Deep Energy RetroFits (DER’s) are an area of specialization for Haycon. Within that space, we identify and address problems with existing conditions while planning for the future. The challenge of the RetroFit is the element of the unknown and one example of that is what we uncovered at our Brian J. Honan project. The building looked perfectly normal from the outside but as we went through the retrofit process, we found all of the building’s hidden secrets beneath. In this article we share our findings and experiences when uncovering some unknowns. It is based on a combination of our prior building experience and training.
A building that looked fine—until it didn’t
Trevor McCabe CPHB, the lead Superintendent on the project, noted how the building looked fine on the outside upon first glance. “There was no visible rot to the siding or trim. Additionally, even when I took thermal images of the building, nothing stood out as being problematic. As the photos show, however, when the siding was removed, the plywood sheathing below was completely rotted. The rot extended into the framing, with part of the headers above the windows being non existent behind the siding. This building is roughly 25 years old, and in no way should it be anywhere near this kind of condition at this age.”
Upon further investigation, we found evidence of prior water damage that had been repaired incorrectly. There was a flat roof that was pitched incorrectly which should have allowed water to drain into the gutter. It was pooling on the roof. Whether or not this led to the rot & damage we aren’t sure, but one thing is for sure – water is a killer.
Water is what destroys buildings. Water has 3 phases: solid, liquid, & gas (Ice, water, & vapor). Bacteria & Fungi (the primary cause of wood decay & rot) needs water, oxygen, & food (carbon) to survive. Oxygen is in the air around us, and carbon is in most building materials to some degree. Wood is loaded with carbon. When water is introduced, fungi can survive and grow, consuming wood & other materials.
Ice typically is not a problem on the surface of an assembly, because it doesn’t move, it’s solid. Ice does however pose a problem if it is within an assembly or a certain material, usually because it enters as water (it can move), and THEN freezes. It will physically push out in all directions around it which can cause significant damage to the surrounding materials. It can crack materials, pop fasteners, spread adjacent materials apart.
Water is pretty easy for most to understand, it flows, generally downhill with gravity, through the path of least resistance. Another way water can travel is via surface tension, where it may not travel down, but horizontally, or with enough momentum even uphill, by “sticking” to the surface that it is in contact with. One other way it moves that affects construction design considerably, is through capillary action. Capillary action is essentially when water is able to draw itself through very small openings without the external force of gravity acting on it. It is how plants & trees pull water from the ground, and how paper towels absorb moisture. Building materials can be affected by capillary action, and water can travel great distances this way (think of how tall trees are).
Vapor is the one that gets most people tripped up. Vapor is water in the form of a gas. It is water that is suspended in air. Our atmosphere is made up of mostly nitrogen, some oxygen, and the small remainder is carbon dioxide, water, and trace amounts of other gasses. The amount of vapor that is suspended in air is what we know as humidity.
Depending on air’s temperature, it can hold more or less vapor (More when hot and less when cold). For vapor to condense back into water, it needs to be cooled. This is why a cold drink on a hot day will “sweat” on the outside of the glass. Vapor being held in the warm air comes in contact with the cold glass and its temperature drops enough for it to condense into water. This exact action is a real threat to building assemblies. If the vapor in the air at any given time comes in contact with a cold enough surface, it will condense into water. Water is what destroys buildings because it allows bacteria & fungi to consume building materials.
Why all this is important: A large part of the design in the types of DER buildings that we work on here with Haycon is based on our ability to control the movement of air (and by default vapor), and control where and when it condenses. By doing these things we are able to keep building assemblies alive and well for long periods. This is a real challenge with modern high performance buildings because we are simultaneously trying to make them as efficient as possible. Most building materials, wood in particular, have the ability to get wet to a certain degree, and then dry out, and be completely fine. Wood can get wet and dry wet and dry over and over again and survive, as long as it is not saturated for long enough periods of time for bacteria and fungi to do their damage. This wetting and drying cycle is natural in the course of a year. Seasons come with different temperatures and humidities. Moisture contents of the atmosphere and the materials themselves fluctuate throughout the year. The biggest reason buildings survived so well against rot in the past is specifically because they were so INEFFICIENT. Imagine an old house that has huge fireplaces in all the rooms. That house can get as wet as it wants in the warm half of the year, but as soon as it starts to get chilly, the owners start having large fires to warm the place up. This essentially dries out any part of the building, because all that warm air that is being created within the house is expanding and trying to move towards areas where the air is colder (outdoors). All that warm dry air escaping an old leaky house through gaps and cracks everywhere effectively dries the whole thing out, and really well at that. This same idea happens even with code built homes up until very recently. Assemblies are able to dry affectively because houses are leaky. The phrase “a house needs to breathe” was the gold standard for a long time, and partly for this reason.
In this particular instance where we found all this rot, the cavities were filled with a mix of blown in cellulose and unfaced fiberglass batt insulation. The outlets and windows were not sealed to the drywall. Dense packed cellulose does a pretty good job of limiting air movement, but it’s not perfect. Fiberglass doesn’t do much to stop air movement. The reason fiberglass has paper on one side is so that it can be stapled to the inside face of the framing members, creating a plane to help slow the movement of air & vapor. This assembly as it stood was almost certain to be allowing vapor to condense on the backside of the plywood sheathing. Air could move through all the gaps around the windows and outlets, through the insulation and even through the drywall itself, and contact the sheathing where it would condense into liquid water. Working with great architects like Onion Flats Architecture allows us to construct new building assemblies that are far more resilient and efficient than what was previously in place.
The cavities are filled with TimberHP wood fiber insulation, the drywall was sealed with caulking at all perimeter edges, and around all outlets, and the new plywood sheathing is getting wrapped in Siga Majvest 500SA, which is an air barrier membrane that is vapor permeable, meaning that air cannot move through it, but water vapor can. On top of the Siga will be 5” of Rockwool continuous mineral wool insulation. This will keep the temperature of the plywood above the dew point, ensuring that vapor will not condense on it. Because plywood, Siga, & Rockwool are all vapor permeable, any vapor in the assembly can still move out through these materials to the atmosphere, and the Siga makes sure that the conditioned air remains within the building. There is also an airgap known as a rain screen cavity between the insulation and the siding. This allows the constant movement of air to help dry out this assembly if excess vapor exists. If we weren’t using continuous exterior insulation, we would choose to use a quality vapor retarder (like Siga Majrex) installed correctly on the inside of the wall, underneath the drywall. This would effectively block the movement of vapor into the assembly so that it could not contact the cold sheathing. Because our sheathing is under a blanket of insulation however, we do not need this layer. Also, the wood fiber insulation is fantastic at absorbing quite a bit of water vapor and expelling it naturally without compromising the product. It can act as a buffer when conditions on either side of it are drastically different (think hot humid summer and ice-cold A/C apartment, or hot steamy shower apartment in the dead of winter). This combination of products in this order makes this a very robust, resilient, and efficient assembly.
At Haycon we are always working to deliver the highest quality finished product to our clients, and this DER is a perfect example of how we are able to transform a building from an inefficient, unreliable dwelling to a comfortable, healthy, & resilient home.
