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Ongoing Debates

Basements - 2x6 Framing, SIPs, or Truss Walls - Cellulose, Fibreglass, or Foam

Home buyers and homeowners will find a few topics in residential construction that are hotly debated among builders and suppliers. As is the case with many other subjects, the most common choice is not necessarily the wisest. Some parts of the construction trade are notoriously resistant to change and continue to do things the way they always have, even in the face of good evidence to the contrary. Here are some of the current debates in residential building, along with our reasoning on the matter. (It often comes down to the old adage - if you agree with my assumptions, you will agree with my conclusions.)

Should We be Building Homes with Basements?

A large portion of Southern Manitoba is the site of glacial Lake Agassiz - when flooding occurs, water can spread out for hundreds of square kilometres. Aerial photos of the Red and Assiniboine Rivers are often labelled as the Red Sea - so widespread is the area covered with water. Clearly, any excavations or low spots are likely to fill with water, whether from a flood event or simply summer rain storms.

The Manitoba Cooperator, a rural newspaper published for many decades, ran an editorial in 1993 that included a classic quotation: "on the farm, we used to dig two holes. One we hoped would fill with water and one we hoped wouldn't." Indeed, the slough was needed for livestock watering, but the farmhousefoundation walls basement was supposed to stay dry. This is the single biggest problem with basements - it is difficult to keep water out of them. Even the best laid drainage system around the perimeter (so-called 'weeping tiles') and the secondary sump pit and pump mechanism can be easily overcome by excessive water (runoff from a rain or flooding event) or they can fail mechanically - pipes become blocked or silted up, pumps fail, controls fail, or the electrical power for the pump fails. There is always a risk that water will enter a basement and that makes basements a less-than-reliable storage area.

Most people think of a basement as being similar to a boat's hull - a ring of concrete with a solid bottom - water from the ground would pour in the windows -that's obvious - but the basement itself should hold out water fairly well. The truth is that a basement is like a square cookie cutter, and the basement floor is the cookie. There is no seal between the basement walls and the basement floor: both are concrete, but they are simply sitting together, they are not one piece. Therefore, water in the ground can enter around the edge of the basement floor. All construction that sits on the basement floor has to 'float' because the floor is actually moving up and down with the seasons. In truth, the entire basement wall system moves up and down as well, but the basement floor moves independently of the walls. If you look into a basement of a house under construction, it is easy to see that the basement floor is not part of the basement walls - there is no basement floor until well into the home's construction, but the walls are among the first things poured.

radon leak pointsBeyond water, one of the things that enters a basement is radon gas, and many individuals and agencies are concerned about the health effects of this substance. There are systems available that try to ventilate radon gas to the outside, at ground level, but any such system is only as good as the quality of its parts and installation. When it is new, it probably works well, but as the years pass, will it continue to do its job well enough to hold out radon gas that wants to seep in around the basement floor and through the plumbing openings? How accessible are all its components? What happens when the power goes off? Radon gas is a problem in many areas of the Prairies, but parts of southern Manitoba are especially likely to have radon gas in the sub-soil.

A basement or cellar was originally intended as an area to store coal and to locate a large coal-burning furnace or boiler. For these purposes, an earth floor and about 6½ or 7 feet of headroom was acceptable. Moisture entering through rough stonework was not a problem - neither the heating appliance nor he coal were affected by it. When poured concrete walls began to replace rubble and stonework foundations, people began to find other uses for the space - having a concrete floor instead of earth made the space usable for other things. Laundry rooms and bathrooms were added to the basement. Rec-rooms were initially a place for family members to play on old furniture, make things, or maybe watch TV. On hot summer days, the basement was cool. Headroom began to increase - 8 foot high rooms became common. Various techniques were developed to insulate basements and to reduce the moisture problems. A typical basement these days can include a full bathroom, a family recreation area,concrete pile laundry room and storage area. A home theatre is not uncommon. Many families have a bedroom in the basement, although its existence is often hidden from inspectors. All of these uses, except plain storage, have one problem in common - there is no emergency exit possible in the case of fire or other calamity. Bedrooms are strictly forbidden unless there is a window close enough to the floor and big enough when opened to allow easy egress for children and adults. Such windows almost never exist. The only advisable uses for a basement space are a laundry area and storage. Some people find the task of lugging all the washing into the basement and back upstairs to be inconvenient, and a well-planned laundry area on the main floor is far more user-friendly. That leaves one use for the basement - storage. Given that most basements have very high humidity, especially in summer months, and may flood during harsh weather events, what kind of items can be stored in a basement? Preferably not books, wooden furniture, family keepsakes or photos - none of those items tolerate water very well. The kinds of things that can be safely stored in a basement tend to be not very valuable, which makes basements somewhat limited in their usefulness.

Finally, the normal basement foundation system seen in residential construction fails at its primary task if the soil conditions are clay, which includes many regions of the Prairies. A conventional basement does not provide a stable base for a home. Most of the seasonal shifting and settling in a house that is evident from doors that no longer open and close properly, sloped floors, and cracked stucco or drywall is due to the action of the clay that surrounds the foundation (the basement walls and the wider 'footings' that the walls rest upon). The nature of clay is that it swells when it absorbs water and shrinks when it loses moisture. This happens regardless of freezing conditions, although frost heaving is a related problem. Thus, the clay that the foundation walls sit on can be heading upward if the clay is absorbing water or downward if it is losing water. In addition to weather - having a wet summer or a dry summer, for instance - the moisture in clay is also affected by large trees near the home. Many homeowners are surprised to discover shifting on a side of the home where a large tree has been removed - moisture that the tree formerly took up is now being absorbed by the clay and that side of the house is headed upward. Engineers that are asked to design a stable base in clay soil conditions will specify piles that reach well below the top 10 feet of soil that experiences fluctuating moisture conditions. A typical residential pile might be a hole of 18" diameter bored to a depth of 30 feet and filled with reinforced concrete. The stability results from the portion of the pile that is below the 10 foot depth - the lower 20 feet. To create a stable base for the home, a floor structure is rested on several piles, and a space is left below the floor that allows for the clay surface to move up and down without affecting the floor. In no way does a typical basement foundation system excavated to a depth of 6 or even 8 feet compare with the stability offered by piles, when building on clay.

All things considered, is it wise to build a house with a basement? How do the pros and cons stack up?

Advantages of a Basement
Disadvantages of a Basement
storage space for moisture tolerant objects
damp and cool
workshop space (limited by stair access)
may flood or experience sewer line back-up
passable support for the home, but will shift over time
only natural light from small, high windows
no egress except stairs (not acceptable for living space)
 
radon gas enters many locations
 
not a stable foundation - soil moisture will cause shifting
 
will require extra insurance coverage if 'finished'
 
interior wall construction difficult - floor moves up and down

In our opinion, it is wiser to build homes on a pile foundation and to provide additional above ground living and storage space that is not subject to the limitations of a basement. For instance, making an attic space easily accessible will yield warm and dry storage space or room for an extra bedroom. Radon gas, moisture and temperature problems will be eliminated, and the whole house will benefit from a stable foundations system not affected by soil moisture conditions.

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2x6 Framing, Structural Insulated Panels (SIP's) or Truss Walls?

Simply switching from 2x4 wall framing to slightly larger members, 2x6, doesn't really result in an energy efficient wall system, although many would have you believe so. About 60% more insulation can be added, but the important issue of thermal bridging is not addressed - the studs themselves conduct heat outward and cold inward and this compromises the insulating value of the wall. 2x6 framing was an initial and very crude reaction to the energy crisis of the 1970's. It is promoted by many builders because the slightly larger lumber is almost as easy to work with as 2x4's, and the home can be advertised with higher R values for the walls - it gives the appearance of improved resistance cold and heat, but it may or may not deliver that performance.

SIP's are structural insulated panels. Some of the early versions comprised an outer surface of OSB (oriented strand board) or plywood, then a thick layer of expanded polystyrene (white beadboard, or foamboard) and an inner layer of drywall. Typically, a pair of 4 foot by 8 foot panels were held in a machine while foam was injected between them - thus, the foam glued the panels together and completely filled the space with foam. Many variations have been produced in recent years. On the construction site, the SIP's can be moved by a couple of workers and stood up to form walls. For roof applications, light cranes can lift panels into place and form both the ceiling and the roof surface with one piece. The foam layer in a SIP is often 8" or more, so they are rated as having good insulation qualities. Of course, with no vertical members (studs) reaching from the interior surface to the exterior, there is no thermal bridging. The main challenges when working with SIP's involve 2 aspects: door/window openings, and the routing of electrical lines. Door and window openings need to be specified at the time the SIP's are ordered, or they openings have to be cut and reinforced on-site. In addition to making a hole in the panel, lumber needs to be added in order to have something to which the installer can attach the door or window. The second difficulty is making grooves and depressions for electrical services. Wires need to be sunk into the wall and/or protected with sheet metal to meet the electrical code. The inner panel and the correct amount of foam need to be cut out to locate electrical boxes for lights, switches, and receptacles. Depending upon how many boxes and wiring grooves need to be installed, this can be an onerous task.

Environmentally, SIP's are a dubious choice. As will be further discussed in Cellulose or Foam, current foam technologies are oil-based - extruded polystyrene and expanded polystyrene are petroleum products. Until a foam can be produced that is water-based, uses a product from the waste stream (like agricultural waste, recycled plastic, or similar), and can be manufactured in a closed-loop system (polluted water is not a by-product of the process), then foam use will not be a good choice for the environment. We need products that reduce our need for oil, not increase it.

In the event of a fire, combustion of SIP's generates toxic fumes. Smoke in a building fire is surely the major killer of people in the building, and the fumes produced when man-made materials like furniture, sheet flooring, wood finishes, cabinets, and other plastic-containing substances are burned contributes to a more toxic smoke than would occur if plain framing lumber were being burned. Having a building constructed of SIP's might be no more dangerous to the occupants than a conventional framed lumber home - the danger for the occupants is the contents of the building - furniture, etc. However, when the foam core of the SIP's ignite, toxic smoke is released to the environment, and both the smoke and the rate of combustion are hazards for firefighters. We don't have a lot of case studies of fires in SIP-constructed homes because the method is not yet widespread. But we are learning that man-made building materials behave differently in a fire than the conventional framing materials that we have used for over 100 years. For instance, the floor joist systems that consist of 2 strips of lumber separated by oriented strand board burn and collapse much faster than a common solid wood floor system. Firefighters need to know if a manufactured floor system has been used in a home before they enter, because they have much less time to walk on the synthetic floor system than a conventional solid floor.

If we take a life-cycle perspective on residential construction, are SIP's able to be renovated and recycled? Again, because SIP's are relatively new, we don't have a lot of experience with renovating a SIP-built home. Such a home may be easier or more difficult to renovate than a conventionally framed home: time will tell. As to recycling, SIP's cannot be broken down into their component parts - there is not way to separate the outer and inner skins from the foam core. Dismantling or recycling a SIP-built house would involve removing the SIP panels and re-using them to reconstruct exactly the same house elsewhere, or cutting them down for an alternate use. Window and door openings, and electrical wire grooves cannot be undone.

At some point in time, Canada may move to a factory-based house construction system. All of the attempts to establish a prefab home industry since World War 2 have failed, but pre-fabbing homes is the normal method in many other countries where the cost of labour makes 'site framing' too expensive. In a factory-based system, given our cold climate, SIP's might be the best option. In that case, one would hope that a compatible electrical system is evolved to avoid the somewhat clumsy method we use now. Labour input on a new home would be reduced - SIP production can be easily fully automated. Labour would move to the factory location, and labour needed to erect and finish the home would be reduced. This scenario doesn't favour rural or remote areas.

Truss walls, in our opinion, offer the best option for energy-efficient construction at this time. In one sense, they are a simple improvement to to the Canadian house framing method - a method now being examined in many parts of the world for its economy of materials, simplicity, strength, and resistance to seismic events. Truss walls use essentially the same amount of lumber as 2x6 framing, but achieve dramatically better insulation values. Building members that traditionally reached to the exterior surface of the home's envelope, like floor joists, no longer contribute to thermal bridging because they rest on the interior structural wall and do not extend to the cold outer surface. Truss walls having a thickness of 12" or more lend themselves to cellulose insulation - the best environmental choice for insulating materials. As well, truss wall systems work very well with homes built on a concrete slab -they allow for heavy insulation around the perimeter of the slab while having the structural member rest on the edge of the slab.

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Cellulose, Fibreglass, or Foam? Which insulation makes sense?

Current home construction methods are increasingly using more foam insulation - layers are being added to the exterior of walls and roofing systems. A simple way to add insulation to a frame wall, improve the exterior seal, and reduce thermal bridging, is to apply a layer of 1" extruded polystyrene over the entire surface. The final siding or exterior surface is then applied over the foam. Some stucco systems work well with a foam surface, and this method is common in commercial construction.

There are problems with foam that, in our opinion, make it an unwise choice for its use in areas of the home where simpler solutions exist. To be sure, expanded and extruded polystyrene (often called Styrofoam, which is a brand name) are the only options for insulation where there is contact with moisture: under slabs, around foundation systems, and other such locations. We would still like to have an alternative that is manufactured with material from the waste stream and does not rely on petroleum for its main ingredient, but that ideal 'eco-foam' doesn't yet exist. So we have no choice but to use polystyrene in some locations and for some purposes. However, there are more ecologically friendly and simpler solutions for walls above grade and roof systems - there really isn't a need to use polystyrene in these locations. If we have a simpler solution, we can avoid the environmental cost of producing polystyrene, the toxins produced in the event that these foams ever catch fire, and the added cost of the material itself - foam tends to be the most expensive option in many cases.

The same reservations apply to spray foam products that are becoming more popular. These products are still petroleum-based and will give off toxic smoke if burned. Spray foam systems often promote the advantage of better air sealing, which is true - sprayed foam will totally seal up a stud space and any wiring or plumbing holes in that space. The problem is that the foam acts like very strong glue - to separate the parts of that wall - for alteration, renovation, or recycling - one has to essentially cut everything apart. The actual application of the foam often involves a good deal of waste - after the foam has expanded, it is typical to trim off any material that projects past the face of the wall, and this trimmed material heads off to the landfill. Is it wise to use spray foam in residential applications when excellent air sealing, simple application, and non-petroleum products are available that perform essentially the same task? Is it necessary to glue an entire wall assembly into one piece if there is a chance that renovations or changes will be made in the future? There are agricultural, commercial, and industrial applications where spray foam makes good sense, but it is rarely justified in residential construction or renovation work.

Fibreglass insulation is easily the most common material for residential work. Unfortunately, it doesn't perform as well as its promoters would have us believe. The fibreglass industry spends heavily on promotion, considerably less on research. A significant amount of energy is used to produce various fibreglass products from the basic raw material: sand. The product does not lend itself to using material from the waste stream. Builders and homeowners like the ease of use with fibreglass - anyone with minimal skills and a knife can fit the batts into stud spaces, stuff it into gaps and hollows, or blow a loose version into an attic space. Many users dislike the itchiness and throat irritation that often accompanies the use of fibreglass. But the main disadvantage of fibreglass remains - it simply doesn't trap air and insulate as well as it is promoted to do. In addition, few installers take the time to properly fit the material, and it is difficult to cut and fit around obstructions and irregularities. It offers no environmental benefits - it needs new raw material, uses lots of heat energy to produce, and is rarely re-used, especially if it becomes damp. Despite its over-promotion and supposed ease of use, it really isn't a good choice for residential construction.

Cellulose insulation is our material of choice for all locations except ground contact. It has the environmental advantage of being manufactured by essentially grinding up waste paper - a low energy process for using something from the waste stream. The R-rating for cellulose is about 75% of the R-rating of polystyrene. Foam insulation is typically given a rating of R-5 per inch of thickness and cellulose is rated at R-3.6 per inch. Therefore, we simply need to increase the insulated space by about one third to achieve the same level of insulation with cellulose as we would obtain using foam. Cellulose is inexpensive, easy to handle, and rarely causes any irritation to the installer. Because borax is added to cellulose insulation and because it is packed quite firmly into wall spaces, walls insulated with cellulose tend to smolder in the event of a fire, but they do not burn rapidly and spread fire in the manner experienced with walls insulated using fibreglass batts. (Polystyrene insulation burns rapidly with toxic smoke and must always be covered with drywall or other non-combustible material - this warning is printed on the foam itself.)

Cellulose insulation is simply installed in attic spaces - retailers often lend a basic blower to a homeowner along with the purchase of the material. However, a powerful blower, special netting, and an experienced installer are needed for wall applications - hence, builders and do-it-yourselfers cannot use cellulose as easily as fibreglass or foam. As well, the cellulose industry is as quiet as the fibreglass industry is noisy. Cellulose is simply not promoted, despite its many advantages: performance and environmentally friendliness being the two most obvious.

The combination of truss walls and cellulose insulation is the mainstay of Advanced Design/Build's residential construction method. We have developed methods and processes that allow us to produce highly insulated wall and roof systems that perform extremely well in our climate, are environmentally friendly, and cost-competitive. In the life cycle of a home, our wall systems are easier to work with in the event of renovations than SIP's or walls filled with spray foam. In the unfortunate event of fire, cellulose-insulated walls are the safest choice for both the building's occupants and firefighters.

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