I'll be installing windows soon, and wondered what the best practice is for flashing them. Since there is no building wrap, how do you insure that moisture behind the siding doesn't run down the wall and rot the window frame? On my main floor, I have 24" roof overhangs, so it is not a problem, but there are two windows in the walk-out basement with some 12' of wall above them. I'm using HardiPlank with a drainage plane. My contractor uses a piece of peel 'n stick above windows. Is that enough?

Peel and stick all 4 sides of the window as per standard details. You should also be placing a drip ledge on top of the window, if you siding contractor is installing a drainage membrane ensure the drip ledge back flange is behind this. If not...make the drip ledge with a larger piece of material and add a 45 kick to the back side, measure and cut a slot in the ICF to match and install.

I'm the siding contractor (and everything else). I'm not using a membrane; just furring to create a drainage plane. I get what you are saying about making a top flashing and insetting it into a slot in the foam. That should work well. Thanks!

Posted By Chris Johnson on 21 Nov 2012 07:01 AM
Peel and stick all 4 sides of the window as per standard details. You should also be placing a drip ledge on top of the window, if you siding contractor is installing a drainage membrane ensure the drip ledge back flange is behind this. If not...make the drip ledge with a larger piece of material and add a 45 kick to the back side, measure and cut a slot in the ICF to match and install.

Oops, not the bottom side, at least not over the flange. You don't want to create any kind of a pocket to catch moisture that may happen to run down around the window behind the flange.

I would also create a sill pan using a piece of waterproofing membrane. Prior to installing winow, stick the membrane to the bottom of the jamb and up each side 5-6". Be sure it is graded to the exterior. If you window does leak (as seen on rare occassion from a strong driving rain), this will prevent the water from entering the pourous concrete and running down inside the cavity until eventually finding its way out and causing water damage to the drywall below the window. This is a last line of defense, in case window is not properly sealed/flashed.

Here is a good diagram of window installation and flashing.

http://www.quadlock.com/images/engineering/QL_Window_Buck_3D.png

I prefer aqua flash from drivit. It's not expensive, but messy and seals to blocks, tyvek, treated lumber, concrete, etc. if your worried flash the block to the buck all the way around prior to setting the window. Then flash the sides and top. Leave the bottom to breath in case it ever does leak, it will have a way to weep out. It will depend upon the mounting style of the window. A top drip edge is a must before the siding. You can never flash enough. One trip back and it starts costing you. I don't like butyl tape as sometimes it doesn't stick well after its been exposed a while.

Posted By South Texas ICF on 26 Nov 2012 10:15 PM
I prefer aqua flash from drivit. It's not expensive, but messy and seals to blocks, tyvek, treated lumber, concrete, etc. if your worried flash the block to the buck all the way around prior to setting the window. Then flash the sides and top. Leave the bottom to breath in case it ever does leak, it will have a way to weep out. It will depend upon the mounting style of the window. A top drip edge is a must before the siding. You can never flash enough. One trip back and it starts costing you. I don't like butyl tape as sometimes it doesn't stick well after its been exposed a while.

Any pics or PDF details?

Since I'm building this house by myself, the blocks are weathering a bit due to prolonged exposure (several months). Although the weathering is minor, I've noticed that things don't stick well to the chalky surface. How should I freshen the surface up for peel and stick? I've heard of roughing the foam up with a steel broom as a prep for stucco- Too much? I don't want to find out the hard way that my waterproofing membrane has pulled away under the siding.

Windlock makes a rasp you can rough and clean the surface with

Here is what I did when I installed my second phase of basement waterproofing myself: (in the first phase of basement waterproofing, my contractor didn't prime the wall as recommended by the peel-and-stick waterproofing manufacturer, and I noted the membrane didn't stick that well to bare clean foam).

Scrubbed the foam with a nylon bristle brush (definitely no need for steel bristle here).
Washed the wall with clear water.
Let it dry a day or so.
Applied two coats of Black Jack Ultra Roof 1000 Elastomeric roof coating to the foam because I couldn't find the waterproofing system manufacturer's primer.
Let the elastomeric coating thoroughly dry.
Applied the peel-and-stick membrane to the wall. It stuck really well this time. If I put any pressure on the peel-and-stick over a decent sized surface area, I couldn't pull it off.

For window and door flashing, you could use the same process.

Be sure to get the 10 year rated elastomeric roof coating (I had to order 5 gallons from Lowes). I had previsously experimented with some Kool Seal 7 year rated elastomeric coating and the 10 year stuff is so much thicker when wet and way more pliable when dry.

Black Jack Ultra Roof Elastomeric Coating

Use a pressure washer to knock the oxidation off. Before you put the flashing on use a stiff wire brush where the membrane goes. If it's cold out, use a heat gun while you install the membrane and it will stick like glue!

Unless you are sure that they are completely wrong, it seems like a good idea to follow the window manufacturer's flashing protocol.

A hard nylon bristle brush with water rinsing will do a good job on the weathered foam without removing healthy foam.

The manufacturer (Marvin) shows building wrap in their instructions. I actually considered using a vapor barrier on the two basement windows, hanging all the way down from the eaves. That is my main concern- water coming from the upper part of the wall. I think inserting a flashing into the foam above the window will do the trick. I'll cut a slot with a circular saw, angled to prevent the water from backing up into the slot.

That cut-in flashing is hard to beat.

Please take some pics and post them here so we can see the details!

I'll post pics, but it may be a couple months- be patient!