Tag Archives: moisture management

Air sealing the roof

Although I usually enjoy writing blog posts, this one doesn’t necessarily fall in the “fun” category. I am talking about my well intended roof insulation that required a partial do-over.

I did a very thorough job, starting with rock wool insulation between the roof joists, followed by four inch thick XPS foam board that we mounted under the roof joists and then airsealed with close cell spray foam. I subsequently discovered that my insulation assembly was upside-down and that I had created a cold roof deck. So I started the process of removing the carefully installed XPS insulation, which ultimately should be installed on top of the roof deck.

With the XPS insulation removed, I needed a new vapor permeable air seal. It needs to be vapor permeable to allow for seasonal drying of the roof assembly. Out of the handful of methods available, using half inch drywall in place of the XPS boards seemed to be the simplest and most reliable solution.

Once we had the drywall mounted under the roof joists, I made sure we mudded and taped it carefully to create an effective air barrier.

To seal the edges, I installed two by twos with a small gap that I filled and sealed with foam.

attic-33 attic-34

With my new air barrier in place, I started rebuilding the ceilings where needed and then I moved on to installing the ventilation duct work.

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Do-over dilemma

Blower door test – after insulation

Double duty

Attic insulation – foam board component

Stuffing the attic – Part 2

Stuffing the attic – Part 1

Spatial challenge

Advancing on the attic

Sump pit lid

It’s down to the finishing touches on the back porch enclosure. And to make it not just user friendly but also safe, I had to get a lid for the sump pit – a gas-tight lid to prevent moisture and potential radon from diffusing.


There were a number of lid options out there, and I probably have been looking at most of them. But I am a cheapskate and those lids were expensive. That may be because some of them have a vehicular traffic rating, which we really didn’t need. Foot traffic is all this lid will see.

Because I didn’t want to reach deep into my pocket, I decided that a three quarter inch plywood cover should do. But how would I fit it onto the pit without creating a trip hazard?

Well, we cut out a one inch wide ledge from the upper most concrete adjustment ring. And we made it just deep enough so it would accommodate the three quarter inch plywood cover.

To prevent mold from growing on the bottom of the the cover I attached two layers of a 6 mil poly sheet. Those sheets will also serve as a vapor barrier. And to make the system gas-tight, I grabbed a neoprene gasket and installed it on the ledge. The plywood cover, which was now flush with the floor, is held down by six screws.

Cutting out the ledge was tricky, yet fairly easy thanks to the great help of our friend Rubani!

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Porch enclosure – flashing and house wrap

Even though the exterior sheathing on our back porch is weather resistant, I did’t want to leave it exposed for longer than necessary. To complete the exterior part of the enclosure, I needed to install flashing, house wrap and siding. In this post, we address the flashing and house wrap.

The sequence of installing flashing, house wrap and siding is similar to that of roof tile installation: You would start at the lower roof edge and work your way up to make sure that each roof tile sheds water across the next one.


The sill is our low edge. We covered it with aluminum flashing that has a drip edge at the bottom. We also made sure we had the flashing overlap across the bottom of the sheathing. We applied the same principles around the windows and doors and made sure everything is properly caulked and sealed.

The only flashing that had to wait until later – until we installed the siding – was the one at the very top edge.

With the flashing in place we could install the house wrap, again from the bottom up, so all overlaps shed water away from the assembly.

The more technical term for house wrap is “water resistive barrier” or WRB. Its function is to keep liquid water that may get past the siding away from the sheathing and as such keep the wall assembly dry.

Even though it sheds liquid water, the house wrap or WRB is vapor permeable. This allows for seasonal drying of any excess moisture content in the wall assembly.

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Access enclosure – house wrap

Let’s wrap up the roof access – pun intended.

We have three defense mechanisms against the elements:

  1. There is the fire rated, exterior grade and weather resistant sheathing.
  2. Next we need to cover everything in house wrap – or, to be more precise, a water-resistive barrier (WRB).
  3. And last but not least we will finish the job with siding.

The house wrap should keep liquid water that makes it past the siding out of the wall assembly. Yet I would like it to be vapor permeable. This allows any moisture that makes it into the wall to dry out over time.

We started the job by carefully caulking all the seams on our first line of defense – the sheathing. Installing the house wrap under windy conditions is not a good idea. So we waited until it got calm enough and started from the bottom up with a water shedding overlap at each new layer, all the way to the roof flashing.


The key is to have any liquid water flow across the house wrap, but not behind it. We taped the house wrap to the sheathing, and taped it again across the overlapping seams.

For the roof access assembly, I opted for a ventilation gap, or rain screen, between the house wrap and the future siding. Vertical furring strips provide that gap and also firmly secure the house wrap.

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Adding more floor components

I get to play a game that I know! And the game is called “installing a radiant floor slab”.

I outlined in the last post the installation of the aggregate base for the concrete floor. The gravel had to be carefully screened to assure that I have the right slopes towards the two floor drains.

And now I get to play with the next four components of the radiant floor slab assembly:


  1. Insulation
  2. Vapor barrier
  3. Welded wire mesh
  4. Pex tubing


Installing the insulation was a bittersweet process. Bitter, because the four inch XPS boards I used came from the very carefully installed attic insulation assembly, which I had to take down again. Sweet, because I got to reuse the insulation and it didn’t to go waste.

I mentioned that the aggregate base was finished with the correct slopes towards the floor drains. That means that I had to line up the seams of the insulation boards with the slope ridges and valleys. If not, I would end up with suspended and wobbly boards that would crack or break.

I again paid attention to the bond breaks around the future radiant floor slab. A bond break is a piece of vertical insulation that will thermally separate the concrete floor from the adjacent foundation wall and footings. This assures that the heat in the radiant floor slab is effectively transferred into the room and not syphoned off into the foundation wall or other thermal mass structures.

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Vapor barrier and wire mesh

Even though I had an effective capillary break with the open graded aggregate base, I still needed an effective vapor barrier under the concrete floor slab. A large 6 mil polyethylene sheet would do that job. I carefully cut it to size and fit it around the sump, floor drains and footing. To prevent it from shifting around while installing the welded wire mesh, I taped it along the edges.


PEX tubing

The radiant floor slab will be heated with hot water. To get the hot water into the slab, I used ½ inch PEX tubing, which I attached to the welded wire mesh with zip ties.


I opted for two heating zones. Zone number one is heating the future workshop to the west. Because this section needs to be kept reasonably warm, I spaced the PEX tubing six inches on center along the edges and 12 inches on center towards the center.


Zone number two is the eastern half of the space and just needs to be kept above freezing. For that reason I spaced the PEX farther apart. I also made sure avoid PEX tubing in areas where I need to anchor into the future concrete floor, such as under the future steps and bottom plate that separates the workshop from the rest of the space.

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