Saturday, September 19, 2015

Construction Update 1

Construction Update #1

It has been a week or so since I did my last update. With regards to passive house details and different construction techniques, not much new has happened.

Basement waterproofing
In the Passive House world you hear the term "Belt and Suspenders". Basically double up on things to make sure you get the result you want. We used Mel-Rol; a water based liquid applied waterproofing membrane. Then we installed a prefabricated dimple membrane over that.

Finished grade will come to the top of the black membrane. Above that we will finish with a Conproco waterproofing product.

Basement Steel Delivery

We will have 4 posts in the basement that support 2 steel beams. The beams will only span from the front (West) side of the basement to the stairs along the back (East) wall. Remember we do have 8" of foam under the footer under the post.

Comfofond Heat Exchanger Tubing

When we had Zehnder design our whole house ventilation system we had them include the geothermal incoming air preheater. Basically, we will be pumping a brine through the tubing to a heat exchanger coil in the house and the incoming air will pass over it. This provides some tempering in both the summer and the winter.

In the summer the brine loop will "precool" the air before it reaches the air to air heat exchanger allowing the overall efficiency to increase and give us up to a half ton (6000 BTU/hr) of cooling.

In the winter the brine loop will "preheat" the air before it reaches the air to air heat exchanger allowing the overall efficiency to increase and keep the air entering the house within 3 degrees of extract air.

We will revisit the overall design of the system when we install the system later on.

According to Zehnder's design specs, based on our soil type, and system size we need roughly 200' of tubing 

Since the perimeter of our house is just under 160 feet - doing 2 full loops would be a little too long, so we went around 3 sides of the house and doubled back. Our total length of buried tubing is in the 230 feet range.  

Back Fill

Once the tubing is laid we can begin to push the soil back against the house. 

With the back fill done, you can see we need more dirt...

The Pond

We dug a pond to give us some "free" fill.

The overall pond is roughly 5000 square feet. We made it to 7 feet deep before we hit a natural spring.

We did find some really nice damp clay under the top soil. So this is what we used to distribute around the rest of the house.

Photo looking at the front of the house

Photo looking at the south end of the house

Photo looking at the back of the house

Photo looking at the north side of the house (Breezeway and garage side). 
We had to wait on the foundations for those for truck access to the raised fill septic system.

The tube you see sticking out of the ground is our sump pump. (The tubing sticking out is the temporary discharge line)

Exterior Sump Pump
I am not sure of you picked up on this at all from previous posts, but we will be incorporating an exterior sump pump to our house. This is very uncommon in new construction, but can be used in retrofit situations to keep basements dry. We did this for a few reasons.

  1. A sump pump pumps water out from around the foundation drains. These drain pipes are corrugated plastic pipes with small slits in them to allow water into them. When they are not filled with water they are excellent paths for radon in basements. the gasses can easily get into the pipes and into the sump crock in the house. We are building in a higher risk area of radon, and wanted to ensure we would be radon free. 
  2. A sump pump would be penetrating the sub slab insulation creating a pretty substantial "Thermal Bridge". There is no good way to insulate around a sump crock.
  3. We eliminate a penetration in the foundation wall where the pump would pump the water out into the yard.
Our exterior sump pump will discharge into our pond. We did make sure the building official and the pond engineer were OK with this situation before we decided to do it. The pump will be installed on a lanyard so it can be easily changed out in the event it fails and there will be an indicator light on a float switch in the even the sump pump either fails or cannot keep up with the incoming water.

We will be framing the deck soon and getting started on the septic system!  


  1. Really nice post! Didn't know that they used brine thought they used Anti-Freeze compound in stead.

  2. Nice thought, Typical NaCl brine has a freezing point of -6 F. If we are using -6 F brine to preheat incoming air we are in trouble - and if the sub soil ground loop reaches -6 F I think we have bigger problems! Also if the system leaks brine is not as harmful as antifreeze.

  3. Why would anyone consider backfilling with on-site materials?

  4. Charles, Thanks for the comment. Due to the site conditions we needed dig the pond to serve as a reservoir. We are near a creek that has flooded in the past. The top of the slab is well above any flood plain, but I wanted to give the land a place to drain to. We were only planning on using the dirt to raise the yard elevation, but found some decent clay under the top soil. We allowed the damp clay to dry out before back filling. Using the site material as back fill saved us roughly $10,000. We did back fill over the drain tile with fine stone first however. On a separate note, the heat capacity of damp clay is the highest of soil types, so it will help our short brine loop be even more efficient.

  5. What a very thorough report thank you for sharing all this with us. My husband was not aware that all this work went into construction so we thank you for this as we had planned to do some building of our own but now it looks like we will be holding off till we have sufficient help, thank you again.

    Melba Collins @ Vermeulens

  6. What kind of pipe did you use for the brine loop? SDR11 HDPE? Some manufacturers seem to indicate that even NSF14 rated pipe requires sand backfill to eliminate point loads.

  7. How deep did you set your footers? I'm guessing your frost line is around 40-48"


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