Weatherproofing Walls Ada OK
When building a new home or adding on to an existing one, most homeowners don't give much thought to the exterior walls. Weatherproofing issues usually are not high on the list of priorities. By the time the last bit of crown molding has been installed and the new floors have been finished to a fine sheen, the home's insulation and building envelope are distant memories, if they are recalled at all. Yet these components represent one of the biggest hidden investments you can make during the building process.
When you are in the planning phase for your building project and are partnering with your builder, you can incorporate some key concepts, products and techniques to maximize the investment you will be making in your building's shell. You really have only one chance to get it right. After the drywall and siding have been installed, a multitude of sins may be covered up in the walls, resulting in unseen air and moisture infiltration problems that can prove costly in years to come.
Photos Courtesy Mark Marcoplos
The most important component from a weatherproofing standpoint is the insulation package. If a home is insulated correctly, air and moisture infiltration points will be minimized and you will reap substantial returns in comfort and lower energy bills.
The three basic types of insulation you will likely consider are fiberglass batts, cellulose and sprayed foam insulation. Sprayed foam is the superior insulation due to its ability to plug every hole in the wall so effectively, but it can be expensive for homeowners on a budget.
For my money, sprayed cellulose is the way to go. Like sprayed foam, it can penetrate nooks and fill behind electrical boxes, wires and plumbing pipes. Yet it costs only about $100 more per thousand square feet than fiberglass. You will likely save this up-front added cost within the first two years as a result of lower heating and cooling bills. Combine the use of cellulose with a thorough air-sealing job and you will have generally achieved the high level of insulation that spray foam can provide, but at a lower cost.
There are two simple techniques you can ask your builder to use to ensure your home is well insulated. These techniques won't take long to implement and can significantly improve your building envelope.
First, request that a bead of caulk or silicone be applied on the floor decking where the bottom plate of the outside walls will be attached. This will form a good seal at that joint. Second, specify that insulating foam board be used as the center sandwich between the wood members of headers.
Headers are the short beams that span window and door openings. They are constructed of two boards and, in the case of 2x4 walls, require a half-inch of material to be sandwiched between them. Common practice is to use scraps of half-inch plywood, but using foam board provides significantly more insulation in that space.
If you are building 2x6 walls, the two header boards should be installed next to each other flush with the outside of the wall framing. Then you can fill the interior side with insulation.
In addition, there's one odd task to keep track of: Tubs and showers are often installed before the insulation crew arrives, resulting in sections of wall that aren't insulated because they are blocked off. Make sure your builder insulates these areas before the plumber arrives and seals them off.
Sealing and Sheathing
When it comes to air sealing the building envelope of your new home or addition, you can't do too much. Few contractors go beyond the code-required foaming and caulking. Many will claim - and they are not entirely wrong - that the sheathing and house wrap they installed make air sealing redundant. Yet considering the relatively small investment in cost and time, you might as well seal every potential leak and err on the side of tightness.
One option is to follow behind your contractor with some spray foam and a caulk gun and augment the job he does. I guarantee you will find cavities and cracks that need to be plugged.
Even if caulk was applied underneath the exterior walls, an insurance bead can be applied where the bottom plate meets the sub-floor. Fill any small spaces you see - at the edges of headers, areas where different floor and roof levels join, anything. When in doubt, seal it.
Additionally, make sure your builder insulates around window and door openings with foam. Cramming in scraps of fiberglass insulation is not an effective way to seal these spaces.
The next important part of the building shell is the sheathing. Typically, half-inch plywood or OSB (oriented strand board) is installed over the outer walls, house wrap is sometimes applied and then siding is attached over that layer. But this approach misses several opportunities to tighten up the structure and ensure a better investment.
First of all, unless you are building on the coast or in some other high-wind zone where the building codes require rigid plywood sheathing, you have an opportunity to add to the insulation capabilities of your walls by using insulating foam board sheathing.
Since the corners of structures need to be reinforced, you can use diagonal metal bracing to meet the structural requirements and thus have space for foam board sheathing. Often a window or door opening will be located too close to the corner to allow for metal bracing. In this case you have to use plywood or OSB, or maybe a slight design change can make it possible to fit in metal bracing.
Wood is about R-1 per inch, so if you substitute half an inch of foam board at around R-3 for the R-.5 of plywood, you have made a big improvement in your home's building envelope.
Whatever the sheathing material, the next step is to tape over all the joints with special house wrap tape, which is usually made of polypropylene and coated with a cold-weather acrylic adhesive. This forms another barrier against air infiltration.
Jumping to the inside, you have some options with drywall that will add another layer of draft protection and lessen air movement through the building envelope. The most ambitious request you can make is to ask your builder to seal the drywall. One of the primary reasons for sealing drywall is to prevent air from leaking through seams in the finished interior walls and rising up inside the walls to the attic, which creates a chimney effect that in turn pulls air from any available openings in the building.
The best ways to seal drywall are to glue it across the top and bottom edges as the panels are being installed or to attach a drywall gasket to the framing. If this is too overwhelming for the builder and drywall crew, an effective fallback technique is to apply a bead of caulk at the bottom edge of the drywall where it is attached to the bottom plate of the wall. This will prevent air from being pulled in at that joint.
Then from the attic, do the same thing across the top of the drywall joint. This prevents air from being pulled out of the wall cavity by the ventilation air movement in the attic.
What About House Wrap?
So now the walls are filled with cellulose insulation that effectively seals all the nooks and crannies and fits tightly against the framing. Nearly all the cracks and holes in the framing are caulked and foamed, the sheathing joints are taped and the drywall is sealed around the edges to further prevent air movement. What else do homeowners need to do before the siding goes on?
This is the controversial part of the process. House wrap has become ubiquitous and nearly synonymous with energy-efficient construction. Manufacturers would have you believe that if you can see the brand name of their house wrap emblazoned over and over on newly framed walls, then you have achieved the goal of a tight house. That may be true. It certainly cannot hurt. House wrap improves the tightness of a typical house in which few, if any, of the measures described above have been taken.
However, in my experience, if you utilize all the approaches I've described above, adding house wrap will be unnecessary. A recent study backs up that claim. According to the Cellulose Insulation Manufacturers Association, a cellulose-insulated and house-wrapped home was tested for air tightness. Multiple holes were then cut in the wrap and the house was retested. There was no measurable change in the amount of air leakage. The same results would not have been achieved with fiberglass insulation, which is more susceptible to air infiltration.
Ultimately, it's your decision whether or not to use house wrap. But by working closely with your builder and following some simple techniques during the building process, you can ensure that your home has a tight building envelope that will effectively reduce or eliminate air and moisture infiltration. And in the long run, you'll ensure you have a comfortable, efficient home.