[Greenbuilding] Exterior insulation retrofit

Sam Ewbank g.l.ewbank at gmail.com
Fri Apr 29 06:32:02 PDT 2011


Sounds like Roxul is very dense stuff.  (I've been accused of worse)
The link that Jason provided yesterday was for Roxul Curtain Wall which from
my understanding of the literature has a moisture sorption rate of .01%
under ASTM C1104 but does not state if it is hydrophobic or not.  The
product sheets for Roxul Drainboard and Cavity Rock state they are
hydrophobic.  XPS is hydrophobic and it's moisture sorption rate is tested
under different ASTM specs but they seem to have similar values when Roxul
is installed with a air barrier behind it and a cavity or rainscreen
cladding for moisture management. Would you agree with this?
What I don't know is the difference in pricing which is likely more then the
fastener choice.

As for shingles, if one were to pre-dip or pre-finish the shingles and then
seal any cut edges during installation would that ease your worry?  This may
take away from the common belief that wood shingles repel moisture better
when they swell up and make tighter joints but proper installation and
attention to detail should create a proper barrier to the elements.  Sealing
the material should also help negate the effects of reverse vapor drive that
you mention, where the siding or cladding is soaked by rain and then the sun
comes out driving the moisture held by the siding in towards the structure.
I don't recommend installing any wood siding product without sealing prior
to installation.
I agree  that wood clapboard needs to be sealed on all sides, especially end
cuts while also making provisions for water behind all field joints.

Thanks for your time

Sam


On Fri, Apr 29, 2011 at 7:55 AM, John Straube <jfstraube at gmail.com> wrote:

> I do not, but beleive, if done with care, they can work.
> We have played with 4, 6 and 8 pound per cubic foot Roxul, and attached
> siding to this for mockups. Seemed to work really well.
> Inward vapor drives need to be handled since Roxul is highly permeable, but
> should be OK with good ventilation behind the cladding.  Cedar shingles
> worry me, as they store a tremendous amount of rainwater.  Fibercement or
> painted (all size sides) would clapboard would be OK if on the 1x3 furring
> strip.
>
> We have use GRK: very nice.  Too expensive when we bought them, but really
> nice.
>
>
> On 2011-04-29, at 7:51 AM, Sam Ewbank wrote:
>
> John et all,
> do you know of any projects where Roxul or similar rockwool product was
> used in place of foam in the same style as the Sears Roebuck house
> installation?
>
> I have been happy using GRK fasteners and are locally available at
> lumberyards in my area.
> http://www.grkfasteners.com/index.asp
>
> Sam
>
>
>
> On Fri, Apr 29, 2011 at 7:34 AM, jfstraube <jfstraube at gmail.com> wrote:
>
>> I am not near by: Waterloo and Boston.
>> If you look at at the article by Betsy Petit in the retrofit of a 1916
>> Sears Roebuck house, you will see one approach we have used numerous times.
>> strip to board, drill holes and densepack with cellulose, IR scan to
>> confirm all cavities full, Tyvek Drainwrap taped and seal (as air barrier
>> and secondary drainage plane), special care at mudsill and roof with tapes
>> and foam, then two staggered layers of foam insulation, outer layer taped
>> (as primary drainage plane), 1x3 screwed to nominal 1" sheathing boards,
>> cladding.  I think TimberLok are too big and I know that we dont need them:
>> we use them because they are locally available in the 6-10" lengths we need.
>>  For other project we order roofing screws from commercial roofing supply
>> stores.
>>
>> You would be "safe" with just 1.5" of polyiso over 2x4 with cellulose, but
>> I would recommend more, two, 1.5" layers would mean you are done for the
>> next 100 years.
>>
>> The larsen truss on the exterior requires more care and effort to get good
>> performance, because foam plastics are air impermeable, non-hygroscopic, and
>> vapor semi-impermeable: using cellulose as exterior insulation is a
>> completely different animal and requires better care and control of air flow
>> control, reverse water vapor drive (particularuly with shingle cladding)
>> etc.  Is, has, and can be done, but lots more things that have and do go
>> wrong.
>>
>>
>>
>> On 2011-04-28, at 9:43 AM, bill.allen at verizon.net wrote:
>>
>> > John,
>> > I am in Mt. Vernon, NY, climate zone 4 about 15 miles north of New York
>> City.
>> > Looking for recommendations for new barriers....some say taped styrofoam
>> is good enough for both but I am open to suggestions....
>> > Are you near by?
>> > Bill
>> >
>> > -----Original Message-----
>> > From: "John Straube" <jfstraube at gmail.com>
>> > Date: Thu, 28 Apr 2011 12:57:16
>> > To: <bill.allen at verizon.net>; Green Building<
>> greenbuilding at lists.bioenergylists.org>
>> > Reply-to: jfstraube at gmail.com
>> > Subject: Re: [Greenbuilding] Exterior insulation retrofit
>> >
>> > I have done this. What climate are you in? To avoid condensation even
>> 1.5" is usually more than enough but I would recommend more for energy
>> > what is your new water control layer?
>> > Air control layer?
>> >
>> > Sent wirelessly from my BlackBerry device on the Bell network.
>> >
>> > -----Original Message-----
>> > From: bill.allen at verizon.net
>> > Sender: greenbuilding-bounces at lists.bioenergylists.org
>> > Date: Thu, 28 Apr 2011 12:45:46
>> > To: Green Building<greenbuilding at lists.bioenergylists.org>
>> > Reply-To: bill.allen at verizon.net,
>> >       Green Building <greenbuilding at lists.bioenergylists.org>
>> > Subject: [Greenbuilding] Exterior insulation retrofit
>> >
>> > Hi all,
>> >
>> > I am researching a project for my single family home. Classic 1926 stick
>> construction. Zero insulation in the walls...time yet again for an external
>> paint job. Would really appreciate comments on the following plan:
>> >
>> > We never want to paint again...are thinking of natural cedar shingle
>> siding, maybe with preservative but otherwise left natural.  Don't like the
>> embodied energy in the various cement siding solutions....alternatives?
>> >
>> > While the siding is down, fill the wall cavities with cellulous from the
>> outside.
>> >
>> > Replace original double hung windows with new construction insulated,
>> R-5 if we can afford it, windows mounted "innie" on the plane of the
>> original dimensional 1x lumber t+g sheathing.
>> >
>> > Add external insulation....rigid styrofoam.  Since there is no interior
>> vapor barrier (plaster on wood lathe), I am worried about the dew point
>> ending up in the center of the wall...therefore, per the building science
>> article, add 4" of styrofoam to the outside to keep the dew point external
>> of the sheathing.
>> >
>> > Will require careful details at windows and other penetrations.
>> >
>> > Big job...has anyone done this?  Any comments on any part of the above
>> would be most welcomed.
>> >
>> > Thanks,
>> > Bill
>> > _______________________________________________
>> > Greenbuilding mailing list
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>>
>> John Straube
>> www.BuildingScience.com
>>
>>
>>
>>
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>
> _______________________________________________
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>
> Dr John Straube, P.Eng.
> Associate Professor
> University of Waterloo
> Dept of Civil Eng. & School of Architecture
> www.buildingscience.com
>
>
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