Energy Revolution in a Brooklyn Townhome
Monthly Archives: March 2010
We are installing a rain barrel for to capture some of the roof runoff for use in the future garden. The rain barrel that the client has selected is the “Abe” model by AquaBarrel. http://www.aquabarrel.com/product_rain_barrel_complete_80gal.php. While this isn’t part of the Passive House Standards, Passive House ideologically encourages additional sustainable measures in building practice.
We recently conducted a preliminary test of the air leakage in the house by using a blower door and an infrared camera. While we are not close to the Passive House standard of 0.6 ACH50 which for this house is 300 cfm50, the test was a success because we were able to come up with a system to address the leakage points that still exist. When we tested the house with the blower door prior to the start of construction the house was at 8500 cfm50. A blower door test that we did prior to the new year and before all of the window area, cellar, and addition spray foam was installed was a disappointing reading of 7100 cfm50. The next blower door test yielded 4100 cfm50 which is still higher than the code requirements for new construction at 5.5 ACH50 or 2750 cfm50. This was after getting the final main areas of spray foam installed.
Because we still had a long way to go we needed a method that would pinpoint our leaks more exactly. We started by using temporary heaters to bring the house temperature up to around 50-60 degrees (still significant stratification due to air leakage), and then turned the blower door on for brief periods to draw in the outside air which was around 30 degrees. With our Flir i7 infrared camera, we went around and looked for the cold points along all of the walls. The air leaks were surprisingly easy to see and it was the first time that I could prove that the spray foam insulation was not performing as well as expected in terms of a continuous air barrier. We had holes in the middle of the spray foam in some places even with 3″ of depth and many of our corners did not perform well. We used a low VOC spraypaint to quickly mark all the areas that we found and over the next week filled them all in. Once we ran the test again we got down to 2,500 cfm50.
Still a ways off, we repeated the testing method with the blower door and the IR camera and found more leak spots. Our last test as of the begining of March is at 2,100 cfm50. I would like to get the numbers down to 1,000 cfm50 prior to drywalling all of the walls. Because of the long lead time of the German windows, we can’t wait for their installation before we have to close up all of the other walls. This is nerve-wracking because it would be much better to leave everything open, install the windows in an air tight way, and then test everything again. This way we could be assured of reaching the 300 cfm50 required prior to sealing off any areas.
We are in the process this week of detailing more leak points in the envelope and will be putting a lot more man power into tackling this issue. We still have as a backup our drywall layer as a secondary air barrier which we are planning on air sealing anyway, but I don’t want to rely too heavily on that because of the large increase in surface area of the drywall layer as opposed to the exterior wall sealing.
This is an image around the chimney header just under the roof decking taken while the blower door was running. The blue area is the cold air leakage streaking across the underside of the roof deck.
The cellar floor and insulation system was a complex layering of elements designed to keep the water from infiltrating the cellar side walls or slab and to maintain a continuous air and thermal boundary. The client plans to use the cellar as recreation and work space so even small amounts of moisture are of greater concern than it might otherwise have been.
The steps involved in the cellar are:
1) Remove old cracked slab.
2) Excavation about 12″ below existing slab height. Attention was given to verify that the foundation wall footing was below 12″ at all points so as not to disturb the earth around it.
3) Dig three narrow trenches running parallel to the party walls about 10″ deeper than the existing excavation and gently slope the rest of the ground to be pitched toward the trenches. Tamp the earth to reduce future settling.
4) Install recycled content HDPE percolating 6″ pipes into the trenches. These pipes need to be gravity pitched to the sump pump in the front of the house. (See cellar 3D diagrams in the Building Envelope tab)
5) Cover the trenches with gravel and the pitched earth with 2-3″ of gravel. This releases the hydrostatic pressure from the ground below the slab.
6) Tamp the gravel down to reduce settling.
7) Remove and reinstall gas lines, meters, and electrical panels off of the cellar front stone wall so that the insulation layer can be continuous behind.
8 ) Frame out the cellar walls with 2×3″ wood studs spaced 1 1/2″ off of the cellar walls and 6″ from the level line of the gravel below. No bottom plate will be installed; instead we are temporarily bracing the wall with diagonal supports to keep the wall supported and level prior and during the insulation installation.
9) Install 2″ of spray foam insulation on top of the gravel floor and then 3″ of closed cell bio-based spray foam up the walls. Because there is no bottom plate, this spray foam can be a continuous from the floor to walls.