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We are about to replace the patchwork of poor condition original and more recent wood exterior siding on our house with Hardie. We have an old bungalow so the entire exterior is wood siding. Several associated questions:

Hardie is pretty thin. Will the structural integrity of the walls be reduced if we replace wood with Hardie? Does plywood or some other reinforcing material need to be installed beneath the siding?

With siding off, we plan to install fiberglass bat insulation in the walls.

Should we use a vapor diffusion retarder/air barrier directly beneath the siding? What kind? Tyvek house wrap?

Don't want to end up with moist, moldy insulation in the walls.

Edited by martin3
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First off, check out Hardie's website, they have recommended installation instructions, as well as details in PDF format. You can also call their customer service to answer any questions regarding recommended installation.

The answer to your first question is yes. Most bungalows were built without lateral bracing, rather they relied on the redundancy of the nails in the interior shiplap and exterior siding to provide lateral support (not the greatest system). Removing the existing siding will reduce structural integrity that Hardieboard cannot match.

If it were my house, I would install Hardie Siding over Tyvek Housewrap over 1/2" or 5/8" plywood sheathing attached directly to the studs.

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We are about to replace the patchwork of poor condition original and more recent wood exterior siding on our house with Hardie. We have an old bungalow so the entire exterior is wood siding. Several associated questions:

Hardie is pretty thin. Will the structural integrity of the walls be reduced if we replace wood with Hardie? Does plywood or some other reinforcing material need to be installed beneath the siding?

With siding off, we plan to install fiberglass bat insulation in the walls.

Should we use a vapor diffusion retarder/air barrier directly beneath the siding? What kind? Tyvek house wrap?

Don't want to end up with moist, moldy insulation in the walls.

Insulation is usually installed from the inside.

That said there needs to be a solid layer of sheathing over your studs and insulation: the best is probably plywood but most builders use OSB these days because it's cheaper and almost as strong. THEN you put the waterproofing on: Tyvek or some other similar product (Lowes sells a store brand). And after that goes the exterior siding. The sheathing is actually what holds everything together.

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Insulation is usually installed from the inside.

That said there needs to be a solid layer of sheathing over your studs and insulation: the best is probably plywood but most builders use OSB these days because it's cheaper and almost as strong. THEN you put the waterproofing on: Tyvek or some other similar product (Lowes sells a store brand). And after that goes the exterior siding. The sheathing is actually what holds everything together.

OSB works fine as long as it doesn't sit out in the weather for a long time.

There are some recent conflicting reports on the vapor barrier issue... there has never been a lot of research for our climate and the new research suggests different techniques than are normally used for the vapor barrier. I wish I could elaborate... I'll try to find the link for the research.

But, traditionally it is Siding, Vapor Barrier (Tyvek), OSB, Studs w/ insulation between...

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Hardi has to be installed with a pnuematic nailer and compressor. It should be attached so that nails are hidden by overlapping boards, called blind nailing. This will reduce the number of nails that are exposed, giving it a clean look, and reducing the amount of prep work for the painter. Chalk lines should be marked on the Tyvek to serve as a guide for keeping the siding straight and level. Hardi is flexible, but breaks easily. You must use a skil saw with a concrete bit to make cuts.

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Funny thing about Tyvek. They sell as a vapor barrier, yet their specs say it is not rated as a vapor barrier. Also, there are conflicting reports whether it is a help or a hindrance in this part of the country. Look at it this way...if it is keeping wator vapor out, it is also keeping water vapor in. I am not the least bit sure that I'd want that crap wrapped around my house. If you are concerned about wind and cold entering the house through the walls, I'd consider caulking the seams between the OSB boards instead. With caulked boards and the insulation you added, the house will be insulated 10 times better than it was anyway.

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Funny thing about Tyvek. They sell as a vapor barrier, yet their specs say it is not rated as a vapor barrier. Also, there are conflicting reports whether it is a help or a hindrance in this part of the country. Look at it this way...if it is keeping wator vapor out, it is also keeping water vapor in. I am not the least bit sure that I'd want that crap wrapped around my house. If you are concerned about wind and cold entering the house through the walls, I'd consider caulking the seams between the OSB boards instead. With caulked boards and the insulation you added, the house will be insulated 10 times better than it was anyway.

All vapor barriers keep moisture out. The moisture inside a home is removed by running the HVAC system which lowers the Relative humidity to around 40% . If you do not install a vapor barrier on the outside walls, the HVAC system will not have an air barrier that will prevent moisture from being drawn in from the outside and the relative humidity cannot be controlled. Air barriers also serve as a medium to which condensation will form. Your home works a lot like a cold glass of water on a summer day. When the inside is cold, moisture condenses on the outside and the home sweats. This condensation normally forms on the moisture barrier, and drains off by gravity. If you do not install a moisture barrier, the condensation can form on the OSB itself, which will eventually lead to rot.

Tyvek is widely used because it is much stronger than felt paper and is easily installed. It comes in 8' widths, which are great for 8' walls. They also make a special Tyvek tape that can be used to tape the seams together to create a tighter building envelope. There are better vapor barriers out there that also act as insulation. OSB or plywood provides almost no insulation value becuase is allows heat to easily be transferred from one side to the other. Dow foam board is one and it will add a continuous R3 to the outside walls.

Fiberglass insulation in a 2x4 wall is R13. Studs, plywood sheathing, or OSB have values at around R=0.3. So at every stud you have an area that allows heat transfer. The foam board is one of the best ways to improve the energy effieciency of your home.

Edited by cgallagher
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All vapor barriers keep moisture out. The moisture inside a home is removed by running the HVAC system which lowers the Relative humidity to around 40% . If you do not install a vapor barrier on the outside walls, the HVAC system will not have an air barrier that will prevent moisture from being drawn in from the outside and the relative humidity cannot be controlled. Air barriers also serve as a medium to which condensation will form. Your home works a lot like a cold glass of water on a summer day. When the inside is cold, moisture condenses on the outside and the home sweats. This condensation normally forms on the moisture barrier, and drains off by gravity. If you do not install a moisture barrier, the condensation can form on the OSB itself, which will eventually lead to rot.

Tyvek is widely used because it is much stronger than felt paper and is easily installed. It comes in 8' widths, which are great for 8' walls. They also make a special Tyvek tape that can be used to tape the seams together to create a tighter building envelope. There are better vapor barriers out there that also act as insulation. OSB or plywood provides almost no insulation value becuase is allows heat to easily be transferred from one side to the other. Dow foam board is one and it will add a continuous R3 to the outside walls.

Fiberglass insulation in a 2x4 wall is R13. Studs, plywood sheathing, or OSB have values at around R=0.3. So at every stud you have an area that allows heat transfer. The foam board is one of the best ways to improve the energy effieciency of your home.

4. Is DuPont
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Fiberglass insulation in a 2x4 wall is R13. Studs, plywood sheathing, or OSB have values at around R=0.3. So at every stud you have an area that allows heat transfer. The foam board is one of the best ways to improve the energy effieciency of your home.

How do the sprayed foam insulation and foam board insulation options stack up against one another?

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How do the sprayed foam insulation and foam board insulation options stack up against one another?

I would go with foam board and tape the seams. The performance is about the same, the cost of foam board is much less. You just can't beat a system that creates a continous insulation barrier. I once saw a thermal image presentation where they showed two images - one home with foam board and one without. At every stud, you could see a red or "hot spot" where the heat transfer was the greatest. When they took an image of the home with the foam board, the studs were a lighter blue, which showed a lower temperature gradiant and less heat loss through the studs.

Structurally insulated panels (SIPS), are a new construction method in which they prefab the walls with a heavy duty foam board sandwiched between two structural panels. It creates continuous insulation that is usually several inches thick. You just can't beat that system.

http://www.sips.org/content/technical/index.cfm?pageId=20

Spray in foam has some outstanding qualities as well. But it typically makes the home so tight, that highly efficient AC units with fresh air intakes must be used to cycle fresh air into the home. The builders that aren't installing the right AC units are the ones that are bad mouthing spray foam.

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And I still say that putting Tyvek on a home that was not designed for it is a questionable practice. Old homes were designed to breathe, unlike the airtight construction of today. Wrapping a house in Tyvek when the rest of the structure is open and breathing can have unintended consequences. While Tyvek may be the greatest thing since sliced bread in your new construction, I wouldn't put it on my bungalow until I saw the research that said it was 1) worth the money and 2) not harmful to my existing structure.

This is a similar argument to sealing the floor joists. It is worth noting that virtually every mold problem occurs in newer construction. It happens that way for a reason. Even though I am a big fan of energy conservation, it can conflict with mold.

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And I still say that putting Tyvek on a home that was not designed for it is a questionable practice. Old homes were designed to breathe, unlike the airtight construction of today.

That's true of nearly any building material relating to a building's structure, but I don't think that anybody was making an argument to the contrary. "Questionable" only means what it sounds like it means. It doesn't mean bad, nor does it mean that there is not an answer to the problem. The fact is that questions to the answers are often fairly easy to come by.

Moreover, today's construction practices hardly call for airtightness. Asphyxiation would be a common problem if that were the case. Builders do like to find ways to keep water away from the sheathing and wall joists because excessive moisture creates mold problems and ultimately leads to rot. It's not that complicated of an issue.

Edited by TheNiche
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That's true of nearly any building material relating to a building's structure, but I don't think that anybody was making an argument to the contrary. "Questionable" only means what it sounds like it means. It doesn't mean bad, nor does it mean that there is not an answer to the problem. The fact is that questions to the answers are often fairly easy to come by.

Moreover, today's construction practices hardly call for airtightness. Asphyxiation would be a common problem if that were the case. Builders do like to find ways to keep water away from the sheathing and wall joists because excessive moisture creates mold problems and ultimately leads to rot. It's not that complicated of an issue.

Actually, it IS that complicated. And, airtight construction IS an issue. But, this is going off topic. As you are fond of saying, use your Google bar if you'd like more information on the subject.

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Actually, it IS that complicated.

Sounds like you and I have different concepts of what complicated is.

And, airtight construction IS an issue.

In your job, you must hear a lot about recently-deceased people. How frequently does the building they're occupying asphyxiate them? My guess is not very. To be clear, I didn't say that it wasn't an issue that architects and contractors have to be aware of. However, airtight buildings are neither the norm or the goal of modern construction practices.

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In your job, you must hear a lot about recently-deceased people. How frequently does the building they're occupying asphyxiate them? My guess is not very. To be clear, I didn't say that it wasn't an issue that architects and contractors have to be aware of. However, airtight buildings are neither the norm or the goal of modern construction practices.

I don't have a response to this. I just wanted to quote it, so that you can't delete it later. :rolleyes:

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And I still say that putting Tyvek on a home that was not designed for it is a questionable practice. Old homes were designed to breathe, unlike the airtight construction of today. Wrapping a house in Tyvek when the rest of the structure is open and breathing can have unintended consequences. While Tyvek may be the greatest thing since sliced bread in your new construction, I wouldn't put it on my bungalow until I saw the research that said it was 1) worth the money and 2) not harmful to my existing structure.

This is a similar argument to sealing the floor joists. It is worth noting that virtually every mold problem occurs in newer construction. It happens that way for a reason. Even though I am a big fan of energy conservation, it can conflict with mold.

Old homes weren't designed for HVAC systems either. But you make a good point, the entire building envelope needs to be considered before a moisture barrier is installed that wasn't installed before.

There are three main causes of mold. Plumbing leaks, roof leaks, and moisture traps. The first two usually cannot create enough mold for even a person with average health to be effected, and are usually detected and repaired before mold starts. Moisture traps are caused by the installation of two moisture barriers. One is usually outside the home and the other is on the interior walls.

The home that started the stachybotrys litigation cases, also seen on Oprah, was when a builder installed a material on the surface of the inside walls that acted as a moisture barrier. Used in conjunction with a vapor barrier on the exterior walls, this created a moisture trap in the stud cavities. Through differences in pressure inside and outside the home, moisture could be drawn between the two barriers, but couldn't get out. The situation created an ideal environment for mold growth. When they tore off the interior barrier, mold had grown floor to ceiling all throughout the home.

Most new construction has no more mold problems than old homes. I've seen exterior veneers removed from old homes that revealed mold and rot, usually from tile that was installed over greenrock in showers, or missing vapor barriers. Properly constructed new homes are no more susceptible than older homes.

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Getting back to the original question.....

You need to take into account the final thickness of the fiber-cement plank siding as relates to window, door, and corner trim. If you remove the existing siding and sheath with 1/2" material, you just might be able to maintain a reveal at existing trim. If you go over existing siding, you will end up "proud" of the trim and it will look awful. Typical fiber-cement siding when lapped the required 1 1/2" minimum ends up around 3/4" in depth and when first used around here (1995 or so) butted up to 1x trim, looked awful. Some builders started using treated 2x4 trim and that didn't look very good either. In the old days they used 4/4 trim to create a nice reveal with beveled siding or 117. Today you can't buy 4/4 off the shelf although you could rip down that 5/4 treated deck material for a nice historic effect.

We are about to replace the patchwork of poor condition original and more recent wood exterior siding on our house with Hardie. We have an old bungalow so the entire exterior is wood siding. Several associated questions:

Hardie is pretty thin. Will the structural integrity of the walls be reduced if we replace wood with Hardie? Does plywood or some other reinforcing material need to be installed beneath the siding?

With siding off, we plan to install fiberglass bat insulation in the walls.

Should we use a vapor diffusion retarder/air barrier directly beneath the siding? What kind? Tyvek house wrap?

Don't want to end up with moist, moldy insulation in the walls.

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Getting back to the original question.....

You need to take into account the final thickness of the fiber-cement plank siding as relates to window, door, and corner trim. If you remove the existing siding and sheath with 1/2" material, you just might be able to maintain a reveal at existing trim.

the original question is about maintaining the integrity of the structure which you have failed to address.

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Absolutely right, sorry.

Yes the old wood siding offered racking strength and ideally plywood or OSB would be used under the fiber-cement. However if this is a one story bungalow with shiplapped interior, and has relatively little wind exposure, putting the siding right on the studs should not be a problem. Most new construction uses this very design, just inside out, with the racking strength on the outside, with the drywall interior offering little racking strength.

The fiber-cement can offer some racking strength, but only if face nailed and not blind nailed. Blind nailing is allowed by manufacturer Hardie (in fact now recommended (Aug 2008); they change their installation instructions regularly) but there are restrictions on the wider exposures (like use roofing nails). Ike revealed what will happen to the 10" and 12" product when blind nailed with regular siding nails. Lots of blowoffs at inner city townhouses. Oops.

Face nailing means more exposed nail heads and puttying and painting and installers will charge more.

For a "historic" emulation of beveled siding, you can't beat the 5.25" or 6.25" fiber cement plank. Avoid rigid adherence to a fixed exposure: if you walk the neighborhood, observe at the original beleved-siding houses that there is a full course above window drip caps, and a full course under the window sills. This is not an accident. It provides a cleaner look and saved the original carpenters from having to rip pieces. The way to achieve this is to vary exposure slightly at the applicable courses, using a "story pole." When done right it adds to the historic look even when using non-wood siding. With a fixed exposure it just screams "new siding."

the original question is about maintaining the integrity of the structure which you have failed to address.

post-7654-1240236700_thumb.jpg

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Yes the old wood siding offered racking strength and ideally plywood or OSB would be used under the fiber-cement. However if this is a one story bungalow with shiplapped interior, and has relatively little wind exposure, putting the siding right on the studs should not be a problem.

if one has to be worried about wind, it doesn't sound like something most homeowners would want.

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For a "historic" emulation of beveled siding, you can't beat the 5.25" or 6.25" fiber cement plank.

If you've got some extra money in the budget, the new Hardiplank Artisan siding will look much more authentic. It 2x the thickness (and 2x to 3x the cost...) of regular Hardi, but it will give you a much better-looking shadowline, and more closely emulate original cypress siding. The Artisan product will also match up better to existing 5/4 trim, if you pull off the old siding and attach directly to the studs.

http://www.artisanluxury.com/

Another advantage to the Artisan is that you can miter the corners, which creates a much more finished look, IMHO. However, mitering the corners would bump up the labor cost.

I understand at the latest Heights historic district meeting there was talk of trying to require the Artisan product on new construction.

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I'm not sure I understand what you mean? Wind resistance is a factor of wall height and if its a one story structure, siding right on studs (with interior walls planked) is probably OK.

if one has to be worried about wind, it doesn't sound like something most homeowners would want.
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