Radon

Back when we started construction of the foundation, someone asked me if we were going to include a radon mitigation system.  My response was something along the line of, “No.  We don’t need one.  It’s a Passive House and will be so well sealed no radon will be able to creep into the structure through the basement foundation.”  So much for uninformed confidence.

Flash forward to last month, when I came across a blog post by Paul Honig, who lives in a similar Passive House in Connecticut.  Surprisingly (at least to me) he wrote about his own discovery that his house had tested high in radon, and required the installation of a mitigation system.

In case you are unfamiliar with them, these mitigation systems are incredibly simple. Generally, a four to six inch hole is drilled through the basement slab.  Some stone and/or dirt is removed.  A PVC pipe is inserted.  The pipe is either run up and out through the rim joist (below the first floor) and then up to the roof, or all the way up through the attic to the roof.  A special fan is installed on the pipe, either outside the house or inside the attic.  The fan then runs 24/7, sucking air from under the slab, and thereby depressuring the sub-slab area and moving the radon outside. From what I’ve read, these systems generally cost around $1,000, give or take.

A homeowner can test for radon several different ways.  He or she can purchase a short term test on the web or at stores like Home Depot or Lowes.  They generally come with two vials.  The homeowner is then instructed on where to place them and how long to leave the caps off.  When the necessary amount of time has passed, the caps are replaced and they’re sent to the testing facility.  A week or so later, the results are viewable online.

Paul used a continuous electronic monitor called the Safety Siren Pro Series3 Radon Gas Detector, which sells for $130 through Amazon.com.  It’s very simple to use.  Just plug it in, wait 48 hours, and it starts providing a short and long term radon level reading, updated each hour.  The long term reading is an average of the hourly short term readings.

My curiosity was piqued enough to make the purchase.  Living is such a tight house, I had no desire to take a chance with radon just to save $130.  It proved to be a wise investment, as it reported a radon level of 6 pCi/L.  This is 150% above the remediation limit of 4 pCi/L.

I decided to check the accuracy of the Safety Siren by using a short term test that I purchased from Home Depot (that test cost me $15 plus a $30 lab fee).  The lab results showed one vial reporting a level of 4.7 pCi/L and the other reporting a level of 7.2 pCi/L.  The lab interpreted this to be an average reading of 6 pCi/L, the same as the Safety Siren.

I had almost zero enthusiasm for installing a traditional radon mitigation system.  Given the amount of insulation in the attic and the fact that the house has two stories, it would have been both difficult and messy to run a 4″ PVC pipe up through the roof.  Additionally, the first floor pent roof and the porch roof almost complete surround the house.  Therefore, there is very limited space to run an exterior pipe up the wall, and that space is near the front of the house, which would be less than appealing.  And finally, I have no desire to drill a 4″ hole through the basement slab and vapor seal.  Fortunately, after thinking about the issue for a while I came up with a possible alternative.

Instead of using wood to form the footers for our house, we used a product manufactured by Certainteed, called Form-a-Drain. Form-a-Drain footer forms are hollow, plastic, and have hundreds (or thousands) of small slots on both sides to allow water to drain away from the foundation.  Before the concrete is poured, a short section of PVC pipe is installed to connect the inner and outer forms.  Then another 4″ pipe is run to daylight to complete the drainage path.  Although I didn’t know it at the time, Certainteed bills the system as a “three-in-one concrete footing form system, foundation drainage system and sub-slab perimeter radon reduction system.”   Here are a couple of photos of the installation:

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The drain pipe on our house exits the ground on a slope about 30 feet from the southwest corner of the building. The idea I came up with was to install a Fernco rubber 4″ elbow on the end of the pipe, run a two-foot section of PVC up from that, install a radon fan on the top of that pipe, and cap the horizontal outlet.  My initial thinking was that no measurable water actually exited the drain, so I suspected that a cap wouldn’t cause a problem.  I was wrong.

During rain and melting snow, a fair amount of water did build up at the end of the drain pipe; somewhere between a half-gallon and a gallon per day.  In one sense, that complicated the installation of my radon mitigation system.  But on the other hand, I took it as a positive sign that the system was working as designed.  So I had to come up with a way to allow water to drain from the pipe while maintaining the system pressure being developed by the fan.

After doing some research, I concluded that there were two possible solutions to this problem.  The simplest would be to drill a few weep holes in the end cap; enough to let the water trickle out, but not so much that it would cause a critical drop in air pressure.  The other solution, which I chose, was to install a waterless “J-Trap” on the tee instead of a cap.  The product I found was the Hepvo Waterless Value, which sells for about $23.  It’s an incredibly simple device that works like a J-Trap in that it allows water to drain, while preventing sewer gas from entering the house.  But it does this without actually holding any water in a trap.  That’s important at our house because any sitting water would freeze in the winter.

For the fan, I chose to use the Energy Star-rated RadonAway RP-140, which can be found for less than $130 on the Web.  At 15-21 watts, it has, by far, the lowest draw of any fan I found.  It also has lowest airflow, maxing out at 135 CFM.  But everything I read indicated that it was more than sufficient to handle the problem.  Installation was incredibly simple; a Fernco union attached it to the lower pipe, another Fernco on top connected it to two PVC elbows (to keep rain water from entering the system.  For testing purposes, I ran an extension cord to one of our outdoor outlets, figuring that if the system works, I’ll run a buried line to it this summer.

And work it did.  It took a couple of days, but the radon level is now at 1.0 pCi/L, well below the 4 pCi/L limit.  The only things left to do are install the underground electric supply and disguise the fan and pipe, which should be much simpler than the alternative. Here are a couple of photos taken before I replaced the end cap with the Hepvo waterless J-Trap:

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Carrying the Vapor Barrier Over the Basement Wall

As I discussed in my last post, our intent is to bring the vapor barrier from the basement slab, up the inside of the basement wall, then over the wall to the outside of the building, and then up the outside of the wall via Zip System sheathing.  But to give the basement walls as much time as possible to dry, we won’t be covering the basement walls until the house is completed (which I anticipate to be sometime next spring).  To prepare for that, we needed to bring the barrier over the top of the basement wall now, before the framing begins.  As you’ll see in the following photos, we did this with the same peel and stick membrane used on the outside of the basement walls:

Before:

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And after:

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Because the membrane is a bit challenging to work with, we used the following process to complete the task:

1. The membrane comes in 36″ wide rolls (75′ long).  So we cut a length in half (18″), which was the perfect width to cover the top of the walls (which are 15 1/4″ wide).

2. We then cut each 18″ strip in half.  This precluded the need to try to fit a single piece over the sill bolts.

3. Finally, we laid each strip down, lapping the inside strip over and down the inside wall (about an inch-and-a-half) and the outside strip over and down the outside wall.  We were able to cut around the sill bolts as we went along, and we matched the pieces up fairly easily, with only occasional minor gaps between the two.  Since the slight gaps that existed here and there ran down the middle of the walls, we knew that the sill seal would cover them.

Here’s a photo of the wall after the sill seal was in place:

IMG_0055 The product we used is Protecto Wrap Premium Energy Sill Sealer. It’s a 3/8″ closed cell polyethylene foam with an aggressive self adhesive waterproofing membrane that conforms and seals off the voids and irregularies between the top of the foundation and sill plate.  Because the walls are wide and we used a 2″x10″ sill plate, we used two side-by-side strips of 5 1/2″ sealer.  We also put a bead of caulk down each strip before placing the sill plate on top of it and bolting it down.

The Sill Sealer doesn’t come cheap.  It can be purchased for about $40 per 75′ roll (or $1.60/lf).  But its thickness and bottom adhesive did give us confidence that we’ll seal the irregularities that are inherent in the foundation sill.  Hopefully, it will make it that much easier to meet the .6 @ 50 pascals target.

 

The Basement Slab, Insulation, and Vapor Barrier

As I indicated in the last post, we chose a third option with regard to the vapor barrier in the basement.  If anything appears clear to me, it is that, like so often in life, there is no perfect solution to this issue.  Rather, it’s a balance of time, money, and effort.  What we ended up doing was this:

Once the four inches of gravel was sufficiently leveled with a laser level, they placed three two-inch layers of XPS Green Guard Foam (R-30) on top of it, laying each level perpendicular to the one below it.  This is a photo looking in from the Bilco door opening.  They’re working on the third layer:

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Once that was completed, they covered the foam with a layer of 16 mil polyurethane (i.e. the vapor barrier, and taped it to the ICF foam. The lally columns sat directly on the footer pads.  So we taped the poly to the columns, and then wrapped the columns with a kind of bubble insulation that could later be ripped out (after the concrete was poured) and filled with spray foam:

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We initially anticipated running the poly up the wall and taping it above the concrete so it would be easy to connect to the barrier that we will run up and over the walls.  But that idea was nixed because it would make it difficult to chalk a line for the leveling of the slab.  While not a perfect alternative, we feel that taping the poly to the ICF at the point where it meets the sub-slab foam will work fine.  When the house is completed (eight or nine months from now), we’ll bring the vapor barrier from the top of the slab up to the top of the basement walls, and tie it into the barrier that we will (next week) place over the top of the foundation walls.  Essentially, that will leave only one avenue for sub-grade vapor to enter the house; it would have to come up from the footers through the foundation walls and then through the EPS ICF foam and into the slab.  We don’t see that as a serious concern because a) the potential area that is open to vapor infiltration is less than 50sqft (the 132 linear feet of the edge of the 4″ thick slab), which amounts to less than 1% of the entire building envelope (which I estimate to be over 6,000sqft), b) while not a vapor “barrier” (i.e. less than .1 perm, the EPS foam is certainly a vapor retarder at less than 1 perm, c) even without the EPS vapor retarder, my research indicates that 50sqft of 4″ concrete can only allow the transmission of a maximum of about 2 tablespoons of water vapor in a 24 hour period, and d) the Form-A-Drains provide a more favorable route for water vapor than the cement itself. I’m sure my conclusions can be debated.  But I’m comfortable with them.

Once the poly was properly taped, the concrete was poured:

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Note the detail at the Bilco door entrance:

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That was a misstep in that it was just one of those small details that didn’t make it into the plans.  If left as poured, there would be no “thermal break” (i.e. insulation) between the Bilco well and the slab.  Fortunately Hugh caught it before the Bilco was installed, and the correction was relatively easy; an hour spent with a grinder and 2″ of XPS:

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Insulated Concrete Forms and the Foundation Walls

Once the footers were completed and vertical rebar was added to aid in the connection between them and the walls, the foundation sub came in and built the ICF walls for the basement/foundation.  They used Foxblock brand ICF, with an 8″ core and 2.625″ of EPS foam on each side, giving it an R-Value of 23.  An interesting aspect of the ICF assembly (at least to me) was that they left something like a 3/4″ gap near the center of each wall, which was needed as a “fudge factor” (my words) so the walls could be properly plumbed after assembly.  Then, before pouring the concrete, they filled the gaps with a spray foam and screwed a temporary piece of plywood over the joint (as seen in the second photo below).

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They placed vertical and horizontal rebar in the walls as they were assembled.  The walls were poured using a pumper truck ($800 for the day) and a 6 inch “slump,” which is fairly soupy.  My understanding is that they did this because of concerns with using a vibrator on the walls (i.e. they were concerned with the potential for blowouts).  Hopefully that was sufficient to avoid any significant voids in the walls; small voids evidently are to be expected.

Once the walls (and the three lally column pads) were poured, they spent considerable time adjusting the (yellow) supports while checking with a level and with chalk lines that were strung along the top of each wall.  This was done to ensure that the walls were straight, level and plumb.

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A day or two later, a 2″ layer of Green Guard XPS Type IV (R-Value of 10) was screwed to the outside of the walls everywhere except where the EFIS (Exterior Insulation Finishing System) will be applied.  EFIS is an above ground foundation finish that is similar to Stucco in appearance.  Apparently, they use a different two-inch foam board as a backer for the EFIS.  The ICFs have heavy plastic strips embedded in the foam every eight inches for attaching things like an exterior sheet of foam (or an interior sheet of drywall).

After attaching the XPS, a “peel and stick” waterproofing membrane was applied over the entire exterior.  They used Resisto brand for most of this work (and Soprema brand for the repair work discussed below).  Resisto is a “40-mil-thick self-adhesive membrane composed of elastomeric bitumen and a trilaminated woven polyethylene.”  It appears to be very durable, and it’s extremely sticky.  Touch two of the adhesive areas together and you’ll never get them apart.

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We ended up having the sub return to fix the Resisto application in some areas where, for unknown reasons, they applied an upper section first, and then lapped the bottom section over it.  Though they expressed confidence that no water would enter the joint, “Flashing 101” told me that it was the opposite of what should have been done.

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We also had them apply a dimple board over the Resisto/Soprema membrane.  Dimple board is designed to keep the hydraulic pressure off of the foundation by providing an air gap so any water that gets past it can drain to the bottom.  The product that we used is Delta-MS.  The dimples, of course, face the foundation.  They’re what creates the gap.  Installation of the dimple board resulted in roughly a $1,900 up-charge, or somewhere around $2/sqft.

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One final point…there was a lot of discussion about the vapor barrier (a 16 mill sheet of polyurathane) as it pertained to the footers and foundation walls.  The architect had intended that it would run over the foam (that was to be placed under the basement slab) and then under the footers and up the outside of the walls.  But there was some concern about how to actually accomplish that without ripping countless holes in the barrier for the Form-A-Drain stakes and the stones.  A second alternative was proposed, which was to run the barrier between the footer and the ICF wall.  But there was some concern about the “cold joint” that the barrier would create between the footers and the walls.  [This concern may have been unwarranted, as I’ve since learned that the makers of Delta-MS also make a product for that purpose.]

Another concern was that either of the two options would have required strips of the vapor barrier to be placed on, or below, the footers.  Then those strips would have had to be taped to the eventual vapor barrier that would later be laid on the foam slab insulation.  In a practical sense, that would have been difficult to accomplish; a lot of tape connecting two sheets of poly.

Looking back, maybe the second option would have been ideal because it would have provided a vapor barrier that would have extended between the walls and footers and, even if imperfect, would have kept the walls from wicking moisture up from the ground.  But we ended up using a third option using a third option, which will be discussed in the next post.

And one final minor point…we debated about the number and placement of foundation penetrations for things like the septic, well, electrical, ERV, and HVAC.  In the end, we decided to install only two (PVC) sleeves; a 2.5″ for the well (to handle both the electric and water line) and a 6″ for the septic. We placed the water sleeve about 4′ below grade and the septic a couple of inches above the basement floor surface level.  The rest of the penetrations will be through the rim boards, where they’ll be easier to execute.

All-in-all, it seems like the foundation should be pretty bullet-proof.

Footers – Part 2

I think Norm Abram said “Measure twice. Cut once.”  But regardless of whether it was him or someone else, I’ve heard it, and recited it, hundreds of times.  I’ve also learned, and re-learned, that lesson many times while building furniture or performing repairs around the house.  And still, when my excavator and I measured for the lally column footers (which were 3’x3’x1′) I didn’t double check the measurement.

The problem was that the plans showed them centered at 10’5″ from the inside edge of the ICF core and we had strung our line at the outside edge of the ICF core.  So when we measured, we should have added eight inches to the 10’5″, and instead we subtracted. This resulted in the footers being 16″ off center.

Luckily the foundation sub discovered the error when he was making the ICF cutouts for the main beam in the foundation walls.  But as luck would have it, the footers had already been poured, and the columns would have been sitting on the edge of each pad.

The mistake was discovered on a Thursday, and the basement walls were scheduled to be poured on Monday.  There was no way I could remove the two footers; each one consisted of nine cubic feet of concrete and rebar.  The only viable alternative seemed to be dig out three new footers.  So on a 90+ degree Sunday, I spent about six hours doing just that.  All worked out well; when the basement walls were poured, we had the foundation sub re-pour the three footers:

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If working all day in the heat didn’t reinforce the lesson, carrying the dirt out of the basement bucket-by-bucket made it crystal clear.

Beginning Construction – Footers

We started with the excavation in late June, and it seemed that the minute the excavator was finished with the basement, the skies opened up and rained for the better part of two weeks.  In fact, this seems like one of the rainiest summers I can remember.  Needless to say, it’s caused some delays.  But we’re managing to slowly push forward.

One of the first deviations from the plans was the use of Certainteed’s Form-a-Drain in place of a traditional footer form and foundation drain system.  If you’ve never seen or heard of the system, it’s pretty simple.  The forms are hollow plastic retangular “lineal sections.” The have slits cut into both sides that are intended to drain water to the exterior, and they’re connected to a pipe that drains to daylight.  The reasons for the change were ease and speed of installation, and the resulting cost savings (which, frankly, I never did confirm and I’m doubtful occurred).

We did have a bit of a debate about how to dig for the footers.  The foundation sub wanted the excavator to take the entire floor down to footer level.  His basic reasoning was that it made his job easier, and avoided the problem of arriving to see inadequately dug footer trenches.

My excavator, on the other hand, wanted to take the foundation floor down to eight inches above the footer floor and then “scratch out” a three foot wide by eight inch deep footer area around the perimeter (the footers are 12″ deep by two feet wide) on the day that the footers were poured.  He thought that, to take the entire floor down the additional eight inches would only mean that I’d have to pay for an additional eight inches of stone to fill it back up.  And he also knew that rain was on the way, and didn’t think it would be a good idea to leave the footer floor open if the footer pour was delayed (which it was, by over a week).

The excavator won the debate, and the day the footers were eventually poured he and I got out there at 5:30am.  An hour-and-a-half later, we had “scratched” out the footer trench and the two pads for the lally columns (well, he scratched them out with his backhoe while I checked the depth and cleaned them out with a shovel).  A couple of hours later, the footer forms were in.  We then backfilled the footer trench (the area outside of the forms) with 12 inches of stone, and the rest of the floor with four inches of stone.  By 11am, the footers were inspected, and by 3pm they were poured.  All in all, it was a pretty smooth process.  Of course, little did I know that it was not an error free day…

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