| Author |
Message |
mcc351 (Unregistered Guest)
Unregistered guest
| | Posted on Monday, June 29, 2015 - 09:48 am: |    |
We have an existing brick masonry wall with a 2" cavity and 4" concrete block back up. It previously did not have insulation so we will be adding. Our first choice would have been to add spray foam but the client has ruled out due to concerns of fire. We are now looking at adding extruded polystyrene. I believe the best approach would be to add a vapor permeable, fluid applied air barrier to the back of the block and then the rigid. My concern is changing the environment of the existing masonry and having drying issues with the masonry. This is in the northeast climate so it gets hot and cold cycles. Does anyone have experience with this? What have others done? |
Ronald L. Geren, FCSI, AIA, CCS, CCCA, SCIP
Senior Member
Username: specman
Post Number: 1322
Registered: 03-2003
| | Posted on Monday, June 29, 2015 - 11:25 am: | |
There is just as much of a fire concern with extruded polystyrene as there is with spray foam--both are combustible foam plastics.
Ron Geren, FCSI, AIA, CCS, CCCA, SCIP
www.specsandcodes.com |
Guest (Unregistered Guest)
Unregistered guest
| | Posted on Monday, June 29, 2015 - 12:31 pm: | |
Have you be performed a dew-point analysis? That should "tell" you where to locate vapor-retarder and insulation? |
ken hercenberg
Senior Member
Username: khercenberg
Post Number: 921
Registered: 12-2006
| | Posted on Monday, June 29, 2015 - 01:59 pm: | |
I think you are wise to be concerned about disturbing the equilibrium of your wall but you'll already be doing that when adding the insulation.
XPS has sufficient NFPA 285 related testing in brick walls with CMU backup that you should be able to make a case with the Owner. Of course there is always mineral fiber insulation (Roxul or Thermafiber) that have excellent cavity products.
I agree with your assessment in using a vapor permeable air and water barrier. At least in theory this will allow your wall to dry out as well as in. When checking perms, look at which test is cited. Many consider the 'wet' perm test to be more appropriate since that better imitates the drying out scenario. |
Phil Kabza
Senior Member
Username: phil_kabza
Post Number: 560
Registered: 12-2002
| | Posted on Monday, June 29, 2015 - 04:08 pm: | |
From what I'm picturing, you are not proposing addressing the brick cavity, but rather are proposing adding an air barrier to the interior face of the backup cmu, followed by rigid XPS foam board. This is a simple and inexpensive application and is very common.
The XPS has a low enough perm rating to serve as a vapor retarder, and as a closed cell product likely will pass negligible air if seams are taped. Because it is in a protected location unlikely to experience wetting, you could consider polyiso board as well with its somewhat higher R value. Both types of foam plastic board require thermal protection to the interior side using gypsum board finishes.
You do not say where the to-be-retrofitted building is located, which will have an affect on the assembly's moisture behavior. If interior moisture formation is a concern, the mineral wool board Ken suggests is a good recommendation as it passes moisture quite readily while maintaining R value, as well as is non-combustible. It does, however, burn a hole in the construction budget. Above all, remember it is difficult to precisely predict moisture behavior, and make certain your paints are quite breathable and avoid wall coverings. |
Lynn Javoroski FCSI CCS LEED® AP SCIP Affiliate
Senior Member
Username: lynn_javoroski
Post Number: 2029
Registered: 07-2002
| | Posted on Monday, June 29, 2015 - 04:26 pm: | |
Can we assume the brick will be removed before adding the barrier(s)? Or will all remain in place? With only a 2 inch space, there's not a lot of room, wiggle or otherwise.
I'm having trouble envisioning the process if the brick isn't removed. |
ken hercenberg
Senior Member
Username: khercenberg
Post Number: 922
Registered: 12-2006
| | Posted on Monday, June 29, 2015 - 05:03 pm: | |
If Phil's interpretation is correct, the installation will be on the interior face of the CMU. If that is the case, and the Owner is concerned about long term fire and life safety, I would go with the mineral fiber. If this were my house and my family was in the building I would not want plastic foam inside even with a thermal barrier as permitted by Code. In this case Code definitely is the lowest level of protection.
As to adding an air barrier, I'm curious as to what you're considering. No matter what you use, it will not be continuous (obviously also true for your insulation).
Adding insulation to the inside will prevent the interior air from conditioning your block. In the Northeast that means your block will be very hot in summer and very cold in winter. You may be moving your 'dew point' into your building. You haven't mentioned the nature of your windows and doors or how old this building is. What is they use of the building? Will most of your humidity be coming from inside or out?
I'd be very concerned about the changed equilibrium of your building envelope. It will be significantly modified by this work. |
mcc351 (Unregistered Guest)
Unregistered guest
| | Posted on Monday, June 29, 2015 - 09:32 pm: | |
All - thanks for your input. To clarify, we're not touching the cavity. We're adding the insulation on the inside face of the back up CMU thus moving the dew point into the building. We haven't done a dew point analysis yet but it will most likely tell us the dew point is inside the building. The client concern of fire is with the potential of spray foam to catch fire during installation. They have no issue with rigid as it is only a concern when there is a fire as opposed to being the fire source. I like the thermafiber idea but we may not have the space to do it. The building's existing drawings are dated 1968. The use is an office building ... No unusual humidity loads.
For an air barrier, I know you can theoretically tape the joints of rigid board and technically have an air barrier. Because of discontinuities of the rigid (gaps, inaccessible areas)I like to have a separate air barrier. It would be a fluid applied vapor permeable air barrier. I'm leaning towards a Carlisle product. |
J. Peter Jordan
Senior Member
Username: jpjordan
Post Number: 852
Registered: 05-2004
| | Posted on Monday, June 29, 2015 - 10:12 pm: | |
As Ken suggests, I would want to know the location of the building before suggesting particular products. There is a difference in insulating a building in a warm, humid climate as opposed to a colder, "dryer" climate. |
Ron Beard CCS
Senior Member
Username: rm_beard_ccs
Post Number: 426
Registered: 10-2002
| | Posted on Tuesday, June 30, 2015 - 03:34 am: | |
Over the years, I have been confronted with the above scenario but in older historic structures on numerous occasions including the old clay tile (pre-CMU‘s) units and stone backup walls (in solid masonry walls with face brick but no cavity often 16" to 24" thick). I have found that a thin application of a low-perm, closed cell foam insulation applied to a thickness of 1/2" to 1" provides an adequate air barrier, good thermal value, and provides an even/smooth surface (in the case of stone). Any of the above referenced insulations can then be applied on the inside of the existing wall system with either a steel stud partition or ‘Z’ furring strips followed by a film sheet vapor retarder and GWB (which provides the necessary fire protection requirements raised by Ronald and should be satisfactory protection required by the Owner).
No reference has been made to the R-value needed for the wall assembly. The higher cost of the thin layer of foam insulation can be offset by using a standard blanket insulation product provided the desired R-value is not too high. Polyiso or XPS boards will be necessary if higher R-values are needed.
One further point to check is whether the existing cavities are properly vented (top) and weeped (bottom). Any moisture that reaches into the cavity needs at least a minimal amount of cross ventilation to stay dry.
"Fast is good, but accurate is better."
.............Wyatt Earp |
ken hercenberg
Senior Member
Username: khercenberg
Post Number: 923
Registered: 12-2006
| | Posted on Tuesday, June 30, 2015 - 08:46 am: | |
A closed cell foam will probably provide a decent barrier, keeping in mind that your wall will no longer be able to dry in and your building will not be able to dry out. Still, depending on location, it may be better than nothing which is what you're starting with in terms of insulating value.
My understanding about foam combusting during installation is that the installer can only apply up to 2 inches at a time. After that the heat created by the foam can cause combustion. There are some well-represented products around such as BASF that can help make sure the work is done right.
If you decide on foam, decide whether you want to install your studs first and then spray around them. If you leave a 1 inch gap between studs and the back of the CMU, you should be able to use the foam to prevent thermal bridging. Two inches of spray foam should give you an aged R value of about R-11.
As Ron Beard noted, you may also want to open vent holes at the top of each masonry run since you probably only have weeps (if you're lucky). I'd check those weeps and if possible try to run water through the cavity and see if they're working. You'll probably need to open some head joints and stick a hose against the opening. If your weeps aren't working, you definitely want to fix them. Otherwise you're probably going to have a very upset client in about a year or so. You can then use your test head joints as vents. I like to line the vents up vertically with the weeps. |
Greta Eckhardt
Senior Member
Username: gretaeckhardt
Post Number: 15
Registered: 08-2013
| | Posted on Tuesday, June 30, 2015 - 09:21 am: | |
A couple of things to add to this interesting discussion:
An air barrier membrane applied to the interior surface of the CMU is necessary because CMU by itself can leak air. Taping joints of insulation will be difficult due to interruption of the insulation by furring support of the interior gypsum board finish.
The question of permeable versus non-permeable air barrier and insulation should be evaluated using hygrothermal analysis (WUFI) performed by someone trained to use the software and interpret its results. Simple dewpoint analysis does not address the need for the wall to dry in different directions due to changes in weather throughout the year.
Based on my experience researching and specifying spray polyurethane foam, I agree with Ken's comments about this product. As it cures, the foam gives off heat which must be allowed to dissipate quickly so that the temperature does not build up. This requires that each application be thin enough to allow the heat to dissipate - the allowable thickness should be in accordance with the foam manufacturer's recommendations. |
Wayne Yancey
Senior Member
Username: wayne_yancey
Post Number: 746
Registered: 01-2008
| | Posted on Tuesday, June 30, 2015 - 04:21 pm: | |
mcc351,
Go to http://www.cebq.org/documents/Insulatingsolidmasonrywalls-BEF_000.pdf for a paper on insulating solid masonry walls. If you cannot locate it e-mail me at wayne.yancey@callison.com |
4specs.com Home Page