# Insulating for differently constructed walls (and ceiling)



## rightit (Mar 5, 2011)

I am on the verge of insulating my garage enclosure to office conversion and need some advice. This is not your normal garage enclosure, as I have spent much time and effort on all aspects of this project.
Specifically, I need information regarding a south wall, a small west wall with a window and the ceiling. 

*Before I get too far into this, a few salient facts:*
*1.* I live in a very hot and humid *zone 2* climate (winters are short and mild. Occasional cold winters (just below freezing).
*2.* Vapor barriers are not required by code.
*3.* The space will be air-conditioned
*4.* Outside air will be introduced into the space and conditioned via the return air of the A/C system, so the space will be under a positive pressure. There will be occasional exhaust to the outdoors using the bath ventilator.
*5.* I have already ordered the insulation. I will be using Roxul rock wool. _*This insulation has no vapor barrier.*_
*6.* All openings and holes in top plates of the space are sealed with either _3M CP 25WB+ Fire Barrier Sealant_ or (for the bigger openings), _Dow Fire Foam_. Also,_ Great stuff Cracks and Gaps_ for other gaps (not in top plate). Window and door frames will be sealed with _Great Stuff for Windows and Doors._

*7.* (edit): I should also add that all electrical outlets in the space will be sealed against air & sound with putty pads.
*South wall facts:*








*1.* 20’ L x 8’H. Pre-existing brick veneer, black board sheeting (well, brown inside. Black outside…not sure if it’s really BB or what the specs might be). It’s not in great shape. 
*2.* _No house wrap on the exterior side of the blackboard_
*3.* Staggered stud wall.

*South wall questions:*
*1.* I guess I won’t require a vapor barrier, but I assume that I will _need to air seal the wall?_
As can be seen in the image, this could be quite a task, depending on what material I use. A foam board is not practical, given the number of cavities, small spaces and obstacles involved, and it would also mean that I lose an inch of space, compacting the Roxul.

I think I could use Tyvek. If so, how? Cut and staple in the stud cavities and spaces? Is some type of brush on sealant required at the staples and seams? 

Given my budget, foam in addtion to the Roxul is not really an option, even if I could get someone to take on so small a job.

I am looking to minimize labor without diminishing quality of results. So what is my best option for this wall considering the facts?

*West Wall*
This is a new 2x6 wall that I built after removing the garage doors:
From outside in, brick, Tyvek, ½” plyboard. I will be using 5.5” R-23 Roxul.
Am I correct in thinking that just putting in the R-23 Roxul (and again no VB) will do the job for this wall? Top plate gaps and holes are all foamed.

*Ceiling:*
2x8 joists, 20’x10’. The attic side is decked with ½” plyboard. I will be placing Roxul 7.5” R-30 insulation.
Will this also be all that is required for the ceiling? I'm assumming there is no need for a VB? The attic is vented with a power ventilator. The soffit vents are covered, but I will be addressing that in the near future. 
I will also be placing Styrofoam rafter vents (do these need to be placed at every joist possible, or every “so-many” feet?

Thanks for staying with me so far…any advice is appreciated.

Thanks,
Mark


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## Windows on Wash (Aug 30, 2011)

rightit said:


> I am on the verge of insulating my garage enclosure to office conversion and need some advice. This is not your normal garage enclosure, as I have spent much time and effort on all aspects of this project.
> Specifically, I need information regarding a south wall, a small west wall with a window and the ceiling.
> 
> *Before I get too far into this, a few salient facts:*
> ...


I think the efforts to seal the outside wall are probably uncessary at the end of the day with the type of insulation you are specifying.

Roxul (mineral wool) is very dense and highly resistant to wind washing and diminished R-Value. Make sure the interior wall is sealed up tight and that will be the more primary seal.


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## rightit (Mar 5, 2011)

Hi Windows on Wash. Thanks for the information. The spray foam kits seem to start at around $600. Given that I've gone way over budget on this project (and some of the information you've provided) and still have more to spend, I'm now considering using GS Gaps and Cracks foam to seal up holes, seams and the top and bottoms of the BB (where it meets the top and bottom plates). 

Also, I do plan to seal the drywall at edges and seams. Can you (or anyone) suggest a 50 yr. caulk that actually remains flexible? The Sherwin Wms 50 yr caulk I've used just doesn't cut it. It's not 'hard' and cracking, but certainly not soft and flexible as is stated.

Thanks again for the information.


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## Gary in WA (Mar 11, 2009)

I’d caulk the new top plate/old long header joint under the plate to stop any attic vented air from reaching the wall cavities. Also the bottom plate/slab joint – again to stop outside air as it doesn’t appear a poly sill sealer (air/thermal/capillary break) was used under it. Hopefully, poly was used under any new slab… 
At the South wall, caulk every cavity at sheathing/stud joint and plate joints, top and bottom- to ceiling/slab to help stop the solar (pressure) drive from wet bricks. It goes right through your blackboard (fiberboard), the caulk will stop any air currents from spreading it to other bays. http://www.buildingscience.com/documents/reports/rr-0104-solar-driven-moisture-in-brick-veneer

Add rigid foam board on the stud interior face- air seal and tape/canned foam (top/bottom/seams), then ADA the drywall. http://www.buildingscience.com/documents/information-sheets/air-barriers-airtight-drywall-approach/
Then your cavity condensation will occur on the inside face of the foam rather than wet/rot/mold the paper-faced drywall. Stop all outside (moist/warm) air from getting inside – over/under/around the exterior frame wall on the inside face (air barrier location). The foamboard changes the condensation (dew point) location—think Thermos bottle. http://www.buildingscience.com/documents/reports/rr-9302-humidity-control-in-the-humid-south

Requires electrical box extenders or just cut your own from identical new box for foams added thickness. After reviewing all your posts, did you drill weep holes below the soffit, or are there existing ones to the attic- need intake *and* exhaust to create “rainscreen theory” in the brick wall? There are two types: http://books.google.com/books?id=5T...esnum=3&ved=0CCQQ6AEwAjg8#v=onepage&q&f=false


For your reading enjoyment: 
http://msdssearch.dow.com/Published...foam/pdfs/noreg/179-04569.pdf&fromPage=GetDoc

http://www.greenbuildingadvisor.com/blogs/dept/musings/when-sunshine-drives-moisture-walls

The rafter vents should be in every bay, for optimal performance. The Roxul should not touch the roof deck to transfer temperatures there, f.b. laid flat is better at the low height of the wall/roof juncture. Incorporate the air baffles using f.b. waste from the walls, rather than buy special: http://www.buildingscience.com/documents/published-articles/pa-crash-course-in-roof-venting

Gary


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## Windows on Wash (Aug 30, 2011)

Of the stuff that you can buy commercially (i.e. Big Blue/Orange) silicons are probably your best along with urethanes.


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## rightit (Mar 5, 2011)

Windows on Wash said:


> Of the stuff that you can buy commercially (i.e. Big Blue/Orange) silicons are probably your best along with urethanes.


Again, Thank you!


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## rightit (Mar 5, 2011)

Hi Gary,


GBR in WA said:


> For your reading enjoyment:


Thanks for the links. I’ve read some of these, and the others look to be excellent reading.


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## rightit (Mar 5, 2011)

Windows on Wash said:


> I think the efforts to seal the outside wall are probably uncessary at the end of the day with the type of insulation you are specifying.


Windows on Wash,

Just wanted to come back with a big thanks for the information you provided. Correct climate based information is very difficult to come by. Due to the huge amount of confusing and contradictary information out there, it's almost a monumental task to get the correct information necessary to do the job _right_. 

Even after reading your response, other information seemed to contradict, and had me scurrying for more information. However, one document that seems to clearly define can be found at Buildingscience.com and is entitled, ironically, "Understanding Vapor Barriers". I post a link for those who might be searching in the future:

http://www.buildingscience.com/docu...SD-106_Understanding Vapor Barriers_r2011.pdf

The image below is an excerpt of the document (pg 10) that describes the vapor barrier for my wall assembly and my climate:









As you can see, it shows a wall assembly that dries in both directions. The only deviation from that in my case is the lack of house wrap, but additional factors in my favor (as you previously stated) are a higher R-value of insulation (R-13-15 is recommended in contrast to my R-23) and a positive air pressure provided by dehumidified and conditioned outside air. The importance of positive pressure in the space is mentioned in this document excerpt (also buildingscience.com) from page 6 of the below linked pdf:

"The only method of controlling air leakage in the
humid south is controlling air pressure differences across building envelopes and within building cavities.* Where problems have occurred, it is because interior conditioned spaces have been at a negative air pressure relative to the exterior* and/or building cavities have been at a negative air pressure relative to the exterior"

Link:
http://www.buildingscience.com/docu...y-control-in-the-humid-south/at_download/file


The information you provided for my zone and circumstances is right on the money, and I can now proceed with confidence that my wall assembly will dry (I will, however, monitor temp and relative humidity in the cavities when finished just to make sure that the cavity behind the brick remains well ventilated and that the positive pressure inside the space exceeds that of the exterior). 


Again, thank you!

Mark

*search terms:* hot, humid, south, brick, vapor barrier, zone 2 climate


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## Windows on Wash (Aug 30, 2011)

Mark,

No sweat. Air loss is always the biggest issue because it carries 100X as much moisture.

Tyvek is so open that it allows drying so that is no worry either.


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