Air Leakage of Old House - Does it matter?

*** Update - Upon further reflection of this topic, I do feel there is one additional reason to perform energy upgrades and discuss it in my project journal http://www.theenclosure.ca/windy-house ***
 
This blog entry will analyze the air leakage of a 1954 house and relate that to the energy use and durability of the house.

Before I started tearing down my 1954 single storey 1500 sq ft bungalow to make way for theEnclosure.ca, I decided to have the house tested for air leakage by Michael and Deborah from H&H small home solutions inc (hhsss at shaw dot ca).  H&H typically perform leakage testing to determine the EnerGuide rating for new construction, so this was going to be a new experience for them (and their blower door).

They came by in late March of 2014 after I had moved out but before I had completely emptied the house and before any deconstruction had been performed. The house was prepped by sealing the wood burning fireplace insert, range hood, and the through-wall mailbox before setting up the blower door.

We first ran the door in a B configuration and were unable to get up to the final test pressure of -50 Pa. But even in this configuration we got some scary results.  I had not really made any great attempts to air seal this house over the years.  There was weather stripping on 1 of the 3 doors, and the cedar siding had each coarse sealed to the next and the siding sealed to most of the window and door frames. But no attempts had been made to seal the interior interface with the attic plane and 1 of the doors had a cat door in it and the main door itself had very large gaps around it.

Prior to starting the test I had predicted an air leakage around 8-10 ACH (Air Changes per hour) @ -50 Pa, but early in the test we could tell it was going to be well above this. Deborah could tell just from the sound the fan was making (there previous worst house they tested was 11 ACH @ -50 Pa which was scary as it was new construction).

Right off the bat we reached 28 air exchanges at only -15 Pa!  To give you an idea, 15 Pa relates to a wind speed of only 11 MPH.  In the fall, I regularly recorded winds speeds on the property at this speed or higher so during those events all of that CONDITIONED air in the house was potentially changing over 28 times every hour. That is a lot of extra load on the heating plant and also explained the drafts my wife typically was feeling.


Over the next hour or so we tested at various configurations until we ran the fan at full open configuration (no restrictor plates). Only then could we get enough air volume to allow us to reach the target test pressure of -50 Pa.  AT the full test pressure we recorded an air leakage of 21.74 ACH -50Pa.

Now wait, some of you may have noticed that that is less air leakage than what we observed at only -15 Pa.  How is this possible you say?

Well, it is actually quite common.  As more and more negative pressure is placed on a dwelling, the two surfaces on each side of an air path (leak) can start to come together.  Eventually they can close up tight and stop that leak.  This why I have a bit of an issue (actually quite a bit), of testing dwellings at -50 Pa.  This relates to a wind speed of 20 Mph which is much higher than some locations would experience on a regular basis and much lower than other locations average wind speeds.  As such, it is my opinion that their should be a standard test pressure PER geographical region.  This could be a table much like the climate zone charts, but would be based on the average yearly mean wind speeds for a specific area.  Homes in higher wind speed regions should be tested at higher pressures than homes in lower wind speed regions.

(Side bar - the reason the wind speed is important is that it is this force that will effect the pressures on a dwelling.  Yes a house can depressurize under mechanical ventilation, but these are usually infrequent where wind depressurization or pressurization of the dwelling could occur for months at a time in windy locations).

So - these tests showed that the house was VERY leaky.  What does that mean in terms of heating bills, comfort, and building durability.

Heating Bills

The truth is, this air leakage did not really make a huge difference in energy costs.  My heating bills (for space and domestic hot water) were typically well under $2000 a year (We are under $2000 for both gas AND electrical use).  As I am a heavy bath user, it is safe to say aprox 40% of this was domestic hot water use.  This leaves an estimated $1000 in annual space heating costs.  That works out to less than $100 a month, or well less than the cost of a weekend dinner out.

We typically had the heat set for 72-73F in the wintertime and basically did not tough the thermostat all year.  It was not uncommon for the heat to come on during cold late spring and early fall evenings.  We did however use a programmable thermostat that was set to come on at 7 AM, step down to about 65F at 8:30 AM, come back to temp at 4 PM, and step back down to about 68F at 11:30 PM.  This was only partially for energy savings.  The night time set backs were used because we had hydronic heating through large built-in wall registers (1-2 per room) via a 1980's gas boiler.  The pipes went through and rubbed on the wood sub-floor assembly, so if the heat came on during the night the 'clicking' would wake me up.  So we partially closed the bedroom door (so cats could still get in and out and not cause another source of nighttime wake-ups) and used an electric oil heater to maintain a comfortable temp in the bedroom.

While air tightness is important, it will not make a huge difference to your pocket book unless you have a very large and leaky house.

Comfort

The air leakage did however make a big difference in occupant comfort and should, in my opinion, be the biggest (and probably only) reason to upgrade an older home.  The house was uncomfortable to sit in near any exterior wall in the winter months due to the drafts present.  I was quite surprised when I saw how leaky the fixed, but home made, windows in the living room were.  The builder had just placed the single pane of window glass against a wood surface and clamped it with a second wood component.  At -15Pa, the wind just whistled through these locations.  There is no question, that making the house more air tight would have made the house more comfortable.

Durability

Normally when one discusses the reasons for making a dwelling air tight, it is in the context of a 'modern' home with current levels of code required insulation.  With modern levels of insulation, it is critical to ensure that air leakage does not occur, in order to prevent interior air leaking into the wall or roof assembly and condensing on cold sheathing.  Left unchecked, this will often lead to mold and rot within the assembly.

The key here is the qty and location of the insulation.  As soon as enough insulation is placed inside of the sheathing to allow the sheathing to cool down below the dew point of the interior air, you now have an assembly with a very high liability should any appreciable amount of air leak into that assembly from the conditioned interior. This is because air currents are the #1 mover of moisture next to bulk water leaks caused by plumbing leaks or incorrectly detailed cladding or roofs that permit bulk rain water entry into the assembly.

But in older houses like the one I took down (which had ZERO insulation in the walls), there is not enough insulation present to block the heat loss from the house enough to allow the sheathing to get to the dangerous dew point conditions.  If you never reach the dew point, you can have huge amounts of moisture moving into the wall via air leakage and never have to worry about it because it stays in vapour form and just moves on through either to the outside of the dwelling or back into the inside. There is never liquid water that results from this air leakage. This is the reason why older homes have performed so well over many decades without the presence of air barriers, vapour barriers, or even effective water shedding surfaces.  The heat loss has always been enough to 'cook' any accumulated moisture out of the assembly.

Conclusion

We have identified in this article that there is not a huge financial penalty for a leaky house.  In my case, the costs per month for space heating were under $100/month in what is considered a cold-heating-dominated climate.  This $1200 annual investment would not get very far in paying for a deep energy retrofit which typically would cost 10's of thousands of dollars.  Lets say you could reduce the heating load even as much as 75% (purely speculative and most likely could not meet), this would represent $900 annual contribution to renovation costs.

A REALLY cheap stud level renovation for my home (including new windows and doors) would have been at least $60K (going to need to rip out parts of bathrooms and kitchens so most likely will totally renovate those rooms - my budget of $60 assumes very low end cabinets for these rooms).

A very intensive attic floor plane sealing regime would have been at least $15K (not going to do this process without bringing attic up to current insulation levels when done).

At a highly inflated $900 annual savings, these two projects would have a 66 and 17 year payback respectively. The attic plane sealing payback would most likely be much longer as only sealing this plane would probably represent only 50-70% of all air leakage present and therefore there would be reduced energy savings.

And my house did not represent an unusual annual energy bill. This US Energy Summary shows that for the West, the average annual winter heating bill per household varies between $1300 and $800 depending on year.

In the end, due to our really low energy costs, and the likely hood that they will not appreciably escalate for many decades due to Government interference, it makes very little sense to upgrade an existing homes energy performance for personal financial savings.  Therefore the type of renovation needed to reduce air leakage or increase thermal performance, only makes sense if the home is being renovated anyway for cosmetic or occupant comfort reasons.

On a separate track - this logic also holds true when analyzing extreme new construction programs like Passive House.  The costs to reach passive house levels of energy reduction will not be paid back over the lifespan of the dwelling in most cases. The added detriment of these programs is that the embodied energy of the insulation products built into these dwellings also do not have a pay back within the lifespan of the dwelling.  Instead for new construction, it makes more sense to build a "Pretty Good House" (coined by Joe Lstiburek) and then use the excess capital available to either contribute to distributed or on-site energy generation.

It is however critical that air leakage be reduced down to a minimum (experts do not agree how little is adequate - but the number is somewhere between 1ACH+/-50 and 3ACH+/-50) for new construction or energy retrofits IF, you have built an assembly with enough insulation inboard of the sheathing to cause the sheathing to cool down to the dew point potential of any leaking interior air.   If you build a safer assembly with the insulation outboard of the sheathing (or enough outboard to maintain the sheathing above the dew point potential), then while air leakage is still important to address from an energy loss standpoint (the costs to get it right during construction are minimal and will be paid back by reduced energy usage), it usually will not cause a durability concern for the assembly.  This of course is all from the perspective of a heating dominated climate.  The direction of flow and order of layers for the assembly are different in a cooling dominated or mixed climate.

Batt Insulation - Not all are poor!

Gregory La Vardera posted this excellent primer over at Green Building Adviser on the differences between fibreglass and mineral wool batts.

As Gregory points out, ROXUL Mineral Wool batts are not associated with the typical failings of a fibreglass batt installation. This is due to the density of the product and the ease of cutting and trimming. The product also sheds water and is fireproof.

My only critique of his article is is statement "I don't need my insulation to make an air seal, because I used that good ol' housewrap on the outside. Nope, nothing wrong with housewrap — but it provides no help with the air sealing you need at your vapor retarder. The air seal in this case wants to be on the warm side of the wall, to prevent interior moisture from entering the wall cavity and condensing during the winter heating season."

This is actually incorrect, an air barrier ANYWHERE in the assembly will block air flow through the assembly.  I will talk more about this in an upcoming blog entry.  For now, I did not want to detract away from the rest of the posters review of ROXUL mineral wool insulation.

January Update - Slowly we are proceeding.

I am getting a few questions as to where I am at on the build and so will provide this short update.

We are getting there! OK, that may have been too short.

Currently, we are waiting to hear if our development variance will be approved.  The notice went out to the neighbours between Christmas and New Years (Many Thanks to Erik at the District of North Vancouver for getting this out so quickly).  The neighbours had till Wednesday to respond with only one neighbour providing official comment (positive).  The next step is for staff to write the report to Council and for Council to deliberate on the application at the next available meeting.  This currently is scheduled for Feb 17 (I today found out it is too tight to make the Feb 3 meeting which is disappointing but totally understandable).

Back in November when I was discussing this Variance with staff, I was under the impression that they would allow me to apply for the building permit in advance of the Variance permit approval and proceed on the condition the variance is approved.  I found out this week, that I had it wrong, and that I cannot apply for the building permit until after, and if,  the variance has been accepted.  This news filled me with disappointment as I was budgeting 8-10 weeks for building permit approval based on previous conversations.  However, the kind District Plan Checker has advised they will do their best to fast track the application and could complete the process in as little as 2-4 weeks.  This would end up putting me slightly ahead of schedule.

The District staff have also confirmed I can apply for the demolition permit at any time.  This will again help, as regular readers remember, I plan to dismantle the existing dwelling by hand and reuse, sell, give away, or recycle/salvage as much of the materials as possible.  I estimated this process was going to take a month to complete.  Current plans are to move out the first few days in March, spend a couple of weeks dealing with all of 'my stuff' in the garage and attic and storage shed, and then start tackling the dismantling of items like flooring, cabinets, end the like, all stuff not controlled by a permit.  I would then schedule the services to be cut near the end of March and then start on the official 'demolition'.  These efforts would all take place in advance of the building permit and further improve my schedule.

I am also nearing completion with Tacoma, the structural engineers I hired.  This process has gone on longer than I believe both Tacoma and I expected, but we have made excellent progress and I believe are getting to the final drawing edits, having been through all the drawings at least once to date.  There has been a struggle with my desire for a thermal bridge free envelope and Tacoma's desire to ensure the dwelling stays standing for decades to come, that has been worked out with lots of 1 and 0's flying through the internet email pathways, and I am grateful for Tacoma and specifically Heather's patience through this process.  In the end, it is difficult (impossible?) to build a thermal bridge free structure utilizing 2x4 wall construction, and while complying with zoning requirements, and I have had to compromise in several areas in order to allow us to proceed with permit drawings in any reasonable time frame.  There are a few areas I will try to 'upgrade' after the permit process, but will only be able to do so if ROXUL is able to provide some compressive strength testing results for their insulation in a 6" wide configuration (what I will have as continuous insulation on the exterior of the sheathing).

As you recall I recently completed a proposed plumbing waste pipe design and am now waiting for the licensed plumber to approve or adjust as required.

I also recently commissioned EcoLighten Energy Solutions to complete a room by room heat loss calculation that I will then use to design my radiant panels.  I will speak to this a lot more in the future, but it is my feeling that the method I was taught as part of the TECA Residential Hydronic Designer course, is too crude for high performance homes.  I plan on doing a comparison between that which EcoLighten provides and that completed using the TECA method, and will post the differences here.  The preliminary model from EcoLighten shows that I will use around 50% of the energy used by a 'code built' home.  With the levels of insulation and air tightness I planned, this is actually a disappointing result, as I was hoping for something closer to a 70%+ reduction. I will go over the model in the upcoming weeks and see if there are any assumptions that can be tweaked to represent what I believe will be the final reality.

I have also commissioned HoneyComb Creative to build the project website.  HoneyComb created my home inspection website and were an obvious choice to approach for my build needs.  The website www.theEnclosure.ca should be 'live' in approximately 4-8 weeks with at least the basic functionality, and then will be fleshed out as the project proceeds.  The site will include 'live' video, time laps photographs,  a link to this blog, a daily project diary, special component installation videos, dwelling design details, sponsorship links with promotional literature for sponsored products, and finally information and basic instrument readings for the science lab (once the dwelling is complete).  I am looking forward to the site launch and have been very pleased with the initial artwork provided.

Well, I believe you are caught up.   I will be posting documents pertaining to the variance application and the permit application, including all drawings, as I get through those hurdles.

As always, thanks for reading!  Please drop me a line if you have any questions or comments.

  

It's All About The Air Barrier!

Building Science Corporation has just released their report (available here ) that confirms that if you give insulation a chance by air sealing the assembly, all insulation will perform the same from a thermal transfer stand point.


The report highlights the increasing level of importance attributed to getting the details right as you increase the performance of an assembly by adding more insulation. Loosing 10% of your nominal value when you have a R15 assembly is a lot less critical than when you have a R50 assembly.

In order to complete this study, BSC had to design and build a hot box that significantly improved upon past designs.  

Key improvements include the ability to: 

• test higher R value enclosure assemblies (which have lower heat fluxes),
• expose enclosure wall samples to realistic temperature differences while maintaining the interior temperature at normal room temperatures, and
• measure the impact of imposed airflow at a given pressure difference across the specimen in both directions

This new and improved hot box was able to measure and confirm the effects of thermal bridging, the performance of insulation at various temperature gradients (for instance some polyisocyanurate insulations used in the TM Research Project exhibited a sharp increase in thermal conductivity - and decrease in Rvalue/in. - as temperatures approach and go below freezing), and the effects of air movement through part or all of the assemblies.

An interesting outcome of the air leakage measurements:

"Air leakage always increases the total heat flow through the building enclosure. However, air interacts with the materials in an assembly as it travels through. This interaction changes the temperature field in the assembly and through an assembly. The Thermal Metric wall test results provide strong evidence of the interaction between conductive and convective heat flows. This interaction results in heat exchange between the air and the materials inside the wall assembly and the total measured heat flow will be less than predicted by the commonly used discrete air leakage model"

Also of interest was the observation that "All of the reference test wall assemblies were subjected to significant temperature differences: up to 50°C or 90°F in the winter tests and up to 40°C or 72°F in the summer tests. Natural convective looping was not noted in any of the wall assemblies."

One of the most important confirmations for me was that "All wall assemblies experienced a loss in thermal performance due to air movement through the assembly. This is true for all of the assemblies tested regardless of the type of insulation material used (e.g. cellulose, fiberglass, ocSPF, ccSPF, XPS)".  With the failure of an effective air barrier that I typically see on spray foam jobs, this research helps to confirm that without an effective AB, even the might spray foam has diminishing thermal resistance. The report also confirmed "spray foam insulation only seal areas where the spray foam is installed; significant leakage paths often remain at wood to wood connections"  This confirms my conviction that spray foam is highly over rated.  If it does not guarantee an air tight assembly (see 3.6.4 on pg 102 of the report to see air barrier failures that occurred even in these lab conditions), why use it when there are cheaper products of lower environmental impact available?  I see attempting to use insulation as an air barrier as being just as foolish as attempting to use a poly vapour barrier to double as an air barrier.  Both products are hard pressed to represent an effective and durable air barrier.

Finally, it was interesting to note that they were able to measure the various resistance to air flow that different insulation represent. In 1.1 the report confirms that wet sprayed cellulose has more resistance to air movement over various fibreglass bat products.  It is too bad that they did not test mineral wool as it would be interesting to see how it compares to WPC.  Maybe next time!

Thermal Bridging and Dew Points

Anyone who has heard me speak for more than 10 minutes has probably heard me talking about dew-point potential.  It is at the heart of good building science principles.  Move the dew-point to somewhere outside of your assemblies, and your assemblies will have a built-in safety regardless of any air movement through them.

But for many, this dew-point conversation is esoteric and abstract, they can not usually visualize a dew-point occurring (that they are aware of, the condensation on the outside of a glass or can of cold liquid is a demonstration of dew-points) and so cannot appreciate the importance of reducing its potential in building enclosure construction.

Well by happenstance, I had an excellent example present itself to me at my home this afternoon.  I was coming back from my neighbour’s house after ‘supervising’ the dismantling of some scaffolding, when I observed condensation on the inside of the window near my front door.  Now, I generally have single pane heavy aluminum frame windows throughout my home, so condensation around the frame margins of the windows is not an unusual occurrence.  However this window had a wood frame (site built) and did not usually suffer from condensation.

Why the difference?  Insulation and air films!

Condensation spotted on the inside of the window.

Inside of window is condensation free except behind some mail propped up against window.

Condensation is definitely on the inside face of the window.

General window surface temperature 56.5° F

Surface temperature drops to below 51°F behind the mail.

Temperature in nearby region is 68.1°F

Temperature behind mail 56.4°F with an RH of 64%

So, what does this all mean? 

I have to admit, that this took a lot longer than it should have to figure out.  On the first round of measuring, I had RH levels well below 50% and temps of 66.3°F ‘near’ the window (my office is at 44% and 72°F on the other side of the house and benefiting from all the heat being pumped out from the computer equipment). At these windows temps and RH, the dew-point should have been around 47°F which was clearly well below my initial recorded window surface temp of 53°F behind the mail. 

So why the condensation? 

It then occurred to me that this was a delicate microclimate and by removing the mail for too long to do the testing and photos,  I had inadvertently changed the local conditions and disturbed the air film that would have been against the surface of the window.  So, I put the mail back to let the conditions come to equilibrium again and reran the measurements to get the figures in the photos above.  As you can see, the temperature within a couple of ‘ft’ to the window was now over 68F and the humidity that was building up behind the mail was over 64%.  This works out to a dew-point around 56°F and with a window surface temp of just under 51°F, I was well below the dew-point and had condensation.

The mail was creating enough of a barrier to heat loss (acting as insulation), that it was lowering window surface temperatures over 5F and at the same time was creating a micro-climate where the humidity was ‘trapped’ by still air and building up well above the rest of the house.  

This demonstration highlights how delicate the balance can actually be and why heat-bridging in assemblies is so critical.  Whenever you have isolated conditions that allow a small area of your assembly to cool in relation to the assembly as a whole, or that allow the build-up of humidity, you have the recipe for  liquid water formation and when hidden inside an assembly, that can and often does lead to disaster!