# Rigid Foam Insulation over existing wood siding



## Hexar (Mar 5, 2010)

Hi guys,
First post here. 

I live in Calgary, Alberta, Canada, I have an old one story bunglow (built in around 1965), the exterior wall is 2X4 and the existing siding is wood, the windows are two single paned sliders.

I am thinking to add insulations to the walls and retrofit the windows at the same time. I am thinking to use either 1" or 1.5" rigid foam insulation board over existing wood sidings, and then apply a layer of house wraps, then apply vinyl sidings.

Will this work? And for the windows, especially the "edge" between windows and the walls, I have not figured out how to do. All the "how to" sites I found are for either windows or insulations, not the combinations of the two.

I think I need to:

add a 1" or 1.5" wood frame around the outside of window rough opening, so that this new "frame" is flash with the foam insulation board added to the siding, then I need to apply sill flashing and etc to the "frame" and opening, then install the window.

Seems like the window will be installed "outside" of the original 2x4 wall. 

Will the above steps sound correct?

Thanks!


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## CustomBuild (Oct 20, 2009)

Are replacement windows an option for you? If so, you can focus on making a jamb extension for each window that would serve a s a nailer for the ends of your siding and also for "j" channel around the windows.


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## lemon714 (Jul 18, 2009)

I would remove the existing siding and then install foam and vinyl siding. I give you points for creativity with the new frame on the outside. By the time you do all that, it would have been cheaper to just start from scratch then to retrofit. Plus youll be able to address any problems with the sheathing etc. if there are any....

good luck

Brian Fox


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## Hexar (Mar 5, 2010)

Thanks CustomBuild and lemon714, I appreciate the advices.
lemon 714, I was thinking tearing down the existing wood siding was too much trouble, but I guess doing so will make things much easier... Thanks for that.

I searched the topic, and found this:
http://www.dow.com/PublishedLiterat...foam/pdfs/noreg/179-07305.pdf&fromPage=GetDoc


It seems that dow's method of applying the rigid foam is like this: 
http://www.flickr.com/photos/[email protected]/4415302983/

But it seems to me that nailing the window fin through the rigid foam seems a little bit too weak? I mean, the foam is "soft" right?


I am thinking doing this: adding a 2x2 (or whatever the thickness of foam I am going to use, 1.5 or 2") around the window opening so that this frame's face is flash with the foam, and I can then apply flashing tapes and etc. And I can nail the window fin to this new frame.

http://www.flickr.com/photos/[email protected]/4416069502/

What do you think? Is this ok or this is flawed?

Thanks!


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## ccarlisle (Jul 2, 2008)

I'm glad you found that info on the house wrap because I think it will guide you to the other aspect you don't seem to be addressing in you olans: air infiltration. Consider this: about 30-40% of your heating dollars is being lost because of a lack of proper air infiltration barrier. 

This has nothing to do with the *amount *of insulation you're putting in and you can't just increase the level of insulation to compensate for it. You have a leaky house - and that will cost you heating $$$.

You don't say why you are leaving the siding...another poster mentioned that that would be a good move to inspect your sheathing - and I agree - but to add to that, I'd say that is the best approach to add an air barrier just like the diagram you showed us. Then insulate. 

The fact is that you could get by equally with less insulation+an air barrier than more insulation+ no air barrier. In other words you could get the same performance (if not better) from air barrier + one inch polyisocyanurate foam board than you could from siding+two inches styrofoam and nbo air barrier...

The bonus to this is you don't have to reframe your windows...


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## Hexar (Mar 5, 2010)

ccarlisle, Thanks for the reply.

I am planning to do now is:
1. take off the existing wood siding, exterior window trims, inspect and fix any minor problems with sheathings.
2. apply 1.5 or 2" thick rigid foam insulations onto the sheathing, using nails with 1" fishers.
3. seal all the foam edges/joints with tapes.
4. wrap the whole house with house wraps.
5. nail 1x4 boards through the foams into the sheathing, so that sidings can be nailed to
6. install vinyl sidings.

The thing I don't know for sure is: should I use dow's technique when installing windows: nail the window's fin through foam to the sheathing (maybe further deeper into the window frame?), that I need at least 3" nails.

Or, I install an window frame extension around the rough opening, using wood with the same thickness as the foam insulation, so that this frame extension's face is flash with the foam.

Which way is better?

Thanks!


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## ccarlisle (Jul 2, 2008)

You may have to rethink the order of installation, at least from what you said; the housewrap goes on against the sheathing, _then_ any insulation. I would never use 3" nails to go through foam, in order to secure my windows. They go against the wrap. So sheathing, wrap window, then insulation.


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## Frostbite (Mar 8, 2010)

Agreed with above, the foam insulation have no structural rigidity at all and the process you suggested will have the 1x4 board and your siding help up by cantilevered nails. You'll need some wood rails in between the insulation to nail your siding to. Also the wrap needs to be supported on both side so it should be sandwiched between the sheathing and the insulation.


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## Hexar (Mar 5, 2010)

Thanks guys. I guess i did not express myself too well. 

Let me try again: 

I am planning to insulate walls and retrofit my windows at the same time. Initially I did not plan to tear down the existing wood sidings, (that thinking affected my "original" plan and made things more confusing), right now, I think I will tear down the existing wood sidings.

The things I don't understand is: how to deal with the area around window openings, how to insulate that areas.

So I searched google, and found dow.com has several PDF files detailing how to do exactly that. 

Please take a look this:
http://www.dow.com/PublishedLiterat...foam/pdfs/noreg/179-06007.pdf&fromPage=GetDoc

dow.com is suggesting that I apply the foam board to the opening, and install sill pan, and flash the window opening directly against the foam. 

I found the above method strange. 

Like you mentioned, I agree with foam being non-structural, that is why I think dow.com's method is kind of strange. that is why I was planning to add an extension to the window frame, and install foam "side-by-side" to this frame extension, so that the exterior faces of foam and the extension are flush. I will install sill pan over the wood frame extension, install the window and nail the window fin against this new wood frame.

So basically, the method 1 is Dow.com's method, and method 2 is "my planning", but I don't know if my method is the right one. Therefore my previous questions. 

Sorry for the confusions !


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## Tom Struble (Dec 29, 2008)

either method will work fine,main thing is getting the window flashed

1-1.5'' dow board over a flat surface is as firm as it needs to be


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## Frostbite (Mar 8, 2010)

I think what Dow suggested is fine, the flashing weights very little and the window frame is being supported by the wood frame around it. Although rigid insulation is none structural it can take some load if it is spread evenly, just don't nail through it since the nail will both act aas a thermal bridge, rip the foam and be a point of condensation.


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## Skuce (Nov 2, 2009)

Foam over wood.

There is a rot situation if I ever heard of one.


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## Tom Struble (Dec 29, 2008)

it been and being done millions of times with no problems

whats your point?


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## Frostbite (Mar 8, 2010)

I generally dislike having rigid insulation on the outside of a house, but it is waterproof. I have heard that it is prone to insect infestation though.


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## Tom Struble (Dec 29, 2008)

thermal break is a good thing,no more prone to insects than any other sheathing


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## Gary in WA (Mar 11, 2009)

*Avoiding Potential Insect Problems*

When insulating a foundation you need to consider that, although insects don't eat foam board, they *can easily* tunnel through it. Insect burrows reduce the R-value and structural integrity of the insulation. For these reasons, some manufacturers treat their foam products with an insecticide, usually a borate compound. Many building jurisdictions also mandate treating the earth around the building with insecticides. These jurisdictions may also want an inspection area several inches wide and all around the foundation of a house kept bare of insulation board. http://www.energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11620
Water resistant, not waterproof: a Class 3 vapor retarder = vapor semi-permeable: http://www.panhandleinsulation.com/buildingmaterials.html to be a vapor barrier (vapor impermeable), Class 1- would need to be 8” thick.: http://www.buildingscience.com/docu...rol-for-new-residential-buildings?full_view=1
Has anyone read any new info on sticky window tape on the sheathing instead of on the house wrap? http://www.diychatroom.com/f15/capping-windows-aluminum-vs-flashing-aluminum-63535/index2/ 5 window manufacturers and Typar, Tyvek, and a few others still have the old way as mentioned.


Be safe, Gary


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## Hexar (Mar 5, 2010)

Thanks guys, I appreciate the comments and advices.

How about these steps:
1. take out the existing wood sidings, and inspect/repair the sheathings
2. build out the window openings with 2x4, this will give me a solid nailing base for the windows, 
3. then install 1.5" rigid foam insulation, and bring the foam up to the new 2x4 nailers built in step2.
4. tape the edges/seams of the foam
5. install house wrap, seal and flash according to the dow.com recommendations.
6. install vertical furring strips (for sidings to be nailed to)
6. install the windows, and flash/tape them
7. install sidings.

there are some images and videos I found on the internet/youtube.










http://www.youtube.com/watch?v=12DvyHjqu4Y
http://www.youtube.com/watch?v=dSqpKyiWbsA

but these videos show flashing over foam which is what dow suggested...


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## Gary in WA (Mar 11, 2009)

Now you’re into rain screens: http://www.greenhomebuilding.com/pdf/RainScreen.pdf

http://www.nchh.org/Portals/0/Contents/Article0440.pdf

http://www.coastalcontractor.net/article/135.html

Be safe, Gary


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## ccarlisle (Jul 2, 2008)

I repeat:Why do you _insist_ on putting the house wrap *after* the insulation, when the diagram shows you don't...?
:no:


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## Hexar (Mar 5, 2010)

GBR in WA said:


> Now you’re into rain screens: http://www.greenhomebuilding.com/pdf/RainScreen.pdf
> 
> http://www.nchh.org/Portals/0/Contents/Article0440.pdf
> 
> ...



Thanks GBR for the docs, they are VERY helpful!


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## Hexar (Mar 5, 2010)

ccarlisle said:


> I repeat:Why do you _insist_ on putting the house wrap *after* the insulation, when the diagram shows you don't...?
> :no:


Sorry ccarlisle,
I did not "insist" on putting the house wrap outside of insulation, I thought the diagrams, especially the ones from dow.com show that the house wraps are outside of the everything, except the sidings?


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## Hexar (Mar 5, 2010)

this page shows using two layers of felt, one on each side of the foam...

http://www.hammerzone.com/archives/exterior/siding/replace1/prep/wall.htm


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## Tom Struble (Dec 29, 2008)

housewrap should be directly under the siding,that's where your drainage plane is,not under the foam,the foam should be considered a sheathing extension and the windows and doors packed out to the level of the foam,then wrb installed on top of the foam,


nice illustration op that's how i would approach this project

closed cell foam is about as good an air barrier as your going to get

and again it no more suseptible to insects than any other non treated wood based sheathing,good building practice and keeping everything atleast 8'' above grade will help keep the insects at bay


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## Skuce (Nov 2, 2009)

tomstruble said:


> it been and being done millions of times with no problems
> 
> whats your point?


Millions and million of rotted sills.

What's yours?


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## GreginAlaska (Nov 8, 2009)

Skuce said:


> Millions and million of rotted sills.
> 
> What's yours?


How long did it take to rot them? We put rigid foam and vinyl siding over T-111 about 10 years ago, it was still OK when we sold the place 4 years later. We sold it to people we know and everything still looks ok on the surface anyways.

Did you guys know that Quadlock has a retrofit system for putting foam over an existing wall?


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## Tom Struble (Dec 29, 2008)

Skuce said:


> Millions and million of rotted sills.
> 
> What's yours?


more likely caused by window,door or roof leaks or built too close to grade
foam insulation has proven itself over the years,are there some problems and disadvantages to it...yea sure just like every other building product

it all comes back to building practice...


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## Hexar (Mar 5, 2010)

Hi Guys,
I finally started! 

I took the sidings (on one half the wall) down today, and I am glad I did! There are lots of problems hidding inside. I think the previous window installer did not do a right job. 

This is a window (facing north), I think he did not:
1. flash the window
2. insulate the gap 100%, so the cold air can go from the trims into the gap and into the window frame, and into the space between the two window panes, and from there into the room. 

No wonder the window is very drafty in the winter, and fully of condensations!










I have a question now:
The red lines I drew on the pictures should be where the rough opening is, correct? I should tear down the white frame and the pink/redish sill when I un-install the window, correct?

Thanks!

Hex


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## Do Over Gal (Apr 21, 2010)

*House Wrap Over Foam or Fan Fold*

Every single house that I have done in my 15 yrs of construction I have realized if you want the correct answer you go straight to the source. The issue of house wrap is this ....you can blow smoke through one side and not the other which make the outside air stay out and lets the inside air out. This means the house can breathe !! I was told by a Tyvek rep visiting our local Spahn N Rose lumbar yard that the wrap is to be put OVER any insulation on any older home . New construction can be very well insulated from the inside before sheet rock is put in place. The wrap , capped nailed over what ever insulation you use on the exterior , allows the house to breathe. If you cover the wrap with your insulation you are not allowing the wrap to breathe. Personally have had to re-do other homes that were full of mold due to the application of foam over wrap. Not fun when insurance adjuster shows up or general contractor for your lending institution. It's very simple to pick up the phone and call your state agency to find the codes where you live and call your insurance company. 

Input from a person that has been there is better than no input at all !!


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## jogr (Jul 24, 2007)

Do Over Gal said:


> The issue of house wrap is this ....you can blow smoke through one side and not the other which make the outside air stay out and lets the inside air out.


 
Sorry, that's not true. Tyvek isn't directional. It stops air flow either way. It is permeable to water vapor (either way also).

There seems to be a regional difference in the use of Tyvek with foam board insulation. In some areas contractors put the Tyvek under the foam and in others they put it over. Both probably work fine if the flashing is done correctly for the approach taken and both probably fail if the flashing is incorrect.


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## Chemist1961 (Dec 13, 2008)

*Don't forget ACH/ fresh air*

The DOW site shows wrap over foam, however again there are regional breakdowns on their site. 
Despite regional differences, think about warranty, if you don't do it their way and have an issue forget it.
Once you cure the leaky drafty home remember your ventilation may need to be addressed. My air sealing of the rim joist and behind baseboards has reduced the draft tremendously. Caulking inside has reduced the ACH, (air change per hour) rating by close to 50% in my 35 year old brick/stucco home. I am now just over 3.5ACH, down from 6.4 and approaching the level of new construction
If I continue with house wrap and insulation to replace the upper level stucco as I plan on I will need to add an HRV!!!You need to be aware of this as you will experience a HUGE change in your retrofit:thumbsup:


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## Tom Struble (Dec 29, 2008)

one thing ive learned is to not belive everything a ''rep'' tells you:no:


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