Sheathing, Foam, and Wrap. opinions needed

[gball]

So i need some others thoughts on a dilemma i am having with the garage addition (this one http://www.garagejournal.com/forum/showthread.php?t=170311 ). Some of the key facts: The House is 2x4 framed with 1/2" 2 sided foiled foam, no wood sheathing - I am residing the whole house while doing the garage - I live in northern Michigan (it's cold here) - It is a farm so we have flys and other critters that like to get behind siding and other places they are not wanted.

This is my plan. Remove siding and foam (I devised a way to remove the foam so it can be reused). Clean out the wall cavities and insulation of dead fly remnants. Put in new insulation where the original builder left empty spots. Put 1/2" OSB tight to the studs... now this is where i am confused.

Should i put on the OSB, then house wrap then foam? or should it go OSB, Foam then wrap. I Plan on firing out around all doors and windows and all along the bottom edge. The strip along the bottom i was thinking of using drip edge nail into the strip so it returns back and under to the block (make sense?) to close the bottom up.
It seams like a better idea to have the wrap on the out most layer but trying to staple the wrap to the foam with out the wind blowing it all over seams like a pain...

Opinions please.

 

[windward]

I think the foam will act as a vapor barrier, so you may not need the wrap. You might want to consider going with thicker foam.....here is a good article.

http://www.greenbuildingadvisor.com...m-insulation-cause-mold-and-moisture-problems


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[pattenp]

House wrap is not a vapor barrier, it's an air barrier. Vapor barriers go between the heated space and the insulation. Air barriers go under the exterior siding to prevent air infiltration.

 

[theoldwizard1]

Sheathing needs to be applied directly to the studs. Sheathings main purpose is to prevent the wall from racking.

 

[gball]

Oldwizard, that is my plan on putting the OSB right on the studs. the house was built with just the foam. it is no wonder there is nail pops and cracks in the drywall everywhere. house was built in 1979 and i guess, from looking at a lot of houses around here, that is how they did it then... pretty crappy i'd say. can't even see how the squared walls and stood them up without them flopping all over the place.

Windward, i thought about thicker foam but the extra cost would be pretty big, plus i have the 1/2" already and can't see wasting it.

pattenp, so are you suggesting the wrap go on the outside, over foam and under vinyl siding?

 

[volleyball]

The foam is the sheathing. You don't need OSB. You should find some old time angled framing to keep it from racking.
I would leave the foam. Seal the edges. Install new foam on top with no overlapping joints.
Seal that. You then side over that. And fir out the openings, or reposition the windows and doors outward and add jamb extensions.
There are some good youtube videos of Alaskan building that will get you in the right direction.
If you think you have major voids at the bottom. just cut off a foot of the original foam and fill. Maybe run any new wiring or structure wiring at this time the walls are open.

 

[bimmer1980]

Fine homebuilding magazine has some great article on this....

They usually recommend sheathing, then the house wrap, then the foam and then a wood batten system to leave an air gap for the siding. Usually this is a 1x3 that is fastened at each stud location. This allows any water that get's behind the siding (because it will) to drain to the bottom and out.

For Brick veneer systems, they make special brick anchors that go through the foam and screw into each stud. In this case the wood battens are not needed.....

Hope this helps....

 

[pattenp]

Yes, but I'm sure building techniques in your area are different because of the climate. Here the house wrap (when used) goes over the sheathing, be it foam or wood, and then the siding goes on.

Oldwizard, that is my plan on putting the OSB right on the studs. the house was built with just the foam. it is no wonder there is nail pops and cracks in the drywall everywhere. house was built in 1979 and i guess, from looking at a lot of houses around here, that is how they did it then... pretty crappy i'd say. can't even see how the squared walls and stood them up without them flopping all over the place.

Windward, i thought about thicker foam but the extra cost would be pretty big, plus i have the 1/2" already and can't see wasting it.

pattenp, so are you suggesting the wrap go on the outside, over foam and under vinyl siding?

 

[Architorture]

if you decide to go the route you have described dont go striping an entire wall of foam sheathing before you at least get it replaced with OSB at the corners and work on 1 side at a time. it might be acting as bracing, it might not...but best to be safe about it and not expose the whole structure without sheathing.

for the building wrap it goes over the sheathing...the foam you have from the 70's might not have a whole hell of a lot of insulation value left to it...you might consider getting new fan fold

 

[volleyball]

Fanfold is to smooth out the surface, not as a useful insulation. The original stuff is structural. Foam doesn't lose its insulation with age any more than any other.

 

[JCfreak]

Bimmer1980 has the right answer.

 

[Architorture]

Fanfold is to smooth out the surface, not as a useful insulation. The original stuff is structural. Foam doesn't lose its insulation with age any more than any other.

1/2" fan fold will insulate the same as 1/2" any-other-foam. the point is to get him back to as close to the original wall thickness as possible so he doesn't have to rework every opening in the wall.

Pretty much all foams degrade and lose insulation value over time one way or another. EPS and XPS degrade from environmental factors such as VOCs released by other materials in the assembly and polyiso is notorious for losing value as the blowing agents work their way out of the material over time...this can be as high as 30% lose all on its own.

foams have an expected like like any other building material. Going on half a century it is probably time to replace it

 

[gball]

I think i may have come up with a plan. The two side foiled foam on the house is 3/4" and not 1/2" like i thought... It says on it it is R-5. weather it has degraded some or not, it still has to have some R value and i already have it and can't see tossing it. So what i am thinking is putting up the OSB then wrap, then the old foam. then put furring strips over the foam on studs. The use new 3/4" foam cut to go between strips. This will give 1 1/2" foam over open wall cavities and 3/4" over studs. this will also keep me from using 2 1/2" nails for my siding... What do you guys think?

 

[theoldwizard1]

I think i may have come up with a plan. The two side foiled foam on the house is 3/4" and not 1/2" like i thought... It says on it it is R-5. weather it has degraded some or not, it still has to have some R value and i already have it and can't see tossing it. So what i am thinking is putting up the OSB then wrap, then the old foam. then put furring strips over the foam on studs. The use new 3/4" foam cut to go between strips. This will give 1 1/2" foam over open wall cavities and 3/4" over studs. this will also keep me from using 2 1/2" nails for my siding... What do you guys think?

When they do replacement vinyl siding in SE MI, especially is the old siding is rotten, the peel it down to the sheathing, apply house warp and then 1/2 non-foil foam. The hangers for the vinyl are applied right on to the foam with nails long enough to penetrate the sheathing. No furring strips.

If the stud cavities are empty, I would blow in fiberglass or cellulose before the top row of siding is installed.

Over fill your attic with blown in fiberglass or cellulose. Just make sure you have baffles to allow air up from the soffit vents to above your additional insulation.

 

[theoldwizard1]

The foam is the sheathing. You don't need OSB. You should find some old time angled framing to keep it from racking.

I would hope you are correct, but the OP did not mention it. That is VERY "old school" and a lot more labor intense (the angled framing is called wind bracing and must be "let in" to pocket cut in the studs and then nailed at each stud).

This sounds like a building done where there were no building inspections.



Now a days, there is sheathing that does give some insulation value. From an insulation stand point, you would probably be better off with 2x6 construction, OSB sheathing and house wrap on the outside and kraft faced fiberglass or "wet" cellulose insulation on the inside.

 

[gball]

Sorry, there is batt insulation in the wall cavities... The foam was the only sheathing used. No wind bracing... Not very well built. They got away with quite a bit. Inspections were done from the road.

 

[volleyball]

The old school method of bracing has been used when the foam sheathing came top market. Another method was to use plywood just in the corners. Not as efficient.
Bracing is easy with todays power tools

 

[Ajustable]

I think i may have come up with a plan. The two side foiled foam on the house is 3/4" and not 1/2" like i thought... It says on it it is R-5. weather it has degraded some or not, it still has to have some R value and i already have it and can't see tossing it. So what i am thinking is putting up the OSB then wrap, then the old foam. then put furring strips over the foam on studs. The use new 3/4" foam cut to go between strips. This will give 1 1/2" foam over open wall cavities and 3/4" over studs. this will also keep me from using 2 1/2" nails for my siding... What do you guys think?

This method you describe was recommended to me by our siding installer. you end up getting less exposed joints for wind infiltration. you can tape the joints as well. Make the decision now about vertical board and batten siding or horizontal siding. The furring strips will need to be layed the opposite of your siding choice. I will be siding our new to us house this way, As the present wall has only Gyprock as an external sheathing, no nail holding power with that stuff.

When I was residing a 150 year old farm house, I added 2" ridgid foam. I was replacing all the windows as well. what I did was framed all the windows rough openings with 2x4 laying flat, (like a picture) then framed the perimeter of the wall with with 2x6's, did the corners as well. The wood gave me a good nailing base for corners, J trim, and window install. I didn't use furring strips on the wall itself just used 2 1/2 " nails holding the vinyl siding. the sheathing on the original wall was 1" pine boards. I did one wall at a time so as not to expose to much and could spread the work load out. Its been on now for 15 years windy side of the house. I have never lost piece of siding to the wind.

 

[gball]

Ajustable, Thanks. I am also replacing all the windows and thought of the 2x4 framing like you mentioned. did you use wrap also, and where was it placed? over the pine board sheathing or over the foam?

 

[Ajustable]

My main concern was wind Infiltration, as the old farm house was quite cold on a windy winter day, I think I went a little over board on the 2" foam but the foam was free so I went with it. I did tyvek the insulation on the out side. I'm not sure that it was needed or in the proper place. From my understanding the tyvek lets air escape with the condensation but sheds moisture from penetrating from rain etc.

If you do frame the window openings with wood 2x Or 1X keep the thickness the same as the Insulation so you have a flush surface when applying the siding.

The floor in the kitchen was so much warmer on those windy winter days so much better.