Book smarts – An exclusive sneak peek inside the CHBA’s new renovators’ manual – Apr/May2019
As you know from previous columns, CHBA has a Renovators’ Manual in the works. Similar to CHBA’s best-selling Builders’ Manual, the Renovators’ version applies building science to renovations. Existing buildings are going to be important as Canada takes steps to limit climate change. This month we offer a small sample of what readers can expect from the new book, when it is released to the public.
Canada has more than 14 million existing houses. Over half of these were built before 1980. That’s important because these older homes were not built to be anywhere near as energy efficient as houses being constructed today. In fact, a house built today is 47% better in terms of energy efficiency than a house built in 1985.
Building Codes are addressing the energy efficiency of new houses. Current plans are for new houses to reach Net Zero Ready levels of energy efficiency by about 2030. Currently, builders are constructing approximately 200,000 housing units per year. This number has been quite consistent in recent years, although it is expected to slowly drop in the face of an aging population. Some simple math shows us that over the next 10 years, building at the anticipated rate, we can expect between 1.8 and 2 million more houses to be created. While these will be far more efficient than the houses we have now, there is no scenario for reducing the total amount of energy used by homes without addressing the existing housing stock.
The Renovators’ Manual will help with those renovations as renovators are asked to significantly improve the energy efficiency of existing houses. Looking a little deeper, this means that renovators will be asked to “apply” the building science they know to existing houses. This is not as easy as it might seem, since applying building science to the materials and systems that are already installed is quite different than starting with a clean slate when designing a new build. The process also involves combining new materials with the existing structure they are renovating.
Net Zero Ready houses are typically being constructed with R-65 ceilings, R-40 walls, triple-glazed windows, R-35 basement walls, and R-10 under the basement floor slab. They will also have air tightness of less than 1.0 air change per hour at 50 Pa of depressurization (ACH50). Even the most ambitious renovation of an older home would find these performance characteristics difficult to match, but renovators will want to know how close they can come, and how to avoid technical problems in doing so.
The challenge will come from the correct “application” of the building science. The houses that need the most work are expected to be the older ones. Many of these have little to no insulation. Even if these houses have been renovated previously, it is unlikely that the renovation will have added a significant amount of insulation. It will be useful to review the most likely starting condition of the house, for example;
- 2×4 wood frame or masonry structural exterior walls
- Little or no insulation in the walls
- Little insulation in the ceiling
- Little or no insulation on basement walls or under the basement floor
- Poor airtightness characteristics (i.e. drafty)
- Large humidity swings – low in winter and high in summer
- Large furnace and/or air conditioner
- No heat recovery ventilator – bathroom fans or windows for ventilation
- May have a wood-burning fireplace
- Poor drainage around foundation
- Double-glazed windows
Other important considerations are the climate where the house is located, and the characteristics of the occupants of the house. A maritime climate has different characteristics than a prairie climate. A house with two seniors has different operational characteristics than a house with young children. As renovators, we can’t change the occupants, so we need to provide a home that suits their specific lifestyle and needs.
In the case of the house described above, lets look at what has been happening over the years since it was built.
- The house has had little insulation so large amounts of energy has been flowing though the building envelope.
- The house has numerous holes and air leaks that result in large heat losses, however the benefit of such high air exchange rate is better, if uncontrolled, indoor air quality. If there is a wood-burning fireplace, these typically allow large amounts of house air to exhaust through the open chimney. Even with “tight-fitting doors or flue dampers, the fireplace chimney is generally a huge energy (and air) loss source for the building.
- Relative humidity in the house is expected to have been low in the winter, due to the high air exchange rate and high in the summer, for the same reason. This would lead to the house being hard to heat and cool, but also uncomfortable.
- Windows, in particular in the “wet” rooms such as the bathrooms and the kitchen, were likely subject to condensation on the glass in the winter and the shoulder seasons.
When looking at such a typical existing house the first step is to examine the decisions that need to be made. In this case, let’s pick a traditional war-time, Victory Home which are common in many cities across the country.
The renovator will need to decide on the building science features which need to be addressed.
- If the drainage is poor, this needs to be fixed, regardless of what the house is made of.
- The basement floor is uninsulated. This will not be a comfortable floor without insulation. It is unlikely that removing the basement floor, adding insulation, and then re-installing a concrete floor makes sense unless the existing floor is in poor condition. Therefore, insulation can only be added to the top of the floor. This will be limited by the basement ceiling height.
- New triple-glazed windows will be needed to improve the envelope.
- The wall thickness will need to be increased to accommodate the increased insulation.
- The key building science features needed:
- Weather barrier
- Rain screen
- Thermal barrier
- Air barrier
- Vapour barrier
This house will be wood-frame. It is unlikely that the exterior of the house is historically significant, and therefore the renovator has options. The insulation can be added to the interior or the exterior of the building. While working on the inside of the home is easier, the Victory Home is a modest size and the owners may be reluctant to reduce their floor area. To accommodate this, the decision may be made to add thickness to the exterior. The method of increasing the thickness of the wall studs will be the most problematic decision. This can be done in a number of ways and an architect should be consulted for a suitable solution. Typically, the frame of the existing house is structurally sufficient enough to allow the extensions to be “hung” from the existing walls. If that decision is made, then several items fall into place.
The weather barrier is the exterior cladding. Unless an air space is incorporated into the cladding by the nature of the cladding itself, it needs to be installed on strapping to provide an air space.
The rain screen is the air space between the cladding and the house wrap or the insulation installed over top of the studs.
The thermal barrier could be selected to do “double-duty” by selecting foam insulation which also has air barrier properties.
The selection of the vapour barrier is required. Keep in mind that vapour diffusion is a relatively weak process for moving moisture and is dependent on the surface area covered. If 90% of the surface is covered, then 90% of the vapour diffusion is prevented. Moving air is the primary transport mechanism for moving moisture. If the air barrier feature is being handled by another material, the vapour barrier can be a vapour retardant paint (if the interior drywall was not removed, the vapour barrier may already be in place with the existing, multiple coats of paint). If the walls were opened, there is an opportunity to install a sheet-type vapour barrier. This can be polyethylene, or it can be one of the materials where the vapour permeance changes with humidity. This will allow any moisture which happens to get into the wall due to poor flashing details or poor window installation to dry.
The ceiling can be sealed by removing the existing ceiling insulation and applying two or three inches of spray foam insulation to provide the air barrier properties. The desired amount of insulation can then be blown in on top of this to provide the thermal barrier function.
The basement walls and rim joist space decisions will generally be based on the type of foundation present. The most likely options are concrete block or poured concrete. Poured concrete is considered an air barrier, while concrete block is not. If poured concrete, spray foam insulation may be the best solution for connecting the air barrier in the walls, the rim joists, and the basement wall. If concrete block was used, an alternative such as airtight drywall, a vapour permeable, air barrier sheet material or spray foam insulation against the concrete block wall. Typically, drainage is poor in these older houses so a mechanism to allow these walls to dry to the inside is preferred. A provision must be made to ensure that the air barrier is connected to the concrete floor as well. How to do this detail will depend on the method chosen to provide the air barrier for the basement wall.
Now, with the house better insulated, with better windows and more airtight, the air conditioning and heating systems will be over-sized. If left as-is, oversizing will lead to short cycling and this may lead to inadequate distribution of heat and cooling in the house. Also be aware that with the improved air tightness, mechanical ventilation will be required to eliminate cooking odours and to control humidity levels. Therefore, the renovation should include an upgrade to the heating and cooling equipment as well as adding a heat recovery ventilator.
Hopefully this example highlights some of the challenges that renovators might expect and demonstrates the role the new CHBA Renovators’ Manual will play in helping renovators with the decisions they will be making to improve the energy efficiency of housing across the country.
|Gary Sharp, CHBA|