Siding replacement dilemma


Old 06-03-15, 03:59 PM
Thread Starter
Join Date: Jun 2015
Posts: 6
Received 0 Votes on 0 Posts
Siding replacement dilemma

New to this board,
Im going to be replacing my 60 yr old cedar with vinyl siding. stripping off old cedar down to the 3/8 plywood. I want to add a little insulation so exterior foam board @ 1/2= 3.x r-value. Most contractors want to install tyvek "housewrap" under the insulation. Some indicate no need for tyvek just install insulation over plywood and tape.
My dilemma....
-according to tyvek's website "housewrap" must be installed over the foamboard, otherwise if installed under foamboard - water/vapor will get behind it trapped and result in rot etc.
-also according to tyvek's website there is a product called "drainwrap" that looks right and is intended for installation under foamboard.
*tyvek also points out to utilize the wrap that will cover over window flanges... in my case - i just installed all "new construction" pella windows. So the "drainwrap" is more applicable to me.
*tyvek also points out that there should be a metal dripedge along the bottom where the siding meets the foudation.

Now all of this seems somewhat straight forward....but more questions...
-how come contractors are doing it wrong? I mean Ive had 6 come over and none have it down? is it really not a big deal?
-I dont mind paying the premium for the "drainwrap" (about 50% more than housewrap) - but no one carries it?? wondering why?
-I love the idea of the metal dripedge - no one carries anything like it either. also wonder why...Do I have to make my own with a brake?

Any help or previous experiences with this topic would be helpful,
Thank you,
Old 06-03-15, 04:18 PM
XSleeper's Avatar
Group Moderator
Join Date: Dec 2004
Location: USA
Posts: 26,533
Received 779 Votes on 718 Posts
Your WRB should almost always be right behind the siding, and so window flanges are always installed on the same plane as the WRB and vis versa, so if you installed new windows you should have planned for the added insulation and installed them 1/2" farther out than they were originally. All the other stuff is Tyvek trying to protect themselves from lawsuits and/or complaints.

Vinyl siding is often an exception because foam is commonly added on top of the WRB as a cushion for the siding. Tyvek is just protecting themselves by saying there should be a drainage plane behind the foam (debatable) plus it gives them an opportunity to market a more expensive product (drainwrap) for that purpose. Not saying it's wrong, I'm sure it's a good practice, just not absolutely critical, IMO.

Tyvek is also not a flashing, so if it's back side is exposed along the bottom couple inches, it could deteriorate faster due to being exposed to UV and weather.

If you plan to add foam, it will be a good idea to cap the bottom edge of the foam, and yes the most common thing is to make your own from trim coil that matches the color of your vinyl siding. You could also get galvanized z-flashing and install it backwards, same difference.
Old 06-03-15, 04:27 PM
chandler's Avatar
Banned. Rule And/Or Policy Violation
Join Date: Dec 2005
Location: USA
Posts: 39,965
Received 6 Votes on 6 Posts
Welcome to the forums! Do you really feel the foam board insulation will give you the insulation you need? How much insulation do you have in your walls? Adding the 1/2" insulation may interfere with your new window trim, protruding too high. Tyvek is no longer wrapped inside window frames, but cut about an inch or so short around the windows and window tape installed to bridge the gap including the Tyvek, OSB and window frame flange. Bottom is done first, sides next and the top taped without including the Tyvek. The Tyvek is cut at an angle from the edge of the frame about 3", lifted up and the tape is applied to the flange and OSB. Then the Tyvek is draped back over the tape and flange and the angle cuts taped with Tyvek tape.
Old 06-03-15, 04:36 PM
Join Date: Jan 2011
Location: USA
Posts: 4,855
Received 83 Votes on 78 Posts
Little late now but your trying to do this in the wrong order.
Should have been plywood or OSB around window and door openings, foam, Tyvek wrapped around the window openings, then install the new windows
Some pictures of how the windows are trimmed out may be a help.
The biggest issue being the foam throws off all the window and door opening and they need to be built out.
Adding foam after the windows have already been installed can have issues.
If it was mine I'd be installing Tyvek over the foam not under it.
Need to see what type windows you installed.
The right way would have been to add the plywood or OSB to space the window out away from the wall and use windows with built in J molding.
Old 06-03-15, 04:43 PM
Thread Starter
Join Date: Jun 2015
Posts: 6
Received 0 Votes on 0 Posts
valid points... I didnt build out the frames - because i didnt want to have the expense of custom interior jams to match up to the walls and casing/trim. And I originally was going to go with the 1/4 inch fanfold r value=1. The aluminum frames of the windows come out about 1 1/4-1 1/2 - so adding 1/2 inch plus the the siding 1/2 inch keeps me below window frame plane. Shouldnt look too bad. Im really looking for sound insulation and a bit of thermal insulation never hurts + plus it levels out the siding well.
My biggest concern is the moisture. I just read an article (greenbuilder adv)that indicates no insulation is best and if you have to - go thicker. because it will result in water trapped and rot away your wood.
What do you think?
Old 06-03-15, 05:02 PM
Thread Starter
Join Date: Jun 2015
Posts: 6
Received 0 Votes on 0 Posts
When i replaced all of the windows - I installed them correctly as per spec... utilizing house wrap and flashing tape. The home was built in the 50's. there is no housewrap or tar paper below the cedar. So I opened up the cedar around the window opening and completed the installation. The house wrap from the windows is now ready for remainder of exterior plywood to be wrapped and meet up with.. --> the wrap around the windows. Does that make sense?

-I saw a video on youtube thats shows how the drainwrap works. Impressive. but i wonder if the regular house wrap would do the same?

-Some articles indicate that a 1inch r5 minum be used in temp zone 5... thats me in ny. I guess my question to them would be - If i have housewrap or drainwrap between foamboard and plywood... if condensation occurs - it should flow down the wrap plane and out? correct?

I also think I should avoid the foil faced insulation boards.

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: