Historic Resources Committee

This message has been cross posted to the following Discussion Forums: Housing Knowledge Community and Historic Resources Committee .
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We're working on the restoration of a c.1875 vernacular Italianate home. The exterior walls are composed of full 2x4s with 3/4" painted shiplap siding nailed directly to the framing (no sheathing). The cavities were filled with brick nogging. At the interior, the lath and plaster comprised a 1-1/4" overall thickness. Due to the discovery of extensive rot and insect damage, the damaged interior plaster wall finishes have been removed as has the nogging, and the bare wood back face of the siding has been exposed (and yes, most of the siding boards have a slight convex curve at the exterior). We're planning to insulate the cavities, then sheath the interior with 3/4" plywood and cover that with 1/2" GWB, which will get our wall surface back where we need it to be in relation to the casings and mouldings we've preserved. My questions are as follows:

- We're considering priming the exposed back of the siding using an oil-based primer or even a liquid house wrap product such as Ben Moore Super Spec Latex Vapor Barrier Primer Sealer 260 to help stabilize the siding and provide a measure of protection for the insulation that will of necessity be immediately beneath the siding. Both we and the owners are skeptical of the test results for such liquid house wraps with regard to their potential toxicity.
- While rigid or batt insulation will not meet code requirements for R-value, both we and the owners are reluctant to use a higher R-value spray foam insulation such as icynene for the same potential toxicity reason. The owners and local officials are, if necessary, willing to take what they can get in terms of R-value.

Can anyone weigh in on the the use of primer, liquid house wrap, and spray foam insulation at a dwelling of this type, or provide other solutions with which you've had experience? Much appreciated---

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Robert Silarski AIA
Principal
S&Co.'Architecture+Design
Nyack NY
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If there is mildew on the back of the siding, spray ti with a mildewcide, let it dry and apply a clear preservative.

Why are you applying 3/4" plywood over the studs prior to installing drywall? You can use vertical furring strips if all you are trying to do is put the face of the drywall in the same plane as the original plaster.

I'm not sure of the results of installing the rigid insulation in the wall cavities or how that will compare to the more traditional fiberglass batt insulation. Depends on how much you use, I guess. With the traditional fiberglass batts attached to the back of the studs or vertical furring strips you do have an air space for drainage, etc. and you have an effective stud depth of 5 3/4".


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Donald Yelverton AIA
Yelverton Architects, PA
Charlotte NC
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If you are in a cold climate like the midwest dont forget your vapor barrier behind your drywall (warm side of insulation).  We have wrapped tyvek around in the old cavity against the siding and around the studs...it only takes a little labor, stapled to keep up in cavity...
Then you can blow cellulose, use batts, etc. to fill cavity.  

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Nelson B. Nave AIA
Owner
Nelson Breech Nave, AIA Architect
Kalamazoo MI
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Original Message:
Sent: 07-26-2013 17:52
From: Donald Yelverton
Subject: Insulating a c.1875 Italianate

If there is mildew on the back of the siding, spray ti with a mildewcide, let it dry and apply a clear preservative.

Why are you applying 3/4" plywood over the studs prior to installing drywall? You can use vertical furring strips if all you are trying to do is put the face of the drywall in the same plane as the original plaster.

I'm not sure of the results of installing the rigid insulation in the wall cavities or how that will compare to the more traditional fiberglass batt insulation. Depends on how much you use, I guess. With the traditional fiberglass batts attached to the back of the studs or vertical furring strips you do have an air space for drainage, etc. and you have an effective stud depth of 5 3/4".


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Donald Yelverton AIA
Yelverton Architects, PA
Charlotte NC
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If there is mildew on the back of the siding, spray ti with a mildewcide, let it dry and apply a clear preservative.

Why are you applying 3/4" plywood over the studs prior to installing drywall? You can use vertical furring strips if all you are trying to do is put the face of the drywall in the same plane as the original plaster.

I'm not sure of the results of installing the rigid insulation in the wall cavities or how that will compare to the more traditional fiberglass batt insulation. Depends on how much you use, I guess. With the traditional fiberglass batts attached to the back of the studs or vertical furring strips you do have an air space for drainage, etc. and you have an effective stud depth of 4 3/4".


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Donald Yelverton AIA
Yelverton Architects, PA
Charlotte NC
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I'd be reluctant to do anything more than primer.  You don't want the coating to stop the siding from drying toward the backside when the siding gets wet from wind driven rain.

You might try something like I did on the restoration of a historic cotton gin into my home.  I that case, we nailed 1 x 1 strips to the studs and up tight to the siding, then attached a 1/8" thick weather barrier sheathing to the 1 x 1's.  This created an air space, making the siding a rain screen.  The siding had never been painted so we wanted it to breathe as it had before.  We made the decision to use low density spray foam to get as much r-value as we could from the remaining stud cavity and to install an energy recovery ventilator to keep the indoor environment fresh.  You could probably do a similar thing by putting the 1/8" sheathing directly on the siding and then putting the 1 x 1's on top bedded in sealant which would preserve more stud cavity for non foam insulation.  I think the critical thing is to create an air barrier to stop infiltration transfer of heat and more importantly, moisture.

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James Smith AIA
HagerSmith Design, PA
Raleigh NC
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What you describe sounds like a bad strategy and may actually make the moisture problems in the wall worse than they were.  The lap siding is not watertight and will continue to allow water into the cavity.  The original brick nogging provided lots of moisture storage capacity and may never have dried out completely contributing to the mold and rot. Filling the cavity with batt insulation without an air gap will not improve the situation much since the insulation will become saturated and lose its R-value.  The wood framing will continue to get wet from water leaking through the joints and gaps in the siding. The proposed 3/4" plywood may also collect moisture and damage the drywall.  You really don't want to create a vapor barrier exterior to the insulation since this will inhibit any drying to the exterior.  To really address the moisture problem, I think you need to think about removing the siding and installing a breathable waterproof membrane over the exterior side of the studs.  This may also mean adding sheathing since most membranes require a solid substrate.  Instead of the 3/4" plywood on the interior, furring strips would be better and provide space to allow and air gap on the exterior side of the insulation.

Ideally, this should be modeled in WUFI to test the moisture flow with different configurations and materials to select the best solution.  In lieu of that, you should consult with a reputable building envelope consultant who should be able to help design a solution that minimizes the risk of future moisture problems and improves the wall performance while maintaining the integrity of the historic building fabric. Although this will add cost to the project, it may be worth the money to you and your client to insure against future problems and the cost of remedial work.

Good luck. 

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George Bryant
Philadelphia PA
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Let me suggest a simpler, easier and cheaper solution: leave the siding on and fill the cavity with blown in cellulose (chopped newspapers) treated with borates.  Hurricanes occasionally drive water all the way through my 1899 walls (cedar clapboards with no sheathing) but a recently cut opening to install a backer board revealed that there was no mold at all after 10 years.  

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Ward Bucher AIA
Bucher/Borges Group PLLC
Easton MD
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Original Message:
Sent: 07-30-2013 09:47
From: George Bryant
Subject: Insulating a c.1875 Italianate

What you describe sounds like a bad strategy and may actually make the moisture problems in the wall worse than they were.  The lap siding is not watertight and will continue to allow water into the cavity.  The original brick nogging provided lots of moisture storage capacity and may never have dried out completely contributing to the mold and rot. Filling the cavity with batt insulation without an air gap will not improve the situation much since the insulation will become saturated and lose its R-value.  The wood framing will continue to get wet from water leaking through the joints and gaps in the siding. The proposed 3/4" plywood may also collect moisture and damage the drywall.  You really don't want to create a vapor barrier exterior to the insulation since this will inhibit any drying to the exterior.  To really address the moisture problem, I think you need to think about removing the siding and installing a breathable waterproof membrane over the exterior side of the studs.  This may also mean adding sheathing since most membranes require a solid substrate.  Instead of the 3/4" plywood on the interior, furring strips would be better and provide space to allow and air gap on the exterior side of the insulation.

Ideally, this should be modeled in WUFI to test the moisture flow with different configurations and materials to select the best solution.  In lieu of that, you should consult with a reputable building envelope consultant who should be able to help design a solution that minimizes the risk of future moisture problems and improves the wall performance while maintaining the integrity of the historic building fabric. Although this will add cost to the project, it may be worth the money to you and your client to insure against future problems and the cost of remedial work.

Good luck. 

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George Bryant
Philadelphia PA
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We have recently conducted a fairly disciplined study for insulation in historic structures, the final draft of which exists on the Preservation League of New York State's website (http://www.preservenys.org/energyworkshops/?page_id=1898).  While it may not be the ultimate authoritative stop on your research for solutions, it is a reasonable attempt and a disciplined review of what happens when we insulate old buildings in NYS.

Conclusions from building to building can change based on the age, exposure and integrity of the construction assembly; how the building is heated and cooled; the climate it's in and propensity for infiltration.  We utilized a pretty broad platform of software for the analysis (including WUFI), and it may be worth doing some derivation of the same, if only to a limited extent for your Italianate before moving forward.

My own house is an 1867 Italianate in Voorheesville, NY.  The previous owner blew cellulose into wall and ceiling cavities in 1980 and the building has survived remarkably, with no envelope degradation, in part because of its substantial roof overhangs, wrap-around porches and intact wall assemblies.  Perhaps the most significant factor may be that it's heated and air conditioned with an air system and has exterior and interior storms in addition to the double hung windows (helps cut down the noise when CSX goes by).

The point is to take a broader, calculated look at all the contributing factors specific to your building before making a final decision on how to treat the existing fabric and how if not whether to insulate.




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Stephen Reilly AIA, LEED AP, BD+C
EYP Architecture & Engineering P.C.
Albany NY
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Original Message:
Sent: 08-07-2013 15:52
From: Ward Bucher
Subject: Insulating a c.1875 Italianate

Let me suggest a simpler, easier and cheaper solution: leave the siding on and fill the cavity with blown in cellulose (chopped newspapers) treated with borates.  Hurricanes occasionally drive water all the way through my 1899 walls (cedar clapboards with no sheathing) but a recently cut opening to install a backer board revealed that there was no mold at all after 10 years.  

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Ward Bucher AIA
Bucher/Borges Group PLLC
Easton MD
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I agree with Ward - I like cellulose insulation.  Recycled newspaper that kills roaches and termites.  Best use of newspaper.  Make sure the bottom of the wall has blocking if it is ballon construction.  Make sure the lap siding is attached to the studs well.  Blow it in dense.  

Taking the siding off, insulating and putting an air barrier is best, but expensive.  Here I would use damp blown cellulose to fill the cavity.

I have blown dry cellulose in two older house by removing a lap siding half way up and at the top.  Blow it in dense so it will not settle.  Have had no problems.  It might get wet at times but will dry out soon afterwards.  Have never seen mold problems.

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Edward Cazayoux FAIA
Principal/architect
EnvironMental Design
Breaux Bridge LA
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Original Message:
Sent: 08-07-2013 15:52
From: Ward Bucher
Subject: Insulating a c.1875 Italianate

Let me suggest a simpler, easier and cheaper solution: leave the siding on and fill the cavity with blown in cellulose (chopped newspapers) treated with borates.  Hurricanes occasionally drive water all the way through my 1899 walls (cedar clapboards with no sheathing) but a recently cut opening to install a backer board revealed that there was no mold at all after 10 years.  

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Ward Bucher AIA
Bucher/Borges Group PLLC
Easton MD
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