[Greenbuilding] rigid foam inside Larsen truss
Beatrice Dohrn
beatricedohrn at yahoo.com
Sat Jan 6 16:46:01 CST 2018
THanks. That was very helpful. It clarifies some things I have had a gut feeling for.
I live in a house I designed and built (myself) from Faswall blocks.... I chose the polyiso foam insulation inserts for the above ground parts — for max R value and seems maybe a good idea in that context. I also have a 9” polyiso foam sandwich on the roof under metal. (I live in the hills outside Eugene Oregon). I think that the ants burrow in the roof foam a lot. I am not sure how much of it they might be carrying away, or compromising. In the spring when I see them making their lines up and down I worry. I am not much into poisoning them..... THere are only a few places, though, where I see bits of foam in the spider webs.... I’ll turn 60 this year (finished the house about 8years ago). Maybe it’ll be someone else’s problem?
THanks again for the detailed response. Best, B
Sent from my iPad
> On Jan 5, 2018, at 3:48 PM, Gordon West <gordon.west at rtnewmexico.com> wrote:
>
> Hi Beatrice,
>
> R-value is only one factor of many in the thermal performance of a building envelope. Heat transfer happens in three basic ways; conduction, convection, and radiation. R-value only measures conductive performance, and that is usually determined under a narrow range of conditions (it is the only way that fiberglass manages to masquerade as a reasonable insulation). Foam and blown cellulose perform well for all three transmission modes, though foam is overrated to R-value, in that it degrades over time down to about the equal of cellulose. However, foam boards must be installed with a great deal of care (it often is not), or they will perform poorly against air infiltration. Cellulose also has built-in mass, which improves thermal performance in the envelope system.
>
> But aside from thermal performance, cellulose is a better match for the basic construction of old homes. In my experience, vapor barriers are necessary because other elements of building system have been compromised - no vapor barrier is needed or wanted in a wood and cellulose building envelope - the materials virtually grew up handling moisture in their cellular structure and are fully capable of breathing as needed without condensing anywhere. Foams usually are vapor barriers, which can cause problems if not properly placed (as other commenters noted).
>
> Foam has a very poor greenhouse gas footprint. Cellulose has the best ghg footprint of all the insulation materials. It is also made from recycled materials, not chemicals.
>
> Last, cellulose is nontoxic, nonflammable, mold and mildew resistant, insect resistant, and rodent resistant. It won’t burn, while foams can burn ferociously while emitting poisonous gases.
>
> Gordon
>
>
>
>
>
>
>> On Jan 5, 2018, at 12:00 PM, greenbuilding-request at lists.bioenergylists.org wrote:
>>
>> Send Greenbuilding mailing list submissions to
>> greenbuilding at lists.bioenergylists.org
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>>
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>> than "Re: Contents of Greenbuilding digest..."
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>>
>> Today's Topics:
>>
>> 1. Re: rigid foam inside Larsen Truss? (Gordon West)
>> 2. Re: rigid foam inside Larsen Truss? (Beatrice Dohrn)
>> 3. Re: rigid foam inside Larsen Truss? (Mike O'Brien)
>> 4. Re: rigid foam inside Larsen Truss? (Reuben Deumling)
>>
>>
>> ----------------------------------------------------------------------
>>
>> Message: 1
>> Date: Thu, 4 Jan 2018 12:57:04 -0700
>> From: Gordon West <gordon.west at rtnewmexico.com>
>> To: greenbuilding at lists.bioenergylists.org
>> Subject: Re: [Greenbuilding] rigid foam inside Larsen Truss?
>> Message-ID: <73694A4B-4757-4E54-8474-5210D0AEA6DA at rtnewmexico.com>
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>> ------------------------------
>>
>> Message: 2
>> Date: Thu, 4 Jan 2018 22:05:09 +0000 (UTC)
>> From: Beatrice Dohrn <beatricedohrn at yahoo.com>
>> To: Green Building <greenbuilding at lists.bioenergylists.org>
>> Subject: Re: [Greenbuilding] rigid foam inside Larsen Truss?
>> Message-ID: <308684163.598792.1515103509555 at mail.yahoo.com>
>> Content-Type: text/plain; charset="utf-8"
>>
>> If you are up for saying why -- I love to learn!?
>> ?Beatrice Dohrn?
>>
>>
>> From: Gordon West <gordon.west at rtnewmexico.com>
>> To: greenbuilding at lists.bioenergylists.org
>> Sent: Thursday, January 4, 2018 12:43 PM
>> Subject: Re: [Greenbuilding] rigid foam inside Larsen Truss?
>>
>>
>> Forget the foam, stick with cellulose.
>> Gordon?
>>
>>
>>
>>
>>
>> On Jan 4, 2018, at 12:00 PM, greenbuilding-request at lists.bioenergylists.org wrote:
>> Send Greenbuilding mailing list submissions to
>> greenbuilding at lists.bioenergylists.org
>>
>> To subscribe or unsubscribe via the World Wide Web, visit
>> http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org
>>
>> or, via email, send a message with subject or body 'help' to
>> greenbuilding-request at lists.bioenergylists.org
>>
>> You can reach the person managing the list at
>> greenbuilding-owner at lists.bioenergylists.org
>>
>> When replying, please edit your Subject line so it is more specific
>> than "Re: Contents of Greenbuilding digest..."
>>
>>
>> Today's Topics:
>>
>> ??1. rigid foam inside Larsen Truss? (Reuben Deumling)
>> ??2. Re: rigid foam inside Larsen Truss? (David Wentling)
>> ??3. Re: rigid foam inside Larsen Truss? (RWT)
>>
>>
>> ----------------------------------------------------------------------
>>
>> Message: 1
>> Date: Thu, 4 Jan 2018 08:32:58 -0800
>> From: Reuben Deumling <9watts at gmail.com>
>> To: Greenbuilding <greenbuilding at lists.bioenergylists.org>
>> Subject: [Greenbuilding] rigid foam inside Larsen Truss?
>> Message-ID:
>> <CAE5fceAvHZHxN4uShFNPCysJcYD3R2mD8tVaxz_EBk0na+JNVQ at mail.gmail.com>
>> Content-Type: text/plain; charset="utf-8"
>>
>> I have a line on 3-1/2" rigid foam panels for pretty cheap. My 1894 house
>> has (of course) 2x4 walls into which I've blown dense pack cellulose. For
>> stage 2, I was going to add a Larsen truss (another 2x4 wall with a big
>> cavity between inner and outer walls) and blow cellulose into the rest for
>> an eventual 11" thick wall. But with these panels showing up I'm wondering
>> if there are reasons not to place these as the middle layer of a cellulose
>> sandwich? Seems like a quick and in this instance cheap way to get a lot of
>> 'r'. But I also don't want to do anything stupid when it comes to moisture.
>>
>> Thoughts?
>> -------------- next part --------------
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>>
>> ------------------------------
>>
>> Message: 2
>> Date: Thu, 4 Jan 2018 09:54:59 -0700
>> From: David Wentling <dpwentling at ymail.com>
>> To: "greenbuilding bioenergylist.org"
>> <greenbuilding at lists.bioenergylists.org>
>> Subject: Re: [Greenbuilding] rigid foam inside Larsen Truss?
>> Message-ID: <0C7356AE-A21F-45E3-8008-5B0EE1CCD6AA at ymail.com>
>> Content-Type: text/plain; charset="us-ascii"
>>
>> Historically, we have used the ratio of 1/3 R-value outside of any vapor retarder. ?Depending on the vapor characteristics of your foam, the amount of insulation R-value you add, and the framing and sheathing present, will determine if there would be a potential problem in the future.
>>
>> There are simple vapor models you can feed wall characteristics into and they estimate where condensation may occur.
>>
>> You are right to be concern. Perhaps modeling may show just install the foam board on the exterior and apply siding over, skipping the cost of the Larsen truss. Or not.
>>
>> You do to know what you can not measure.
>>
>> David Wentling
>>
>> On Jan 4, 2018, at 9:32 AM, Reuben Deumling <9watts at gmail.com> wrote:
>>
>> I have a line on 3-1/2" rigid foam panels for pretty cheap. My 1894 house has (of course) 2x4 walls into which I've blown dense pack cellulose. For stage 2, I was going to add a Larsen truss (another 2x4 wall with a big cavity between inner and outer walls) and blow cellulose into the rest for an eventual 11" thick wall. But with these panels showing up I'm wondering if there are reasons not to place these as the middle layer of a cellulose sandwich? Seems like a quick and in this instance cheap way to get a lot of 'r'. But I also don't want to do anything stupid when it comes to moisture.
>>
>> Thoughts?
>> _______________________________________________
>> Greenbuilding mailing list
>> to Send a Message to the list, use the email address
>> Greenbuilding at bioenergylists.org
>>
>> to UNSUBSCRIBE or Change your List Settings use the web page
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>> ------------------------------
>>
>> Message: 3
>> Date: Thu, 4 Jan 2018 17:34:27 +0000 (UTC)
>> From: RWT <archilogic at yahoo.ca>
>> To: Green Building <greenbuilding at lists.bioenergylists.org>
>> Subject: Re: [Greenbuilding] rigid foam inside Larsen Truss?
>> Message-ID: <1842894756.428117.1515087267398 at mail.yahoo.com>
>> Content-Type: text/plain; charset="utf-8"
>>
>> Reuben;
>> In the Olde Days before sim programs existed (ie before Win-Doze)? if one didn't want to bother graphically determining the dew point for a double stud wall assembly, the rule of thumb was to place the thing behaving as a vapour retarder/air barrier membrane within the first 1/3 (from inside -> out) of the total R-value of the wall assembly, in primarily heating climates like mine (Ottawa Ontario Canada).?
>> ?For? 11" wide double-stud wall that used the same insulation in the three layers (ie 2x4 interior? bearing wall + 3.5" cavity + 2x4 exterior curtain wall) this meant that the VDR/AB membrane could be placed on the outside of the bearing wall (usually backed up by structural sheathing) and the outside 2/3 of the insulation placed in the walls before the walls were tilted up? ... meaning that the walls were very well insulated and air-sealed before the interior was sheathed (same procedure for ceiling) so that the interior was toasty-warm in the middle of winter before any HVAC was installed.??
>> ?It also meant that services could be installed in the bearing wall cavity without having concerns (nightmares) about sub-trades compromising the integrity of the VDR/AB membrane.
>> ???On Thursday, January 4, 2018, 11:34:48 AM EST, Reuben Deumling <9watts at gmail.com> wrote: ?
>>
>> I have a line on 3-1/2" rigid foam panels for pretty cheap. My 1894 house has (of course) 2x4 walls into which I've blown dense pack cellulose. For stage 2, I was going to add a Larsen truss (another 2x4 wall with a big cavity between inner and outer walls) and blow cellulose into the rest for an eventual 11" thick wall. But with these panels showing up I'm wondering if there are reasons not to place these as the middle layer of a cellulose sandwich? Seems like a quick and in this instance cheap way to get a lot of 'r'. But I also don't want to do anything stupid when it comes to moisture.
>>
>> Thoughts?
>> _______________________________________________
>> Greenbuilding mailing list
>> to Send a Message to the list, use the email address
>> Greenbuilding at bioenergylists.org
>>
>> to UNSUBSCRIBE or Change your List Settings use the web page
>> http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org ?
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>>
>> Subject: Digest Footer
>>
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>> ------------------------------
>>
>> End of Greenbuilding Digest, Vol 89, Issue 1
>> ********************************************
>>
>>
>> _______________________________________________
>> Greenbuilding mailing list
>> to Send a Message to the list, use the email address
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>> Message: 3
>> Date: Thu, 4 Jan 2018 14:19:01 -0800
>> From: Mike O'Brien <obrien at hevanet.com>
>> To: Green Building <greenbuilding at lists.bioenergylists.org>
>> Subject: Re: [Greenbuilding] rigid foam inside Larsen Truss?
>> Message-ID: <00684607-0D4E-4C2A-9EC9-46DB0E68E0EB at hevanet.com>
>> Content-Type: text/plain; charset="utf-8"
>>
>> Hi Reuben?
>>
>> After your eloquent advocacy on behalf of making your house as sustainable as possible, I am surprised you would consider using polystyrene as an insulation material. Styrene manufacturing has historically been a toxic polluter, and styrene products may themselves damage health. Here?s some background from the CDC: https://www.atsdr.cdc.gov/toxprofiles/tp53-c6.pdf.
>>
>> Oregon code requires insulation under an electric water heater set on concrete, so we have one square of weight-bearing polystyrene to meet code, but I would have preferred zero.
>>
>> Best,
>>
>> Mike
>>
>>
>> On Jan 4, 2018, at 2:05 PM, Beatrice Dohrn via Greenbuilding <greenbuilding at lists.bioenergylists.org> wrote:
>>
>>
>> From: Beatrice Dohrn <beatricedohrn at yahoo.com>
>> Subject: Re: [Greenbuilding] rigid foam inside Larsen Truss?
>> Date: January 4, 2018 at 2:05:09 PM PST
>> To: Green Building <greenbuilding at lists.bioenergylists.org>
>> Reply-To: Beatrice Dohrn <beatricedohrn at yahoo.com>
>>
>>
>> If you are up for saying why -- I love to learn!
>>
>>
>> Beatrice Dohrn
>>
>>
>>
>> From: Gordon West <gordon.west at rtnewmexico.com>
>> To: greenbuilding at lists.bioenergylists.org
>> Sent: Thursday, January 4, 2018 12:43 PM
>> Subject: Re: [Greenbuilding] rigid foam inside Larsen Truss?
>>
>>
>> Forget the foam, stick with cellulose.
>>
>> Gordon
>>
>>
>>
>>
>>
>>> On Jan 4, 2018, at 12:00 PM, greenbuilding-request at lists.bioenergylists.org <mailto:greenbuilding-request at lists.bioenergylists.org> wrote:
>>>
>>> Send Greenbuilding mailing list submissions to
>>> greenbuilding at lists.bioenergylists.org <mailto:greenbuilding at lists.bioenergylists.org>
>>>
>>> To subscribe or unsubscribe via the World Wide Web, visit
>>> http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org
>>>
>>> or, via email, send a message with subject or body 'help' to
>>> greenbuilding-request at lists.bioenergylists.org
>>>
>>> You can reach the person managing the list at
>>> greenbuilding-owner at lists.bioenergylists.org
>>>
>>> When replying, please edit your Subject line so it is more specific
>>> than "Re: Contents of Greenbuilding digest..."
>>>
>>>
>>> Today's Topics:
>>>
>>> 1. rigid foam inside Larsen Truss? (Reuben Deumling)
>>> 2. Re: rigid foam inside Larsen Truss? (David Wentling)
>>> 3. Re: rigid foam inside Larsen Truss? (RWT)
>>>
>>>
>>> ----------------------------------------------------------------------
>>>
>>> Message: 1
>>> Date: Thu, 4 Jan 2018 08:32:58 -0800
>>> From: Reuben Deumling <9watts at gmail.com>
>>> To: Greenbuilding <greenbuilding at lists.bioenergylists.org>
>>> Subject: [Greenbuilding] rigid foam inside Larsen Truss?
>>> Message-ID:
>>> <CAE5fceAvHZHxN4uShFNPCysJcYD3R2mD8tVaxz_EBk0na+JNVQ at mail.gmail.com>
>>> Content-Type: text/plain; charset="utf-8"
>>>
>>> I have a line on 3-1/2" rigid foam panels for pretty cheap. My 1894 house
>>> has (of course) 2x4 walls into which I've blown dense pack cellulose. For
>>> stage 2, I was going to add a Larsen truss (another 2x4 wall with a big
>>> cavity between inner and outer walls) and blow cellulose into the rest for
>>> an eventual 11" thick wall. But with these panels showing up I'm wondering
>>> if there are reasons not to place these as the middle layer of a cellulose
>>> sandwich? Seems like a quick and in this instance cheap way to get a lot of
>>> 'r'. But I also don't want to do anything stupid when it comes to moisture.
>>>
>>> Thoughts?
>>> -------------- next part --------------
>>> An HTML attachment was scrubbed...
>>> URL: <http://lists.bioenergylists.org/pipermail/greenbuilding_lists.bioenergylists.org/attachments/20180104/e5869fb9/attachment-0001.html>
>>>
>>> ------------------------------
>>>
>>> Message: 2
>>> Date: Thu, 4 Jan 2018 09:54:59 -0700
>>> From: David Wentling <dpwentling at ymail.com>
>>> To: "greenbuilding bioenergylist.org"
>>> <greenbuilding at lists.bioenergylists.org>
>>> Subject: Re: [Greenbuilding] rigid foam inside Larsen Truss?
>>> Message-ID: <0C7356AE-A21F-45E3-8008-5B0EE1CCD6AA at ymail.com>
>>> Content-Type: text/plain; charset="us-ascii"
>>>
>>> Historically, we have used the ratio of 1/3 R-value outside of any vapor retarder. Depending on the vapor characteristics of your foam, the amount of insulation R-value you add, and the framing and sheathing present, will determine if there would be a potential problem in the future.
>>>
>>> There are simple vapor models you can feed wall characteristics into and they estimate where condensation may occur.
>>>
>>> You are right to be concern. Perhaps modeling may show just install the foam board on the exterior and apply siding over, skipping the cost of the Larsen truss. Or not.
>>>
>>> You do to know what you can not measure.
>>>
>>> David Wentling
>>>
>>> On Jan 4, 2018, at 9:32 AM, Reuben Deumling <9watts at gmail.com> wrote:
>>>
>>> I have a line on 3-1/2" rigid foam panels for pretty cheap. My 1894 house has (of course) 2x4 walls into which I've blown dense pack cellulose. For stage 2, I was going to add a Larsen truss (another 2x4 wall with a big cavity between inner and outer walls) and blow cellulose into the rest for an eventual 11" thick wall. But with these panels showing up I'm wondering if there are reasons not to place these as the middle layer of a cellulose sandwich? Seems like a quick and in this instance cheap way to get a lot of 'r'. But I also don't want to do anything stupid when it comes to moisture.
>>>
>>> Thoughts?
>>> _______________________________________________
>>> Greenbuilding mailing list
>>> to Send a Message to the list, use the email address
>>> Greenbuilding at bioenergylists.org
>>>
>>> to UNSUBSCRIBE or Change your List Settings use the web page
>>> http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org
>>>
>>> -------------- next part --------------
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>>>
>>> ------------------------------
>>>
>>> Message: 3
>>> Date: Thu, 4 Jan 2018 17:34:27 +0000 (UTC)
>>> From: RWT <archilogic at yahoo.ca>
>>> To: Green Building <greenbuilding at lists.bioenergylists.org>
>>> Subject: Re: [Greenbuilding] rigid foam inside Larsen Truss?
>>> Message-ID: <1842894756.428117.1515087267398 at mail.yahoo.com>
>>> Content-Type: text/plain; charset="utf-8"
>>>
>>> Reuben;
>>> In the Olde Days before sim programs existed (ie before Win-Doze)? if one didn't want to bother graphically determining the dew point for a double stud wall assembly, the rule of thumb was to place the thing behaving as a vapour retarder/air barrier membrane within the first 1/3 (from inside -> out) of the total R-value of the wall assembly, in primarily heating climates like mine (Ottawa Ontario Canada).?
>>> ?For? 11" wide double-stud wall that used the same insulation in the three layers (ie 2x4 interior? bearing wall + 3.5" cavity + 2x4 exterior curtain wall) this meant that the VDR/AB membrane could be placed on the outside of the bearing wall (usually backed up by structural sheathing) and the outside 2/3 of the insulation placed in the walls before the walls were tilted up? ... meaning that the walls were very well insulated and air-sealed before the interior was sheathed (same procedure for ceiling) so that the interior was toasty-warm in the middle of winter before any HVAC was installed.??
>>> ?It also meant that services could be installed in the bearing wall cavity without having concerns (nightmares) about sub-trades compromising the integrity of the VDR/AB membrane.
>>> On Thursday, January 4, 2018, 11:34:48 AM EST, Reuben Deumling <9watts at gmail.com> wrote:
>>>
>>> I have a line on 3-1/2" rigid foam panels for pretty cheap. My 1894 house has (of course) 2x4 walls into which I've blown dense pack cellulose. For stage 2, I was going to add a Larsen truss (another 2x4 wall with a big cavity between inner and outer walls) and blow cellulose into the rest for an eventual 11" thick wall. But with these panels showing up I'm wondering if there are reasons not to place these as the middle layer of a cellulose sandwich? Seems like a quick and in this instance cheap way to get a lot of 'r'. But I also don't want to do anything stupid when it comes to moisture.
>>>
>>> Thoughts?
>>> _______________________________________________
>>> Greenbuilding mailing list
>>> to Send a Message to the list, use the email address
>>> Greenbuilding at bioenergylists.org
>>>
>>> to UNSUBSCRIBE or Change your List Settings use the web page
>>> http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org
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>>> ------------------------------
>>>
>>> Subject: Digest Footer
>>>
>>> _______________________________________________
>>> Greenbuilding mailing list
>>> to Send a Message to the list, use the email address
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>>>
>>> to UNSUBSCRIBE or Change your List Settings use the web page
>>> http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org
>>>
>>>
>>> ------------------------------
>>>
>>> End of Greenbuilding Digest, Vol 89, Issue 1
>>> ********************************************
>>
>> _______________________________________________
>> Greenbuilding mailing list
>> to Send a Message to the list, use the email address
>> Greenbuilding at bioenergylists.org <mailto:Greenbuilding at bioenergylists.org>
>>
>> to UNSUBSCRIBE or Change your List Settings use the web page
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>>
>>
>>
>> _______________________________________________
>> Greenbuilding mailing list
>> to Send a Message to the list, use the email address
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>>
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>> ------------------------------
>>
>> Message: 4
>> Date: Thu, 4 Jan 2018 14:27:19 -0800
>> From: Reuben Deumling <9watts at gmail.com>
>> To: Green Building <greenbuilding at lists.bioenergylists.org>
>> Subject: Re: [Greenbuilding] rigid foam inside Larsen Truss?
>> Message-ID:
>> <CAE5fceCJLJTiQBaB0Z5M0kiJa75rquhogGsm4sQ9cLw+2B1qcA at mail.gmail.com>
>> Content-Type: text/plain; charset="UTF-8"
>>
>> This is a remainder/seconds lot, something my local discount building
>> supplier has (or had) on hand. As an inveterate scrounger I tend to
>> think of the secondary market (this stuff could be seen as fitting
>> into that category) sends a less direct or even no signal to the
>> suppliers and as such can perhaps be more easily justified.
>> I'd not be inclined to purchase enough of these panels to sheet an
>> entire house at new prices, both because of cost and the reasons you
>> suggest.
>>
>> I'm always open to learning more. I like the skip the foam panels
>> suggestion, seems simpler, but figured I should check with you folks
>> first.
>>
>>
>>> On 1/4/18, Mike O'Brien <obrien at hevanet.com> wrote:
>>> Hi Reuben?
>>>
>>> After your eloquent advocacy on behalf of making your house as sustainable
>>> as possible, I am surprised you would consider using polystyrene as an
>>> insulation material. Styrene manufacturing has historically been a toxic
>>> polluter, and styrene products may themselves damage health. Here?s some
>>> background from the CDC: https://www.atsdr.cdc.gov/toxprofiles/tp53-c6.pdf.
>>>
>>> Oregon code requires insulation under an electric water heater set on
>>> concrete, so we have one square of weight-bearing polystyrene to meet code,
>>> but I would have preferred zero.
>>>
>>> Best,
>>>
>>> Mike
>>>
>>>
>>> On Jan 4, 2018, at 2:05 PM, Beatrice Dohrn via Greenbuilding
>>> <greenbuilding at lists.bioenergylists.org> wrote:
>>>
>>>
>>> From: Beatrice Dohrn <beatricedohrn at yahoo.com>
>>> Subject: Re: [Greenbuilding] rigid foam inside Larsen Truss?
>>> Date: January 4, 2018 at 2:05:09 PM PST
>>> To: Green Building <greenbuilding at lists.bioenergylists.org>
>>> Reply-To: Beatrice Dohrn <beatricedohrn at yahoo.com>
>>>
>>>
>>> If you are up for saying why -- I love to learn!
>>>
>>>
>>> Beatrice Dohrn
>>>
>>>
>>>
>>> From: Gordon West <gordon.west at rtnewmexico.com>
>>> To: greenbuilding at lists.bioenergylists.org
>>> Sent: Thursday, January 4, 2018 12:43 PM
>>> Subject: Re: [Greenbuilding] rigid foam inside Larsen Truss?
>>>
>>>
>>> Forget the foam, stick with cellulose.
>>>
>>> Gordon
>>>
>>>
>>>
>>>
>>>
>>>> On Jan 4, 2018, at 12:00 PM,
>>>> greenbuilding-request at lists.bioenergylists.org
>>>> <mailto:greenbuilding-request at lists.bioenergylists.org> wrote:
>>>>
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>>>>
>>>> Today's Topics:
>>>>
>>>> 1. rigid foam inside Larsen Truss? (Reuben Deumling)
>>>> 2. Re: rigid foam inside Larsen Truss? (David Wentling)
>>>> 3. Re: rigid foam inside Larsen Truss? (RWT)
>>>>
>>>>
>>>> ----------------------------------------------------------------------
>>>>
>>>> Message: 1
>>>> Date: Thu, 4 Jan 2018 08:32:58 -0800
>>>> From: Reuben Deumling <9watts at gmail.com>
>>>> To: Greenbuilding <greenbuilding at lists.bioenergylists.org>
>>>> Subject: [Greenbuilding] rigid foam inside Larsen Truss?
>>>> Message-ID:
>>>> <CAE5fceAvHZHxN4uShFNPCysJcYD3R2mD8tVaxz_EBk0na+JNVQ at mail.gmail.com>
>>>> Content-Type: text/plain; charset="utf-8"
>>>>
>>>> I have a line on 3-1/2" rigid foam panels for pretty cheap. My 1894 house
>>>> has (of course) 2x4 walls into which I've blown dense pack cellulose. For
>>>> stage 2, I was going to add a Larsen truss (another 2x4 wall with a big
>>>> cavity between inner and outer walls) and blow cellulose into the rest
>>>> for
>>>> an eventual 11" thick wall. But with these panels showing up I'm
>>>> wondering
>>>> if there are reasons not to place these as the middle layer of a
>>>> cellulose
>>>> sandwich? Seems like a quick and in this instance cheap way to get a lot
>>>> of
>>>> 'r'. But I also don't want to do anything stupid when it comes to
>>>> moisture.
>>>>
>>>> Thoughts?
>>>> -------------- next part --------------
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>>>>
>>>> ------------------------------
>>>>
>>>> Message: 2
>>>> Date: Thu, 4 Jan 2018 09:54:59 -0700
>>>> From: David Wentling <dpwentling at ymail.com>
>>>> To: "greenbuilding bioenergylist.org"
>>>> <greenbuilding at lists.bioenergylists.org>
>>>> Subject: Re: [Greenbuilding] rigid foam inside Larsen Truss?
>>>> Message-ID: <0C7356AE-A21F-45E3-8008-5B0EE1CCD6AA at ymail.com>
>>>> Content-Type: text/plain; charset="us-ascii"
>>>>
>>>> Historically, we have used the ratio of 1/3 R-value outside of any vapor
>>>> retarder. Depending on the vapor characteristics of your foam, the amount
>>>> of insulation R-value you add, and the framing and sheathing present, will
>>>> determine if there would be a potential problem in the future.
>>>>
>>>> There are simple vapor models you can feed wall characteristics into and
>>>> they estimate where condensation may occur.
>>>>
>>>> You are right to be concern. Perhaps modeling may show just install the
>>>> foam board on the exterior and apply siding over, skipping the cost of the
>>>> Larsen truss. Or not.
>>>>
>>>> You do to know what you can not measure.
>>>>
>>>> David Wentling
>>>>
>>>> On Jan 4, 2018, at 9:32 AM, Reuben Deumling <9watts at gmail.com> wrote:
>>>>
>>>> I have a line on 3-1/2" rigid foam panels for pretty cheap. My 1894 house
>>>> has (of course) 2x4 walls into which I've blown dense pack cellulose. For
>>>> stage 2, I was going to add a Larsen truss (another 2x4 wall with a big
>>>> cavity between inner and outer walls) and blow cellulose into the rest for
>>>> an eventual 11" thick wall. But with these panels showing up I'm wondering
>>>> if there are reasons not to place these as the middle layer of a cellulose
>>>> sandwich? Seems like a quick and in this instance cheap way to get a lot
>>>> of 'r'. But I also don't want to do anything stupid when it comes to
>>>> moisture.
>>>>
>>>> Thoughts?
>>>> _______________________________________________
>>>> Greenbuilding mailing list
>>>> to Send a Message to the list, use the email address
>>>> Greenbuilding at bioenergylists.org
>>>>
>>>> to UNSUBSCRIBE or Change your List Settings use the web page
>>>> http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org
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>>>>
>>>> ------------------------------
>>>>
>>>> Message: 3
>>>> Date: Thu, 4 Jan 2018 17:34:27 +0000 (UTC)
>>>> From: RWT <archilogic at yahoo.ca>
>>>> To: Green Building <greenbuilding at lists.bioenergylists.org>
>>>> Subject: Re: [Greenbuilding] rigid foam inside Larsen Truss?
>>>> Message-ID: <1842894756.428117.1515087267398 at mail.yahoo.com>
>>>> Content-Type: text/plain; charset="utf-8"
>>>>
>>>> Reuben;
>>>> In the Olde Days before sim programs existed (ie before Win-Doze)? if one
>>>> didn't want to bother graphically determining the dew point for a double
>>>> stud wall assembly, the rule of thumb was to place the thing behaving as a
>>>> vapour retarder/air barrier membrane within the first 1/3 (from inside ->
>>>> out) of the total R-value of the wall assembly, in primarily heating
>>>> climates like mine (Ottawa Ontario Canada).?
>>>> ?For? 11" wide double-stud wall that used the same insulation in the three
>>>> layers (ie 2x4 interior? bearing wall + 3.5" cavity + 2x4 exterior curtain
>>>> wall) this meant that the VDR/AB membrane could be placed on the outside
>>>> of the bearing wall (usually backed up by structural sheathing) and the
>>>> outside 2/3 of the insulation placed in the walls before the walls were
>>>> tilted up? ... meaning that the walls were very well insulated and
>>>> air-sealed before the interior was sheathed (same procedure for ceiling)
>>>> so that the interior was toasty-warm in the middle of winter before any
>>>> HVAC was installed.??
>>>> ?It also meant that services could be installed in the bearing wall cavity
>>>> without having concerns (nightmares) about sub-trades compromising the
>>>> integrity of the VDR/AB membrane.
>>>> On Thursday, January 4, 2018, 11:34:48 AM EST, Reuben Deumling
>>>> <9watts at gmail.com> wrote:
>>>>
>>>> I have a line on 3-1/2" rigid foam panels for pretty cheap. My 1894 house
>>>> has (of course) 2x4 walls into which I've blown dense pack cellulose. For
>>>> stage 2, I was going to add a Larsen truss (another 2x4 wall with a big
>>>> cavity between inner and outer walls) and blow cellulose into the rest for
>>>> an eventual 11" thick wall. But with these panels showing up I'm wondering
>>>> if there are reasons not to place these as the middle layer of a cellulose
>>>> sandwich? Seems like a quick and in this instance cheap way to get a lot
>>>> of 'r'. But I also don't want to do anything stupid when it comes to
>>>> moisture.
>>>>
>>>> Thoughts?
>>>> _______________________________________________
>>>> Greenbuilding mailing list
>>>> to Send a Message to the list, use the email address
>>>> Greenbuilding at bioenergylists.org
>>>>
>>>> to UNSUBSCRIBE or Change your List Settings use the web page
>>>> http://lists.bioenergylists.org/mailman/listinfo/greenbuilding_lists.bioenergylists.org
>>>>
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>>>> ------------------------------
>>>>
>>>> Subject: Digest Footer
>>>>
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>>>> ------------------------------
>>>>
>>>> End of Greenbuilding Digest, Vol 89, Issue 1
>>>> ********************************************
>>>
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>>
>>
>>
>> ------------------------------
>>
>> Subject: Digest Footer
>>
>> _______________________________________________
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>> ------------------------------
>>
>> End of Greenbuilding Digest, Vol 89, Issue 2
>> ********************************************
>
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