The christmas gift that keeps on giving - an airtight ceiling.

After the first week of December, Northwest Ontario was put in a deep-freeze (check out those daily mean temps). The early arrival of such extreme cold made the completion of the ceiling assembly in our house all the more timely. One morning I woke up to find the thermometer outside reading -39C. Taking a stroll to the house, I found the thermometer in the basement reading a balmy -2C. It seemed almost weird given that I was only occasionally firing a small propane construction heater in the basement for heat - the benefits of air-sealing, super-insulation and passive solar heat gain! A nice early Christmas present indeed.

It may not look it through the window but on this clear morning of December 31, it's -39C (-38.2F) and feels like a blistering -51C (-59.8F) in the wind. In this kind of weather, it is nice to be able to keep all the warm air trapped inside the house and then have the ventilation controlled either by HRV or by window if necessary. The advantages are many and include energy savings, durability and controlled clean air supply.

Echoes - The Wilderness Of Manitoba

So how did I put together my "airtight" ceiling?

Step 1, ledgers, hangers and ceiling joists:

After determining the desired ceiling height, I measured and marked the exterior wall for the 2x4 ledger that runs around the entire perimeter. After nailing up the ledger, I "tacked" the hangers to the bottom chord of each truss using a single 3" deck screw. The hangers were cut to length from 2x3 stock so that with the top of the hanger flush with the top of the truss bottom chord, the bottom of the hanger was at the same height as the bottom of the ledger. The hangers were installed at 48" o.c. along each truss with each truss being 24" o.c. (ie, hangers 48" o.c. one way and 24" o.c. the other way). Once the hangers were all tacked in place, 2x4 ceiling joists were fastened to each in the same plane as the ledger.

With the ceiling joists fastened to the hangers I used a laser level to check the height of the ceiling at each hanger. If any minor adjustments (up or down) were needed, they were easily made by backing out the single screw holding the hanger to the truss. With all minor adjustments complete, it was then just a matter of going around and nailing each hanger to its truss.

Step 2, plywood sheathing:

Sheathing the ceiling with plywood was straight forward. Again, I first used screws to "tack" each sheet into position, then followed up with nails once all the sheets were installed.

Closing in the ceiling with plywood really changed the feel of the space inside the house (not surprisingly) - it is really starting to feel like a house we can live in now!

Step 3, a little insulation:

While I plan to blow a thick blanket of cellulose into the ceiling for insulation, I'm not ready to do that yet. In the meantime, as I installed each new row of plywood sheathing, I took the time to install a single layer of Roxul batts (R14) as I went so that the ceiling would at least have some insulation in it until the cellulose gets blown in.

After all the work that went into insulating the walls of our house, I had collected many bags full of bits and pieces of waste insulation. After installing the Roxul batts between the ceiling joists, I took the opportunity to dump all that waste insulation into the ceiling - to be sequestered underneath the layer of cellulose that will be coming. Waste not, want not.

Step 4, some very sticky stretchy tape:

Last but certainly not least, all seams (including the junction between the wall sheathing and the ceiling sheathing) were taped with 3M 8067.

Almost done... that's one heck of an air barrier boy.

Some final comments:

The ceiling isn't entirely finished yet - I left out one plywood panel until I figure out exactly where the wood stove chimney will go, but that will take a little while yet. In the meantime, with the ceiling closed in the way it is (taped with one layer of R14 batts installed) I have been able to keep some heat in the house without much trouble despite the cold winter we've been having. In fact, a small 900 watt heater has been keeping the basement between about 1-2 degrees C day in, day out, for the last couple of weeks while outside the temperature has been averaging somewhere near -17C.

Until I get around to sorting out the chimney, these 4" XPS boards are serving to plug the hole. Very, very nice to be working out of the cold for a change.