Re: Venting & Drying Brick Veneer Wall

[Guest guest]

Tony, :

any chance that one of the siloxanes you've found in indoor environment air samples is decamethylcyclopentasiloxane (DMCPS)?

Wane

> > > > (Apologies for thoise that don't like attachments)> > Interesting on the siloxane. What did you use for the method and what levels are you finding?> > - see attached head pressure test (standpipe held on with plumber's putty) on a siloxane based coating on a commecial brick building. Note that both tests are on the mortar which is the weakest point. Manufacturer warranties the coating for 15 years. I did the capital equivalent calcs for 21 years based on re-coating and tuckpointing every 7 years (don't trust the manufacturer's data). It was better to coat than replace. We figured with minor cracks and the like that 7 years for the brickwork as well.> > > Tony> ..........................................................................> "Tony" Havics, CHMM, CIH, PE> pH2, LLC> PO Box 34140> Indianapolis, IN 46234> > cell> > 90% of Risk Management is knowing where to place the decimal point...any consultant can give you the other 10%â„ > > This message is from pH2. This message and any attachments may contain legally privileged or confidential information, and are intended only for the individual or entity identified above as the addressee. If you are not the addressee, or if this message has been addressed to you in error, you are not authorized to read, copy, or distribute this message and any attachments, and we ask that you please delete this message and attachments (including all copies) and notify the sender by return e-mail or by phone at . Delivery of this message and any attachments to any person other than the intended recipient(s) is not intended in any way to waive confidentiality or a privilege. All personal messages express views only of the sender, which are not to be attributed to pH2 and may not be copied or distributed without this statement.> > > > > Re: Venting & Drying Brick Veneer Wall> > Jeff:> > Your use of a siloxane-based sealer is a great method, and it is one of the best methods to reduce water absorptivity while not substantially changing porosity of the clay body. However, from an IAQ perspective, I am finding a lot of siloxanes in indoor air samples. Something that was not present 15-years ago. Still unsure what it all means.> > For what it is worth....>

[Guest guest]

Thanks for taking the time. I'll respond in bold font for ease of reading. Great thoughts to consider.>> > > For some reason prior to occupancy, he removed a 6 foot linear section of> > plastic from a second floor bedroom wall (west-facing gable end of the> > 2-story home) and replaced the drywall & unfaced insulation without the> > plastic vapor barrier. The drywall in this section shows marginally> > damp, which I believe is partially due to this section being the sole> > water vapor inlet along this wall.> > It may be the pathway by which vapor is drawn in from the wall cavity as you > suspect, but I would want to know the reason the sheetrock and insulation were > removed in the first place. If there was prior water damage in this area, > the cause may be something more direct and local (i.e., water entering at the > roof rake). Don't remember the reason (he told me, but forgot), but don't think it was water event-related. If it was, I'll follow-up.> > I would also try to assess the common problem of capillary bridging caused by > mortar falling into the air space and contacting both the facade and the air > barrier, which can wick moisture into the sheathing. Tyvek is porous and felt > tar paper will eventually become microbially digested if constantly wet. IR > thermography might be the best tool to find the wet spots -- especially after a> good rain when the heat is on to intensify evaporative cooling. IR camera doesn't see evaporative cooling because of vapor barrier which stops water from getting to drywall, except at transition points, seams, etc. At least, that's when I have seen temperature gradients with IR. But, water that condenses and flows to bottom plate inside wall, if it makes to floor, would be visible. Thinking of using dataloggers, though.> > Power venting of a wall system does not seem cost-justifiable or feasible > over the life of a building. Maybe just adding more weep holes will improve > passive/convective ventilation. Applying and maintaining a silicone treatment to > the exterior might also be a somewhat effective band-aid. Yep. Kind of what I was thinking. Always a fan of passive approach for maintenance reasons (i.e., never gets done). Siloxane type is going to be used. I've gotten info from bia.org tech notes regarding sealants. Saw some interesting posts about this topic as well.> > Just some thoughts. I'm involved in a couple of situations involving brick > exteriors now.> > Steve Temes>

[Guest guest]

Amen, a great book that I regularly recommend to builders and aggressive DIY homeowners. $45 or $50 well spent for the applicable climate>> Hi Bruce> Allow me to suggest a site that offers builders' guides for mixed climates. > Few builders understand permeable vapor retarders or simply put "vapor > migration" and the consequences of a vapor barrier placed in a structure.> > www.eeba.org http://www.eeba.org/bookstore/book.asp?BookID=1> > Valin>

[Guest guest]

Good point. Although this appears to be a well-built home by an very highly regarded 30 year builder, no fresh air intake/exchange to HVAC and a 2 story home with ridge roof vent and ductwork in attic makes for negative pressure situation (quick smoke pencil confirmed, at least qualitatively). At this point, retrofit SCS-type air barrier and positive pressurization of HVAC makes sense. Of course that doesn't address vapor pressure differential driver across the vapor barrier, which is where increased venting of the rain screen (brick veneer) will play a role, I believe.Thanks for the thoughtful input>> > One other thought, did you check the home to assure negative pressure> doesn't develop with the doors of different areas closed?> > Terry, remember that residence in Hallandale, Florida you and I were on,> where the picture was stuck to the wall? There was so much mold behind> it, it was holding it to the wall.> > It was the model for the full employment act for consultants, no air> space between the wall and the picture, Glass front, negative pressure> and 68 degrees indoors in the middle of summer.>

[Guest guest]

Can you explain the negative pressure

differential please

Jeff

London

-----Original

Message-----

From: iequality

[mailto:iequality ] On Behalf

Of Bruce N. Fergusson, PE

Sent: 17 September 2006 02:58

To: iequality

Subject: Re: Venting

& Drying Brick Veneer Wall

Good point. Although this

appears to be a well-built home by an very highly regarded 30 year builder, no

fresh air intake/exchange to HVAC and a 2 story home with ridge roof vent and

ductwork in attic makes for negative pressure situation (quick smoke pencil

confirmed, at least qualitatively). At this point, retrofit

SCS-type air barrier and positive pressurization of HVAC makes sense. Of

course that doesn't address vapor pressure differential driver across the vapor

barrier, which is where increased venting of the rain screen (brick veneer)

will play a role, I believe.

Thanks for the thoughtful input

>

>

> One other thought, did you check the home to assure negative pressure

> doesn't develop with the doors of different areas closed?

>

> Terry, remember that residence in Hallandale, Florida you! and I were on,

> where the picture was stuck to the wall? There was so much mold behind

> it, it was holding it to the wall.

>

> It was the model for the full employment act for consultants, no air

> space between the wall and the picture, Glass front, negative pressure

> and 68 degrees indoors in the middle of summer.

>

[Guest guest]

I'll try to explain by first referring you to Dr. Joe Lstiburek's work, which can be found on the Buildingscience.com web site with lots of good info.One Driver: Bouyancy of heated air creates upward air movement through leaks at the top of the structure. Makeup air comes from into the structure via leaks from lower in the structure, hence the negative air pressure of the house with respect to outdoors. One More Driver of inward vapor movement is described by the good old second law of thermo, which in this application comes into play due to relative high water vapor content in the cavity behind the brick veneer with respect to the stud wall cavity during/following a summer rain. The air conditioned inside air is then relatively drier than the drain plane cavity behind the brick veneer. SO when high vapor "wants" to "meet" low vapor in the "middle" and there's a vapor barrier in the "middle" that stops this marriage by being at dew point temperature, life becomes cool and wet, which is no fun at all. Crude for the purists out there, but, hey, it's been 20 years since I graded my professor-ex-wife's thermodynamics homework papers...and nobody flunked> >> > > > One other thought, did you check the home to assure negative pressure> > doesn't develop with the doors of different areas closed?> > > > Terry, remember that residence in Hallandale, Florida you! and I were> on,> > where the picture was stuck to the wall? There was so much mold behind> > it, it was holding it to the wall.> > > > It was the model for the full employment act for consultants, no air> > space between the wall and the picture, Glass front, negative pressure> > and 68 degrees indoors in the middle of summer.> >>