chimney and roof question

Hello...on one side of my house the roof runs down to a chimney that stretches 6 feet and water has a tendency to sit in this area before it rolls around the chimney to the cutters. It does not leak (yet) but I want to redo this area somehow. I am wondering what is involved in modifying the roof to butt up against the chimney and then have some sort of a flashing (if that is the right word) to prevent water from running down the brick on the chimney and seeping under the roof. I assume that I will have to rip up the plywood to somehow modify the roof. ...This part of my house is on the side, so looks are not a concern but I do not want to have a water problem. I will be reshingling the entire roof soon and I want this job done at the same time. Any suggestions would be great......thanks

 

The usual way to prevent water from going into the chimmney is to build a "cricket" or "saddle" at the back of the chimney, facing the slope, which will deflect the water away from the chimney. It is a pretty simple thing to do. Once you build one, you will have two valleys to make as well.

 

What is the slope of the cricket? The highest point should be at the chimney and run back towards the roof? so the water stays away from the chimney. The plywood needs to be torn up in this area in order to attach this cricket to the existing beams. When shingling the roof, I believe there are metal? strips (I do not know the name). that run between the shingles where valleys on the roof meet. Do I have the right idea? thanks again.

 

A chimney cricket is usually made up of two triangular sections. Think of a right-angled (one corner is 90 degrees) triangle, with the base of the triangle running from the midpoint of the chimney to the edge side edge of the chimney, the hypotheneuse of the triangle running along the roof, and the long side of the triangle forming the ridge between the chimney and the roof. Obviously, the long sides of the two triangles join along the whole length to form the cricket ridge.

In terms of slope, it is not a bad idea to have the slope of each side of the cricket be about 45 degrees, but you can make it lower.

The cricket joint along the chimney will look like an inverted "V" and should be flashed with metal to prevent water from entering the chimney or mortar. The top of the flashing should have a 90-degree bent towards the chimney, and be inserted into a slot cut in the brick/mortar parallel to the slope of the cricket. This is then caulked.

The cricket joint to the roof is a valley, and valley flashing techniques should be used.

It is not necessary to remove the plywood to install the cricket. Most roofers will strip the roof, then build a support structure with 2x4's on top of the existing plywood and place the cricket plywood triangles over this support structure. It's certainly not a bad idea to then cover the cricket and surrounding area with ice-and-water shield membrane, then the metal flashings, and then your roof covering of choice.