. I figure this is to hide exposed foam or chimney is pulling away from the house.
The chimney front chimney from original pics was for gas boiler. Lots of water stains coming out of clean out and streaked on basement foundation. Inside of clean out had lots of debris. Water stains in attic sheathing/walls on both chimneys. Level 2 it is.

Ron Bibler
05-16-2008, 01:24 PM
David good eye on this fire place. Q. what did this look like from the sub-area or basement?

We get a lot of fireplace problems in No Calif due to clay soil condition.



Bob Harper
05-16-2008, 02:15 PM
The mortar btw chimney and house could be normal from how they built it but you have to suspect the chimney is not tied to the house and is pulling away. I see it is crooked as a dog's hind leg. The wide head joints and smaller footprint than the original tells me these bricks are probably nominal in size while the lower originals are true 8", thus the way it truncates in at the cold joint. I recommend those footings be probed to see how far out they extend. That starter course has already had problems so what's up there? Water pulling up from the ground? Weak mortar mix/ cure?

David, the joint btw masonry and frame construction is always a joke. The code calls for a 1" clearance to combustibles. Finally, the IRC realized there was no way to literally comply with this so they came up with an allowance of minimal material touching the chimney inside and out to form a weather seal. However, you cannot pack this joint with insulation. Since it is not really properly flashed, it will forever be a potential water intrusion point. You have two ways to build a chimney on an exterior wall: frame a gash in the side of the house and fill it with brick & mortar or frame out an opening but sheath over the exterior wall then run your brick up the outside trying to maintain your 1" airspace to the frame construction. If this is done, how do you seal the lower edge of the frame out at the header so it meets the energy code with clearance to combustibles? This joint is a major source of air infiltration. With warm moist air entering this interstitial space, you have a major propensity for condensation in the wall cavity. It is an energy hog, water intrusion threat and fire hazard all designed by code. That's what minimum stds. will get you.

how was the flashing and crown wash? Those are two of the usual water intrusion suspects.

Good job!

David Banks
05-17-2008, 04:27 AM
Thanks Bob! Here is pic of basement.