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Community and Q&A

Flashing best practices request

user-3091810 | Posted in General Questions on

I have a 1965 home in Houston that I am doing a deep renovation on. One of the problem areas in the house is the intersection of the upstairs exterior walls with the downstairs roof. There was a vinyl siding with 1/4″ foam sheathing.

Today I removed the vinyl siding and foam sheathing. I did not like the vinyl, did not like it’s color, and had leaks where it met the roof.

As a green building note, I took off about 200 s/f a month ago and someone took it from my driveway. I have no idea what they would do with used vinyl siding…. Only thing I can guess is that someone is using it as patch material or for a shed, etc. So here’s to hoping it gets reused.

Back to my problem. The vinyl was harboring all sorts of insects and spiders. The roof and wall intersection was badly flashed. As best I can tell someone decided to reuse the original flashing from the cedar shake roof when they re-roofed. It was not step-flashed and it did not go up high enough behind the vertical lap wood siding. Worse still there were some gaps in the flashing which explain why I get leaks there during certain heavy rain conditions.

The wood siding has some defects and patches, mostly minor. The majority of the wood siding is structurally sound, but visually deficient. I’m planning to use it as sheathing. I’ll apply Tyvek house wrap as a moisture / air barrier and then install Fiber Cement Trim and Siding. I’m planning to insulate with foam and the walls are going to be closed cell, although if I run out of my first closed cell set, I’ll switch to open cell upstairs. The roof will be open cell. I own the equipment to do two component SPF application as well.

I think the right thing to do is to use a piece of aluminum flashing, about 16 to 20″ wide, bent at 90 degrees and running half of that up the wall and half out onto the roof deck. Then the 30# felt would go over that and the shingles would be step flashed. The wall portion would have the fiber cement on top of it with the tyvek going over the flashing, a trim board probably 3/4 to 1″ up from the bottom with z flashing over it.

I am trying to protect against two conditions:
1) torrential rain with wind blowing against the wall/roof interesection during normal sub-tropical downpours.
2) Hurricane force winds with accompanying wind.

My goal is to produce a highly water resistant intersection.

Will what I have described work? Is there a better way to do it? Can anyone recommend a book or reference site on flashing best practices?

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  1. Expert Member

    Brian, The 20" flashing serves little purpose. No water should be allowed to get that far into your roof assembly and if it did the flashing will be perforated by the roofing nails used on the shingles.
    Rather than the flashing use a strip of Grace Ice and Water, which is adhesive and self-healing. Lay this over your roofing felt or underlayment. Shingle the roof and include step flashing. If you want to include a secondary protection, counter-flash above the finished roof with a 6"x6" hemmed L flashing attached to the wall, not the roof. Before siding the wall apply as trip of adhesive membrane to cover the tops of all the wall flashing.
    Edit: Don't forget a kick-out flashing at the end of the roof.

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