How is thermal bridging prevented?
The construction process of our home, in southeast Iowa, was completed in January 2014. The house has fiber cement lap board siding and an interior spray foam insulation. In March of 20014 we noticed moisture accumulating, in a vertical line pattern, on the east elevation of the house.
After our contractor failed to honor the home warranty, we contacted the fiber cement board manufacturer, to determine the cause of the problem. Based on the photos we provided, we were told the siding was installed incorrectly and there is a thermal bridging problem. A supervisor with the siding manufacturer also reported the blown on interior insulation is also a problem. Based on the manufacturer’s suggestions we hired a home inspector, certified by the American Society of Home Inspectors.
The inspector has extensive experience with this manufacturer’s fiber cement lap board siding. We were told the following: 1) the fiber cement board lap siding was installed incorrectly and a number of required flashings were not installed at all, 2) the siding needs to be installed to manufacturer’s specifications, 3) because the house has spray foam insulation it is very tight and cannot breath, and 4) the inspector suggested getting the HVAC system balanced and bringing in fresh air into the house through the use of a ERV or HRV system (the HRV system was reported as the preferred system).
We have been trying to get a qualified HVAC contractor to perform the HVAC load balance analysis for several months; however, those qualified are too busy so we continue to wait. We have been told not to install an ERV or HRV until the results of the HVAC load balance analysis is completed.
Experienced fiber cement board siding installers from Des Moines, Iowa have been contacted and requested to provide a price for the correct installation of the siding; however, they put us off. There appears to be some other issue/s of concern; however, they do not say what it is.
All elevations of the house are now affected by the thermal bridging.
Question 1: Does the fact the house cannot breathe, the HVAC system is not balanced and the house is insulated with spray foam insulation affect the thermal bridging?
Question 2: What are your recommendations to the thermal bridging problems?
Thank you for your kind response.
S. (Southeast Iowa)
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Replies
Thermal bridging can't be prevented, only mitigated with a higher-R layer over any more thermally conductive materials.
But I'm skeptical that thermally bridging framing is responsible for an actual moisture PROBLEM on the siding, even if differences in dew or frost patterns were visible. I'm assuming the vertical lines corresponded to the location of framing studs?
Is there an air gap between the sheathing and the siding, or is the siding tight to the housewrap?
Missing or mis-lapped flashing is a far more likely proximate cause of moisture problems on the exterior sheathing &/or siding.
Open cell or closed cell foam?
If closed cell, how many lifts of what thickness were applied, and what is the total thickness?
Were the studs clean when the foam was applied (thus assuring a good bond to the foam)?
If the foam is air tight it PREVENTS rather than causes moisture problems. If the foam is leaking air from the warm humid interior along separations between the studs and foam from the foam shrinking and not adhering there is some potential for both heat & moisture striping corresponding to the studs. If it's closed cell foam that was applied more than 2" per lift shrinkage & bonding issues are common. If that were the case it's still a bit hard to imagine sufficient moisture getting in there to be visible on the exterior of the siding but maybe. If it's air-tight, the balance of the HVAC system doesn't matter- no air is moving through the assembly, so there is no air-transported moisture accumulations.
If the ventilation is so poor that that the relative humidity is 50-60% + all winter (or if you actively humidify to high levels) you would have major moisture accumulation in the sheathing, and it would be the space between the studs, not at the studs with the moisture issues.
Care to post some pics?
I'm not sure you've gotten an accurate diagnosis yet. From a quick look at the weather around then, that was after a very cold February and March was also cold. If you had thermal bridging, that would mean heat from inside the house would warm that spot and dry it extra well. More likely sources of moisture seem to me to be moist air leaking out from inside, or perhaps snow melt from the roof dripping down, perhaps as a result of an ice dam. Or moist air leaking from inside leading to frost accumulation somewhere near the top of the problem area, dripping down as it melts.
It's hard without seeing it in person. Picture could help if you are willing to upload here.
As for whether you need ventilation because your house is too tight, that is reasonably likely given the spray foam, and becomes even more likely if you find and seal up some leaks. You could opt to get a "blower door test" to see how leaky the house is and find some leaks to seal (which might lead to finding the source of the first problem). My guess is that when you are done fixing problems you'll want a ventilation system, so I'd go ahead and start looking at your options there in parallel with solving the other problems.
The possible interaction between these issues would be if the moisture source is warm moist air from inside leaking out, ventilation would help reduce indoor humidity in the winter. Also, if you monitor indoor humidity, you can get an an idea of how much you need ventilation--if it's >50% in Feb, you need to add ventilation. If it's say 35-45%, adding ventilation might be optional, but you still might benefit from adding ventilation, and you might also want to seal some air leaks. If it's <30%, you have a lot of air leaks and that should be a bigger concern than adding ventilation.
Thank you for your responses, thus far. As requested please find a PDF with photos. While these photos were taken during the winter of 2014-2015, the thermal bridging occurs year round. It is just more apparent during the winter months.
I will check on what type of spray foam was used, (Closed vs. Open). As for the humidity, I will monitor that over the next couple of weeks and throughout the winter.
I will get back with your regarding the type of spray foam and I will try to acquire additional information regarding the depth of the spray foam.
Hopefully, the pictures will be helpful.
S. Schneider
The first attachment of photos was too large for the system; therefore, no number of photos was reduced. Please see the photos, which are relative to my response of 10 6/15 @ 1:19 PM ET.
S. Schneider
From the horizontal lines at the seams of the clapboards it looks as if the whole wall is wet.
The frost lines following the studs is probably due to the thaw/freeze that's happening due to the higher temp of the sheathing along those stripes due to the thermal bridging. As the outdoor temps warmed up I would assume those vertical stripes would dry first. Notice in photo-1 there is no vertical striping on the roof gable but there is still the horizontal frost.
It looks like far too much moisture to be caused by mere vapor diffusion through open cell foam. This has to be related to missing & mislapped flashing (a true installation error) combined with no back-ventilation of the siding (something that's good to have, but not required by code or by the manufacturers.)
This is not a heating system problem, but if there isn't mechanical ventilation you may still have issues with the sheathing after fixing the sheathing and weather resistant barrier if it's open cell foam, and you don't add a vent space behind the siding. Even 1/4" of space is a great capillary break and enough vent cavity to dry things out quickly, as long as it's open to the outdoor air at both the bottom & top of that thin cavity. It doesn't take much.
The vertical stripes look too close together to be caused by thermal bridging of studs unless they're like 12" OC or something.
Besides, the vertical stripes are where there's frost, not melting. If greater amounts of heat were escaping through the studs, I would expect vertical bands where there's no frost, not where frost is collecting. Almost seems like maybe thermal bridging through the fasteners causing the frost to melt.
If you drive through the subdivisions near where I live, you can see which houses were built before and after rain screen was introduced in our code. All the ones where the cement board was fastened directly to the sheathing show vertical lines at the studs. I've never seen anything like what the photos here show.
Nate: During the mostly frozen period the elevated temp at the stud sometimes enhances the frost accumulation at the surface of the siding, since part of the day the sheathing becomes warm enough to cook off some moisture, but the siding is still cold enough that it freezes there. Only when the temps warm up to just about freezing would the striping be drier than the field between the studs.
Malcolm: That's good to know! Iowa doesn't have anywhere near the rainfall or wintertime moisture of coastal B.C., but I'm sure it's part of the same phenomenon, and likely the same solutions. Fiber cement doesn't the same moisture-reservoir capacity of brick or stucco, but it still hangs on to some- a lot more than wood or vinyl.
If the siding has to come off to deal with the flashing problems, it's absolutely the right time to add a rainscreen gap.
Some good insights, but I'm still not sure where the moisture is coming from in the first place. Wind driven snow that stuck to the siding and then melted and soaked in? Or is there something else going on? Could there be a rainscreen, but without vents on the top or bottom, and with air leaks from the interior, such that the rainscreen gap gets filled with warm moist inside air?
As Nate notes, those stripes look like they're 12" OC; I'm inclined to think those are furring strips. If there's enough moisture entering the wall to saturate the furring they could hold a good deal of moisture while reducing back drying, which could partially explain what we're seeing.
Also, is it just me or does picture #9 show the opposite of all the other pictured, with the frost melted only over the strips?
So if there's furring there, that's means there's an airspace, which means that if vents get added top and bottom, that could help tremendously. Add to that a blower door test to make sure we don't have big air leaks somewhere behind the siding and an a detailed inspection of the flashing details.
In any case, finding the people to do it seems to be challenging. Any recommendations on how to make some progress there?
S. Schneider,
Tim made an interesting observation: Photo #9 seems to show opposite conditions from the other photos.
To solve this mystery, we need more information. It would be interesting to use an infrared thermometer to see if any temperature differences can be detected on the siding when stripes show up. Is the temperature at the vertical lines different from the temperature at the spaces between the lines?
It would also be good to know the indoor relative humidity.
In general, if moisture is accumulating on vertical stripes, and the spaces between the stripes are dry, that means that the areas with vertical stripes are the coldest parts of the wall. That might happen if the wall is either uninsulated or poorly insulated.
This is S. Schneider:
Thank you all so much for your responses. I was on site when some of the fiber cement lap board siding was installed. The siding was attached directly to the Tyvek wrap. There are no spacers between the Tyvek and the siding. Nor are the flashing installed. I am told the siding should not have been butted tightly to the roof overhang and there should have been a flashing installed there. I believe it is called a "kick back flashing."
As for the Blower Door Test, we had the test done. I will search for the report and attach the results for your review, ASAP.
As a consumer & home owner not familiar with these problems, I call the problem: "Weeping Walls."
The walls "Weep" year round. It is just more drastically apparent during the winter. It appears there is a lot of moisture freezing behind the siding, during the winter.
The spray foam installer was contacted by our insurance representative and the spray foam contractor provided a document entitled, "Proper Design of HVAC Systems for Spray Foam Homes." (Dated April 2011). Humidity, proper ventilation, house pressure are a few of the things discussed. I have attached a copy for your reference. Meantime, I will also continue to press for an answer about the type of spray foam used. Thank you again so much for your assistance. We have been seeking answers since March 2014. S. Schneider
This is S. Schneider:
In response to a request for a Blower Door Test see the attached report, from Home Star Iowa.
Thanks for the blower door test report. A quick summary for those who don't want to download it: 2.45 ACH50, Also noted that the house is depressurized, presumably by the operation of the HVAC.
The depressurization must mean that air is being blown out somewhere, presumably through duct leakge, perhaps ducts leaking in an the attic. If the attic has no deliberate venting, but is also not deliberately connected to the main conditioned space, perhaps the attic is pressurized while the house is depressurized, and somehow that air from the attic leaks out through a path behind the siding, carrying moisture with it? That seems a little far fetched.
So the auditor who did the blow door test knew about the siding moisture issue, but didn't have any theories or advice about it? Shall we ask him to join this discussion?
I'm trying to make sense of the photo he included, but having a little trouble. It looks like an attic space over an unfinished room. Is that right? Is that unfinished room connected to the rest of the house? Do you know what the ducts shown in the picture are?
This is S. Schneider
In response to Charlie Sullivan's comments:
1. Yes, the Door Test Report identifies the house as depressurized. The home inspector says the house is under negative pressure. We assume they are one in the same.
2. The attic does have insulation.
3. The auditor that did the blow door test did know about the siding moisture issues. He did not go up into the attic. I can ask him to join the discussion, if that would help.
4. The photo is of an air intake for the wood burning fireplace, which is located above the basement ceiling / below the first floor. We have not used the fireplace because of a back draft problem. This vent needs to be taken to the outside of the house. At this time we do not believe this is the source of the problem, because we are not using the fireplace.
5. We will call and ask the auditor to join the discussion.
This is S. Schneider
I just spoke with Rob Novak with Home Star Iowa. He is the one that did the Door Test Report. He said he would get online and participate in the conversation on Monday, Oct. 12th.
Thank you for your feedback.
I haven't had a chance to read through the entire thread. I'm hoping to sometime on Saturday. I did talk to Sandra today and reviewed my notes. Please let me know if anyone has a burning question for me.
S. Schneider,
Any investigation of this problem has to start with the basics, and that means that someone needs to collect some data.
Question #1: Where is the moisture coming from: the indoor air, the outdoor air, or some type of leak?
To begin to narrow down the possible answers this question, we need to know:
1. The temperature of the condensing surface when the phenomenon occurs. This can be determined with an infrared thermometer.
2. The outdoor temperature and outdoor RH when the phenomenon occurs.
3. The indoor temperature and indoor RH when the phenomenon occurs.
Leakage of 2.45ACH/50 is not a big deal- not super tight, but not super leaky. It's under current IRC code maximums, and is well below leakage of average homes built before 2009, most of which do not have this symptom. This is not a proximate cause or even a second-order factor on the phenomenon in question.
With the house depressurized any air leakage is pulling dry outdoor air in at the wall levels (and probably out the attic), not pushing moist indoor air out to condense & freeze on the siding.
If the ventilation rates are super low allowing the indoor air humidity to rise to insane levels (a bit hard to do in an 2.45ACH/50 house that's de-pressurized, but not impossible) and the foam is open cell, with no interior vapor retarders AND you have no rainscreen behind the siding MAYBE you'd get enough moisture into the sheathing via diffusion to become visible on the exterior. But with moisture levels that high you would have copious condensation on the windows and potentially even visible mold on interior surfaces. Does it feel like the tropics indoors?
The fireplace may be part of the depressurization, since they are rarely air-tight to the interior, and by-design have stack effect drive even when cold.
The missing flashing is a likely suspect, and needs to be fixed anyway. At that time you'll be able to assess just how damp the sheathing has been (or is), Re-installing the siding with even 1/8" thick lath forming a capillary break & vent space will likely make the striping go away, but 1/4"-3/8" would be even better to guarantee rapid drying.
Dana, good call on the fireplace stack effect being a likely source of the depressurization. Rob, if you have notes on the actual depressurization, in Pa, and if you know whether it was about the same with and without the furnace fan running, that would help confirm whether that's the main driver.
Although I was leaning toward complicated building science explanations, those sorts of theories are not seeming promising. More likely it is simpler along the lines of what Dana concludes--wind driven rain and sticky snow getting the siding damp, and no rainscreen (vent space behind the siding) to help it dry. The missing flashing is part of that story.
The only complex theory that still seems possible is that the air leakage paths somehow end up damping some of the siding and that moisture spreads. As Dana notes, that can't possibly be through the walls given depressurization, as well as the relatively small leakage. If it's up the fireplace chimney, it's then out the top of the chimney nowhere near the walls, so as bad as that is it's not the cause of the siding issue. So that would leave the possibility that it's stack effect throughout the house with leaks in the attic floor plane driving the depressurization. Most likely there's a ridge vent, and the air goes out there, again not causing a siding issue. But perhaps, if there's no ridge vent, but there are air leaks from the attic through the gable ends, the moist air is coming out there, condensing, and then wicking and dribbling down. For that to explain it, there would also have to be air leaks out of the attic at the eaves as well.
But I think there's an argument that says that if there's a simple explanation and a complex one, you should go for the simple explanation first!
One other question for Rob--I assume you didn't take any thermal images, but if you happen to have some they might give us some great clues!
Charlie,
"I think there's an argument that says that if there's a simple explanation and a complex one, you should go for the simple explanation first!"
Yes -- Occam's Razor.
This is S. Schneider
The vertical wet lines occur year round. It does not have to rain. The lines are the most apparent in the morning and as the heat of the day burns the moisture off, the lines disappear.
S. Schneider,
I'm still waiting for some temperature information and RH measurements.
Could the clothes dryer vent be the moisture source?
All of the ductwork is in the conditioned envelope. There is no ductwork in the attic.
Unfortunately, I don't have any infrared images.
The house was depressurized by 13 Pa.
Audit on Feb. 3, 2015. Low of 11 F, high of 33 F. Suppose the audit was done at 25 F outdoor temperature. And suppose the chimney height is 20 feet and the indoor temperature is 70 F. That's 21 and -4 F, or 269 and 294 K. That gives a density difference about 0.1 kg/m3, which would result in a stack effect pressure of 6 Pa for a 6 meter high stack.
Unless the fireplace chimney or the house is significantly taller than I thought, that doesn't explain the 13 Pa measured pressure difference. But the afternoon of Feb. 3 was kind of windy, e.g. 15 mph for the 1 PM and 2 PM hours. So perhaps some of it is stack effect and some is wind. With all the ductwork in the conditioned space, there shouldn't be any reason the furnace fan would drive the depressurization.
But that seems like a side issue--the main issue is the siding moisture and it does not seem likely that the depressurization causes the siding moisture.
I completely agree.
"the main issue is the siding moisture and it does not seem likely that the depressurization causes the siding moisture."
Will try to find a source to provide the requested temperature, RH measurements and infrared images.
S.
S.: You can buy a cheap humidity meter at a hardware store or home center for $10 to $20. I've found La Crosse brand consumer grade instruments reasonably accurate, and Menards is one source for them. Humidity would be good for you to keep track of in general, as your house has the potential to be underventilated and develop high winter humidity.
I was asking about thermal images, in case Rob had some. Thermal imaging is expensive. But Martin was suggesting a much cheaper option--an IR thermometer. Same idea, but it just gets the temperature of one point on a surface, rather than a whole image. They cost $20 to $100 or so. I have a $20 one that is sometimes useful but sometimes gives wacky readings--you might want spend at least a little more than $20.
I'm not sure that that further information will lead us to a different solution, particularly given that you say the problem happens across many different conditions, and on all sides of the house. It seems likely that after all of this, we will send you back to where you started, needing to reinstall the siding with flashing and a small airspace behind it (which is confusingly called a "rainscreen"). But more information might give us an added clue.
Charlie,
Don't mean to be pedantic, but the "rain screen" is the whole assembly - screening the wall from bulk water intrusion. The airspace is usually called the cavity. If you think of it in those terms it isn't quite as confusing a name.
Thank you Mr. Sullivan for the information about acquiring the requested information for a less expensive means. I will search for the equipment you referenced and start taking the readings.
I have been giving a great deal of thought to all the comments that have been made. There was a comment about the east side of the house thermal bridging looking different than the west side of the house. There has also been discussions related to the attic. This got me to thinking about a difference in the construction between the east side of the house and the rest of the house and how it might affect the air & moisture in the attic. When the contractor installed the Tyvek to the house, he covered all the elevations to the roof line, except the east elevation. The triangular section, which runs from the roof peak to the horizontal line across the east elevation, from the lowest points of the roof, where left without Tyvek. I had never seen that done before nor since. The contractor said it was left that way so the house could breath. I am wondering if that could be a source of some potential moisture problems that affects the attic and the whole house. What are your thoughts?
Mr. Holladay:
I purchased an ACU>RITE: digital weather thermometer with a built in humidity instrument. The digital display unit is kept indoors and the sensor is mounted outdoors. It operates as a wireless sensor system. Menards had none and Lowe's had the ACU>RITE line. Our insurance agent has loaned us his Mastercool Infrared Thermometer to take readings of the weeping walls. We will keep a daily record of the outdoor and indoor temperatures and humidity, along with the daily results of the infrared scans. (Note: the infrared thermometer is a Mastercool, 52224-A with an output of <1mw at 630 - 670nm, class ii laser product.)
Is there anything I should know to successfully accomplish this task? How far away from the weeping walls should I be when activating the infrared thermometer. I assume that same distance should be repeated for each test at each location. Can I also assume the readings should be taken at the same time each day? Your advise would be most appreciated! Thank you.
S. Schneider
S. Schneider,
If possible, you should get about 2 or 3 feet away from the surfaces you are measuring with your infrared thermometer. Try to aim the device so that it is measuring the surface at a 90-degree angle to the surface. See if you can get a reading of the area with condensation, and also the area without condensation. I'm curious to know if there is a difference in temperature between these regions.
I think that these readings should be taken whenever the phenomenon occurs. Once a day should do it, as long as the phenomenon is occurring.
By any chance have you been in touch with Mark Parlee? He's in Urbandale and is a national expert on fiber cement as well as an excellent inspector and diagnostician of exterior problems.
Mr. Holladay:
Thank you for your suggestions. I will take the readings in an area with condensation and in an area without condensation. Because of the difference in the installation of the Tyvek between the east and west elevations of the house, I believe it advisable to take readings at both of these elevations. It may provide data related to the lack of Tyvek within the upper triangle of the east elevation, as I noted in a previous posting today.
Mr. Kolbert:
No I did not know of a Mark Parlee. How do I reach him? I sure could use someone with his expertise. I have 2 emails: 1) [email protected] & 2) [email protected]. Would it be possible for Mr. Parlee to contact me? Or maybe you could email me his contact information. I have been trying to get an expert here since October 2014, when I found out the problems with the installation of the Hardy Plank siding, within the home inspectors report. Thank you for your assistance in this matter.
I'll check with Mark on how he'd prefer to do it. He's a great guy in addition to being very smart.
I sent my contact info to both emails.
Give me a call at your convenience.
[email protected]
http://www.thebuildingconsultant.com
Mr. Kolbert:
I did receive an email from Mr. Parlee and we have spoken about details of the home inspection report and numerous other issues related to the problems with the house. I am collecting documents to send to Mr. Parlee, many of which will go out Thursday afternoon.
After Mr. Parlee has an opportunity to review the documents and I have the opportunity to follow up on some requests for information, I anticipate we will meet.
I did take temperature, humidity, and the thermometer scan on the west elevation this morning. The weeping / thermal bridging had already burnt off the east elevation by the time I could take the readings this morning at 7:30 a.m. Today the outdoor temp at 7:30 a.m. was 44 degrees & the outdoor humidity was 79% The indoor temp was 67 degrees (we had windows open to get fresh air in the house) and the indoor humidity was 52%. The weeping / thermal bridging on the west elevation was not real prominent. The wet area temperature at 3 feet distance from the surface and at a right angle to the surface was 35.6 degrees. The non-moist area was 34.9 degrees. By 7:30 a.m. the thermal bridging was faint. Some days it is much more prominent. I am not sure I understand the readings. There is not much difference and I would have expected the temperatures to be the opposite. As more readings are taken I assume a pattern will develop.
I want to sincerely thank all of you for your very kind thoughts and advise. I will continue to take readings and will work with Mr. Parlee.
Best regards,
S. Schneider
Thanks for the readings. 44 F at 79% humidity corresponds to a dew point of 38 F. The siding surface, around 35 degrees, is colder than the dew point, and so can have condensation on it.
So at least for this example, an explanation is that the siding is still cold from the cold overnight temperatures, and it gets wet from condensation (dew) forming on it. The fiber cement siding has higher thermal mass than some other kinds of siding, and stays cold in the morning longer than they might. It also has the capability of absorbing some moisture, which also prolongs the time that it stays wet.
If there was a vent space behind the siding, that would help the siding to dry faster and possibly help it warm up faster in the morning.
I expect Mark Parlee can help better than we can. I for one would be interested to hear about his diagnosis and your progress, even after you no longer need help from this forum.
" I for one would be interested to hear about his diagnosis and your progress, even after you no longer need help from this forum."
I'm curious as well. Any progress?