I've tried looking for an answer to my insulation woes but I just get cross answers. I have a house built in 1953 in the Washington DC area. I was able to increase the insulation in the attic last year and I hope to do something about the walls soon. They have nothing but a fiberboard sheathing and old siding. I want to replace the siding which seems like a great time to do some air sealing and insulating. But how much and what options to choose is the question of the day. I have heard that blowing in cellulose from the outside without a vapor barrier on the wall side is a bad idea. I've read that if you vapor barrier the outside and then a layer of ridged foam that the cellulose is ok. Then there is insulated vinyl siding to consider. I know it only has a R value of about 2 but every bit helps doesn't it? I need help. Whats would be the best option without tearing into the inner walls? If you don't blow in cellulose should you house wrap then foam board on top? Please guide me out of this mess.
Insulation Conundrum
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If you are looking for R-Value, don't be under the misguided impression that the foam backed siding products give you any.
This climate does not require a vapor barrier so the installation of one specifically would be uneccesary and potentially problematic.
If stripping the existing siding, now is your chance to fix a great many issues in the exterior wall insulation.
Pull everything down, air seal the larger gaps and cracks in the interior wall, install proper depth insulation, rigid foam to the exterior (tape and seal all seams) in a sufficient enough depth to prevent dewpoint, new siding.
This climate does not require a vapor barrier so the installation of one specifically would be uneccesary and potentially problematic.
If stripping the existing siding, now is your chance to fix a great many issues in the exterior wall insulation.
Pull everything down, air seal the larger gaps and cracks in the interior wall, install proper depth insulation, rigid foam to the exterior (tape and seal all seams) in a sufficient enough depth to prevent dewpoint, new siding.
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Stripping the sheathing is probably cost prohibitive and perhaps excessive?
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We usually find the fiberboards are trashed on and full of holes. They certainly are not real structural members and are removed pretty simply.
Depending on the structure of the home, you don't need to re-sheet the exterior and can apply the foam directly over the studding.
Dense packing cellulose would be more cost prohibitive than pulling the sheathing and installing traditional batting.
Pulling the board also allows you the ability to foam and seal any penetrations in the interior wall/envelop layer.
I agree with you that it is more expensive, however, I would be willing to bet that if you are doing foam and batting, it would probably be cheaper than foam and dense packing.
Depending on the structure of the home, you don't need to re-sheet the exterior and can apply the foam directly over the studding.
Dense packing cellulose would be more cost prohibitive than pulling the sheathing and installing traditional batting.
Pulling the board also allows you the ability to foam and seal any penetrations in the interior wall/envelop layer.
I agree with you that it is more expensive, however, I would be willing to bet that if you are doing foam and batting, it would probably be cheaper than foam and dense packing.
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http://www.buildingscience.com/docu...bracing-requirements-for-insulating-sheathing
You would need to check with your count to see exactly what they require but it can be done with other bracing methods than complete re-sheeting of the walls.
http://www.finehomebuilding.com/des...ns-for-shear-bracing-foam-sheathed-walls.aspx
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Dense packed cellulose is considered and air barrier but the amount of time it will take to do the whole home, and the expense could probably account for the complete stripping of the exterior, sealing, installing batts, and then doing a rigid foam exterior.
I believe my house already has diagonal braces so this sounds feasible. Doesn't it make siding more difficult since you have to hit the studs and can't rely on the ply substrate? Wouldn't you use the foam sheets as a vapor barrier and tape all of the seams? any other considerations with this whole method?
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Screw the foam board into the studs and use that are your alignment marks for the siding.
You are getting a bit hung up on the vapor barrier aspect. We don't need one in this climate but you do need a proper air barrier.
Tape and stagger the seams. Foam sections that are larger than the tape can cover.
You are getting a bit hung up on the vapor barrier aspect. We don't need one in this climate but you do need a proper air barrier.
Tape and stagger the seams. Foam sections that are larger than the tape can cover.
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1. What type of siding have you decided on?
Check the fasteners on the Celotex fiberboard, many were structural when they first came out. I used it on houses around here in the early '70's, need to use ring-shank nails to get the minimal shear value; http://www.inspectapedia.com/structure/Fiberboard_Sheathing.htm
Check alongside an electrical outlet for fiberglass faced with paper or foil, only R-7-9, worth replacing as WoW said. Leaving it in place will change the exterior sheathing choice....
Gary
Check the fasteners on the Celotex fiberboard, many were structural when they first came out. I used it on houses around here in the early '70's, need to use ring-shank nails to get the minimal shear value; http://www.inspectapedia.com/structure/Fiberboard_Sheathing.htm
Check alongside an electrical outlet for fiberglass faced with paper or foil, only R-7-9, worth replacing as WoW said. Leaving it in place will change the exterior sheathing choice....
Gary
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Alside Prodigy is my favorite in the foam back family of product.
If you put a rigid foam over the exterior, you can just as easily go with a hollow back.
The important thing is the water vapor that you and your family create in your home.
Water vapor comes from cooking, washing, breathing, indoor plants, fish tanks, chikdren, animals.
Water vapor always moves from warm to cold.
If the inside of your walls and roof are cold, water vapor will condense on the wood and if it cannot dry, will create mold and in time wood rot.
If you fix polystyrene sheets, or some similar closed cell insulation over the outside, you will keep the frame and everything else inside warm.
Close fitted sheets of polystyrene are both wind proof and water proof.
If you fit water vapor proof plastic sheets between the frame and the polystyrene you will have a cosy dry home.
Water vapor comes from cooking, washing, breathing, indoor plants, fish tanks, chikdren, animals.
Water vapor always moves from warm to cold.
If the inside of your walls and roof are cold, water vapor will condense on the wood and if it cannot dry, will create mold and in time wood rot.
If you fix polystyrene sheets, or some similar closed cell insulation over the outside, you will keep the frame and everything else inside warm.
Close fitted sheets of polystyrene are both wind proof and water proof.
If you fit water vapor proof plastic sheets between the frame and the polystyrene you will have a cosy dry home.
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Perry,
With all due respect, this last statement is completely wrong and terrible advice.
This clients climate zone does not require a Class 1 vapor retarded and putting one to the exterior of the home is both unnecessary and ill advised.
Not only will you be created a double vapor retarder between the foam and the plastic, but you will actually be trapping any accumulated moisture inside the space between the foam and the framing and/or the interstitial wall space and the foam.
Air barrier detailing on the foam should be very careful, redundant, and perhaps duplicative.
If the homeowner removes the fiberboard, they can quite easily air seal the entire interior wall and therefore reduce (probably by about 100X) the amount of moisture coming into the inside space of that wall via bulk air transfer.
Putting a well applied and seal foam to the exterior (provided of sufficient depth and R-Value) will keep moisture from entering from the outside and keep the framing well above dew point and eliminate the potential condensation problem.
Putting plastic between the plastic foam and the home is not recommended.
Everything else that you said was spot on with the exception of that last statement.
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They may tell you cellulose doesn't need a vapor barrier: http://www.applegateinsulation.com/CEDocuments/Downloads_GetFile.aspx?id=249418&fd=0
http://www.cellulose.org/HomeOwners/AirVaporBarriers.php
Gary
http://www.cellulose.org/HomeOwners/AirVaporBarriers.php
Gary
So I've got 1 company striping the house to the sheathing and installing the Prodigy insulated siding over Rain Drop house wrap. I've got another that wants to leave the asbestos cement tiles and side over it with brigade board insulation and Mastic XL55 (i think the brigade board replaced the fanfold he suggested when i said i wanted more insulation). Thoughts?
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