Monthly Archives: March 2018

Slab Happy – Revisited

March 30, 2018

Well, I am thrilled to advise I finally have a basement floor!

I poured the floor last Monday and it turned out phenomenal. John and his crew from High Def Concrete knocked it out of the park!  I had asked for a machine finish, and by the time that John left that night at 9:30 PM the floor was as smooth as glass and should provide years of undamaged use (I will leave the concrete exposed in many parts of the basement).

John from High-Def Concrete working hard into the night to give me an A+ finish

But lets back up a bit.  When I last updated you, I had just finished the slab edge membrane attachment to the footings and was working on installing the RockWool ComfortBoard 110 Semi-Rigid mineral wool panels.

I can advise that this product stood up well to the rigours of prepping for the slab pour.  I was able to walk on the product without significant compaction but did use plywood kneeling plates as the concentrated weight on my knees would leave a noticeable divot (as also occurred with the XPS and EPS panels I installed in the science lab).  In areas that I was repeatedly accessing, I put down 2×6 runners to protect those pathways from over compression during the pour prep, and you would also want to do this if running a hard wheeled dolly or barrow over the area.  There were also no issues that arose during the actual pour, I had calculated volume needed for an exact 4″ slab + an extra cubic metre + and extra 1/2 M3 that stays in the pumper truck hopper, and I was only left with the extra M3, meaning there was no significant compression of the insulation during the pour (and my takeoff skills were sharp!).

Compared to the rigid foams, the mineral wool is also easier to install because it is more forgiving due to its slight ability to compact.  For instance if their was gravel chunks higher than the rest, they would just embed into the bottom surface of the insulation panel (a big deal when using rigid foam and 3/4″ crushed).  This really helped to maintain the required elevations of the floor.  It was also easier to fill irregular areas with the mineral wool as those areas could just be ‘stuffed’. The only down side is that in the confined space of the basement, the air quality got quite poor and I had to wear a mask, and even then my chest was not happy for a day or two after handling.

This was a concrete ‘cap’ over my buried tech cable electrical service. As spray foam readily soaks up water, I used mineral wool to fill in around this irregular shape. Something you could not do with rigid foams. This was the EPS panel for the sub slab building science lab.

I also was impressed with the durability of the 15 Mil Perminator membrane I installed below the slab.  It was fairly easy to install except that due to its thickness and rigidity, any creases folded into it at the factory were difficult to get rid of and therefore air seal around.  But its thickness meant it stood up well to construction activity and resisted all tears and punctures.

The 12′ wide Perminator membrane is folded in half. There was no way you could pull the edges hard enough to flatten out the crease, so you had to run your finger along it to flatten it out.

The Perminator membrane was sealed to the membrane I previously installed along the slab edge that was tied back down to the footing providing an air-tight continuous interface.

For internal footings, I sealed it to the VB Poly I had installed into the footing stay in place XPS forms back in Jan 2015.

The only thing I would have changed if doing again is to have used the Perminator membrane around the internal footings instead of the VB Poly I did use.  Back in Jan 2015, I had not yet researched what sub-slab membrane I was going to use.  The poly flaps had been protected all this time with strips of plywood, but there were still a lot of holes that needed to be sealed up prior to the slab pour.

For any floor drain penetrations, I was able to cut a hole in the exact location by folding the membrane up against the drain and then marking with another loose piece of ABS.

For Drain Penetrations, bring the membrane up to the drain and fold over. Place the same sized pipe against the drain and trace.

Your left with a cut-out in the exact location needed. The membrane can now just slip over the drain pipe (as long as you have not fastened the far end as it needs to be pulled up to get over the pipe before settling back down into position). Just remember to only cut through the one layer 🙂

For pipes and other penetrations that you could not slip the membrane over, I just had to do a slit cut and then reseal.  On all penetrations, I was concerned that the slight compression of the mineral wool, would just tear any taped seal I did around the penetration.  So, I instead made a ring of membrane that I knew would stick well to the Perminator and then I used my favourite liquid flashing material: R-Guard Joint and Seam.  This provided a very flexible, air and water tight interface, and was fast and easy to install.

Foil Face membrane ring was adhered to Perminator (primed with Protecto-Tak) and then sealed off with R-Guard Joint & Seam

Reinforced Bucks were used anywhere we did not want concrete, like this shower basin.

This is the sub-slab insulation science lab area. The far left panel is testing 10″ of mineral wool followed by a panel with only 4″ (matching the rest of the basement floor). The Pink panel is Foamular C-200 XPS followed by PlastiSpan® HD Type II EPS Insulation

Each test panel has two sets of four duff gauges that will record the temperature and moisture content between the insulation and granular layer, at the insulation mid-point, between the insulation and Perminator membrane and between the membrane and concrete floor slab.

With the insulation and membrane installed on all four lab panels, I built the bucks that will later form the concrete lids over the test lab. I also installed some rebar to reinforce the edges as I will have a rolling jig to lift out the 4ftx6ft concrete lids to remove the insulation samples for testing.

The last task was to install the slab edge insulation.  Now slab edges are negligible down 12ft below grade except that the perimeter drainage system is constantly removing thermal energy from the perimeter of the foundation, so some insulation is still useful.  You also want a bond break between the floor and foundation/footing to allow independent movement.

To set the elevation of the XPS slab edge insulation, I measured down from a laser line.

The XPS strips were glued to the ICF with foaming adhesive. I held the strips in place with blocks of wood till the foam setup. The top edge of the strips provided the grade line for the top of the concrete slab

Now to the title of this entry – Slab Happy.  This was not randomly chosen but represents an article written by Joseph Lstiburek at the Building Science Corporation. In his building science insight #59 Joe talks about the proper placement of the sub slab ‘vapour barrier’ SHOULD ALWAYS be placed between the insulation and the concrete slab, NEVER UNDER the insulation. Joe further previously elaborated on the issue in his article Concrete Floor Problems discussing the California practice of placing sand between the vapour barrier and concrete to the same end result.

Most builders reading this entry will have thought up to this point that I had put the Perminator membrane in the wrong location, and in fact my Municipal inspector confirmed that they “always” see the membrane installed under the insulation.

So why should it go above?  Simple answer – Physics.  You see, when the membrane is put below the insulation, it means that there is no barrier between the insulation and all that bulk water incorporated into the poured concrete.  The insulation becomes 100% saturated.  This is only part of the problem, the second part is that although it was wetted by liquid bulk water, its only drying capacity is by vapour transport up through the slab, and this is a very slow process retarded even further by the fact that as the interior of the dwelling becomes heated, the vapour pressure will always be pushing downwards. The insulation stays saturated for years, if it ever dries out, and wet insulation is pretty much useless insulation!  So always put your membrane in contact with the concrete.

Now that this milestone is behind me, I will frame out the remaining walls in the basement before re-starting on the exterior of the dwelling.

Thanks for visiting.

“In any moment of decision, the best thing you can do is the right thing, the next best thing is the wrong thing, and the worst thing you can do is nothing.” —Theodore Roosevelt (1858-1919) 26th U.S. President


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The Barriers

March 6, 2018

No, I am not talking about some 70’s alternative music group, but the various components that allow for the separation of conditioned indoor space and non-conditioned outdoor space in a building.  These barriers create the envelope or more appropriately named Enclosure of a building.  After my recent update identifying a resolution of the difficulties I was having with my Enclosure and the Municipality, I thought I would follow up with a more in-depth discussion of the barriers and their purpose.

There are 5 barriers employed in most building enclosures;

The first defined barrier is the water shedding surface (WSS).  The code describes this as a ‘Primary Plane of Protection’.  Its purpose is to deflect the vast majority of storm water away from a building.  This is also the only visible barrier, in that it is made up of the cladding, windows & doors, flashings, and roof. This barrier is often not 100% continuous , and it is expected that some liquid water can penetrate through this plane (except low slope roofs which have a 100% water tight WSS). The materials of this barrier are not important as long as they are able to shed water and are not adversely effected by wetting.

The second barrier is the Water Resistant Barrier (WRB), also sometimes called the Weather Resistant Barrier.  Its purpose if to provide the last line of defence against water penetration into the assembly and is called the ‘Secondary Plane of Protection’ by the building code.  For walls, it is most typically a type of sheathing membrane in residential construction.  Any materials located outside of this barrier should be chosen that are not adversely effected by wetting.  This barrier is expected to be continuous and not allow ANY penetration of liquid water past its defence.  This does not mean it has to be air sealed, only shingled in a way to shed water. What is important is that the materials of the barrier are generally vapour open in a heating dominated climate (different rules apply to hot or mixed climates and are outside this author’s focus).  Like Gore Tex, you want this layer to be water tight but allow perspiration to escape. The allows any build-up of humidity within the assembly to bleed out to the exterior low pressure side of the assembly.  This is also why, for a durable assembly with the maximum built in safety factor, you only want a vapour open insulation when installing insulation exterior to the WRB.

The next barrier is the Vapour Barrier (VB).  Its function is to prevent moisture, in the form of vapour, from entering the assembly through diffusion (think cell to cell movement) and then condensing on cold surfaces within the assembly possibly leading to rot or mould.  This barrier only needs to stop diffusion and as diffusion is a slow process moving small amounts of moisture, pretty good is good enough.  A VB that covers 90% of the wall, will still make a very effective barrier – there is no need to seal your VB around penetrations and make air tight.  Leave that for the air barrier!  A VB should ONLY be installed on the warm side of an assembly (high vapour pressure side). Materials selected for this barrier are again flexible as long as they are generally vapour tight.  For Canada this is on the inside of the assembly and has typically been detailed as a poly sheet installed beneath the drywall. But you could also use Vapour Barrier Paint which is a bit more permeable than poly and offers some additional safeties to the assembly as it allows some drying inward if there was a failure somewhere leading to very high moisture levels within the assembly.

The last barrier is the air barrier which, in Canada as a whole, has never been taken seriously by the building codes and construction community, but is one of the most important barriers from an energy efficiency and assembly durability standpoint.  Its purpose is to block air movement through an assembly. Air movement, when it exists, can bring with it vast amounts of moisture, in vapour form, into the assembly where again, it can condense on cold surfaces possibly leading to rot or mould.  The beauty of the air barrier is that its location is flexible.  It can be installed at any point within the assembly and will still prevent air movement THROUGH the assemblyBut while it is flexible as to its location, it MUST be continuous in all planes to be effective. This does not mean it is one material, but rather a group of materials all linked together in a continuous air tight fashion.

Air barrier is much more important than a vapour barrier in preventing the movement of moisture into an assembly.

In the vast majority of single family constructions in British Columbia, over the last couple of decades, the air and vapour barrier have been combined utilizing a ‘sealed’ poly sheet installed beneath the drywall. Futile attempts have been made, over and over, and over again, to seal this poly sheet in a lasting manner as an effective air barrier.  In my previous profession as a home inspector, I never once saw an effective poly air barrier.  It is just too difficult to seal a poly sheet around the myriad of penetrations through the outside walls and ceilings.  My recent video on sealing HRV ducting demonstrated how difficult it was to even seal the end of a metal duct for testing with red tuk tape.  Imaging trying to seal around every wire, plumbing pipe, gas pipe, cable vision/alarm/telephone wire, air duct, etc, penetration not to mention around floor trusses and other awkward structures throughout the whole building.  GOOD LUCK!

The effectiveness of the air barrier has never really mattered in Canada because until the most current code iteration, the language of the code has required an ‘air barrier’, but has never required the testing to confirm a barrier is present.  Now that the codes are finally taking this seriously, builders are left flummoxed as one after the other fails their air tightness testing.  One of my friends at RDH spends many of his Saturdays at a small warehouse in South Vancouver, educating builders on the proper installation and execution of an air barrier for builders in Vancouver that have failed their air seal inspection.

Now that the code in the rest of the Province will also require air barrier testing, it will most likely result in a change in strategy by the build community and adoption of the exterior air barrier approach preached by many in the Building Science Community.  In this approach, the air barrier and the WRB are instead combined to create the air barrier on the exterior side of the sheathing.  At this location, you only need to worry about sealing the sheathing membrane to itself and around the perimeter of penetrations like windows and doors.  But the penetrations themselves are already sealed to be water tight, so now you are only talking about the addition of sealing the sheathing membrane seams.  Unlike trying to seal poly around irregular shapes, it is much easier to seal straight long seams between membrane courses.  And if you use a self adhering membrane, like Delta Vent SA, this process becomes even easier.

The only caution expressed by proponents of an interior air barrier, is the risk of air movement into and out of the assembly from floor to floor (air moves from interior into wall and then back into the interior on another floor), but a dense stud cavity insulation all but eliminates this risk (mineral wool or dense packed cellulose).  This risk is also typically quite low as it requires a pressure difference to initiate an air flow.  This would typically only be present in homes with a significant temperature variance between floors (something not recommended in a high performance home).  While we are discussing the stud cavity, utilizing a dense insulation also prevents convection currents occurring within the cavities, a process that can bleed energy away as it picks up heat from the drywall surface and loops it over to the sheathing’s surface where it is lost by conduction.

In the past, the correct detailing of many of these barriers was not as important, because as we did not insulate our buildings to any great degree, heat loss from the interior of the building could often cook out any moisture accumulation within the assembly.   But as we increase the insulation levels in our assemblies, we now increase the temperature differential within them, and our exterior sheathing becomes colder and colder as they loose the ability to be heated by energy escaping the interior of the structure.   A colder sheathing will more often be at or below the dew point of any interior air escaping into the assembly.

As we strive for ever more efficient buildings and ramp up the insulation levels of these assemblies, it becomes critical to get these barriers right if we are to prevent widespread failure of our building stock.  We need to start doing things better!

Thanks for visiting and as always, I look forward to any comments you may have.

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