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Old 10-26-2013, 07:36 PM   #1
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Siding and different depth of sheathing


My window questions have led to me posting here on siding....

Our old home was added onto and as we tore off siding the older part does not match with how the new addition was put on. There's about 2.5-3" difference between the two sections. So I have a couple of questions.

1. Should I fur out the older part with furring strips and sheathing or can I or should I use 2" foam board to make up the difference and add some insulating at the same time?

2. Do I install fan fold or house wrap first? Is it necessary to do both? I'm in Iowa if that makes a difference.

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Old 10-27-2013, 12:13 AM   #2
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Siding and different depth of sheathing


Got a picture?
With that much difference I'd consider just using an outside corner and leave the wall alone.
Building it out that much would throw off any window or door opening and the soffit would also come into play.

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Old 10-27-2013, 07:34 AM   #3
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Siding and different depth of sheathing


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Got a picture?
With that much difference I'd consider just using an outside corner and leave the wall alone.
Building it out that much would throw off any window or door opening and the soffit would also come into play.
Well, this all started with installing a window. We removed all the old siding and realized that the addition had been put on even with 2 layers of old siding. Now that it's all off, we are short a couple of inches.

There is only one window on this exterior wall and we have a new construction one waiting to put it in, so there's no worries on that. Soffit was also put on on top of the 2 layers of old siding so building it back out will actually make it look right.
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Old 10-27-2013, 07:37 AM   #4
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Siding and different depth of sheathing


Here's a look at the area I'm referring to above. I pretty much need to build it out to make it look the way it's suppose to. Just need to know what materials would be best to do so.
Siding and different depth of sheathing-image-3473670824.jpg
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Old 10-27-2013, 09:01 AM   #5
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Siding and different depth of sheathing


What I'm considering is to build out 2.5 inches....

1" rigid foam board to the old sheathing, then house wrap, then 2x4's or furring strips to get my 2.5 inches total that I need. ANy problems with that?
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Old 10-27-2013, 09:06 AM   #6
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Siding and different depth of sheathing


Get a real measurement on the difference in thickness.
Shingles and step flashing will need to come off.
I'm not a big fan of adding foam on the outside of a wall. There's nothing hard and solid enough to nail the trim and windows to that way.
If it was mine I would also get rid of the tar paper and use all house wrap on that wall.
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Old 10-27-2013, 09:28 AM   #7
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Siding and different depth of sheathing


sounds like someone didnt locate the wall properly when they framed it. if its a 12" difference it would fine, as that happens on alot of modern house designs. in your case i would rip 2x6's down to 2" fasten those over the existing studs. then fill between the furring strps with rigid 2" foam then install 1/2" plywood over top and then house wrap

by sheathing with plywood it will make for a flatter surface to install siding to, ive had to do this on older homes that needed rigid foam on the outside however were being sided with cedar shingles.. you cant install shingels direclty over foam, need a solid nailing base
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Old 10-27-2013, 09:41 AM   #8
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Siding and different depth of sheathing


Okay thanks. The depth is 2.5 inches. I could use 2x2 strips attached to studs...fill space with rigid foam board at least 1.5 inches ...add osb and wrap? Does that sound right. So basically I'm using rigid foam just not as sheathing??
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Old 10-27-2013, 09:45 AM   #9
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Siding and different depth of sheathing


Oh and that black stuff is fiberboard sheathing not tar paper
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Old 10-27-2013, 09:54 AM   #10
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Siding and different depth of sheathing


Could I use the whit expanded polystyrene or does it need to be the pink Owens Corning stuff?

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Old 10-27-2013, 07:22 PM   #11
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expanded foam breaks down over time and actually acts as a sponge holding moisture. it was used heavily in the 90's but its not a good idea to use it for exterior purposes
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Old 10-28-2013, 08:20 AM   #12
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Siding and different depth of sheathing


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expanded foam breaks down over time and actually acts as a sponge holding moisture. it was used heavily in the 90's but its not a good idea to use it for exterior purposes
Well, I used it, so hopefully there won't be any long term issues. I did cover the expanded foam with 7/16 OSB and then house wrap/ fan fold. It is sealed up where water or moisture should not come into contact with it.
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Old 10-28-2013, 08:46 AM   #13
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Siding and different depth of sheathing


So on the other areas of our house we are anticipating the same 2 layers of old siding under our steel siding. Since we need to install windows properly, we're most likely going to be removing the old siding along with the steel to get to the original sheathing.

At this point, we'd like to add some rigid insulation to add a bit of warmth for our rural home as it is very windy where we live. We will most likely side with cement board using either lap siding or panels to make a board and batten look.

How do you best insulate an exterior with rigid foam? What size, etc? I found a link to give you an idea what I'd be doing, but not sure if this is the correct method especially for fiber cement board siding.

http://www.hammerzone.com/archives/e.../prep/wall.htm
http://diy.stackexchange.com/questio...ation-possible

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Old 10-28-2013, 10:59 PM   #14
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Siding and different depth of sheathing


The first link is installing fiber cement siding (water reservoir) directly over foam rather than sleepers over foam then siding. Para. above Photo 2; http://www.buildingscience.com/docum...term=hockey+pu

The thin faced fb was wrong in that it was not thick enough to control the dew-point on the wood sheathing boards. Now, without an interior vapor barrier/retarder next to drywall- moisture exfiltrating out through vapor diffusion or air leaks in the P&L will condense on the wood- cannot dry to the outside for foil facing; pp.9; http://www.buildingscience.com/docum...apor-retarders

Adding screws rather than nails stops the wood sheathing from expanding/contracting with the seasons/humidity which is why they split in the first place- should have nailed them after cutting better gaps, not trying to immobilize them with screws allow no movement forcing them tighter and against the studs. Should have added a stucco wrap/drainable HW at the sheathing/foam to let it dry/drain.

Thin (1/2") PIC is only R-3.25; works to prevent sheathing condensation only in a few Zones; 1-4; http://www.buildingscience.com/docum...r-requirements

Exterior application foil faced is better suited to warm climates where you want the vapor barrier on exterior. So when a future owner lives there, pull P&L add cavity insulation and a vapor barrier next to new drywall- vapor sandwich- a no-no. Low foam thickness did not raise the dew-point so it still will condense on boards---foil stopped vapor exfiltration at the sheathing boards---- so they can only dry to the inside. Look at other tomorrow.... must sleep now.

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Old 10-29-2013, 11:30 AM   #15
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Siding and different depth of sheathing


I contacted "an expert" in the field of exterior rigid insulation. It sounds like I'd need a minimum of R-7.5 to keep moisture away. Given that, I'd be looking at least 1.5 or 2" of foam board. I might just spray cellulose into the cavities and from the exterior and house wrap like normal. Not sure if I would even see gain from added 5-7 in r value.

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