Siding a dormer

[Brian Robertson]

On a gable style dormer on a sloped roof, must the vinyl siding on the side of the dormer be an inch or two above the shingles, overlapping the flashing? Thanks guys.

[wayne soper]

Not so important with vinyl as there is no decay aspect from water wicking up into shingle ends, but if it is the first layer of roofing there will be no room for another layer making reroofing more expensive for no good reason. 3/4 gap would allow second layer install with no problem.
If it is the second layer it is fine as the roof will have to be stripped next time anyway.

[Brian Robertson]

Yes that was my thinking, there wouldn't be a wicking problem but good advice about the possibility of adding another layer of shingles. Thanks Wayne:)

[Jerry Peck]

Brian,

You are close to being correct, you have the right idea, just the wrong clearance.

The specified clearance between roof shingles and the 'J' channel is 1/2" MINIMUM, so, yes, 1" or so would be good as well.

Go here ( http://www.vinylsiding.org/publications/0804_VSI_2007Manual.pdf ), go to page 22, Figure 34.

[Brian Robertson]

Thanks Jerry and thanks for the thread!:)

[Jim Luttrall]

http://www.vinylsiding.org/publications/0804_VSI_2007Manual.pdf
Check out this generic installation manual or see your brand of siding specific instructions. There is a diagram on page 27 and the full text which includes the excerpts below.

■

Keep the J-channel a minimum of 1/2” (12.7mm) from the roof line. Chalk a straight line up

the roof fl ashing to guide J-channel installation. Tip: You can use another J-channel laid over

the shingles as a spacer to create the straight line desired.


NOTE: Vinyl J-channels should not be in
direct contact with roofing shingles, since
the shingles may transfer enough heat to
the vinyl J-channel to cause its distortion.

[Jim Luttrall]

You typed faster Jerry!;)

[Michael Thomas]

For reports...

[Ted Menelly]

My last concern would be for a second layer of shingles as I have never recommended more than one layer. There is no money savings. A second layer loses years off its life so won't last as long. Later removing two layers is much more expensive to remove and haul away. Possibility of leaks is much greater.

Just some thoughts

[Brian Robertson]

Thanks men!! Appreciated.:)

[Mike Schulz]

The "j" in contact with the roof does turn brown and distort. I have seen it many times. Most builders now hold it up you still find some that don't.

Besides what has been mentioned is nailing the channel through the step flashing so close to the roof. I have in the past repaired many holes from channels causing leakage. Worst place is at a valley pan against a wall. You spend all this time putting in this nice pan folded up the wall 7" AND THEY NAIL THERE CORNER POST & CHANNEL RIGHT AT THE BOTTOM. I got most builders to get there subs to hold 4" up at the pan then taper back down to the 1" requirement on the siding. The corner post would be notched on the side that can't be seen anyway. Water then can flow freely with out building up debris.